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Compression Test What pressure ?

Mal Eade

Well-Known Member
Mar 11, 2010
Country Flag
Hi All
My 80 is now approaching 100,000 miles. I have replaced the BEB 15,000 miles ago.
I still have a little trouble with smoke when the engine is under load, it also uses a little oil.

What compression should I have on a test. ?

If it is low then would a ring change be in order. ?


25 to 35 is what I have been told.

Or do I stand corrected ?

No idea ... but 100k miles isn't alot for an 80. Surely replacing the rings would be overkill?!
Oh .. and btw shouldn't those numbers be in the service manuals which are linked to at the top of the page?
has anyone made a home made gauge or are they better purchased. if so how much would i expect to pay
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You can sometimes hire them from too hire places which can be useful although not expensive to buy.

Also watch for differentials in the readings as this is a good diagnostic reading too. The manual should give an acceptable difference. Could be worth getting the injectors tested while out too, might be nothing to do with why you are doing a compression test but good opportunity all the same.
Its probably the best indicator of your engines health and gives peace of mind I suppose. I'm approaching 200k on the clock but have no verification of the milage. I don't suspect anything wear but would still like to be sure. Its funny that in Oz etc 200k + wouldn't raise an eyelid yet here we all panic when our cars etc get over 100k!
I dunno the value of a car seems to drop once its ver 100k and much harder to sell. LC are the exception if you are in the know. If you owned an l200 you'd be lucky to see 100k!
Changing rings may not cure oil consumption. The new ones have to be very accurately measured for play in the cleaned piston ring grooves. If play is out of spec it's new pistons, and that's assuming the bores are not too worn. Either way the bores will need glaze busting so the rings wear to the contours of the bores.

Low compression may be worn pistons/rings/bores but is more likely to be leaking valves..........another nightmare.

I've reconditioned many big 6 cylinder engines. I would find reconditioning an LC engine very time consuming and expensive.

If the engine is smoking under load it may not be the engine itself but the pump. Black smoke under load is overfueling.

Engine oil consumption is evidenced mostly when you have a hot engine and lift off the throttle. This sucks air past wear in the engine and into the combustion chamber then when you boot it again there will be a cloud of blue smoke.