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TZ Tips part 1.



Picture: Aussie racer Greg Petty flyin' at Oran Park near Sydney in the late seventies ( Mick O'Brien)






Disclaimer:    This submission is not meant to be the ultimate bible for piston port Yamaha owners.

         It is merely a collection of ideas based on what various TZ owners have read, discussed and experienced over their years of ownership of the bikes.
    If you have any ideas or tips, or opposing opinions you want to share with other 2 stroke racers then please e-mail the Webmaster and share your expertise with us all. Your input is most welcome, it can only enhance the site. 

         Each bike and rider is different and will have different problems and requirements compared to the next.

        Remember: The best option of all is to get an authorized Yamaha dealer to do all your maintenance work as per Yamaha’s original recommendations.

Contents This Page:

Click on the blue links below for information:

  1. Pistons

  2. Rings

  3. Crank

  4. ignition


Contents Page 2 of TZ Tips:

Click on blue links to go to page 2

  1. Barrels

  2. Heads

  3. Chambers

  4. Carburettors

  5. Clutch

  6. Gearbox

  7. General Tips and Ideas

   1.    Pistons: 

For the 350's,G model pistons are the best. Next best is E model, but make sure you grind the little extensions off the bottom rear of each piston because I have heard of them breaking off.      Some owners swear by ceramic and other protective coatings, though I've had  no experience with them. (Greg Bennett)

        250 pistons are no longer available in the US for any model, ( though it does appear that Yamaha are going to be re-manufacturing them soon). For the last few years, they have supplied E model pistons for everything from TD3's through to F models.  Hopefully everyone knows that 250G pistons are 0.22mm larger than other 250s and will not fit unless the barrels are replated and honed to suit.

Yamaha changed their piston designs almost every year and the major
differences were the width of the skirts at the back and front of the lower piston edge.  The reason that they change was to match the bottom edges of the transfer ports.  While port timings didn't change all that much at the top, they changed considerably at the bottom in terms of size and angle.

The trick is to push the pistons into a barrel (off the bike) and see how
well the transfers match up with the piston most of the way in.              (  Richard Nowson )

1.    I agree with Richard that there are probably benefits to be had by matching the shape of the bottom of the piston at the sides to suit the transfer port bottoms in whatever barrel you are using.  Am not an expert on the small differences in barrels, but sorting that sort of alignment problem out at least makes you feel like you have done more than blindly fit new parts! 
2.    When fitting new pistons, check that the inlet timing (i.e. the length of the skirt on the inlet side of the piston) is what you want - i.e. is it the same as the ones you are removing.  250C not renowned for top-end performance, so I did what I was told by someone who supposedly knew what was what, and took 2 mm off the intake skirt (he told me 3 but I didn't completely trust him).  This was 1982, and I never checked what the resulting timing was, but it did go better.
3.    Note that the later piston models are different in the gudgeon (wrist) pin area.  Later ones use a shorter pin.  Don't use the shorter pin in the piston requiring the longer one - the pin floats a lot, and could end up dangerously unsupported on one side.  Have accidentally done this, but got away with it.
4.    Standard Yamaha g/pin circlips have a little tag.  This tag is usually angled one way, reference the plane of the pin. (ie, it sticks up away from the bench if you were to lay the clip flat on the bench).  If you look at used clips you'll see a witness mark where the pin rubs on the tag.  If the pistons won't be in that long, give the tag a bit of extra angle and fit the clip with the angle away from the pin, or even better, cut the tag off.  The reason for this is that it is possible for the tag to be cut off by the pin:  goodbye cylinder wall, etc.
5.    If the piston comes out with an odd 'wavy' pattern on the front/rear sides, the rod is probably bent.  have had this.
6.    Early pistons may have skirts of similar/same length.  Make sure the piston is fitted the correct way around - the pin is offset by about 0.050".  This is to reduce 'slap' - noise=power waste, increase the piston, the ring end-gap will be where it should be and there is 2-3% more power (better combustion as the piston stays at TDC slightly longer - same effect as a slightly longer rod).
7.    Make sure there is no sharp 'burr' on the bottom of the skirt against the cylinder - it scrapes lubricant off the walls.  Some people recommend cutting a 0.030" chamfer on the bottom of the skirt to make sure of this - it also gives a bit more inlet timing, but more importantly, it smoothes intake airflow into the crankcase.  This flow is upset by the normal sharp edge on the skirt.

Further to the chamfer note above, the jury is out on this one. Keith Webb says:  "Don't!!! It won't start easily from a push and torque goes out the window, and, you risk it (piston) hitting the base of the inlet port. Yamahas rely on harmonics in the inlet tract to ensure correct filling of the crankcase at low speed."


Tips List


Picture: Just needs a good spray of WD40 and a few laps to bed it back in !  .......... Yeah RIGHT !


9.    Make sure the piston ring locating pin is properly bent over in its little hole.  Having it come out, and the ring end gap snag in the bore is expensive.  Yamaha have end gap over the wall between inlet and transfer ports.  Interesting to note that the 750 pistons (a bit over 66 mm) have the end gap in the middle of the inlet port, and they work fine, incase anyone uses a 373 cc cylinder and Wiseco pistons.
10.  Wiseco's incidentally (don't know if they do 250/250 units, but no reason why not - they did a minimum of 200 (I think) for the 750's), are forged and beautifully made.  They hardly wear and some have gone 1000 miles in 750's in UK without trouble.  They also come with a ring, little end bearing, pin and circlips for the same price as a standard piston from Yamaha that won't last as long.  The ring they supply is for Nikasil-plated bores, but the width allows the use of a Yamaha ring if the bore is chrome.
11.    Pistons can crack.  If in doubt, crack test.  Mark 1 Naked Eye can't do the job.
12.    How long do pistons last?  Dunno.  Used to change them at 300 miles, but run on condition and fit these days.  See discussion on coatings for extended service life.  I'd suggest not running a Yamaha piston more than 600.  Useful to note that Yamaha pistons shrink after a heat cycle or two (after being run).  This could nullify the fit you desired with those tasty new 97 pistons, when a set of 98's might have been better after being run quietly!  Bought a bike once with a box of apparently used pistons: in reality quite a few had been fitted and run just to make them shrink, and then correct fitting 'pre-shrunk' pistons could be chosen, and retain their clearances and hp longer.  Expensive and time consuming, though I think the moral is to err on the tight side and carefully run the motor in with a few low rpm heat cycles prior to using serious rpm.
Carillo TZ rods

13.    Tried to cheat with a pair of HPC coated pistons, fitted with less than 0.001" clearance once in a 350F!  Bike just slowly ground to a halt on the back straight (so Alistair says- riding it at the time)  Stripped the motor - no damage - hardly even scuffed the coating off the pistons - proving the coating's worth as seizure-preventer.  Will always run coated pistons unless the fit is too tight to do so as a result. At about A$25/piston for the side coating, it's cheap insurance, compared to the cost of re-plating a cylinder! 

.14.    Little End Bearings.  Scope for individual expression here.  Have never had a problem with standard Yamaha ones, though there are those who swear by a Kawasaki item (sorry, don't have the part number) that is a bit more rugged (and a bit wider I think).  Have used both - nil ill effects, though I have routinely replaced bearings with pistons changes.  Some of the rod kits available (non Yamaha) come with good bearings.  Some people believe there is power to be had by locating the rod with thrust washers at the little end, and doing away with the washers at the big-end.  Some Yamahas used to be like this, I believe.  Too hard - I'll stick close to the book on this one. (Kerry Wilton)

Rotax Max 125 pistons ( single thin ring ) come in graded sizes 53.96 etc and will fit TZ250's.  Unfortunately they run a 15mm gudgeon pin but luckily Pro-X make a 15mm ID x 20mm OD bearing so that problem is solved. Deck height and skirt length are the same as the OEM TZ250 unit. ( James Clarke )   

Further to Rotax pistons application above:    All the sizes are OK, though the skirts  must be shortened  2 mm, and on the inlet side they are too narrow so they will  flip in the inlet port unless the cylinder is modified.
The inlet ports need to be built up by 1mm on each side prior to having the cylinders re-Nikasiled in order to use the pistons.
The Rotax pistons are a very nice, strong and cheap unit.
I'm trying now Forged TM pistons from ASSO (Italy)
But they need small changes on cylinder (0.5 to 1mm lower and cylinder head flatter)
and also a 15 mm gudgeon pin to suit. Details soon.
( Michel du Maine )

Please note that while the Rotax pistons above certainly appear to fit with modifications, we have not seen anyone actually try them in practice and so would advise caution in this regard. Also... just a reminder to check that you are going to be using a ring that is compatible with your bore lining ( chrome or Nikasil etc. ).

Another brand of alternative piston was made recently by an Italian company (at the request of a Dutch 50cc racer company) to fit the TZ125 and 350 . Tests have apparently proven the 125 item excellent and at present the 350 item is undergoing testing and showing real promise. Both are claimed to be superior to the original Yamaha items ! ( Martijn Stehouwer )

Tips List

                                        2.    Rings:

        If you run Nikasil coated cylinders you can use Wiseco RZ250 and 350 rings, which are half the price of Yamaha items. At least the end gap is close to spec. with the 250 size units, unlike new OEM rings from Yamaha which are always outside the limit from new.
            Wiseco part no. for 350 is (I think) 2520CD
            I’m not sure of the number for the RZ250 rings, ask your local dealer.

Remember:You can use these only if you have Nikasil cylinders. They will destroy a standard chrome bore. (Greg Bennett)

Nikasil Bore.  Chrome rings are best (Goetze are common),  Gap as for chrome.  We used to change the standard rings  (in chrome bores) at about 150 miles, though the chrome ones are just run-in.  They will easily go 500 miles, and some guy in UK are going nearly 1000.  I have seen a chrome ring taken off a seized piston and go back in the same (Nikasil) bore on a new piston - it was fine! 
Standard rings can be used, though the Nikasil wears them out pretty fast.
Chrome Bore. Must use iron rings.  Usual stuff - NPR to the top.  I aim for 0.02" gap.  Use a stone to trim the ends.  Push them in the bore with the top of the piston (for 'square') and look for light around the edge of the ring.  They do not all appear to be round.  Sometime a 'dag' at the end gap can be relieved to improve the fit.  Best ring has no light leaking past it. (Kerry Wilton)

Tips List

                   3.    Crank:

I use Suzuki RG500 roadbike big end bearings in my TZ's. They are a stronger unit than the old TZ ones. Suzuki part no.  09263-22060

                 For inner mains, try Koyo 83548D-9 C3 bearings from your local  bearing service. Heaps cheaper  than genuine Yamaha and yes, they have a little lug to stop them spinning in the case if they seize, though some grind this off. They'd rather have the bearing spin in the case than gouge a groove in it. It’s a matter of opinion. These bearings have the standard steel cages which might put some guys off, but the way I see it, they are so cheap you can afford to change them twice as often and still save money. I've run the same set in my 350 for about 5 years ( I run air filters and rich mixture.)

                    Outer mains?…..   Outta luck. We havn't been able to source a non-genuine bearing to replace them.

If you can find a labyrinth seal grab it !! Yamaha have deleted them. Luckily they don’t really wear out that quickly.

Make sure the primary drive securing nut and the corresponding thread on the crankshaft have been cleaned and thoroughly coated with Loctite. (Greg Bennett)

For anyone truing their own cranks, a tolerance of .ooo is fine.  The more out of round it is, the more energy is wasted shaking.  On a 350 a good crank can be worth 2 HP. (Richard Nowson)

Conrod sets to suit air cooled Yamahas are available from Pro-X  (actually RD units)  also good silver caged big ends and outer main bearings, they work well.

The Prox replacement no.s are
Silver big end cage  22.222816 F
Outer crankshaft ball bearing-groove 23.2010 ( Michel uses them on the
right side-primary drive)
Crank ball bearing left 23.6305 C3 ( No groove, no pin.)
Con rod kit RD 250/350  03.2025   ( Complete with washers, small end bearing, gudgeon pin, and a poor quality big end bearing he replaces with the silver one.)
Michel has been using these parts for 5 years without any failures.

Also available are TA 125 conrod kits for the "tiddler" owner.
They are available from Prox. part no.03.2245   it's a complete set including gudgeon pin, thrust  washers and once again, the big end bearing is the only "dodgy" part.
The price is about  Euro 50 per  set.

(Michel du Maine)

The TD2 rods can be replaced by the Cagiva motocross conrod from Mazzucchelli. These are no longer manufactured, so you will need to track down old stock. ( Martijn Stehouwer )

Tips List

Picture: TZ750C bottom end. (Alistair Wilton)

Indeed the original big-end needle bearing 93310-42255 is silver plated, but this one is superseded by 93310-422L0 (copper plated) I spoke with Mr. Y. Suzuki from the Yamaha Parts Center here in Amsterdam and he has " created" a new part number, 93310-422B0. This is the big-end bearing to use, it was originally designed for the recent TZ125 models and is vastly superior.
Now it is possible that this bearing number does not exist in the USA, Canada or Australian records. If so, let me know.
P.S. Never use a bloody Suzuki part in a Yamaha! (Ludy Beumer)

I checked with my local Yamaha dealer here in Australia on the big end bearing Ludy mentions above. The part number 93310-422BO is listed, and at around $41 Aus. (say $20 US) is actually cheaper than the RG500 bearing I recommended previously. (Greg Bennett)

The 93310-422LO-55 big end bearing for TZ's is $10.50 in the USA (Rick Butler)


General.  TZ cranks are low tech, but critical.  They have a design flaw in that one flywheel has two press fitted components adjacent to each other, and routinely cracks, especially in 350'/750's.  When the crack propagates to the edge of the flywheel it opens up and rubs against the case -sometimes ruining it (the case).  Have had two go - one was just like a seizure, at 130mph.  There is a partial remedy for this (see below).  The cause was fixed with Hoeckle cranks and in later streetbikes (RZ for sure, not sure about LC).  If your motor mysteriously won't rev past 6000rpm, be sure the crank's not broken.  Kevin Cameron believes the natural frequency of the crank is at 12000 rpm.  Revving the motor around this area will enhance the likelihood of a broken crank. 
1.    My first rule with cranks is that it is the heart of the motor.  A used crank is worth $50 to me for the major parts.  Any unknown crank should be rebuilt prior to use.  Not cheap to do, if you want Yamaha parts, but there are other, better, cheaper alternatives.  Don't skimp on the crank.
Conrod bracers 

2.    Rebuild the crank yourself if you have the kit, or find someone sympathetic to do it.  There are lots of people who can technically do the job, though few who will look at the end result with a critical eye and balance the way it went together against its intended use.  I know a guy in UK who has a lot of cranks through his hands.  He has them all rebuilt and will supply you one depending on your planned usage - related to how well it went together e.g static display, parade or race.  Some cranks he throws away.  (If anyone needs to know someone good in NZ, email me at

3.    It's a bit of screwing around, and your 'crank guy' may arrange it for you, but it is a MUST to have the crank flywheels crack tested' every time they are apart. I'd be surprised if you don't often find a cracked flywheel.  If it is cracked, throw it away, or use it as a paper weight.  Had two from the 750 cranks checked  - motor had done a season.  Both were cracked, and the crack was visible with the naked eye.  The crack-testing man wanted to keep one as an example to his apprentices, etc. 
4    While you have the cases apart and looking at cranks, have the gearbox gears crack-tested as well.   Have seen a lot of cracked gears, and a gearbox lock-up from a broken gear is my worst nightmare.  Common for twins to have problems with 3rd and 6th gear.  While they should be technically a matched set, it is quite reasonable to replace one cracked flywheel.  These and replacement gears are available.  Flywheels are available (not from Yamaha) new at about 70 UK pounds each, as are crack-free second-hand ones much cheaper. Gears are available from several sources including ( an English supplier ), though they are about 110 pounds per pair, aftermarket (don't think they are available from Yamaha).  
5.    TIP A trick used in the USA for years, and apparently not widely used elsewhere, is to assemble the centre two flywheels the opposite way around, compared to the way shown in the parts book.  There are those that feel the parts books are misleading in his respect.  This is supposed to change the loadings on the 'weak' flywheel, and cracks are no longer a problem.  Alistair and I have all our cranks done this way now.  (will send scanned diagram of how-to when Alistair sends the drawing to me)

Re: Crank splitting problem that many have experienced. The turning around of the inner webs really doesn't cure it but will delay the onset for a while. Over revving will certainly bring it on faster  than a fast thing, anything over 11k is over revving. The 12k resonance theory is in fact correct  and several machines suffer from this sort of  thing (RD125LC big end spins backwards @10ish K). A lot of damage is done when the crank is split if the proper tools are not  used, this bends the web slightly and starts the crack. ( Chris Pearson )

Tips List


Picture: TZ crankshaft components etc.

6.     Yamaha Rods.  There are essentially two types of crank - late or early.  The late type has a male thread on the end for the rotor nut, while the others have a female thread and a special screw to locate the rotor. 


 For our purposes we'll consider them the same.  Early cranks came with rods marked '278'.  Later type was the '3G2' rod.  The 3G2 rod is known for its breakages.  I ran a bent 278 rod in a 250 for five meetings without knowing.  A friend with a heap of TZ's has a pile of old rods, and measured the ovality of the big end eyes after normal use.  The 3G2 rods were often 0.006" or 0.007" out of round, while the 278 rods were rarely more than 0.002".  Moral:  use 278 rods if you have them.  Use 3G2 rods if that is what is available, but run them and throw them away at normal rebuild intervals.

7.    Other Rods.  We exclusively use an aftermarket rod from ( an English supplier ).  There are two types: light and heavy weight.  The light rods apparently allow the twin engines to rev more quickly than the heavy ones, though should be changed at normal service intervals.  The rod kit, about one third of the Yamaha kit price (for a better rod) has a solid crankpin, big end, little end and thrust washers.  For a few pounds extra it can be possible to put in a Yamaha big-end cage if you want to be cautious, though it has never been shown to be required.  I have read elsewhere that the late model TZ125 uses the same cage, at a reasonable price, though have had no confirmation.
8.    The heavier rod is also fine in the twins, but a little more expensive - about half the Yamaha item, for a much better rod.  We have these in the 750's.  Some 750's running these rods in the UK have run them for the normal 600 miles, stripped the motor, and either rotated the crankpins 180° and re-assembled everything for another 600 miles, or replaced the pins and cages and reassembled them.  No problems. This suddenly makes the rods about one quarter of the price of Yamaha ones!
9.    Crankpins.  Solid and hollow are available.  Try for solid.  Avoid the type with the coarse thread on the outside (RD400, apparently).  This is an attempt to hold the pins in tight, though all it does is ruin the flywheels for rebuilding.
10    RD Rods.  Can look like 278 TZ rods, but for one thing don't have the oiling slot in the b/end eye.  They are sufficiently similar that Alistair has a brand-new pair of 750 cranks with RD rods - from the factory! (and the 278 kits to fix the problem, from the factory when they found out about the error!)
11.    RG Suzuki Big-Ends.  Have also hear they are good, but not tried.
12.    Main Bearings.  Personally prefer the ones with the peg to stop them rotating in the case.  Yamaha cranks require an inside diameter that is (was) 2mm bigger than a common bearing size, hence the need to use theirs.  There is an aftermarket option from ( an English supplier ), as Yamaha ones sometimes not available, though prices are comparable to Yamaha.  Currently, Yamaha items available on the shelf in NZ for about A$400 for the set of 4.  Inner bearings are cheaper, though the outers may be re-used once, effectively halving the cost.  Everyone will have seen the 'channels' gouged by the locating pins.  There is a mod to use a countersunk steel screw in the case to stop them.  Have not tried it.


Tips List

 Picture: A Femsa ignition fitted to a TZ350F (Joris van de Wiele)


13.    Labyrinth Seals.  Some people, who usually seem to know what they are on about, maintain that the bikes won't go well without a good lab.seal.  Apparently unavailable from Yamaha, these can usually be bought from ( an English supplier ) for about 15 pounds each.  Replace each rebuild.  ( An English supplier ) has a stock of Yamaha seals, though he has previously had a batch made (and will do again, when he runs out of the Yamaha ones) for around the same price. The advantage of ( an English supplier ) reproduction ones is that they are slightly (about 0.001" or less) undersize, as he has found that most of the cranks they will be fitted to are slightly worn in the seal area  - they can be hand-lapped to suit the crank, or just assembled and left to find their own fit on the shaft.  We have done the latter, with no ill effects, though it's worth noting that ( an English supplier ) seals generally seem to require a good 'smack' to seat them properly in the crankcase.  Use nothing around the outside of them (some like cellotape or shellac). 
14.   Normal Service Life.  600 miles was the conventional wisdom, though modern synthetic oils seem to be improving this.  I have seen a 350 at 914 miles (mind you, it was tired, as they were all racing miles - I usually count warm-up and slow down miles too!).   
14.     Other Cranks
a.     Hoeckle.  (However you pronounce it at your school).  Better design by removing the second press-fit in the flywheel with integral flywheel/shaft (I believe), and better materials, probably. Expensive, even s/hand.  Most people seem to rebuild the Hoeckle shaft with Yamaha or other components, as the Hoeckle rods break.
b.    RZ(LC?).  Much the same construction as Hoeckle, and made to operate at 10,000 rpm/60hp (supposedly). 
Have heard that, to make the RZ crank a good fit in the TZ case, the outer flywheels need to thinned down a bit, as the total distance from the centre of the crank to the outer edge of the standard RZ flywheels is a bit wide for the standard TZ space for the crank, and that there is a bit of work involved to do this.  I have seen an absolutely stock RZ crank fitted in an RD350A (same cases as TZ), and raced, without problems.  Note that there was 0.004" between the sides of the flywheel and the inside of the crankcases - the kart guys thought this was an excellent start to good hp, and is a factor they watch! Personally, would rather have a TZ unit.

Tips List

15     Rotor Balance.  The perfectionists out there might like to aim for a smoother motor by balancing the ignition rotor.  I haven't, though I have seen people resort to it after the rotor has flown off, taking the end of the crank with it.  One guy broke three cranks this way (slow learner/to much money!).
16.    Crankcase Assembly.  'Janet and John' stuff, but it's new for some:
a.    Make sure the crank (and gearbox) is properly seated and that the seals are the correct way around (the right crank seal has 'outside' on it).  Use a new g/box sprocket seal - it's a pain to replace it if it leaks.
b.    Use a very light film of Loctite Master Gasket (or your personal favourite).  This peels off easily when you next split the cases, and won't dry off until the air is removed from it, so there's no hurry to get things done.  I personally don't like Yamabond or similar 'nail polish' varieties of sealant.  The Loctite also takes up quite a bit of surface irregularity - remember none of these (unless you are lucky) is new, so a little help in this case is useful.
c.    Make sure the dowels are fitted, and drop the top case onto the bottom.  A piece of wood to hold up the front of the bottom case helps to keep things level and allow the studs to go through.  Put all the nuts/washers/screws in, and tighten to about a third of the final torque - in the pattern Yamaha suggests (numbers on the top of the case). 
d.    Rotate the crank.  You should be able to turn the crank by hand with the primary gear or rotor.  If not, something is wrong.  Tighten the cases up in at least three stages and check the crank freedom to rotate each time.  Stop and look if the crank binds up so that you can't turn it.  Nice to find that there are no tight spots in the crank rotation when the cases are fully tightened, though not uncommon to have a minor tighter spot.  Odds are that it'll rotate quite freely after it's been run, but that's not the objective!
17.   Barrels. There are some people who maintain that the matching of crankcase top to cylinder transfer ports is a waste of effort, though again, I do.  They may be right in terms of HP, though I suspect the mid-range might suffer. (Kerry Wilton)

The serrated crank pins are originally designed for snowmobile cranks and the serrated ends are not to hold the pin tight, but to keep the crank straight. Normal straight pins build up torsion when a crank is straightened during assembly, so they can partly flex back to somewhere the old untrueness. Serrated pins are far less prone to this and therefore the crank stays more in-line after assembly.
This is the explanation by one of our Yamaha engineers who worked on these snowmobile cranks. Technically they date also 15 years younger than the old TZ' s. (Ludy Beumer)

Try Yamaha part number: 34X-11651-00. These conrods can be used in TZs up to G model in 250s and H model in 350s. ( Rob Hinton )

Tips List

 4.   Ignition

Hitachi ignitions seem to be very reliable, apart from the need to have the  charge coils rewound when they are getting old.
        ( Any opinions on the other alternatives, eg. Femsa, Motoplat, etc. welcome. The author has no experience with them)

There is something to say about Kröber ignitions, they run perfectly! It is extremely easy to set them up. A German company still produces them and they can make ignition and revolution counters for nearly any bike. They normally cost around 600 euro for a twin cylinder machine. I run Kröber ignitions on my two TA125s, one of the systems is 30 years old!
(Holger Merz)


      Most owners run the ignition advance at the standard (safe) 1.8mm. Pistons are too dear and becoming harder to find..

       Using  NGK B9 or10 EV plugs is a safe bet. Some guys prefer Champion N82 or 84G's.  (At the time of writing the new "Iridium" style plugs are not available in 10's, at least not here in Australia.)
            The author has at times run the same pair of plugs (cleaned regularly)  for 3 or 4 meetings and has yet to have one foul, (using Motul800  full synthetic oil in Shell RF100 at 33:1.)

       Lap the rotor onto the crank carefully with valve grinding paste to help it hold.
            Use Loctite on the tapered shaft and center bolt/nut.

       Make up or buy the correct ignition rotor puller. There is too much risk of damage if you try and use a 3-legged puller.

When hunting for Hitachi components , check out the parts  for the following bikes at your local wrecker/ breaker, I have been told they have coils and pickups etc. common with early TZ's:    74-75  YZ360 , 74-75 YZ250 , 75-76 YZ125 , 74 MX360 ,74-75 MX250. (Greg Bennett)

Coils:   In the long run Ignition Coils and what type you use do mean a lot. The most preferable are the original type with grey insulation and CDI stamped on the bracket that attaches the coil to the frame bracket. You will probably find some at wreckers (breakers) and such as they are the same coils that came off the early model YZ's motocross bikes, the only difference with the numbers stamped after CDI on the bracket would be for the length of the high tension lead to the plug as different models had the coil positioned in different places.
Dont be fooled by after market coils that purport to be CDI compatible, check them out with your "multi-meter" and if they dont give you a resistance of between .8 and 1.2 then have them checked out thoroughly. If they give you a value of around 2.0 to 2.5 then they are coils for battery coil ignition that will work for a while and then give you trouble.
Small Tip: Coils off Kawasaki KLX or KLR will go nicely and they have the added advantage of being able to use a high tension lead of your choice as the coil does not have the lead as part of the coil, these will give you a value of about .6 but believe me they are okay, I use them on my 3cyl Yamaha Special.
Another tip: The orange wires from the CDI box always go to the left cylinder.     Saves you pushing your guts out. (Rob Hinton)

The stock CM61-20CDI-CA111 ignition coils can apparently be replaced by another type of Yamaha unit, the FS1E type.

Agree 100%.  Femsa are good if you can get a good one.  Same for Motoplat. Neither are available new, but PVL do replacement coils for the Motoplat.  PVL also do a killer replacement ignition, available from a company  in Ohio.  There are companies who specialize in RD's, also sell the PVL or Strada ignitions.

If you start modifying a late model ignition just be aware that the advance curve for the old water pumpers is almost dead flat and all late bikes are more sophisticated.  If someone would like to do the dyno time and share the results I'd be really interested.

Plugs - B10EGV are fine, but B10EVX Platinum are even better - they have a smaller diameter tip. Coils are available form your local bike store to fit  YZ80 etc - really cheap aftermarket coils are fine.

Hitachis are fine, but the early single wire pick ups suffer from oxidation on the copper ears, so they should be removed and cleaned and replaced with a dab of dialectric grease where they ground to the stator housing.

Agree 100% about lapping the shaft in and loctiting or wirelocking the center bolt.  I can't tell you how many times I've picked rotors out racers fairing belly pans.  It ruins the stator as well when that happens, so take care.
(Richard Nowson)

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Any of the later ignitions can be used, as long as they are from a parallel twin bike - up to 1990 TZ-A.  As you now show on the site, the advance curve is better and real benefits are to be had in the mid-range. The downside is that the later bikes ran 'backwards', so the ignition will run the wrong way on early bikes.  This is not a problem if the ignition is modified to suit - involving re-indexing the rotor.

Hitachi  Personal preference.  All are old these days, and would benefit by new wires and a tune-up.
Don't use more than 20 thou" plug gap - too hard for the poor electrons!
Don't spin motor over without grounding plugs or leads.
Don't believe the marks on the black 'pulse' coils - may be moulded in the wrong place.  Set the ignition up statically, and strobe it with the engine running - observe the error (i.e. where the coil actually fires) and redo timing.
Use good (non-resistor if you can) plug caps.
Later parallel twin Hitachi can be made to work  with better mid-range.
Femsa.  Don't know much about them, except they always seem to be breaking down, and you can't adjust the timing on each cylinder individually.
PVL  A few people have used them, to my knowledge, in NZ, and not one of them are happy.  Apparently some mix up of components.  Probably a one-off, but would be near the bottom of my personal preference. 


Timing. We never use more than 1.85mm advance.
Earth.  Not fitted as standard to our period machines, though all could benefit by a decent earth for the ignition.  Many TZ's have the engine rubber-mounted at the rear these days, so the only earth for the ignition is via the chain and control cables!  Run a short length of decent wire from the crank cases (we usually put one under the stator mounting screw) to the frame. Others you'll see are from a small crankcase screws on the top of the rear of the case to the frame. (Kerry Wilton)

 Check the tightness of the rotor bolt and the mainshaft nut behind the clutch cover. On Kerry's 350 the rotor bolt has been made in stainless with a bigger hexagon (9/16 I believe) and also has been lockwired. The clutch nut also drilled and wired. We had trouble some years ago with a TA125 rotor bolt and had a couple of spares made. The biggest thing is that the thread inside the c/shaft is 7mm! (Malcolm Wilton)


Ignitions:  The Hitachi is really good but in Europe,  expensive and mostly not working when you find one. A good substitute is the basic PVL, its like the old Motoplat very simple and easy only a bit difficult to install. It costs about 250 euro at ( a Netherlands supplier ) and works really well. (Michel du Maine)

We have used the PVL ignition as supplied by a company in the UK , and have found it to be a good reliable ignition and have used it over the last four seasons.
We use 1.65 mm BTDC as the base timing and run 35 thou squish clearance, which according to a recent dyno run makes 69.8 BHP at the rear wheel.
The only tricky bit is getting the static timing marks set up correctly, this is due to the small amount of rotor movement over the 1.65 mm range. (John Storrie)


A pointer on TZ Ignition stator Maintenance
Fractured wiring at the coils has shorten many a race for TZ riders.
 Ingress of oil and metallic sludge into the coil laminations, and spreading of the laminations can greatly reduce the magnet effect available to the coils. I cleaned the laminations with "Electraclean" spray, removed any burred over-lap on the lamination edges, and gently pressed the ends of the lamination back together. (a good test of how successful your cleaning job was - what oozes out as you press the laminations).  The coils were dried in a vacuum drier and then coated in Industrial motor winding varnish. (Hi-meg or similar).
New wire was soldered to the tails of the coil, (high temp appliance wire), heat shrink over the joint, then the secret....where the wires run from the coils to the cable clamp on the stator plate..... lay a continuous bead of silicone sealant on the stator plate and embed the wire into it. This removes the mechanical stress on the wiring that causes breakage, normally at the coil.  Watch those wires vibrate as you blip the throttle on a standard stator plate. ( Martin Longden )

Krober Ignition:    I use one of these on my triple and it has been totally reliable for the twenty years I have been using it.
There is a lot of wires to accommodate and the boxes are quite bulky and need mounting separately at a minimum specified distance from each other.
The setting of the timing is simplicity itself and can be done for each cylinder, useful when you are using Yamaha TZ parts for the three cylinder crankshaft (oddball firing order 131, 131, 98 spacing).
The ignition advance I use varies from 1.8mm to 2.2mm BTDC, using straight Avgas.
The other advantage of using Krober ignitions is the availability, a guy in England deals in them so all the spares are available if you need them.
If any body wants to know the guy's phone number for the Krober systems then email me and I'll supply them with it. ( Paul Allender ).


Measuring the squish band of a TZ. What I do is use a piece of multicore solder (about 1.5mm OD), put a curve in a length of say 4 inches and with the piston just below TDC push it through the plug hole till i can feel it touch the barrel, gently turn the back wheel over until the piston squashes the soft multicore solder, ease the solder from the plug hole and measure the flattened end with a micrometer, voila! (You must use multicore electrical solder as it is hollow with resin and collapses easily) NO PLUMBERS SOLDER.
Graham Veryard


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      03/25/08 04:51 AM +1000    

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