The GPz750 Modification FAQ

6 Jan 2015 | Autor: | Kommentare deaktiviert auf The GPz750 Modification FAQ
Kawasaki GPZ 500 S (reduced effect)

I replaced the cylinder with an older 807cc Wiseco kit that I used in another motor and a old 1981 KZ 750 head that I got for free from a friend. I did a valve job to the head and milled .032 off the face, right down to the top of the 45 degree angle of the valve. I then ported the head to allow for more flow. I’ve never ported a head so I thought I’d start with something that was worth very little.

I also made a bracket to hold the sprocket cover tight against the cases where the top mounting bolts were missing. Works perfect. After putting 30 quarter mile runs on this motor, I’m very impressed.

The bike will run consistent 10.6’s @ 122mph

The bike weighs 415 lbs. and I’m 185 lbs. dressed for racing. This stock lower end motor has the stock GPz 750 cams degreed to 105. I’ve adapted a set of 36 mm CV carbs off of the stock 89/91 GSXR 1100 with K+N filters and Dyno Jet kit. The bike retains the stock igniter box for now, but I have 2 others that I’m ready to try out.

The clutch basket has been banded by Falicon Engineering for strength and the stock plates and discs are pushed together by Orient Express springs. The Jardine sidewinder exhaust is wrapped with Thermo Tech header wrap to the end of the collector. I run ND w24 es-u plugs firing the 93 octane pump gas that is reformulated with 10% alcohol for emission sensitive areas.

If you have a KZ 750 motor you could drop in a set of cams from the 83-85 GPz that have .5 mm more lift and more duration. Add a set of GPz 750 carbs that have a jet kit and filters in them and you’d have a great power upgrade. If your tach is driven off the exhaust cam you’ll have to fit an electric tach off a later 83 kz or different model bike which I’ve seen done.

Add a Wiseco K 810 piston kit and you’ll really be grinning even with the stock carbs. If you decide to put in a 810 kit, get the carbs you’re going to use sorted out and working properly as far as jetting goes on your old motor. That way if your too rich while sorting out the carbs you won’t have to worry about ruining some thing that you’re going to replace (the bore).

Putting in the 810 kit will have no effect on your jetting. If it worked good on your old stock 750, it’ll work the same on the 810.

The normally aspirated GPz has a 36mm crank and 35mm rod journal bottom end that is of identical size as the GPz 900 and ZX 10 cranks. The Carrillo and Falicon aftermarket rods are still available for this motor that will withstand any abuse. Only the dragracer that has 880 cc or more in this motor running a nitrous system would need this equipment.


For all you owners that do your own valve adjustments, I’m writing about some tricks that I use to get the cams in and out quickly and save some time.

First off, you’ll need a new cam cover gasket if the original is still on. You can re-use the rubber half moon end plugs. Use a light coat of silicone or Hylomar on the end plugs for a tight seal.

Make sure you scrape the gasket surfaces clean and put the new cam cover gasket on dry except for where the gasket meets the rubber end plugs. You’ll also need a torque wrench to tighten the cam cover and cam caps if you remove the cams. A beam type that reads in inch lbs. is perfect. They’re 3/8 drive and I use a CraftsMan for all setting of less than 156 in lbs. (13 ft lbs.).

To find in lbs. multiply ft lbs. times 12 = in lbs.. Here’s a trick I use on the 1981 and later models that use a wedge type cam chain tensioner. After removing the valve cover and with the pistons all lined up somewhat equally (midway between the stroke. remove ignition pick up cover on right side and turn engine clockwise to get into this position.), I push down hard on the cam chain between both cams forcing the cam chain tensioner back and rolling the intake cam forward.

Now that you have a large amount of chain slack between both cams, remove the small 6mm (1.0mm pitch) bolt from the cam chain tensioner (right side) and replace with a bolt that is 1 (or 40mm) lange. You have to modify the bolt so that it has some what of a point on the end with a bench grinder or a file. If you have a metric thread file (Snap- On model TFM 7530B ) you can clean up the threads.

Or you can thread two nuts onto the bolt before trimming and try to clean and reform the threads after shaping. Now screw this modified bolt tight into the side of the tensioner to lock the push rod down into its compressed position. Now the cams can be removed with the tensioner in place because the tensioner push rod is locked in the backed off position.

Cam cover and cam cap bolts are much faster and easier removed and replaced with an electric screw driver ( NOT electric drill). Follow a service manual for checking valve clearances and cam installation. I remove the spark plugs so that the motor can easily be turned over, and cover each spark plug hole opening with a rag so that no debris can fall into the cylinder.

Once you have the cams reinstalled, remove the longer 6mm lock bolt in the tensioner and reinstall the short bolt so that the pressure can be applied to the cam chain. Jetzt, Slowly turn the engine forward to check your cam installation as explained in the service manual.

On the latter models, before replacing the cam cover, notice a rubber cushion on the inside of the cam cover that pushes against the cam chain between the cams. If you were to put the cam cover on with the chain pulled taunt between the cams, you’ll notice that the rubber cushion will keep the cam cover from resting flatly on the head mating surface. To make the cam cover go on properly, again push down on the cam chain between the cams to get a little bit of slack in the chain.

Now if the cover fits against the head mating surface, install, tighten and torque the cover in place. When finished slowly turn the motor clockwise slightly to take up the cam chain slack that remains once the cover has been reinstalled. When you first remove the cam cover the first time to do any service Take Notice as to the free play in the cam chain between the cams after the cover is removed and the motor has not been turned over.

This free play is the equivalent of 4 degrees of cam timing. YES, the intake cams are off 4 degrees in timing from the factory. For those of you that have slotted their cam sprockets and degreed the cams, the intake cam needs to be set to 109 degrees and will actually be 105 degrees once the cam cover is reinstalled.

Call Arias and they’ll make you larger pistons (6 mm over) special order ($750)

Send the cylinder out and have larger liners installed (Über $450).

Send the top half of the case out and have the holes bored to fit larger liners ($100)

Call Cometic and have custom head gasket and base gaskets made. ($100)

Bore and hone ($125)

Add some stronger rods from Falicon ($550.00)

Now you know how to spend $2,100 to get a 879.45 cc motor ( 72mm by 54mm).

And YES, I’ve seen this combination but in the kz 650 motor dragbike of Ms. Monty Fisher of Rockford, IL Runs low 10s and as fast as 9.90 on a very good Day.

As for piston kits, the Wiseco K 810 kit ( 807 cc, 10.25 zu 1) is a less costly way to go compared to the Kaw over size pistons. The kit comes complete with wrist pins, keepers and a Cometic graphite head gasket that is the greatest for sealing tight and having absolutely no leaks. The pistons are forged and machined to exact tolerances so that the set is exactly the same.

The valve pockets are cut deeper for higher lift cams. As for horse power with this kit, expect to get 83 zu 88 at the rear wheel with the stock deck and head heights. The factory manual lists HP at the crank which is always higher in number.

Horsepower Unlimited at 310-827-5595 offers many items that’ll fit the normally aspirated bike. He has stronger clutch springs for $25 (will fit all Kz,Gpz,Zephyr models) and stronger cam chain tensioner spring for the GPz model ($20) to mention a few.

For the normally aspirated motor

I suggest you buy the Wiseco kit that has 10.25 zu 1 pistons and mill .020 off your head and you won’t be disappointed. You’ll have to slot the cam sprockets and degree the cams to make them right because of the head milling though. If you need more HP than this, I can only suggest that you look at a different bike.

It would be much cheaper in the long run Step 2 would be to add the 810 kit and milling .020 off the head is a must !*!*! Along with that slotting the cam sprockets will have to be done so that the cams can be degreed to their proper position. Stronger clutch springs will also be needed.

The Wiseco kit is superior to the stock components and will run as long or longer. The ‘biggest culprit to longevity and reliability is that the carburation is not overly rich, which is the case in many novices jetting kit failures.

The Kz 750 and GPz 750 are the same (bore +stroke,valve size, trans gears etc. etc.) other than the cams in the GPz have more duration and .5mm more lift. My present race motor (83 GPz 750) has a 81 Kz 750 head (stock valves and springs) on it with the GPz cams installed. Great combination because the Kz of that year has a smaller combustion chamber than the GPz.

If they offer a copper head gasket don’t bother getting it. They weep oil and all the gasgacinch in the world won’t seal it. Call Cometic for a graphite one.

Das 1983-85 GPz750 have the hottest cams with .020 (.5 Millimeter) more lift and 16 degrees more duration. Both are interchangeable but if you have a tach that runs off the cam you’ll have to switch to a electric tach which is easy to do off a later model bike.

Das 82 GPz750 has a combustion chamber volume of 24.9 cc which is very good. Das 83-85 GPz750 have chamber volumes of 25.9 cc. The Kz750 H 24.8cc and Kz750 L 25.3 cc.

You can easily switch these heads between motors. My present 83 GPz750 has an 81 Kz 750 L head on it.

I’d also recommend milling at least .010 zu .020 off the head at the same time to get the full advantage of this piston kit. It will make it noticeably better. I’d also remove the cam sprockets and have them slotted so that the cams can be degreed when reinstalled. They won’t be close to what the factory recommends because of chain stretch, new head gasket and milling the head.

VH has a video tape on how to perform this procedure.

When you get the secondary shaft out, take it to the local well stocked hardware store and get a long metric bolt that’ll fit in the threaded end of the shaft. Get a nut that’ll fit on your bolt and some large diameter washers that’ll fit over the shaft. Put the washers between the nut and gear you’re reinstalling.

You now just made yourself a gear pusher. You’ll also need a tool to hold the inner clutch basket hub to get the clutch basket off.

Flywheel Clutch Tool pt# 28-288 $27.99 plus shipping from Dennis Kirk (800-328-9280)

Same internal trans gears in all the 750 Modelle. Das 83-85 GPz750 has the hottest cams of the bunch. The Zephyr and Kz’s share the same cam profiles.

Wiseco had some changes to the top piston ring and gasket configuration in the 1992 durch 1994 models that they made. They went from the thick top ring to a thin top ring and then switched back to the thick top ring which they still use today. The Cometic gaskets for the K810 kit prior to mid 1993 are flawed.

The cutting dies that they had where flawed (off location) and one metal fire ring protruded into the cylinder slightly. I also recommend that you use factory original valve oil seals when assembling the head as the aftermarket ones don’t even compare in sealing quality.

If you do mill the head you need to remove your cam sprockets and have them slotted so that the cams can be moved back (degreed) to the correct position. Most people don’t realize how far off the cam settings become when the cam chain stretches much less changing the height of everything. MAKE SURE THAT YOU LOCKTIGHT THE CAM SPROCKET BOLTS WHEN RE-INSTALLING THE CAM SPROCKETS.

Otherwise they’ll back out over time and your nice hot rod motor will be a big box of junk when this happens. First off, your cam settings are almost never what the factory says they are set to because of chain stretch and the difficulty in keeping the deck heights all the same. At best they’re usually with in 2 oder 3 degrees when new and become possibly better or maybe worse with time depending on which side of the correct reading they’re on.

Any head milling or aftermarket head gasket will also add to the setting being wrong.

On the Kz 750 model when you remove your valve cover, stop and take a good look at the slack in the chain between both cams. Yes you can take and flop this cam chain up and down with ease when the valve cover is off. Now look at the inside of the valve cover in the area between both cams.

There’s a big rubber chain cushion that puts a slight downward belly in the cam chain between both cams. You take the cover off and check the valve clearance and by rotating the engine now the slack that was once between both cams is gone. Now you put the valve cover back on and it won’t sit flat because it’s rocking on the this rubber cushion. Ja, as you screw down the bolts it slowly over rides the cam chain tensioner.

Here’s the method I use to put the cover back on. I remove the right ignition cover and rotate the motor to where all the pistons would be in the midway position. This means that the 1-4 mark and 2-3 mark are lined up horizontally.

Then before I put the valve cover back on, to get some slack in the chain I just push down hard with my thumb on the cam chain between the cam sprockets. This over rides the cam chain tensioner and the intake cam rolls forward and puts some (not to much!) slack in the cam chain. Now the valve cover will sit flat on the head when I re-install the valve cover bolts.

After the valve cover bolts are tightened, I slowly rotate the engine forward a quarter turn to remove the slack in the chain and I’m ready to go.

OK. So where am I going with this. Gut, when you degree the cams you have the valve cover off and there is no slack in the chain between the cams. After you degree the cams and when you install the valve cover the intake cam rolls forward. What has this done to you intake cam degree setting. It’s changed it.

But how much did it change it by and did it increase or reduce the setting. Gut, lets first talk about were we want to set the cams to. The service manual calls for a lobe center setting of 105 degrees for all the 750 Modelle. This is a setting one must calculate given the information listed in the manual.

Here’s how it’s done. Add the open and close settings together .

In the case of the GPz. 38 + 68 = 106 add 180 to this = 286. Now divide by 2 = 143. Now subtract the smaller of the initial cam numbers 143 minus 38 = 105.

This setting will be the same for both the intake and exhaust cams.

I’ve had my cams set from 100 zu 110 degrees and the best all around setting is the one that comes from the factory. 105 Grad. I use this setting in all my motors now.

So now the answer to the cam degree change of the intake cam rolling forward when the valve cover is re-installed. The intake cam will change by 4 Grad. And it’ll DECREASE the setting.

So if you want both cams to be at 105 Grad, you need to set the exhaust cam at 105 degrees and the intake cam at 109 Grad.

For the stock GPz750 and especially for the Wiseco 810 kitted bikes the clutch springs you want are from Orient Express. When you call them you want to specify that you want their gold clutch spring that is 1.5 in length. They’ll cost you $25 plus shipping and cod charge that’ll bring the cost up another $10.

They can be reached on the East Coast at 800-645-6521 oder 516-546-5232.

For those of you with the Kz/GPz 750 that are replacing the stock bore Kaw head gasket I recommend that you use a Cometic graphite head gasket. These gaskets won’t weep oil like the stock Kaw head gasket, and have proven themselves in many racing applications. These are what come standard with the 810 piston kit from Wiseco.

I’ve used these for years and swear by them. Even Harley Davidson uses the same material in their stock head gaskets for all their motors today. And they don’t leak. Cometic can be reached at 216-974-1077 in Mentor,Ohio.

The gasket model you want to order is H0126044G and cut to 66mm Bore size. The price is $38.95 plus $4 for shipping and they take major credit cards. This is cheaper than the stock Kaw gasket.

I’ve seen in the Yoshimura catalog they sell cams for the GPz 750. Stock valve cover gaskets are very good (and no Cometic doesn’t offer valve cover gaskets). When replacing the original valve cover gasket make sure that the surfaces are squeaky clean.

Some people like to put a light coating of grease on the new gasket to keep it from sticking to the mating surfaces and making it easier to reuse. I prefer to put mine on dry and find that if you use a light coat of engine oil instead of grease it’ll do the same and be easier to clean. The original half moon rubber end plugs are re-useable.

Make sure that you use a silicone sealer on the half moon plugs where they mate to the cylinder head and at the top that contacts the valve cover gasket, otherwise they’re likely to leak.

Here’s the specs on all my 83-85 GPz750 motors:

807 cc Wiseco kit 10.25 zu 1

head milled from .020 zu .030

leak down of less than 8%

stock cams degreed to 105

stock clutch with banded basket and aftermarket springs

ND w24esu spark plugs

93 octane unleaded pump gas

I’m always looking to try something that might be less expensive so I ordered a set of racing clutch springs to fit the Kz 900/1000 (pt # 40-0445) from Schnitz Racing Enterprises (800-837-9730) located in Decatur, Indiana. $12.95 for the springs plus $3.50 for shipping put them on my door step for $16.45. These red springs measured 5% shorter than the stock GPz750 springs, but the wire thickness was 25% greater than stock.

After I installed them the clutch lever felt slightly stronger than the previous $30 aftermarket spring that I’m using. The difference was noticeable. The clutch was locked up tight in all gears and there was never a hint of clutch spin. I was so impressed with the clutch springs (and the cost!) after this that I called and ordered 3 more sets for the spares pile.

These springs will fit all Kz/GPz/Zr 750 clutches. The stock 750 springs measure 48 lbs. @ .950 and the Schnitz red racing springs springs are 94 lbs. @ .950. I find the slight increased clutch pull not to be obnoxious even for city riding with these stronger springs. The price of the springs are $13 plus Versandkosten + handling from Schnitz in the USA.

If you or anyone else from out of the USA are interested in these springs let me know and I can send them direct to you at a much reduced cost of shipping.

But here’s a new twist that might be a slightly higher compression stock head gasket replacement for the stock Kz/GPz 750. The factory stock Zephyr 750 head gasket measures .029 thick verses a factory Kaw fiber Kz/GPz 750 head gasket at .039 thick, or a Cometic gasket that measures .041 thick. Das .010 reduced thickness would add approximately .2 to the compression of the stock motor.

I’ve not tried this, but there’s a good chance that this would work. Now that I’ve got this old Zephyr head gasket, the next time I tear down a GPz 750 motor I’m going to do some investigating as to the possibilities.

First you should have .020 (.5Millimeter) milled off the head to ensure the best performance and compression from the kit. This figure is on the safe end as I’m removing much more on my street and race motors. You can safely mill the head right into the intake valve seat and up against the 45 degree angle of the seat. Don’t mill into the 45 degree angle.

This is somewhere in the area of .032 zu .035 of material removed. I’d take a minimum of .020 off and .025 would be even better for the 810 kitted motors. I’ve have four 810 kitted motors with over .030 milled off the head. Three GPz750 heads and one 81 Kz750 head. If you don’t mill at least .020 of the head for the 810 kitted motor you’ll be disappointed with the results.

Although the valve angle is the same, das 750 has larger valves (33mm intake 29mm exhaust) than the 650 so there might be a problem with clearance. The combustion chamber volume of the 83 GPz750 head is 25.9 mL The 80-82 Kz750 or 83 and later H model heads have a combustion volume of 24.8 mL. The Kz and GPz heads use the exact same valves and springs.

The early model 750 heads have the cam tach drive feature also.

From: Allan.Webster@West.Boeing.com (Webster, Allan S)

I emailed you a while ago about my GPZ750 for road racing. Anyhow, I guess the actual horsepower is closer to 100, or maybe 110 This is in the area of .030 zu .035 removed from the head surface. Lower than 93 octane fuel can be used, but you’ll need a 35 degree total advance ignitor from the 1000R Ninja and a jet kit to make not ping.

If you shave the head, you’ll also need to degree the cams.

I’ve read several articles written by people like Warren Johnson about valve trains. Matching the correct spring to the valve lift will produce the most HP. A spring that is too weak will promote excessive valve bounce and valve float, while a spring that is too stiff will rob the motor of horsepower to compress it. I agree that checking the stock spring against the factory specs is the best thing to do.

I’ve often thought of trying some stronger valve springs and perhaps I will someday. If I do it’ll be a set of APE springs made for cams with up to .460 of lift. Schnitz Racing (800-837-9730) offers a complete set of APE valve springs to fit the Kz650 through 1100 2 valve motors ( Teil # VS 900K) zum $46 plus Versandkosten.

Here’s some advice about how to properly set the cam timing on a GPz750 motor. Das 83-85 GPz750 valve cover has a rubber cushion that depresses the valve chain in the area between the intake and exhaust cam sprockets. With the valve cover installed, the rubber cushion moves the intake camshaft forward 4 Grad.

When one degrees the cams, the valve cover is off. This means that the cam chain is tight between the intake and exhaust cams. With the valve cover installed, your 105 degree intake cam setting is now actually 101 Grad! So what you need to do is degree the intake camshaft to 109 Grad, and when the valve cover is reinstalled it’ll roll the intake cam 4 degrees forward to 105 Grad.

For those of you that question what I wrote is true, try this. Before removing the valve cover turn the motor crankshaft forward slightly by hand with a ratchet. Now remove the valve cover. Take a good look at the slop in the cam chain between the intake and exhaust cam sprockets. Take and move the cam chain up and down.

With a degree wheel on the crank, you’ll measure the crankshaft move 4 degrees to make the cam chain tight between the cam sprockets. This is the same condition that exists when you are degreeing the cams.

I added an oil temperature gauge (VDO) about a month ago and it works great but the MOD was a bit tricky. I got a sensor to mount on the engine and there are 2 plugs on each side of the motor (lower front corners) that can be removed and a car sensor can be added. The problem is that the plug is 18mm and the largest sensor is 14mm X 1.25 thread (it might be 1.50 but I threaded it with a 1.25 tap and its working fine.

The sensor is about $12 and the gauge around $29 (I got my gauge at a flee market for $6) My bike took REALLY well to a Dynojet kit, KN internal filter and new pipe. External filters were avoided due to their sensitivity to water, and I ride a lot in the rain. They also are loud enough to wake the dead (intake noise). I originally installed a Yoshimura Supersport pipe intended for the street.

It was much lighter than the stocker (I could feel the difference in handling) and the bike made much more power, especially on top (seat of the pants measurement). It also allowed retention of the center stand and access to oil drain and filter. Unglücklicherweise, it was louder than a rabid banshee, so I removed it and installed a new Hindle Stealth.

According to Sport Rider tests, it was even 3 dB quieter than the new quiet SS2R Vance and Hines and makes as much power (if not more) than all other after market pipes they tested (they tested them properly rejetted for).

I’ve found that it makes noticeably more power in the midrange than the Yosh, and is VERY quiet for an aftermarket pipe. It’s more than socially acceptable. Fitting it to the bike took 1/2 an hour.

Unglücklicherweise, it restricts oil filter access and involves muscling the headers to get it out. This means that muffler compound must be reapplied at the header/collector joint each time I change the filter. I also had to make an aluminum hanger bracket (the provided one is too short) out of a 2-3 lange, 1 wide piece of 1/8th thick aluminum ($2) and used it as an extension piece from the ring clamp around the pipe to the mounting location on the frame.

If this isn’t done, the pipe would have to be moved into a position which causes hassles with the passenger pegs (the passenger pegs would dent the top of the pipe). I also bought hot water tap washers as vibration isolators at the frame, and used nice hex head machine bolts to hold it in place.

This all sounds like a pain in the ass, and it is, but was well worth the trouble IMO. It looks great, sounds fantastic, and makes great power. The throttle response is much improved over stock or with the Yosh, power is improved anywhere (realize that I also added the Dyno-jet kit) and the center stand was retained. The pipe costs around $450 Canadian through Hindle.

If anyone tells you that a pipe kit and rejet do not add horsepower, than you are talking to someone who never rode a 10 year old bike. For more serious modding, I’ll pull from two sources. The following engine info is based on GPz750 hop up articles from old issues of Cycle Canada (’84) and Cycle (’85, Joe Minton). To get any more power from the engine, freshen it up with a 3 (oder 5) angle valve job and shave the head to recommended minimum height. The engine can take it.

That would be a good time to ensure there’s no valve guide slop and to replace the valve seals to ensure no smoking on trailing throttle. I’d be careful about head shaving AND adding a big bore kit as the big bore pistons already up the compression. Shaving the head may lead to detonation with the new pistons, or worse, crown and valve contact (can you say kablooey?). There’s also an 810 Wiseco kit (Meiner Ansicht nach 850 kits too) to pump the engine out even further through a 3mm overbore.

If you ever decide to do any ring/cylinder work, it’s worth looking into these kits. Na sicher, you have to re-jet, but taken in conjunction with the new air filter and pipe, the increase in midrange and top end is apparently 10 ponies or more. The Wiseco gasket kit is aprox 1/2 zu 2/3 the OEM price.

Adding a new carb bank (40mm flat slides are available) adds many a top-end pony, but costs too much to bother with on this bike IMO and will no doubt weaken the already limp midrange. The hop up articles threw in new cams from Mega Cycle and advanced the engine a couple of degrees (107 deg from the stock 105). I won’t bother as the bike seriously lacks midrange already and the cams are biased towards top end.

If you do any head work, install a GPz750 Turbo gasket kit. It’s the same price as the standard, and it’s stronger. Aftermarket gasket kits are available and are much much cheaper than OEM. A larger oil cooler was available from Lockhart.

If you really pump up the engine, look into this. Even relatively stock, I’ve had the bike almost overheat in traffic jams on hot summer days. An Accel Supercoil kit has been reported to improve midrange and throttle response on the GPz.

Seeing as how this is a race bike, I recommend that you use a Cometic(800-752-9850 in Mentor,Ohio) graphite head gasket model #H0126044G cut with 66mm bores. About $50 delivered. This head gasket positively will not leak.

The replacement stock Kz/GPz Kaw head gaskets are very prone to leaking and especially when used in racing applications. The Cometic gasket measures the same thickness as the stock head gasket.

Ja, the Wisco kits include a Cometic graphite head gasket

The stock valve clearances apply with the 810 kit.

There are 2 different types of automatic cam-chain tensioner used on old Kawasakis, which I know as the ball-race and the cross-wedge types.

The ball-race tensioners work very well when new, but the balls do eventually wear grooves in the push rod and in the tensioner casing which means that the precise locking no longer works and it backs out allowing the chain to rattle. When this happens, there is no alternative to buying a complete new tensioner. -( You could try stripping and cleaning it just in case it helps, but they’re generally very reliable until they wear out. The first one on my SR650 went at around 30k miles and its replacement was still ok 20k miles later when everything else in the engine was completely worn out after too many enjoyable Sunday thrashes and it was replaced by a Z750 engine.

jedoch, on the plus side, there’s better news if you’ve one of the newer cross-wedge type tensioners (which I think’s fitted to most 750s and other big Zeds). -) When these wear, you end up with ugly grooves and ridges on the push-rod and on the cross-wedge where the two contacting faces meet. When this happens, the cross-wedge either doesn’t move to take up the slack to lock the push-rod in place or gets pushed back out, again allowing the cam chain to rattle.

I’ve found that if you dismantle the tensioner and use progressively finer (down to 1200 grade) wet and dry paper on a hard, flat surface and finish off with a polishing compound you can smooth the two faces down to a near-mirror finish (or certainly enough to get rid of the grooves and ridges which cause it to stick). Then you clean them very carefully (to get rid of all the abrasive particles) and reassemble with decent grease on the two faces.

You can check that it works before putting it back on the bike by pushing the rod in and out with your hand whilst keeping pressure on the cross wedge with a finger and making sure that it doesn’t stick or jump anywhere. If you do this, you’ll get many thousands of extra miles of use out of it. I did this on my 750 a few years ago and have had no problems since, in a combination of town-riding and Sunday afternoon, flat-out blasting through the twisties.

As an aside, for those of you who don’t mind getting your hands dirty once in a while and want to have absolute confidence in their tensioner, I’ve heard that a manual tensioner from an early Z250 will fit straight in. I had one of these on my first big bike, an old 1980 Z250, and in the 30k miles I thrashed it around I used to check and adjust the tensioner every few thousand miles and never had a single problem with it. You can also get manual tensioners from tuning and aftermarket goodies shops as well, which I shall probably try on the 11 when I want to do something but can’t think of what else to tune up on it.

Hope this is of some use to you.

Joe Smith, Senior Engineer, GenRad ADS

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