Fish's 1992 750C Engine Rebuild and Other Goodies

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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby DaftRusty » 30 Jun 2020, 19:28

Fishrider, I see exactly what you mean. So I went and measured both kz750 and zr-7 transmission input shafts, and they were both 68mm long from the case bearing. The 550 input shaft was 62mm long. So that is 6mm less shaft for the clutch release mechanism to ride in.
The question is, how much of that shaft on the clutch release actually rides inside the input shaft when it is in its normally installed position?? The clutch release lever is always holding onto the end of the release mechanism and doesn't allow it to float around very much. I have a feeling it only has about 1-2mm of play between the part of the mechanism that makes physical contact with the pressure plate. And most of that space is filled with a film of oil at all times. Not that it is a concern, but it is impossible for the clutch release mechanism to unhook itself and float 6mm too far into the clutch basket. (Unless your release rod gets pulled out of the clutch cover, but then you have bigger problems anyway.)
The main concern is there is not enough of the input shaft left and the release mechanism is no longer fully supported. If, for example, there was only 2mm of the release mechanism riding in the input shaft, it could come close to falling out or become misaligned and bind up. If it this were to happen it could lead to a no clutch situation and to a very serious side effects.

So.. we need to know is how much of the release mechanism is actually supported when installed in the 750 input shaft. You could just install your clutch on the 750 input shaft on the bench as it would be in the bike. Put an o-ring around the shaft of the release mechanism and install it to its normal operating position against the clutch pressure plate. The o-ring will act as a "depth gauge" or a witness mark showing how far shaft slid into the input shaft. Then take it all apart and measure where to o-ring is and that will give you/us an idea of how much support the release mechanism normally has.
For example, 20mm of the shaft sits in the input shaft normally. Then loosing 6mm is probably not a big deal. It still has 14mm still supporting it. But...if normally there is only 9mm of support, then loosing 6mm and only having 3mm left is going to be a bad deal. Then it might be necessary to find another possibly longer release mechanism.
I hope this all makes sense and actually helps.
If you get the chance to do some measurements, let us know.
Also, If a solution to this issue is found, then I am going to add it to my 6-speed swap instructions so it can help others.

IMG_3751.jpg
Input shaft differences
1991 zr550
Factory Pro stage 1 jet kit
zx550 pistons and cams
DaftRusty
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 01 Jul 2020, 03:08

So the math comes out exactly how I thought relative to the shaft sizes. The measurement was taken with the pusher up against the hub. The nut fully screws past the shaft end on the 750 output shaft. So I just left the nut off for the 550 measurement. I lose about 5-6mm of length. I only lose about 20% of the length in the shaft which may not be problem. I still think a thicker washer or two would solve the problem as well. I found the washer below which would meet the challenge.
Clutch Spring Pusher 2.jpg

Washer 1.jpg
Fishrider
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby DaftRusty » 01 Jul 2020, 14:25

Nice work with the measurements!
Something else I forgot to take in to account is the amount the release mechanism has to travel outwards in order to disengage the clutch. I know on my 750, the full release movement of the pressure plate was only 2mm. So according to your measurements, when the clutch is applied, there will only be 10mm of the release mechanism shaft still riding (supported) in the input shaft. I'm not really sure if that will lead to misalignments and/or binding when the clutch is applied and released.
I like your idea of putting a spacer on the backside of the roller bearing race. (part # 92025/A) They actually call it a shim and it serves as a machined and hardened surface for the roller release bearing to ride on. So in theory you could stack up more of these "shims" behind it to position the release mechanism further into the input shaft. But....I'm worried that ~5mm shim you have chosen will sink it so far in, that the actual clutch release lever (part# 13106) will no longer be able to grab onto the release mechanism. The release lever has ramped "fingers" that grab onto the end of the release mechanism, and that extra 5mm may not let the fingers make full contact or contact at all. If the fingers are just barely grabbing on, one day you might pull the clutch lever in and hear a "snap" as the leading edge of the fingers breaks off.
It may hopefully be a complete non-issue, or maybe you find you can only get away with a 2.5mm spacer. (which an extra 2~3mm is better than nothing) That is something that you are going to have to check. But, you can't just mock up the clutch and clutch cover and try it out until you get the clutch hub machined so the nut can thread fully on the shaft.
Lots to verify, but I think your idea of a spacer is the right idea!

Screen Shot 2020-07-01 at 8.37.32 AM.png
1991 zr550
Factory Pro stage 1 jet kit
zx550 pistons and cams
DaftRusty
 
Posts: 35
Joined: 07 Sep 2017, 18:31

Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 01 Jul 2020, 16:38

Exactly my train of thought. There are plenty of 2.5-3mm washers available as well. I could give one of those a try. My guess is the set up will be fine. Thanks Daftrusty.
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 05 Jul 2020, 21:07

Anyone have an opinion on valve polishing and whether I should even attempt it? I am loathe to pay for a valve job as there was only 3600 miles on this engine. Can I just put the valves back in, or is there something else I need to do? Not to be lazy, but I would prefer to just follow the installation instructions and be done with it. The valves themselves are in good condition.
Fishrider
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby DaftRusty » 05 Jul 2020, 22:24

Spend an hour and lap the valves to the seats. Since you already have the head apart it is good practice to lap them in just to verify they all are sealing perfectly. The valve lapping tool and paste is super cheap in the scheme of things. If it only has 3600 miles on it, absolutely, positively do not waste money on a valve job. On these shim and bucket heads, just cutting new valve seat angles and matching angle on the valve will lead to all new shims and more than likely having all the valve stems tipped (delicately trimmed) to get the correct stem height. Lots of time and money for absolutely no point on a low milage motor.
But definitely buy all new OEM Kawasaki valve seals or after-market Viton ones.
1991 zr550
Factory Pro stage 1 jet kit
zx550 pistons and cams
DaftRusty
 
Posts: 35
Joined: 07 Sep 2017, 18:31

Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Freddy » 06 Jul 2020, 08:57

Fishrider wrote:Anyone have an opinion on valve polishing and whether I should even attempt it? I am loathe to pay for a valve job as there was only 3600 miles on this engine. Can I just put the valves back in, or is there something else I need to do? Not to be lazy, but I would prefer to just follow the installation instructions and be done with it. The valves themselves are in good condition.


Assuming you kept the valves in their original positions (inserted in a bit of marked cardboard or strip of timber) first check the fit of the vale face to valve seat using 'bearing blue'. If you've got a 100 % fit, just install. Don't lap them if you don't have to, the practice is largely obsolete these days. If they aren't an acceptable fit, as you don't want to get the valves and seats cut you have no option but to lap them in. But you still need to verify the face to seat seal with 'bearing blue'.

If not familiar with how to use bearing blue, wipe a VERY thin film onto the valve face (just a 'whisper' of near transparent color across the complete face), insert the valve into the head and with a little downward pressure rotate slightly back and forth. Withdraw the valve and inspect the valve seat looking for a complete ring of blue on the valve seat in the desired location and width from the blue transferred from the valve . That's why it has to be a super thin film applied. Put it on thick and it'll give a positive reading no matter how bad the fit.

If you have mixed then all up ??????? Good Luck.

P.S. You have I assume completely de-coked the valves and cylinder head.
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 09 Jul 2020, 01:05

Too late Freddy, already tried the lapping. I think I did it right. I suppose I can try the blue as well. I am 85-90% sure I have the valves numbered correctly. I did have them numbered in a plastic storage case in separated units. I am pretty damn sure I followed the numbers on the case. Either they are correct or backward. Of course, you can't mix up intake and exhaust valves. Waiting on some viton seals, and then I can patch up the cylinder head.

I did run into another issue. I found some tiny scratching on one of the crankshaft journals. Probably done by me taking it in and out of the case. One of my many newb mistakes. I am going to take it in to another machine shop just to give it a once over. Better safe then sorry I guess, but it will set me back a week or so.

Been working on the wiring diagram for my Motogadget M-Unit as well as making some handle bar riser spacers in a CAD program. My new handle bars sit too close to the fork bolts. Won't be an issue.
Fishrider
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Freddy » 09 Jul 2020, 01:48

Fishrider wrote:Too late Freddy, already tried the lapping. I think I did it right. I suppose I can try the blue as well. I am 85-90% sure I have the valves numbered correctly. I did have them numbered in a plastic storage case in separated units. I am pretty damn sure I followed the numbers on the case. Either they are correct or backward. Of course, you can't mix up intake and exhaust valves. Waiting on some viton seals, and then I can patch up the cylinder head.

I did run into another issue. I found some tiny scratching on one of the crankshaft journals. Probably done by me taking it in and out of the case. One of my many newb mistakes. I am going to take it in to another machine shop just to give it a once over. Better safe then sorry I guess, but it will set me back a week or so.

Been working on the wiring diagram for my Motogadget M-Unit as well as making some handle bar riser spacers in a CAD program. My new handle bars sit too close to the fork bolts. Won't be an issue.


The use of bearing blue (sometimes called Prussian blue) is a standard part of lapping valves. It's the only way to actually check you have properly lapped in the valve. You lap for a bit, clean both valve and seat, check with blue ..... repeat till you have the desired fit. Trust me on this one, as an apprentice mechanic from the 1960's and always given this somewhat tedious job by the head mechanics I reckon I must have lapped in close to 1 million valves (ok slight exaggeration ..... maybe)

You can't just lap and assume its a match. The lap paste is so thick it will leave a mark all around the valve and seat no matter how poor the fit. The fit must be checked with blue. If you were 100% sure you fitted them back in the same locations all this properly isn't necessary. But as your unsure they came out of the same location, I'd definitely check them, especially the exhausts.
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby DaftRusty » 09 Jul 2020, 02:42

As for the scratches on the crank, if you can feel them with your fingernail, then you may need a professional to polish them out. But if you can’t feel them, then they are superficial and can be polished out with 800 grit wet&dry. A final clean with Acetone is mandatory.
(Yes, it sounds insane, but when I balance crankshafts at work, the aluminum counter weights will sometimes leave light scuffs on the journals. I polish them out with 800 w&d and mineral spirits. Any cranks we get with worse than a scuffs get the band sander with a final 800 w&d.
Your journals won’t have a mirror shine like you would expect, but it won’t have any raised scratches and it will hold oil just as cylinder bore honing does.
If this sound too risky, then definitely take it to an engine machinist and they can fix it up.
1991 zr550
Factory Pro stage 1 jet kit
zx550 pistons and cams
DaftRusty
 
Posts: 35
Joined: 07 Sep 2017, 18:31

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