rb30 compression

Submitted: Wednesday, Mar 05, 2008 at 19:25
ThreadID: 55217 Views:1451 Replies:5 FollowUps:0
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My 93 3l Patrol is playing up & I was suspecting a leaking valve problem, however on doing some dry & wet compression testing I encountered some unexpected results:
DRY
1 2 3 4 5 6
145 170 175 165 180 170

WET
1 2 3 4 5 6
170 185 200 180 185 185

This seems to suggest worn rings in cylinder 1.

Can anyone tell me what the compression should be in an RB30 carbi motor? I would also appreciate any other suggestions. This motor misses & sometimes stalls, uses fuel & lacks power. I have replaced all leads, plugs, rotor & dizzi cap and also tried various timings. This is a dual fuel car but it runs even worse on gas.

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Reply By: Dunaruna - Wednesday, Mar 05, 2008 at 19:34

Wednesday, Mar 05, 2008 at 19:34
Worn yes, stuffed no.

145 is not bad, the percentage difference is low but not cronic. I would not be too worried about those readings.

First thing to do is check the spark, should be a nice clean blue 'snap'.

My gut feeling is carby problems though (common), maybe a vaccum leak.
AnswerID: 290978

Reply By: Robin Miller - Wednesday, Mar 05, 2008 at 19:44

Wednesday, Mar 05, 2008 at 19:44
1196 kpA kev , with 98kpa variation between cylinders

multiply by 0.145 if you wish psi

Your figures don't indicate miss problems - but I would check the fuel pre-heating block between manifold and carbie, particularly if it has cold starting issues, as they often collapse break up and leave bits blocking inlet tract.

Robin Miller

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AnswerID: 290980

Reply By: Kev C - Wednesday, Mar 05, 2008 at 19:52

Wednesday, Mar 05, 2008 at 19:52
Thanks guys

I'm on my way outside to check that heating block in the carbi.
AnswerID: 290981

Reply By: Gerhardp1 - Wednesday, Mar 05, 2008 at 20:19

Wednesday, Mar 05, 2008 at 20:19
You may have carbonised and sticky rings, try running CEM treatment to free them up.

AnswerID: 290988

Reply By: Kev C - Wednesday, Mar 05, 2008 at 21:50

Wednesday, Mar 05, 2008 at 21:50
That carbi heater was complete but very brittle. I had no problems breaking it out. It definatley improved the top end performance but the missing did not improve. The carbi is quite black inside, that could suggest that it may need work.

What is CEM? I will give it a try.
AnswerID: 291019

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