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Mknoxc



Member Since: 17 May 2021
Location: Sussex
Posts: 2

United Kingdom 2011 Defender 110 Puma 2.4 SW Zermatt Silver
V8 Compression Test
I have acquired a 1992 Rover V8 3.5 engine s/n 24G10456B. It came out of a fire truck so has not had a lot of use. I have performed a compression test on the cold engine and six of the cylinders were good at 120 psi (it’s 8.13 to 1), however cylinders five and six are 105 and 100 psi. I squirted some oil into the cylinders and now cylinder five is 120 psi and six is 110 psi.

My question is should I replace the piston rings in those two lowest cylinders that are 100 and 105 psi cold, or can I expect them to be OK when engine is warm?
Post #972120 23rd Nov 2022 11:47am
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tommac



Member Since: 03 Jul 2018
Location: devon
Posts: 26

United Kingdom 2001 Defender 110 Td5 DCPU Alveston Red
Do you know how long the engine has stood? If the comparison has increased with the addition of oil, then halves it will be ok; that said, if it were me, I would probably change the rings for peace of mind.
Post #998293 2nd Jul 2023 5:16pm
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Mknoxc



Member Since: 17 May 2021
Location: Sussex
Posts: 2

United Kingdom 2011 Defender 110 Puma 2.4 SW Zermatt Silver
Thanks for the reply. I ended up doing a full tear down and found all the pistons are worn. Also one bore is below limits (naturally the one with the lowest compression) so I’m going for a +10 rebore and new pistons to match. Cheers!
Post #1000833 19th Jul 2023 4:31pm
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1986RRC



Member Since: 11 Mar 2022
Location: Nicosia
Posts: 4

Cyprus 
Re: V8 Compression Test
Mknoxc wrote:
I have acquired a 1992 Rover V8 3.5 engine s/n 24G10456B. It came out of a fire truck so has not had a lot of use. I have performed a compression test on the cold engine and six of the cylinders were good at 120 psi (it’s 8.13 to 1), however cylinders five and six are 105 and 100 psi. I squirted some oil into the cylinders and now cylinder five is 120 psi and six is 110 psi.

My question is should I replace the piston rings in those two lowest cylinders that are 100 and 105 psi cold, or can I expect them to be OK when engine is warm?



Hello. I have a question in relation to compression tests as well.

Does anybody know what readings or range in Bar should a healthy, newly overhauled 3.5 V8 efi High Compression 9.35:1 engine should give? Std measurement pistons fitted with new liners.

Thank you
Post #1034712 14th May 2024 11:34am
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TexasRover



Member Since: 24 Nov 2022
Location: Paris
Posts: 811

France 2002 Defender 110 Td5 DCPU Chawton White
Well just yesterday I did a compression test on the left bank of my P38 4.0 rover V8. The compression rating is also 9.35:1 and I got readings between 160-180 PSI.

Hot engine, throttle open 4-5 cycles (needle steady), no oil added

I was trouble shooingt a suspected head gasket issue, but concluded (so far) it's an exhaust issue.
Post #1034716 14th May 2024 11:47am
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TexasRover



Member Since: 24 Nov 2022
Location: Paris
Posts: 811

France 2002 Defender 110 Td5 DCPU Chawton White
Just had a quick look at the record I have from a 1984 RRC with a 3.5 Carb engine which I used to own. Also 9.35:1 compression ratio and the readings were 145-155 psi
Post #1034726 14th May 2024 1:10pm
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1986RRC



Member Since: 11 Mar 2022
Location: Nicosia
Posts: 4

Cyprus 
TexasRover wrote:
Well just yesterday I did a compression test on the left bank of my P38 4.0 rover V8. The compression rating is also 9.35:1 and I got readings between 160-180 PSI.

Hot engine, throttle open 4-5 cycles (needle steady), no oil added

I was trouble shooingt a suspected head gasket issue, but concluded (so far) it's an exhaust issue.


OK.....well not sure how mine was operated. I just know that I have readings between 9.5-10.5 Bar in the 5 cylinders. The remaining 3 are dead, 0 compression. And this is a recently overhauled engine!!!! I am laughing at the situation BUT I am not sure if I should be crying or chasing with a shotgun the machine shop owner and my mechanic here in Cyprus! I am in the market for a new engine because the Automotive Engineer I commissioned to examine the engine reported that many things went wrong. Block was skimmed 0.16mm, RH cylinder head 0.15mm and LH cylinder head 0.31mm (and note that I am 2nd owner. Not sure if first owner had cylinder heads skimmed before).
Tragic... this is the skill and quality of machine shops and mechanics here in Cyprus.
Thanks for your reply.
Regards
Post #1034764 14th May 2024 6:44pm
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