Fish's 1992 750C Engine Rebuild and Other Goodies

[Freddy]

Also, as everything looks a bit too clean. Don't forget to fit the pistons in the bores with a good lashing of oil on the cylinder walls, pistons skits, and rings (just like you did with the new bottom end bearing) before assembly. The question of what sort of oil to use (mineral or synthetic) has been a point of debate for the last 30 years, but as the majority of aftermarket performance engine builders seem to favor only mineral oil for breaking in rebuilt engines, you can't go wrong if you stick to that guidance. It aren't going to hurt anything if it is nothing other than an 'old wives tale'.

[Fishrider]

Once again, Thanks Freddy. Probably won't be the last time. I have a mechanic friend who is going to take a look at the cylinder and piston. He talked me off the cliff as well. He seemed to think it was solvable with a new a set of rings too (depending on if there was any other damage on the piston). I thought I oiled up everything pretty good before the process. Although, I guess I should of asked about your PVC fitting trick before hand. Even old dogs seem to learn new tricks the hard way.

[Fishrider]

I finally, got my pistons together. Required a little honing of damaged cylinder. Unfortunately, I did end up purchasing two new pistons. Not the one I had an issue with. Apparently, while fitting the cylinder head the outside tubes came down on both outside cylinders damaging the tops. I decided it was best to replace them. Just some more dumb tax added to the list. For anyone who has never put pistons back in an inline 4 remember three things. 1. Take your time 2. Don't force anything. They should go smoothly once the rings are properly seated. 3. Nothing is easy.

I have moved on to other issues. Namely I am having a problem with cams and valves. I bonered numbering my valve caps and shims. I had them lined up, but I really had no idea where they went. So I I just put them all back in, set the cam chain and then proceeded to measure valve clearances. I figure I will just move them around until I get the proper clearances, and if nothing lines up then I will get some new shims. HOWEVER, after rotating the pistons into place for each set of lobes I noticed I have zero valve clearance on any of the valves. Is it possible that my valves are seated that much lower after cleaning and lapping? Is this common with a rebuild? Do I just get thinner shims and start over?

Edit:
I went ahead and took all the shims out and took measurements with just the buckets on. I am getting no more than about .5mm clearance. The shim sits in the valve about 1.82mm. Since clearance should be between .08-.18mm the math would be (clearance without shim + valve seat hole - (.1mm evenly between .08 and .18) = Shim Size

If I get .5mm clearance with no shim:

(.5 +1.82 -.1) = 2.22mm

so 2.15mm or 2.20mm shim with a clearance of .17 or .12 respectively. I would do this calculation for each valve obviously, and of course re-check once I get the new shims and hope I don't need different shims. Is it better to get closer to the smaller clearance or larger? I would assume the larger clearance as wear on the valve causes clearance to get tighter. Correct?

If I get measurements that give me shim sizes under 2mm do I then have to get the stems ground?

All current shims are 2.25 - 2.35 with one that is noticeably bigger with no markings on it. Which I thought was strange.

Further Edit:
I noticed the buckets have a lip on the inside that sits down into the valve hole as it is smaller in diameter than the shim. This would add another .25-.30mm if I am measuring correctly. That would give me shims, that may very well be, under 2mm. Does that mean I would have to grind the valve stem?

Its hard to see from the angle, but there is no day light there. Its the same with all the lobes.

[Freddy]

I finally, got my pistons together. Required a little honing of damaged cylinder. Unfortunately, I did end up purchasing two new pistons. Not the one I had an issue with. Apparently, while fitting the cylinder head the outside tubes came down on both outside cylinders damaging the tops. I decided it was best to replace them. Just some more dumb tax added to the list. For anyone who has never put pistons back in an inline 4 remember three things. 1. Take your time 2. Don't force anything. They should go smoothly once the rings are properly seated. 3. Nothing is easy.

I have moved on to other issues. Namely I am having a problem with cams and valves. I bonered numbering my valve caps and shims. I had them lined up, but I really had no idea where they went. So I I just put them all back in, set the cam chain and then proceeded to measure valve clearances. I figure I will just move them around until I get the proper clearances, and if nothing lines up then I will get some new shims. HOWEVER, after rotating the pistons into place for each set of lobes I noticed I have zero valve clearance on any of the valves. Is it possible that my valves are seated that much lower after cleaning and lapping? Is this common with a rebuild? Do I just get thinner shims and start over?

Edit:
I went ahead and took all the shims out and took measurements with just the buckets on. I am getting no more than about .5mm clearance. The shim sits in the valve about 1.82mm. Since clearance should be between .08-.18mm the math would be (clearance without shim + valve seat hole - (.1mm evenly between .08 and .18) = Shim Size

If I get .5mm clearance with no shim:

(.5 +1.82 -.1) = 2.22mm

so 2.15mm or 2.20mm shim with a clearance of .17 or .12 respectively. I would do this calculation for each valve obviously, and of course re-check once I get the new shims and hope I don't need different shims. Is it better to get closer to the smaller clearance or larger? I would assume the larger clearance as wear on the valve causes clearance to get tighter. Correct?

If I get measurements that give me shim sizes under 2mm do I then have to get the stems ground?

All current shims are 2.25 - 2.35 with one that is noticeably bigger with no markings on it. Which I thought was strange.

Top End Cam Shafts.jpg

Its hard to see from the angle, but there is no day light there. Its the same with all the lobes.

Cam Lobe 1.jpg

Had to scratch my head a bit on the explanation of how the piston tops got damaged e.g 'by the tubes'. After a bit of thinking, my guess is the engine was turned over with the head and camshafts fitted but without the cam chain fitted. Turn it over with no cam chain on and the pistons at TDC will strike any valve that is being held near fully open by the camshafts, and there will certainly be one or more.

I'm taking it you checked the offending valves to make sure they didn't get bent. If enough force was applied to damage the piston tops, then that's enough to possibly have bent the valve. Rechecking the valve face to set fit with bearing blue would be probably the simplest and most accurate way to check, no way would the seal be correct if the valve had been bent.

Would lapping the valves (if the valves had not been refaced and the seats cut) materially alter the valve clearances, no. It would make a small difference, but nothing major, well not unless you lapped for days and wore a great big groove in the valves. The difference it would make should have been easily accounted for within the normal factory shim range (2 to 3.20mm) . I've had the seats cut on my head, and in a previous rebuild the valves refaced (valves were replaced last rebuild) and yes thinner shims were required but nothing radical and it was still well within the factory shim range.

If you would need to go below a 2mm shim, is grinding the valve stems a solution? IMO,no, its a backyard hack. The correct fix would be to replace the offending valves, and if still a problem have new valve inserts fitted to the head (or alternatively replace the cylinder head). The reason you can't get a correct valve clearance in the factory shim range is (a) the valve stems are stretched, (b) the valves have previously been refaced past their serviceable limit, or (c) the valve seats have been heavily cut. Or obviously a combination of these factors.

Sinking valves into a cylinder head due to resurfacing or cutting the seats increases the combustion chamber area, decreasing compression, so hurts engine performance (the reason I replaced all 12 valves last rebuild rather than reface them a second time).

Valve clearances, if you have the option work towards the .08mm size or the inlets, and 0.18mm for the exhausts. The inlet clearances won't change over time, but the exhausts may tighten up a bit. The reason they tighten up is not valve cap wear but rather the valve face sinking into the seat on the punishingly hot exhaust valve.

Aim for your theoretical shim size, but definitely get a few extras either side. The chances of it working out 100% spot on based on calculations is in my experience next to zero. It should in theory, but for some reason it just doesn't. It always takes a bit of trial and error to get some right.

[Fishrider]

So I rechecked a couple clearances without shims. I was measuring incorrectly at first. My feeler gauge set is short so it was measuring at an angle. While my original assessment of zero gap with current shims is correct, clearance with no shims ends up being much larger, around .6-.8mm. Which would give me shims that are about .1-.3 smaller than what I have now. Enough that there would be zero clearance. Also, I hadn't noticed before, but it looks as though someone has worked on this top end. The shims are not stock. They are Hot Cams. Unless Kawasaki uses Hot Cams, and the odd looking one just didn't have any numbers on it. It measured at 2.30mm. So all shims were 2.3 or 2.35 and one 2.25.

I ordered a longer set of metric feeler gauges so I can take a little more accurate readings. I think my math is at least close. I get 1.45mm + (clearance with no shim) = new shim. Granted, once I do measurements with actual shims things may change, but this gets me close. So hopefully some of the shims will be correct, and I won't be continually guessing and buying new shims.

To the scratching your head about the pistons. I know exactly how it happened. I was fitting the inside 2-3 pistons first, and the outside pistons were off axis when, once or twice, the cylinder came down on them. These are brand new 810 pistons. It was me not being careful. I understood the process a bit better the second time around. Every process I do here is the first time. I just don't have any other experience. I still hope everything in the bottom end is good.

[bunyip]

Whenever I rebuild a head, I fit one valve at a time into the head and slide the cup in without any springs. Sit the cam in place, couple of caps if you like or put a rock on it to hold it down Then just push the valve onto the seat with one hand and measure clearance with the other. Easy to adjust clearance then. You can get very close if not spot on. Check with engine assembled though.
Hope this helps the next poor bugger

[Fishrider]

Interestingly, I used some estimated clearance measurements based on my equation without shims. I used these measurements to replace the current shims where they seemed to have the closest measurement. After replacing them, I now have clearance on 6 valves. Once, I get my new feeler gauge in I will double check the clearances and order some new shims as needed. Kind of excited. Once I get the clearances sorted I will be placing the engine in the frame. Still A lot to do though.

Electrical: Rebuild entire harness with M-Unit. This will be one of the most time consuming of the rest of the project. Includes all new lighting and new speedo/tach, new push button controls.
Front and rear sprocket alignment due to output shaft of 550.
Probably have to make some custom throttle cables and choke. Hopefully, I can re-use the clutch cable.
Carburetor re-build and then testing with new jets assuming the engine runs.
Front calipers
Polish up aluminum parts.
New rear shocks.
Eventually some new paint and fix a ding or two.
I am sure I missing a few things that will come to light as I move through this.

[Fishrider]

Been playing around with the shims for while. I have some 2.25s that I can play with, but wondering if I need to. Changing one can sometimes cause havoc.

Shim Numbers 750C1 1992.jpg (22.73 KiB) Viewed 5767 times

[Fishrider]

Haven't updated in awhile, but I have been steadily working. Here is the break down with problems and fixes I have run into.

-Got the engine in frame. My teenage kids were invaluable help for this.

-Finished Electrical: This was a big job. Not hard, but tedious. My electrical schematic does not show layout, but it does show all connections. I won't really know if the igniter circuit is completely correct until I start it up. I will update on this later. I did not run a kickstand switch or a clutch safety switch. Just more work. I printed a plate that the M-Unit attaches to that uses the original slots for the old electrical fuse box. I ran all forward connections into the light housing. I think it all fits.

Continued in next post...

[Fishrider]

M-unit Installed: I decided to use a ground block instead of the frame. You can kind of see it hiding under the M-unit. The engine remains strapped of course. I had to reposition the M-unit further towards to front after fitting the seat which ended up putting pressure on the output wires. Not a problem with 3D printers. I just reprinted a new plate with screw holes further down.

Continued on next post...