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doesn't look right.....

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Peteypops23
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doesn't look right.....

#1 PostAuthor: Peteypops23 » Tue Sep 07, 2021 8:02 pm

Just done a compression check (cold) and then one with a spoon of oil in the cylinders. Got the following results....
20210907_194408.jpg


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

chrisu
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Re: doesn't look right.....

#2 PostAuthor: chrisu » Wed Sep 08, 2021 5:52 am

Looks like a rebore needed

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warren3200gt
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Re: doesn't look right.....

#3 PostAuthor: warren3200gt » Wed Sep 08, 2021 3:21 pm

When was it last run in anger previously to your test run?
PUM 488 June 2023
76 Z900A4, 77 Z650B1, 77 KZ650B1, 77 Z1000A1, 82 Z1000J2, 89 ZXR750H1, ZRX1100R.

Peteypops23
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Re: doesn't look right.....

#4 PostAuthor: Peteypops23 » Wed Sep 08, 2021 4:07 pm

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

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z1bman
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Re: doesn't look right.....

#5 PostAuthor: z1bman » Wed Sep 08, 2021 8:50 pm

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

kev edwards
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Re: doesn't look right.....

#6 PostAuthor: kev edwards » Thu Sep 09, 2021 5:10 pm

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

Peteypops23
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Re: doesn't look right.....

#7 PostAuthor: Peteypops23 » Sat Sep 11, 2021 2:36 pm

Well......this is it with the engine hot
20210911_152842.jpg

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

weaver
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Re: doesn't look right.....

#8 PostAuthor: weaver » Sat Sep 11, 2021 2:59 pm

looks like rings/rebore required

kev edwards
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Re: doesn't look right.....

#9 PostAuthor: kev edwards » Sat Sep 11, 2021 9:14 pm

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.

Peteypops23
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Re: doesn't look right.....

#10 PostAuthor: Peteypops23 » Sun Sep 12, 2021 5:16 pm

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

Peteypops23
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Re: doesn't look right.....

#11 PostAuthor: Peteypops23 » Tue Sep 14, 2021 5:06 pm

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
20210914_174916.jpg

2 & 3 look like they've been replaced and no.4 has got a bit of battle damage too
20210914_174923.jpg


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

Peteypops23
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Re: doesn't look right.....

#12 PostAuthor: Peteypops23 » Tue Sep 14, 2021 5:07 pm

pistons 2 & 3 just for a comparison.....
20210914_174855.jpg

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z1bman
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Re: doesn't look right.....

#13 PostAuthor: z1bman » Wed Sep 15, 2021 3:48 pm

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

Peteypops23
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Re: doesn't look right.....

#14 PostAuthor: Peteypops23 » Wed Sep 15, 2021 7:08 pm

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

Peteypops23
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Re: doesn't look right.....

#15 PostAuthor: Peteypops23 » Sun Sep 19, 2021 10:04 am

All four pistons have a bit of an indentation above the cut out for the exhaust valve
20210919_105814.jpg

valves not seating correctly or wrong pistons?
Valves look undamaged but they are harder than the pistons.
Any ideas once again greatly received
Pete


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