-82 Kawasaki KZ750 Top end rebuild - low comp

Hi!

Just buttoned up a 1982 Kawasaki KZ750 E2 engine and after the bike is all done new and shiny, I'm having a bit of engine problem: poor compression. Did fit new rings, pistons looked fine as so did cylinders so I thought just replacing rings is ok. I had removed the rings from pistons and thought it's safer bet to put new ones than the ones i've been twisting around. The problem now seems that the new rings aren't sealing properly. I'm getting 75 PSI on all cylinders and after squirting some oil in to cylinders i'm getting 125 PSI. I can get the bike started with the 75 PSI cylinders but it runs very poorly. After the oil trick it runs really neat and nice, takes a nice RPM and sounds like a beast. Smokes like hell of course. After a while it dies out.

But here's the thing: I didn't re-hone the barrels. Was this a massive mistake? I've been kinda seduced to this school of thinking that you don't need re-honing if you do just a ring job(as desrcibed here: www.snowvalley.20m.com/bikes/dnthone.htm ). Now it seems that it might've been a mistake.

Does anyone know can I get the rings seal by running the bike with temporary compression increase with oil or do I have to dismantle the top for honing to fix this. That would be massive bummer but I guess life is learning

-Sami

I always hone new or old. Sure the cam timing is correct?
Steve

Yeah cam timing was my first suspect, so i pulled the cam cover to re-check i had dropped the cams in correct way and they did check out, so they shouldn't be making any problems.

You gotta hone the cylinders. A bottle brush hone is best. 240 or 320 grit.

Also realize that the cam chain tensioner spring cap and wedge must be removed before installing the valve cover or you will over tension the cam chain.

Never, Ever install new rings without honing the cylinder.

Damn, well, i'll fiddle around it a bit and if it looks desperate, just gotta pull the top end apart again. Guess the cylinder and cylinder head gasket gotta be renewed even if the bike has been run only few times for a period of minute or two?

It's so weird, I did a ring job on my Honda CB500 Four few years back without honing and it worked like magic.

May be able to reuse the head gasket but the base gasket could be trashed, maybe not. I used copper coat on mine.
Steve

Have you the same low compression values before you renew the piston rings?
If so, you need a valve job. It looks like some valves do not seal the combustion camber properly.
Fill the combustion camber,( head upside down), with fuel and look into the ports if fuel is leaking.

Before you go through the effort of taking everything apart, do a leak down test first.
That will tell you if the piston rings are leaking excessively or if your valves are leaking. Or both for that matter. But it will give you a good idea what the culprit might be with out disassembling anything.
You might be able to rent a tester from a local auto parts store.

Before ring job the compression was fine, so I'm heavily leaning to the new rings to be the problem. Leak down tester would be really good, it's been on shopping list for too long. Let's see if I can get a hold of one. Starting to be mad at myself for not just using the old rings