Compression test values

I plan to buy an engine to replace the one in my '83 Mxim 750. The one for sale has been sittting (setting?) for 5 years in a shed, but has a pretty good compression. According to the seller, the readings on a cold engine are between 165-170 for three cylinders and 150 for the last one.

I know it is best to have them all within 5% of difference, but I'D like to know if I should worry or not with the one with 150?

This spare engine would come with plenty of bits making it a VERY good deal (carbs, airbox, complete 4-in-1 exhaust system, wire harness, crash bars).

 

Do a compression test yourself first; and then do a wet test if there's still a mismatch.

That being said, the recommended maximum difference is 10%, or about 15 pounds, so you're closer than you think. The difference could simply be a couple of tight valves. There's nothing wrong with 150.

 

I don't think I should trust the seller readings...he definitely needs to get rid of this engine.

I have my own compression measuring tool, I could tell him I'd like to compare his readings and mine.

Do you think 165-170 is normal for a cold engine? It seems a bit high to me, I expected 150 to be the highest readings, not the lowest.

I forgot to ask him if it was a wet test or just a normal test. FOr a wet test, I should add a teaspoon of oil to each cylinder, right?

 

Is 14mm the right size of compression tester attachment for a '83 Maxim 750?