Gt550 engine experiments

Kawasaki GPZ600r gt550 vs vs vs ZL600 gpx600r

The search for upgrades on a motorcycle is for me the ultimate cafe racer feeling. So not the right tattoos, beard and clip-on handlebars but just to find out how you cab upgrade your bike with the minimum of resources. I have a gt550 and which is going to serve as a basis!

So is my gt550 air cooled and shaft driven. The shaft I find cool and practical, the air cooling I find unfortunate. Many cafe racer purists (yes they exist) find that a cafe racer should be air cooled, I think it should be fast and driving as good as possible. Hence the following idea: I am thinkering a lot on the bike and other Kawasakis and found out that the Kawasaki 550 and 600 blocks are very similar. Whether it’s shaft or chain, water or liquid/air cooled. A 600 engine of a gpx, gpz 550 or zl is about the same as the engines of a KZ, GP or GT, but not quite.

GT, KZ, Z, GPZ 550

These engines are very similar. There is a KZ with shaft drive, just like the GT. The slightly different one is a sportier GPZ550, which had a bit more horse. These are all designs from late 70 ‘s early 80 ‘s. The engines had a quite long lifespan used in a Zephyr 550 and 750.

Kawasaki Gpz 550 engine
Kawasaki Gpz 550 engine
Kawasaki GT 550 engine
Kawasaki GT 550 engine
My gt550 engine
My Kawasaki GT 550 engine

The picture above is the engine that was in my GT, got it torn down because it was really worn. I got the motorcycle from a neighbor of a friend of mine. Has been in his backyard for some while and did a lot of kilometers. I found out the engine was refurbished some while ago, found new gaskets, coupling and painted frame. But a few years in a backyard  does a bike no good.


The sportbikes have an engine that is very similar to the ones above. They are water cooled but the stroke is the same, the bore slightly bigger, the gearbox is almost identical, the clutch is almost the same. The engine is from the same origine of the old engines. The good thing about these bikes is they are but ugly and worth nothing making it an awesome parts donor. In Holland a good enough gpz or gpx or is worth maybe 500 euros. The parts might come even cheaper.

GPX 600r-engine


A ZL600 is a in my opinion as hideous as it gets. I actually think all non Harley choppers are kind of fake Harleys … and a Harley is for fat middle aged guys or criminals, please dont take it personal if you are a middle aged fat guy or a criminal, the fact you made it this far on my blog written in poor English makes you cool again 😛 But apart from that, what is great about the ZL is her engine.

Zl600 engine

The zl600 engine is a slightly powered down version of the GPZ/GPX engine. It has a less pointy camshaft and smaller carbs. Many use a head and the zl600 carbs plus ignition of a gpx. You easily win 10 horse.

My plan is to use the ZL600 gearbox and engine carter, the gpx head with carbs, ignition and cilinder-head. This mounted in the GT gives it that extra horses, less engine noise, less smoke, less gass and the convienice and awesomeness of the shaft drive.

This page will also supplement with  comparison information and other stuff i find out. Always handy for anotherone who considers doing something similar.

Gear ratio

The GT550 is sometimes criticised regarding its drive ratio, it will rev quiet high on the highway. The standard GT top speed is 175 km/h, with my 2 cylinder ER5 I make higher figures with ease … and it only has (or once had) 50 horse. For those who continue to drive with an original engine it might be worth upgrading to a different ratio, especially if you are doing a lot of highways. The clutch is equivalent to a gpz/x600r, only the gears are different, the cltch gear on the GT is bigger and the drive gear on the starter shaft is is smaller.

Comparison GT and GPZ/X gear ratio
Comparison GT and GPZ/X gear ratio

If you own a GT you can use the GPX gearing to get some more top speed and be lower in revs on the highway.

Data and partnumbers  GT 550

  • gt550 Clutch: 130,951,030
  • gear: 130971008 (26 teeth)

Data and partnumbers GPZ/X

  • Clutch: 130,951,128
  • gear: 130,971,141 (28 t)
Gearbox GT550 vs GPX600r
Gearbox GT550 vs GPX600r

Above you can see the two gear boxes more or less complete. The clutch is the same, just like the gearbox, the difference is in the ratio of the large gear on the clutch. The GPZ is smaller so you end up going a little faster.

The cool thing is that by combining these two gearboxes you get a ZL600 configuration. That’s what I’m going to use. Big fun is it that the GT and its large 18 inch rear wheel against a 15 inch wheel on the Zl.

Comparison table ZL, GT, GPX and lion-600

Gt550 GPX600r ZL600 Lion-600
HP 56 84 61 84
speed 178 226 181 2xx
Bore x Stroke 58 x 52.4 mm 60 x 52.4 mm 60 x 52.4 mm 60 x 52.4 mm
Compression 9.5:1 11.0:1 11.0:1 11.0:1
Capacity 553 592 592 592

46 thoughts on “Gt550 engine experiments

  1. Hi,
    Maybe you could help me. 🙂
    I have a Kawasaki LTD 550 with shaft drive. The secund piston broked down.
    So I thouth it is cheaper to cahnge the complet motor.

    My question is: can I cange a block with chain dirvie whit a shaft drive. I can buy only motor with chain drive. It is the same?

    Thank your answer

    1. Hi Istvan,

      Unfortunately not. The aluminium carter piece withe the shaft exit of the engine has a different pattern than the chain driven engines. At first I planned to make some kind of adapter plate but that’s is a lot more work and costs. However, you van use all the bits and pieces you broke but it means you have to spit the carter halves to get to the crankshaft.

  2. Great blog – and lots of interesting info. Is it possible to fit the ZL600 gearbox and output shaft into the GPX600r motor, giving a far more powerful engine but with the smoothness of a shaft drive? I’m planning on this mix to upgrade my ZL400 (I’m not fat or a criminal) to a quicker 600. You can convert the 400 engine to a 600 by swopping over the crank/barrels/pistons etc but I’d rather have 84bhp so I’ve bought a GPX600 to use the engine – it’s either swop the gearbox to convert it to shaft drive or convert the bike to chain drive.
    Not sure which way to go….

    1. Hi Phil, thanks for the compliment!

      I don’t think its worth the excessive engineering to fit a shaft swing arm on a gpx600 bike. You will also loose some horse because a shaft is less efficient to an chain.

      The other way around, applying a shaft to a gpx600 engine is not possible because the GPX crank and gear housing won’t fit without extensive milling end engineering. I considered it at start when I did nt have the luxury of having a ZL600 engine. The problem is the cover fitted over the GPX engines output-shaft, it has a different pattern compared to the shaft pattern. The shaft pattern of the ZL and the GT is stronger because a lot of forces are created in a shaft configuration.

      If the ZL 400 engine is the same as the ZL600 engine you might be able to swap the guts of the GPX600 engine. The ZL600 is quiet similar to the GPX600, apart from the shaft area and the output shaft, everything has the same fitting dimensions. The difference apart from the shaft is the cam, ignition and carbs. The ZL600 is torquey and the GPX has high rpm horses. The gear ratio is of your zl400 is different to a zl600 … I guess (you can check the online part libraries and compare part numbers) But the most important stuff is there, the casing and the shaft parts.

      It would be cool if you send my some pictures of your zl400 engine, I would like to add that to this article

  3. Hi – sorry for the delay in replying, and thanks for the info. I’ve just finished stripping down the GPX600 and got the motor out so it’ll be getting torn down to check it over. The ZL600 crank, barrels & pistons and head all swop directly over onto the ZL400 so swopping the GPX600 internals over to the ZL400 is a better plan possibly. I’ll get some photos of the ZL400 engine over to you when we get a decent clear day,

  4. I just tried my GPZ600 clutch and primary drive gear in my derelict GPz550 engine as a test. It fitted perfectly. 600 clutch has 63 teeth. 550 clutch has 65 teeth. That is approximately a 10% overall increase in gear ratio. That means the GT550 should do 110km/h at 5,000 rpm and have a potential increase in top speed of 20 km/h. Assuming I get the power out of the engine I’m expecting.
    Thank you very much for the information that you have provided here.

    1. Awesome! Dus you make some photos? Would be great tot add them to this article.

  5. Interesting concepts here, for me shaft drive makes sense, however, I have 2 ZL’s, I like them, they are an under estimated as a motorcycle on the road., more mid-range than the out and out pocket rocket versions! I too have been toying with the idea of modifications! The 80s ZL engines have 54bhp & 74 bhp respectively for the 400cc & 600cc motorbike, they have much bigger power outputs than the later 90s models!

    However, a GPX 600 manages 84 bhp & the ZZR units are listed @ 98bhp, but the best 636cc newer unit can support 118 bhp have you looked to see what the compatibility of the components for a shaft drive bottom end and an swapped upgraded top-end? Reboring and larger piston swap or inserting a GT750 crank with a 54mm stroke?
    I wouldn’t mind a 636cc ZL which would be 44cc bigger than the original unit! Or using a GT 750 crank with some barrels that would accommodate them!

    1. Hi John,

      I am afraid the zzr engines are totally different. Maybe apart from some bolts they don’t share any part.

      The difference with the gpx units are small, only the carbs, a narrower intake and a smaller air chamber before the carbs tune it down. Changing to gpx carbs, ignition and air chamber will do the trick.

      A time period Kawasaki 750 engine is way different, its wider and has a different gearbox. Not use able. I think for you the best option is upgrading the above. I think on a ZL forum someone did the swap although some issues with the ignition where mentioned.

      1. Thanks 4 your prompt reply. I am going to b busy this next few weeks sorting out a new workshop, when I do this I can play around!
        I have a Z650 B1 to bring out of retirement, I have had the bike since 1986, the same engine was developed into the Z750 and also the GT 750 shaft drive range, though as yet I have not had time/ chance to compare design to the ZL units.
        Probably that is why the ZL 750 is based on a different engine lay-out, perhaps this is based on the old stretched and then adapted for presumably water-cooling, Ben Inamura designed Z650 unit!
        I was looking for little more power as most people seem to be scooting around on 85bhp to 125 bhp machines these days!
        I have given you a link to a Road test in the mid 1980s, which shows the the more flexible ZL600 leaving the GPX for dead in real road situations!
        The camshafts are exactly the same in both bikes it was all down to the smaller carb’s and Airbox design, Keihin’s perform poorly with pods if the original Air-box is replaced. The smaller bore 30mm carburettors make the ZL engine much more responsive throughout the rev’ range, except at Top-end, wide open throttle.
        So the GT 750 bottom-end and gearbox unit is completely different beast, it takes its 54mm stroke from the Z650 unit and you say the gearbox is different, is it the mechanism, component size making it just a lot more robust?

        Just interested in how much of the “DNA” of the First generation, air-cooled fours passed on into the first series of water-cooled variants? Have you any information on compatibility of pistons cranks, suppliers e.t.c? Thanks again. John H

  6. Oh! just another question : I wanted to remove the gearbox so the engine was lighter and therefore easier to work on. I have removed the casing screws and the gearbox still seems to be well fixed to the engine! Is there anything else that needs to be done? I was going to break the gasket seal by gently tapping the casing shell with a hammer hitting a piece of soft wood!

    Thanks John

    1. Do you mean the outgoing shaft housing or do you want to split the casing? Outgoing shaft housing shoult come off once you removed all the bolts. Below I borrowed an Image from the best parts store in Europe, CMSNL.
      Shaft ZL600
      Part 13048 has in indirect connection with the outgoing shaft of your gearbox (you can see the shaft on the first image of this post) so you don’t need to open the rubber cover on top of the housing. This is a safety device if something locks up and it takes some of the vibrations away.

  7. Thanks for your reply and the diagrams. I need to do both tasks as I need to take out the crank and clean the bottom-end out and have it all checked. I also consider the barrels need a re-bore as soon as I have some spare cash, this will also mean new pistons. Maybe there is some cross-compatibility, I am not sure whether there are any oversized pistons available for the 60mm variety but there are some other models with 62mm pistons from the 250cc range.

    I saw a kit advertised where they had taken a 550cc air-cooled 4 out by 3 mm making it 615cc capacity, I will try and find the link!

  8. Hi, got a slipping clutch on my ZL400, will look at it later today do you know whether the GT550 or any other smaller Kawasaki 4 cylinder engine clutch friction plates are compatible?

    From your pictures the clutch mechanism as you say look identical. apart from the large gear’s number of teeth. So I was hoping to presume that the internal clutch plates were identical too!

    Incidentally, the ZL camshafts are identical to the GPX/GPZ range, same part number!

    1. I am pretty sure they are identical, most of the Kawa engines from that time period share parts. If you want to be sure, use the link of the partslibrary in my other reply end compare the numbers 😀

  9. Thanks Matthijs;
    I found some road tests here!
    I will check the parts list too. I have just bought a GPX 400 enginen @ an excellent price, to use as spare parts if needed 4 my ZL 400 engine. As I strip it down I will take photos and check out part numbers!

    I still have to check out the re-bore and piston availability for my ZL 600 unit, since it needs a rebore, I wouldn’t mind boring it out a little to take it up from 592cc to somewhere over 600cc, I found the big bore kit for the 550cc unit but only have a screen-print of the advert!

    Information about the smaller Kawasaki 4’s is scarce, below the 650cc/750cc models and engines, so doing some digging round at the moment 4 information!

    1. Hi John, I think you can upload it to your own wordpress and embed it ussing the link or img tag.

  10. Matthijs, I am looking 4 parts 4 my ZL600A. in particular there is difficulty with finding a replacement (fruit gum warning light 6 in all) headlamp fitted to early ZL 900/1000, ZL400/600 & EL 252 models, plus the small internal headlamp warning light wiring loom, , good main wiring looms, exhaust pipes and silencers of a type that would fit and look good any ideas.

    Is Holland still a lot cheaper than GB? And JAMA exhausts do you know anything about them?

    Many thanks


    1. Jama exhausts used to be a Dutch company and went bankrupt in 2012, they produced pretty decent exhaust. They also used to be owner os Laser exhaust and that still exists. Jamas are decent because a lot of engineering went into performance, they are not looks over function.

      I tend to get parts from the UK but most of them where gt750 parts and they are cheap in the UK. I dont think you will get a better deal overseas, especially since the pound is not on its best exchange rate right now because of you funny British want out of the EU.

      I will take a look at our local ebay, it is called and most of the dutch sell their stuff there, also you can check

  11. Cheers Mattjis, parts prices going crazy over here! Exhausts were from a Yamaha 600 Diversion, considered they could have been adapted to the ZL.
    Remember you stating earlier in your blog, how cheap Kawasaki’s were going for! have U finished your projects yet?
    Apologies, but I voted to Leave the EU, I do not like Political interference in areas i do not deem need it, nothing against Europe or Europeans , it is a shame but our politicians are the most betraying of any on Earth, we need a break and a new system, it is really broken here!

    I paid for a Headlight shell/bowl, but the breakers had stripped out the warning light pod?! I have purchased a new warning light pod, but now need a headlight/lamp wiring to make it operational!
    I have a 600 to resurrect for the Spring bought it in bits, engine needs a complete rebuild too!



  12. Found Link 2 Big Bore pistons 61 mm for GPZ/KZ 550 took the engine out to 615cc from 557 cc I believe by cruisinimage_co Japanese seller!


    John Hall

  13. Hi, Matthijs,
    How are your projects going is the 600cc conversion finished? What about the effect of the upgraded front forks and yokes? I have put some original exhausts back on the ZL400 and it has transformed the power curve with more torque @ lower rpm’s, thus being more flexible in operation and easier to ride!
    Technical information on the First generation Liquid-cooled small Kawasaki fours seems meagre, especially important is Engine parts compatibility/availability. Managed to buy an “Old Stock genuine Kawasaki clutch plates on Evil Bay, for a good price though, I think KLE single uses the same plates as well as the GPX, GPZ 400/600 variants!

    Take care out there!


    John Hall

  14. Hi, Matthijs,I had to replace the clutch on my ZL 400 & the spider-like, Damper spring 39130 had broken that connects the clutch proper to the limited slip sub-clutch had broken, could I undo the clutch nut? No, had to borrow a battery powered Snap-On cordless Socket Drill/Wrench tool to undo it!
    In the GPX & GPZ & 550 chain & sprocket driven, this part doesn’t exist, (Sub_clutch), but is presumably present in the transmission of the GT550 .is This up to date has been the tightest Hub nut I have ever come across! Have you had difficulty in this area with your strip-downs?


    John H

  15. Hi Matthijs,
    My ZL 600 A, turns out to be a Californian import with a Reed-valve pollution recycled gases Cam cover! USA EPA compliant stuff! I have managed to buy some parts for my engine rebuild; Kawasaki GPX 600R, Barrels, matching pistons complete, in right cylinder order, crankshaft n’ connecting rod assembly too, all from the same engine! . The GPX is an upgrade of the GPZ 600 introduced in UK in 1988 to combat the newly released, ( the year before), faster Honda CBR 600 F.
    THe GPX 600 engine has Chrome Molybednum connecting rods, higher compression lighter pistons & if U fit a GPX cylinder head, lighter inlet valves n’ revised, (better), Inlet porting. At the moment do not intend to fit a GPX head as U then loose the faster gas speeds facilitated by the 30 mm Inlet ports of the ZL cylinder head, allowing better mid range n’ lower down pulling power! So I am aware , than a bit of a compromise is going on, perhaps allowing the ZL engine to put out an even more flexible power of about 2 to 3 to 4 bhp more, across the rpm range, giving hopefully a less stressed n’ stronger engine!

  16. Hi. Would you mind helping me out with a question? I want to put a Kwak GT550 engine into a Z550 (one of the “C” models. The engine mounts seem to line up, but I will need to convert the GT550 block to chain drive. From looking at the blow-up diagrams, the GT550 simply has a longer output drive shaft than the chain drive models, so that a bolt-on bevel drive assembly can be fitted. Would it be right to assume that the shaft bevel drive housing can be completely removed, so that a front sprocket can be slipped over it, for use in the Z550? Thanks

    1. Hi Joe,

      (snip original text)

      It seems like you are right. I was writing down quit a story about not fitting but I had the water cooled variants in mind. (gpx600 and zl600)

      Take a look at this image (gt550)
      And this one

      It seems the only difference is the color. You need an outgoing shaft and the cover plate of a kz or z550 and your done… Axle is different and you are probably not able to slip a sprocket on. Keep in mind that a gaskett is probably more expensive than a running 550 chain driven engine… well, at least here it is.




    2. You can try to only remove the bottom half of the crank case…. so you cap swap the axle.

      1. Excellent! Many thanks for the info. So I need to change the output shaft, and obtain a side cover plate for chain-driven models.

        Do you know if it’s possible to turn the engine upside down and remove the lower crankcase by only removing the bolts from under the engine? I don’t want to disturb the head, barrels, etc. It would be great if the lower crankcase could be lifted out by itself.

  17. Hi Matthijs,

    I stumbled across your blog and you may be the person to help me. I ride a very tired GT550 with a very, very tired exhaust. Would you be able to advise me if any other exhaust headers would fit as finding a good GT550 exhaust is probably easier than finding the Holy Grail! Thanks in advance, Barry.

    1. Hi Barry,

      I did kind of found the holy grail… for 60 euro’s I found a stainless exhaust from a gpx600r, the engine I will partly use for my project. For this bike it is also really hard to find an exhaust. I can only advice you to keep an eye on Ebay if you live in the UK, don’t know about the USA, just don’t vote for Trump, will make importing one more expensive 😉

  18. Hello Matthijs

    Do you know whether the pulsing coil ignition covers (aka the pickups covers) are interchangeable between the Kawasaki 400s, 550s and early 600s? To my eye, they look the same size. It would be great if Kawasaki simply used a standard size. Thanks

    1. Hi Joe,
      I do have the 550GT one (might be the same as a z550), a gpx600r one and a zl600 91 model.
      The 550 is different than the 600 ones, its different regarding the cable grommet. There is also a difference in the 600 ones. The later models are plastic, really ugly. Only old 86 zl600 have a metal cover.
      The bolt pattern and the radius are the same though, it should be possible to exchange them with a bit of fiddling.

      1. Thanks, that is interesting. I’m curious about your experiments with this engine. You wrote that you swapped the GT550 head with a GPX600 one. Is that right? The GPX is a 4-valve per cylinder head, but there are no issues with piston-to-valve contact if you stick it on a GT550 engine?

        1. Hi Joe, no I did not 😉

          I swapped the engine for a ZL600 engine and used several bits including the gpx head which is identical to the zl600. So there is no gt550 engine anymore, I sold the parts or trew it away.

  19. Hi Matthijs! Apparently you are the right person to answer a quick question, please!!! I recently bought an 1991 gt550. I’m kind of trying to give it a bit of a cafe racer look, but I would like to upgrade a bit the engine (with a low budget). So my question is: do you know if there is anywhere a set of better carbs (maybe from a 600cc) that will fit like plug and play, on the engine?

    1. The 600 cc gpz and gpx carbs are identical but with wider opening and different settings. I would not use them. The biggest problem is the tame cam profile of you cam’s. You can use gpz550 cams, ignition and carbs to gpz550 specs but it will only gain like 7 hp. You could use pod filters but than its a pain to tune and you have to fiddle with jetting. They are CV carbs so you need a little bit of under-pressure in your inlet to operate the slides.

      If you want to go fast for cheap you’d better buy a ZX9R like I did…

      1. Thanks for your quick reply.
        I’m done with the R’s, traded the speed for comfort and I have a touring bike. Besides, as you know, now, here in Holland (yes, I’m portuguese and living in Holland) we can only drive 100km/h on the highways…
        The engine upgrade was not really a must, but if there was a cheap way of making it run a bit “better”, would be nice.
        So, bedankt for your advice! Take care!

        1. Same here, I can’t control my self on the ZX9R and end up peaking 250 all the time.

          Leave the 550 as is, tuning it will always compromise the torquey characteristics. What you could do is change the ratio as described here.

          Where do you live in the Netherlands?

  20. I live in province of Groningen. I don’t have the skill or the knowledge to do such a job. That’s why I was looking for some easy fix to mKe it a bit better. But, again, it’s not a must. I guess I’ll leave it as it is and just make the looks different. It will be a ocasional fun ride and not daily driver. For that, I have the huge 2013 triumph trophy, that is fast enough (230 with the windshield at 70% high and 3 koffers in) and last year I drove 12k on it. I guess that I’ll just go for a carb repair kit because one is leaking. Thanks for the advice.

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