Can anyone tell me how to do a compression check on an 84 5 cylinder turbo and what the tolerances are for compression? Thanks!

Welcome to the forum!

The compression should be 400psi per cylinder when new. It can run with a lot less than that (200's so I am told) and still run although there will be a lot of smoking due to improper combustion. Make sure you have the valves adjusted before you do the compression to make sure it's accurate.

Good Luck

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1974 240D 3.0L 4(M) - 250K -OM617.910 + 300D FW + Rajay turbo power!
1977 6.9 3(A) - 84k

Thanks for the compression numbers. Since I've not even looked at a diesel before, are the glowplugs similar to removing spark plugs? Is there a special tool required? Thanks!

You get hold of a compression guage made for DIESELS... as those pressures are higher than a gas engine guage...
You make sure you have the proper fittings for it to fit into either the glow plug hole or the injector hole.

You will soon see several people post saying you can't use the glowplug hole... but I have posted a picture from the MB Factory Shop manual which shows using that access....

Then you tie the stop lever to Stop and crank over the engine ( with all the glow plugs out so you get a higher speed ).

Crank the engine about 6 times for each reading , zeroing out the number in between times..... or until it quits climbing. Write down the pressures you see indicated. Don't run the starter more than then number of seconds you are supposed to without the cooling off waiting period.

The pressures ought to be above 300 psi and pretty close to each other... evenness across them is more important than the actual numerical indication.. although certainly the higher the better ( unless it is higher than new...which indicates you have carbon built up inside your combustion chamber or head.

If the pressures all look good and the engine runs fine... close the hood and drive it... if not do a search for ' leak down test' .... which will refine the indications as to what might be wrong with the engine.... delineate between valves/head and pistons/rings..... or gasket....

No special tool required ... but small hands helps.... getting between the fuel injection lines can be a bummer... when taking the out the most important thing is to place a large towel in the space between the injection pump and the block... strong glow plug nut magnet hidden there...

the compression ratio is 21.5 to one. atmospheric pressure is 14.7#/sf at sea level, or 316 psf, less as the altitude goes higher, i dont know what you would get in death valley but it is below sea level so it would be higher.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.