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Rb20 Issue Suggestions Welcome

James_03

By James_03,
in Engines & Forced Induction

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James_03 Mentor

James_03

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Hey guys trying to get a silvertop motor going here and have a very annoying prob.

I got the motor off someone and it had no compression. So I get it home and rip the head off expecting to see scored bores the rings lands melted etc. Upon inspection and taking the bottom end apart it was completely fine.

So then I check the head out, turn both the inlet and exhaust over and all the valves etc are moving fine.

So I put it back together but when cranking it over it the starter motor does not strain what so ever like there is no compression.

So I thought the timing may have been out but its all good, cams on TDC and bottom end on TDC too.

But still just turns over way too easy, I am suspect on either the inlet or exhaust no completely sealing off which may cause it.

About to go out and get a comp tester, but I am 90% sure it will show nothing.

Any suggestion what could cause this?

I have no exhaust many on, but that shouldnt matter.

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https://www.sau.com.au/forums/topic/131873-rb20-issue-suggestions-welcome/
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rust32 Newbie

rust32

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Are the spark plugs in the motor? Also piston rings could look ok, but not seal the combustion chamber. The valves may move ok, but are the seats ok? And if you took the motor apart and re-assembled it with the same head gasket, any chances of making compression are greatly reduced.

James_03 Mentor

James_03

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Are the spark plugs in the motor? Also piston rings could look ok, but not seal the combustion chamber. The valves may move ok, but are the seats ok? And if you took the motor apart and re-assembled it with the same head gasket, any chances of making compression are greatly reduced.

Spark plugs in yeah, rings are ok as I took the head off and put it onto a known good bottom end.

Brand new head gasket too. I suspect on the seats for now, taking the head off now to check it out again.

Tested with a comp gauge and it registered 0 accross all 6. Its torqued down to spec too.

AzzurrA Grand Master

AzzurrA

Posted
Posted

stupid question, but you said the starter felt like it wasn't using much effort to turn the engine over... i take it you're doing the compression test by kicking the engine over using the starter with the coilpacks off?

have you checked that the starter is actually engaging and turning the engine over? I.e. are the belts at the front of the engine turning when you kick it over?

like i said, sounds simple, something worth double-checking though...

James_03 Mentor

James_03

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Posted (edited)

yeah found out what it was, the valves were bent.

At first glance it appears to be fine but when looking under each valve from the side they are slightly bent.

I suspect it was over reved, going to need new valves.

Edited by James_03

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