Engine compression

[ZMQguy]

My engine overheated last week when the fan controller stopped working. Compression is 140's on driver side 200s on passenger side. The compression numbers on the proposed replacement engine are 210, 180, 210, 200, 180, 180. Nissan variation allowance is 14 lbs. General rule of thumb is 10%. Now, I've heard of people getting their numbers closer by doing a carbon cleaning. Any thoughts? Should I go with this motor and hope I can get closers numbers than the seller?

[Ilya]

I wouldn't buy it unless it has a warranty, specifically stating good compression.

[EdBwoy]

...Nissan variation allowance is 14 lbs. General rule of thumb is 10%...

What should the baseline number be?

[ZMQguy]

There is no "baseline" for the variation. Its just measured by the difference between highest and lowest. The compression lbs spec for this engine is anything between 142 and 185, so long as they are all within 14 lbs of eachother.

Im wondering since all cylinders are high, how much could really be wrong with the engine? Would a simple carbon cleaning and re-test with procedures strictly followed produce more consistent numbers?

[EdBwoy]

I figured there's gotta be a baseline/expected number to call the engine healthy. Like when you test an old engine and all cylinders read 100.
Depending on how long the engine has been sitting, I actually think crud & corrosion might give you higher numbers. Maybe I have that backwards.

I really don't know the correct procedures and conditions. Weird to say, but maybe the best time to test is one that has been recently run, but it would be goofy to install then test it. Then isn't the best time to carbon clean an engine when it is ready to run? Used engines are always a gamble to me.

But all in all, I wouldn't worry too much about this one. If the price is right, I'd buy it. Unless you are doing it for a customer then you don't want that boomerang coming back to hit you.

[ZMQguy]

Unfortunately this is for my car. I was under it today just looking things over and holy crap it's going to be a job dropping this all off of the car. The only bolts that looked bad were the manifold to catalytic converter bolts. Not surprising being a Wisconsin car. Alldata lists the job at 10.8 hrs and I just don't see any way that is possible. The engine is $1000, there is also one with even compression for about $1400 it has 195×6. Which is pretty great. It also has 146k on it. I'm hesitant to put in a used motor with more miles than the one I'm taking out. I guess I'm just hoping that I can get more consistent numbers out of the cheaper, lower mileage motor than the scrap yard mechanics did.