whats the compression on the 4.2?

[glbft1]

just did a comp check all all are in the 145 to 150 range is that good for the 4.2???

[scott95LWB]

I spent a few days looking for the values for the cylinder compression test figures for my 1995 Classic Range Rover 4.2 with 8.94:1 compression ratio but there was no info. Even the factory repair manual levels out the info for the 4.2 engine. A few years ago I spent the day at the Rover factory in Birmingham UK on tour and drive event, I remember the gentleman who ran this department was a retired engineer for Range Rover. I was able to get hold of him by email and he responded with the following info:

Hello Scot,
Nicky tells me you are having problems finding the cylinder pressures for your V8 4.2 L. Well guess what, so am I. I can find the pressures for a 3.9L ( Both comp ratios) but not the 4.2L.

So what I have done is to extrapolate the info from the 3.9L into the 4.2L and it looks like this:-

3.9L (8.13:1 ratio) Cyl Pressures should be 150/160 psi.

3.9L (9.35:1 ratio) Cyl Pressures should be 170/180 psi

Extrapolating from the above 4.2L (8.94:1 ratio) Cyl Pressures should be 165/175 psi

[rino]

you can try a wet test, and compare values,

squirt a bit of oil in the cylinder, then take a compression reading, you should find an increase in the numbers, thus indicating worn rings. Time for a mild rebuild on the 4.2


Rino