Technical Pistons?

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Technical Pistons?

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Jan 21, 2008
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Castledawson
i was wondering if the pistons are mean't to hit the valves on the cylinder head? because i'm in the middle of changing my head gasket and noticed ring imprints on the top of my pistons? want to know before i go buying the wrong stuff for a different problem.

Thanks

Shannon
 
Yea it's an 1108, must just be the cut outs. i'll go take some pics now. Also if there is a lack of compression is it always the head gasket? because i took the whole engine down and there was no HG fail but there was serious lack of compression. could it be the spark plugs?

Shannon
 
Could be valves. Unlikely to be spark plugs unless the thread is completely shot. For future reference, always get a compression test done before pulling a head. Anyway, makes sense to skim the head, get the seats re cut, new valve guide oil seals, re-shim the valves.

If the compresssion is low after that, it can only be the rings/pistons.
 
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What actually were the results on all of the cylinders then?

Did you run the test with all the plugs out, throttle open, and a warm engine?

I had low compression on all my cylinder. For me the lands were broken on the pistons. Thought thats not very common, it could be the rings.

How many miles has the engine done?

Kristian
 
There are no witness marks on the valves to suggest contact with the pistons.

How are the bores?

On the engine we stripped to become my race engine, the bores were barrel shaped. Quite tight at TDC on each piston but very wobbly when in the middle of its travel, and this was an engine with no known overheating problems.

Cheers

Gormless Cretin
 
the throttle wasn't open but the engine was well warmed and all the plugs were out. the results i got were very different:

140 psi
105 psi
124 psi
115 psi

but i found recently that the timing was off on the car. Who ever owned the car before me fitted a timing belt and the timings was off as i found today when inspecting it. When taking the head off, i only lined up the crankshaft pully toi TDC but when i checked earlier the camshaft pulley wasn't on TDC when the crankshaft was. so maybe this could be to do with off timing? i'm not sure

the bores are fine. doesn't seem to be any scrape or scratches for the pistons.

Thanks

Shannon
 
Timing shouldn't affect the compression readings. Difficult call now it's in bits.

I think (depending on how broke I was/how much time I had) I'd go through the head carefully, the usual stick everything from one cylinder in one freezer bag rountine, check for guide/valve wear, etc. and then skim, cut in valves, re-shim. That way at least you know you have a good head.

Unless it has done say 80k miles plus, in which case it's unlikely not to need a rebore.
 
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