I need a bit of comparative data please folks.

Has anyone run a compression test on their B48 equipped JCW Hardtop?

Gollum IV was just tested at 92,600 miles, and returned (1-4) 150,145,145,145.

Nice balance, but seems a touch low for what I thought was a 9.5:1 motor.

Anyone else with data from this test?

Thanks very kindly.

Cheers,

Charlie

 

Compression pressure has little to do with compression ratio. Compression ratio is purely geometry based, while actual compression pressure is a function of geometry and valve timing.

Considering your pressures are all within 5%, I'd say your engine is probably pretty healthy. You might benefit from performing an oil analysis to further verify the engine health.

 

So I have learned, which is why I was looking for data from folks here -- having the B48A20B engine.

Apparently most folks do not make this measurement, which does not surprise me too much.

I'd love to find a BMW technical doc for that motor - including geometric compression ratio and a cam chart. No hope I reckon...

I agree the results look encouraging (92,600 miles).

Cheers,

Charlie

 

A compression check is a pretty 'gross' measurement, where it will show if something has really gone bad vs a 'fine' measurement, like a burnt valve, leaking head gasket, broken ring vs just wear. I would add in a compression leakdown test to better gauge engine valve/ring condition. There are a lot of articles out there that describe the process, but basically it is just another 'tool' for engine condition evaluation w/o tearing it apart.

 

My JCW had zero ,180 175 180 with 43000 miles on it.How we managed to blow no.1 piston, no idea.Now running forged rods and pistins.