82 240d compression test results

Just completed a compression check on my high mileage 240d.
#1 120/200
#2 180/320
#3 190/340
#4 180/320

Number one is not looking so great. The test was completed with the engine cold. I did try adding oil and the change was marginal 130/220 on number one.
The engine runs smooth with little smoke at start up. What my next step? Pull the head and have a look at the valves?
Thanks for your imput.
The compression tester and booklet were excellent.

Forums

Diesel Engine Specific Aid

Chassis Model Number

W123

Confirm

Did you do a valve adjustment before the compression test?

Compression test results

Yes I did a valve adjustment and checked the cam lobes carefully which appear in good shape. I thought I might pull the cover and check the adjustment again just in case. Would a diesel purge help clean the valves?

Recommendations

Be slow to open up a high mileage diesel. From my experience it almost always results in an overhaul. Don't remove a head unless you are CERTAIN there is a head problem. 80 percent of compression problems on these diesels can be traced to cylinder wall or piston ring problems. Valves seldom are the problem. It is more common to find a cracked head than a bad valve. Cracked heads usually can be detected through the coolant and will cause the engine to run hot. Blown head gaskets give off their own symptoms as well. Adding just oil works ok for testing compression on a gas engine, but on a diesel (much higher compression) you need something more substantial. Try a mix of 50 percent engine oil and 50 percent STP. Pour in about 2 table spoons through the injector hole. Then crank engine over with injector out to blow out excess (cover hole with towel... ;-) ) Then recheck compression.

If the engine is starting ok, running on all cylinders, not burning excessive oil, not smoking badly, not using any coolant - then I recommend you leave it alone and keep driving. Just my humble opinion of course.