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GS850 No Compression

  • Thread starter Thread starter wdavie
  • Start date Start date
Massive clearance means the valves are sticking open. Maybe bent valves.

Honestly, before installing a head and going though all the work that entails, I strongly recommend pulling the valves out and performing a complete inspection and seal change. A little work on the front end helps save massive work on the back side like is occurring now.
 
Depending on your definition of "massive", yes, it can affect the compression.

"Massive" clearances indicate that the valve is being opened late, not being pushed open as far, then closing too soon.

Tight valves can open the valves too soon, open them too far, then clost them too late (if at all), again reducing compression numbers.

Your best bet is to set the valves properly, then check again. You need to minimize/eliminate as many variables as possible.

.
 
Steve said:
Depending on your definition of "massive", yes, it can affect the compression.

"Massive" clearances indicate that the valve is being opened late, not being pushed open as far, then closing too soon.

Tight valves can open the valves too soon, open them too far, then clost them too late (if at all), again reducing compression numbers.

Your best bet is to set the valves properly, then check again. You need to minimize/eliminate as many variables as possible.

.
Click to expand...


It goes without saying that the valves need to be properly set, but massive clearance occurs when the valves are not closing fully (often because of bent valves), so changing shims won't get it. If for some reason the valves are not bent, and there is still a lot of valve clearance, the compression would be fine which is not the case here.

Something is drastically wrong with this engine so I'd pull the head now and remove the valves and check it properly. Done this work before installing the head would have saved all this trouble (unless the valves were bent at a later time).
 
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Thanks guys, Ed, the head I used was running fine in another engine before I swapped it over so I assumed that it was alright. I only swapped it over as the gearbox was knackered on the donor engine. I doubt if the valves have been bent in the short time it came from one engine to another. I agree though about using bits without inspecting them first but in this instance I used a part from a well running engine:confused:. Will reshim the head and test it again. The clearance on one of the shims was 0.20 Thanks for advice. Wayne
 
:o Have had a eureka moment. When I first put the head on I set timing up wrong, obviously have bent valves when trying to start it with incorrect timing. Glad I now have an idea what I have done wrong and should be able to sort it out now. Thanks to all for the advice. Numpty of the week award goes to me I believe.
 
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