Compression Test

[wilson]

Hi all,

Firstly excuse me if this is obvious, but just been reading through some old threads and wondered what Wet and Dry compression tests are ??  what does that mean ?

Secondly,  I'm about to start putting my 1990 Mk 2 16v back on the road, I took it of the road in february, when I inherited an old merc, just before MOT expired, originally intending to sell it...  however all the time it sat on my drive I never got round to advertising it.. truth is I really didnt want to, I know i'll miss it and finding another one as good will be costly.   Now i've decided to do the few bits needed and start using it again, main things it needs are new tyres wheel bearings and headlights, and i'm sure there will be a few other small things

However one thing that really bothers me is the smoke. its always had a bit of start up smoke in the 2 yrs i've owned it, but it slowly started to get worse the last 6 or so months it was on the road,  it now smokes a little while just on idle, and does puff out some if driven hard.   I really do suspect it to be valve seal smoke, but I do just want to give it a compression test tomorrow to check rings and just for my own mind really.

My question is what should the compression be approx on these engines

The engine has always run fine, quiet and smooth and pulls very very well, right up to when I took it off the road.

Sorry to waffle just for two simple questions !!!   

Thanks
Wilson

[danny_p]

sounds like stem seals to me, 

compression  you should see about 13 bar give or take a bar

[wilson]

Thanks danny,   so looking around 180 ish psi yes?

any answer to what wet and dry tests are ?

Thanks
Wilson

[jezza16v]

For the 'wet' test you squirt some oil into the cylinder, this gives a temporary seal around the piston so you get a higher reading. The difference between the wet and dry pressures gives you a idea as to how much pressure leakage there is past the piston rings so you can see how much wear there is in the bores/pistons/rings.

[wilson]

ah course, that makes sense,  Thanks Jezza

[danny_p]

somehow managed to not read that bit

[wilson]

somehow managed to not read that bit

haha, no worries Danny, thanks.