Z1OwnersClub GB

Just done a compression check (cold) and then one with a spoon of oil in the cylinders. Got the following results....

Looks kinda low to me, would have thought above 100 cold?
The engine was smoking a bit (white) before and after a 20 mile run, put that down to having a bit too much oil in the sump. Some white smoke coming out of crankcase breather and black oily mess in exhaust.
Plugs 1 and 4 don't look too good either.
Initially thought valves or valve stems but compression figures make me think ring's.... sticky or worn?

Bike starts fine with only noise coming from valve shims (between 1.2 and 1.5 mm)

Any ideas folks? Top end or full strip?

Sorry, its a 1975 900 of unknown history

Many thanks
Pete

Looks like a rebore needed

When was it last run in anger previously to your test run?

I've had it running a couple of times before and after I adjusted the valve shims....was smoking a bit too but not a lot.....before that I have no idea as I brought it in from the US.
Pete

turn the engine over with the plugs out & inspect the back of the valves for oil leaking past the stem seals

Compression test's should be done on a hot engine, disregard your findings until done correctly.

Well......this is it with the engine hot
still smoking from exhaust and crankcase breather
Valves look carbon'd up and earlier it took me quite a few attempts just to get a gap on the cams, let alone the correct ones!
Complete rebuild??
Pete

looks like rings/rebore required

If you are down to the smallest shims, you may still not be getting fully closed valves, but with your findings so far it looks like the top end needs looking into.

Cheers folks......I'll take the head off tomorrow and have a peek!
Photos will follow.
Pete

top off.....seems as if no.1 has had a bit of valve action in the past....this would marry up with the mess inside the cam cover
2 & 3 look like they've been replaced and no.4 has got a bit of battle damage too

I was going to leave some oil in the bores overnight to see if some (or all) leaked past the rings....is that worthwhile?
Once I've cleaned the oil off the head i'll have a look at the valves.
Pete

pistons 2 & 3 just for a comparison.....

check the piston rings in the bore & piston to cylinder clearance. you might get away with a hone & new rings. also make sure all the pistons come to the top of the bore

will do....
.
Put some engine oil in the bores last night....No.1 has lost about half, Nos. 2 and three are sealing nicely but no.4 has lost all the oil past the rings......
Also got the head in the ultrasonic for a good clean before I take the valves out.

Pete

All four pistons have a bit of an indentation above the cut out for the exhaust valve
valves not seating correctly or wrong pistons?
Valves look undamaged but they are harder than the pistons.
Any ideas once again greatly received
Pete