Compression test of an engine out of the car.
 

I have an interested buyer for my 280e euro motor. Foolishly I removed the engine from the car without doing a compression test. The buyer wants me to run a compressoin test. I want to do so and I want to be fair to him and to me.

The engine was run for about a half hour a couple of weeks ago before removing it from the car.

I can crank it over with a battery and jumper cables to do the compression test.

My question is should I do anything with the bores before running the compression test? Put in any liquid before testing or just go with whatever is in the bores at the moment?

usually to get a good comp test you need a little oil in the cyl's first.especially if it's been sitting.

NO, do a dry compression test first. If you find a low cylinder THEN put a LITTLE oil in the dead cylinder and spin it a few times without the gauge to make sure there is not so much oil that it will lock. Then test that cylinder again. If the oil brought up the compression, the problem is piston/cylinder/ring related. If not it is valve related.

It has only been a couple weeks since it has run. I am sure it is a sound engine having ran it but have never run a compression test on it.

OK then I will do it dry but make sure I have oil in the sump.

Yes, you should at least have enough oil in the sump to keep the pick up covered.

What kind of engine is it?

It must be an M110.

Tom- I would be curious to know what readings you get. I bought one of these M110s when Upullit had a 50% off sale, just because I like these engines and I have a lot of cars I could put it in (if and ) when I retire. After all that hassle when I got it home and did a dry compression test on it it had numbers that were pretty bad like 110, 130, 140, 110, 130 , 120 or something like that. I happened to find the POs business card in the junk car , so I called him, and he told me the engine ran great, but that it had probably been off the road for 5 years. So, I have been tripping over it in my garage now for a year, after filling it with MMO.

Sigh.

No matter. If that engine is properly oil primed before lighting it off, it will most likely run as good as ever after an hour or less.

Still, the devil in me wants to pull it apart and at least re-ring it.

It's gonna sit a long time if this economy doesn't improve before I have time and motive to mess with it. I should at least repeat the test now and see if the MMO freed up the rings.

Have you learnt nothing from me!

What readings did you expect? That does not sound all that bad to me. US spec engine?

Why, yes I have- that's why it's still more or less in one piece.


Tom- no euro. I think it needs to be more like 160-170 , IIRC. And I think there was more variation, maybe the low was 105ish

If it ain't broke, don't fix it.

It's dry and hasn't been run in awhile. Even if it had, those are not necessarily low numbers. I bet they'll even out and rise after it is run awhile.

It will run, but depending on a lot of factors (like what kind of car it is going in, the price of premium fuel , the size of my 401K) may influence how much attention it gets.

Instead of a compression test, do a leakdown test.