Valve/Compression advice needed (repost from Fireboard)

Hello all, I am in the middle of a winter project on my bike and have started looking at the engine.I measured compression and got 120, 140, 140, 140 psi. When adding oil to cylinder 1 I got 170 in that cylinder, no change when oil added to 2-4 cylinders (I also am little suspicious of the compression meter, hard to get consistent values...)Ok, so I check the valves. All between 0.1 and 0.15 mm except intake on cyl 1 which is 0.05 mm. There is clearance but tight on that one.

So I will try to fix clearance on cyl 1. The advice needed is mainly:

120 psi sounds low, on the other hand there is no real problems with the bike.It runs ok. Do You think I should settle with fixing the clearance? or should I also remove the head and cylinders and hone/rebore? I realise this is of course best but is it necessary? (Tight on cash in the project)

Thankful of any advice

The thing is the parts availability. Stock and oversize pistons and rings are expensive when you can find them. Pistons seem more available than rings, without rings why buy pistons? It could take you a long time to buy a piece or two here and there. Then the rebore cost, etc.

That leaves you with the big-bore kits from the aftermarket, and those aren't cheap either!

The valve clearance needs to be set, and compression may go up. If money is an issue I would ride it and enjoy it, and forget about a rebore until you have the money.

Another option is to buy a motor in better shape than yours, usually cheaper than a big bore kit.

edit:
A friend replaced one piston and ring in his Honda CB650. It ran great. You can do that too and it won't cost much.

Post edited by: OKC_Kent, at: 2007/12/05 13:45

get the valves set right, do a full tune up on the bike, including cleaning the carbs and setting everything as it should be, then run a compression test with the throttle wide open, you did say you did that, if the numbers are within 10% of each other I wouldnt worry about it even if they were a tad low,
Since the money is tight ride it and save some gas money purchase the parts you want to replace when you can afford them, keep doing that until you have everything, you would be surprised how much stuff goes up and how much you saved in the early stages of the purchase

Thanks guys, I will follow Your advice, fix the valves and run it. I will also recheck with a new compression meter since mine is a cheap one. Carbs already cleaned and rejetted, only synching really left.

If you're going to check the compression again, you might consider running a leak down test on it. You'll then know quickly if you have a ring or valve problem.