So the parts jeep i was going to buy did not go threw, turns out the owner does not know the Difference between the 4 cyl. and the 6 cyl.
Anyway, i found a used engine that has 97k miles on it, ive asked them for the compression numbers and this is what he said,
"comp@177 psi average 171 psi being the lowest cyl oil pressure was at 38 psi at idle with 1/2hr run time"
Now the question is, what was the orig compression out of these engines so i have something to compare to?

 

What year jeep is the motor out of ... What year jeep are you putting it in?

 

89 cherokee engine going in a 87 cherokee

 

Compression pressure should be between 120 psi and 150 psi, with a maximum variation between cylinders of 30 psi. If he got 177psi-171 psi, he didn't perform the compression test properly. It's probably closer to 130 psi. That engine sounds like its tighter than dick's hat band.

Check the block casting number on the replacement engine, it should be 53005535 or 8933002665 (1987-1990 cylinder blocks). Your casting number should be the same. Cylinder head should be casting number 2686.

 

My bet is that he pulled those numbers out of his ****.

 

I agree, ask him to find the compression of each cylinder. If hes got 170psi average there is something not right about that motor.

 

yeah, that was kinda at the back of my mind. ive never seen compression that high. ill ask him for the compression on each cyl tomorrow and the casting number. thought for ****s and giggles have one of my friends call him on it and ask him for the readings in a few days, just too see what he says.

 

Yeah, I'm thinking that he probably just made up numbers in that range, since those would be good numbers for some other engines. For the 4.0, however, they're pretty high, so that kinda gives him away.

 

It is possible to get psi numbers higher than spec if you just keep cranking the engine over untill the gauge will not read any higher. This is basically what the Haynes rag says to do (seven compression strokes).

The FSM says to record the psi reading after three compression strokes.

I've seen people posting the higher numbers (like in the 160-170 psi range) on various Jeep forums because they didn't perform the test correctly. I think the seller of this engine mistakenly went by the Haynes procedure.

 

well, i mite have to go by those numbers. called the guy back up asked him the block number, (it was the same) asked him to do the compression test again because the numbers did not seem right, he will call me later. but while i was at it, i called other junk yards heres what i got

190k, 170 lbs comp
235k 165 lbs comp
98k 168 lbs comp
234k 151 lbs comp

3 different yards, could i go by the compression of the 7 strokes if so what would the numbers be?

 

Like the junk yard pukes provided you, except the 151 psi one. If he threw a 7 that motor is scrap iron, but if he did it correctly, it maybe a good motor. hard to tell what the junk yard carpet baggers are up to.

 

i have no idea, im looking more and more in to just rebuilding mine. but ive never done it before, kinda dont wanna screw it up. ive done engine swaps before but never worked on the inside of one

 

Buying a used engine is always a crapshoot. Some people luck out, others don't.

On the other hand, if you've never been directly involved in rebuilding an engine, you could really back yourself into a corner. Requires special tools, detailed instructions, and outside machine shop service. One poster here, i believe, said he has $3000 in his rebuild effort and it still isn't right.

I've been eyeballing a used 99 4.0 on Craigslist for $400 but I just want a core engine I can send to a shop for rebuild. It too could be a boat anchor with beyond repair crank, wallowed out cam bearing bores, ate up cylinder walls, ad infinitum, and I could be out $400.

Depends on how much money you have to spend. A rebuilt engine ready to be may be the ticket.

 

i have about $700 all together, low on funds at the moment (have 2 kids and going to school full time same with my wife)

 

What's wrong with the engine you have now?

How much does that first seller want for that engine with 97K on it? That pretty low mileage on that old of an engine. It may be a good buy if it's within your budget.