Fish's 1992 750C Engine Rebuild and Other Goodies

[Fishrider]

Dropped off the crank shaft at another local machine shop who has a crank specialist. Better safe.

The exciting news was picking up the clutch hub. Fits perfectly! This old codger down in Denver charged me $40. He mostly works on Harleys, but I guess he liked me.

Milled Clutch Hub

[DaftRusty]

It’s looks perfect! You are one big step closer.
Now you can measure for the clutch release mechanism shim.

[Fishrider]

I ended up getting my journals polished on the crankshaft. I rechecked all the clearances, but the guys at the machine shop felt it best to replace the rod bearings as well. So I am waiting on the bearings to be able to finish the lower end. In the mean time I re-designed my home made 3D printed fender eliminator. The new design is sturdier and looks less intrusive. The design is a direct fit for the 750C2 if you are using the stock brake light. Came out rather nice.

[GPzephyr]

Nice work on that fender eliminator.

When I did my six speed conversion years ago I don't recall having any clutch issues. But it was something like 12 years ago now. I do remember the neutral light switch being in the wrong place for the 550 selector.

Keep up the good work
Chris

[Fishrider]

Noted GP. We will see.

Today, I finally, got the bottom together. I certainly hope I did a decent job. I won't know for awhile.

So, I decided to start tackling the pistons and ran into an issue, of course. I am using the Wiseco 810 kit. The cylinder was bored a year and a half ago and I did not check the ring gaps back then. I checked the gap on one set of rings and the gap comes out too large for both rings based on the Wiseco specs.

My measurements are coming out as such.

Cylinder Bore = 2.71 inches x .0045 Top Ring = .0122
Cylinder bore = 2.71 inches x .0055 2nd Ring = .0149
Actual gap measurement of Top Ring = .013 - .014
Actual gap measurement of 2nd Ring = .019

I don't know if this was a bore issue or a ring issue. I checked the measurements in different cylinders.

What should I do here?

The formula is below.

[Freddy]

Consider it's an air-cooled engine which as general rule run looser tolerances than a water cooled engine due to having to deal with a wider range of temperature variations. And as you've quite significantly increased the compression ratio, the engine is going to run hotter. As there is no specification given on the table you've used for an air-cooled engine, I'd look to the Kawasaki service manual for guidance.

The Kawasaki specification for ring gap for either ring is 0.20 - 0.40mm with a service limit of 0.7mm. When I convert your inch measurements to mm I get 0.31mm for the top ring, and 0.38mm for the second. As I'd be wanting piston and ring clearances on the loose side of all specification (from experience) they seem just about spot on in relation to Kawasaki's recommendation.

Stating the obvious, you may want to check with Wiseco, but on the face of it they seem fine to me. But I'd certainly want to be sure pistons are not too tight in the bores. Last time I rebuilt mine there was bad piston skirt damage on 2 pistons when the minimum piston clearance of 0.04mm had been used. Engine is run hard in elevated temperatures, its Australia. This time I used the maximum of 0.06mm and with increased AFR hopefully it won't have have happened again.

[Fishrider]

Thanks again Freddy. After some more searching I came across this thread on KZrider:

https://kzrider.com/forum/2-engine/6074 ... ap?start=0

The OP had the exact same issue back in 2017. He got differing answers from the different companies that made the parts. Upshot was, I think, he just ran it after waffling on maybe even going slightly larger based on advice from MTC Engineering. The thread went on about other issues during break in. Apparently, there had been some talk about going with wider gaps out of the box for some of these manufacturers due to temps causing the rings to expand a bit too much with smaller gaps. Wiseco sort of stood by their numbers, but the OP said he received different answers depending on who he talked to. I doubt I want to go searching for different rings anyway. Sounds like its hit or miss. I am thinking that you are right in your reasoning that the stock specs have a bit wider gap based on the temps of an air cooled engine. I may contact Wiseco myself, but I have a feeling they won't be much help. Sounds like piston gap theory and the basic numbers don't always hold up to real world situations which can be vastly different from engine to engine.

[Freddy]

Thanks again Freddy. After some more searching I came across this thread on KZrider:

https://kzrider.com/forum/2-engine/6074 ... ap?start=0

The OP had the exact same issue back in 2017. He got differing answers from the different companies that made the parts. Upshot was, I think, he just ran it after waffling on maybe even going slightly larger based on advice from MTC Engineering. The thread went on about other issues during break in. Apparently, there had been some talk about going with wider gaps out of the box for some of these manufacturers due to temps causing the rings to expand a bit too much with smaller gaps. Wiseco sort of stood by their numbers, but the OP said he received different answers depending on who he talked to. I doubt I want to go searching for different rings anyway. Sounds like its hit or miss. I am thinking that you are right in your reasoning that the stock specs have a bit wider gap based on the temps of an air cooled engine. I may contact Wiseco myself, but I have a feeling they won't be much help. Sounds like piston gap theory and the basic numbers don't always hold up to real world situations which can be vastly different from engine to engine.

Just reiterating again my take, an air cooled engine run hard in hot temperatures .... certainly better the top end be on the loose rather than tight side.

And don't overlook jetting. The leaner the AFR the hotter an engine runs. These bikes were jetted lean to start with, and as you've significantly increased the compression ratio which increases temperatures it needs to be considered IMO. I got what feels like an extra 10-15 hp (probably a ridiculous exaggeration but its truly what it feels like) but getting the jetting right on my D1. All that I changed was the mains, everything else is stock (on the assumption the needle jet is larger than original due to wear anyhow). Fuel level as high as it can be still within spec.

As you've gone to all this trouble also don't overlook a bit of work on the cylinder head. Absolutely match the intake ports to the rubber manifolds (port matching). Nothing is going to rob power more than a sharp edge sticking into intake system. Plenty of videos on the subject. Car crew use the manifold gasket as the template, but as there is no manifold gasket all you need to do is bolt the rubber intake manifolds on and you can put your finger through and feel and edges that need to be taken down and smoothed out. Also knock any rough angles and surfaces out of the insides of the ports. No need to polish intake ports, that's now considered a bad idea (a slightly dull surface is the ideal), and no need to increase size. You want mid range power on a street bike, not top end.

[Fishrider]

My inexperience got the better of me today. I was using hose clamps to get the pistons in the cylinder. Once I had finished I realized something was off. The pistons would not move at all. I had been tapping the cylinder down and didn't notice that one of the oil rings had come out on a middle piston. Anyway, when I finally got the cylinder head back off, with much effort, one of the inner piston oil rings had come unseated and was pushed into the cylinder as I was tapping it in (maybe I was tapping to hard). I bent the ring and scrapped the cylinder. I can feel the scratch with my nail. Its pretty bad. I may have damaged the piston as well. I can feel a little gouge on it. Obviously, I need a new ring and maybe a piston, but what about the cylinder? Is it salvageable? Super frustrated and kind of depressed. I was really hoping to get past this part. I tried several different methods to get the rings in, and I thought I had it. Now, I may have set myself back weeks and bleeding cash. Need some advice on this please.

[Freddy]

My thoughts ......
Piston is ok. Just carefully remove any high spots (I'd use a bit of 1200 'wet and dry' on a small piece of flat timber) being careful not to remove any of the skirt.
The remaining small dent on the skirt in that position isn't going to give any problem.

Oil rings, replace.

Cylinder bore is the tricky one. The lower oil ring stops 30mm from the bottom of the sleeve. So any indent below that shouldn't cause a problem. Obviously high spots need to be removed otherwise you'll have insufficient piston clearance and it will damage the piston skirt. Either way it needs the machine shop to run their hone through it again. If all the damage is below 30mm (my guess from the photo is it extends beyond 30mm) then it just needs the lightest pass to remove any high spots and life is good as piston clearance should still be fine. If it needs more honing to totally remove anything above the 30mm point, only your machine shop can advise if that can be achieved while still maintaining acceptable piston clearance.

Ring Compressors - Make up a set of 4 decent ones from some PVC drain pipe, like the one in the photo. They need to be wide enough to properly cover all rings, mine are 18mm wide which is good for a genuine piston Use very large cable ties as the tensioners to compress the rings. The top of the pvc compressor is tapered to the same angle as the taper in the bottom of the cylinder liner so the rings are up in the cylinder proper before they pop out the compressor. Just cut the cable ties and pull the compressors out before pushing the block down. Don't forget to install the camshaft tensioner arm which has to go in before the block is pushed home.