360 Compresion Specs?

[Jeep Craze]

Hello all,
I have an 80 360 w/ 78,000 miles on it. Checked the compression on it today (guess i was bored). Here's what I got (engine warm) #1 120, #2 122, #3 125, #4 120, #5 125, #6 132, #7 127, #8 125. Now I have looked through all my books and can't seem to find if those #'s are ok or not. Any help would be appreciated. Thanx in advance Craig

[Gladi8r]

I have looked thru a TSM and all I see is the compression ratio of 8.5:1 Nowhere can I find the actual PSI for each cylinder. I think the important thing is your cylinders are all within 10% of each other. I am sure that one of the regular wrenches here can find the numbers that you are looking for as far as minimum and maximum. Sounds to me like your compression is pretty good. How's it run??

[Jeep Craze]

Thanx Gladi8r,
That was the only # I could come up w/ also. As far as the way she runs, it is in a j-10 and in 2nd gear on black top around 1500rpm if I mat it they will smoke(the tires that is). It has reall good power throughout the entire RPM range there aren't any low spots(or sluggish).Like I said, I was just kinda bored I guess. Plus i am going to be pulling the motor this spring to put a bigger cam init and fix the usual oil leaks. So I am trying to find out if the lower end needs to be rebuilt or just maybe freshened up or even just left alone. Thanx agian Craig

[joe]

Factory specs are 120-140 psi with a max tolerance of 30 psi between cyls. So you're fine for a stock 22 year old motor...be happy smile.gif

Don, the allowable cyl pressures are in the TSM's/eng/360/specs section just below the Comp Ratio's.
In an 80 TSM it's page 1B-71..5th spec down on the left ;)

[Gladi8r]

My book is a 72 and has no such info in it :( Page number is the same though smile.gif 1-B--17

Maybe it is just in the later TSM's :(

[Jeep Craze]

Thank you Joe,
Now that I know that, I will just rebuild the top end in spring then the next time it needs something I will do the entire thing. Thanx agian....Craig

[billyrb]

I agree with Joe, my book says 120lbs to 140lbs, and 30lbs between is acceptable. Your motor sounds really good on compression. If you have time, I would suggest taking an afternoon, dropping the oil pan, and checking the condition of all your bearings & main seals. Get new seals, a new pan gasket, and put it all back together. Better to be safe than sorry, IMHO.

~ryan

[joe]

<blockquote>quote:</font><hr>Originally posted by Gladi8r:
My book is a 72 and has no such info in it :( Page number is the same though smile.gif 1-B--17

Maybe it is just in the later TSM's :( <hr></blockquote>
Seems they changed the TSM's format in '74 Don and that's when they started giving the pressure specs.

[Jerk]

hey, did you warm the engine up first? I've heard your supposed to check compression when its at operating temp, that way the rings have sealed properly. 140psi is the max, I got a "running" 401 that had 165 psi- I pulled it apart after getting it from the junkyard and found the valves were hitting the pistons and the Plastic timing gear had broken 3 teeth off and the chain had moved not allowing the valves to open at the proper time.needless to say, i told the junkyard what I had found and the gave me money back on the now-"rebuilder" 401..heh heh.

[Bob Barry]

Just realize that an AMC motor will read good compression well after its bearings are totally wasted. Dang high-nickel iron blocks... ;)

[Jerk]

pardon me for being a $martGreat Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley Moogley, but what do bearings have to do with compression? actually, I am serious. and curious.

[Bob Barry]

Directly, they have nothing to do with one another. Though, in some engines, both wear out at about the same rate, so that if one is bad, you can presume that the other is not far behind.

Indirectly, however, they are both things that can make you say "Dang, I've got to rebuild this engine!" when either isn't looking to good.

The thread seemed to be heading in the direction of Craig concluding that since his compression is strong, his engine may be spared from a rebuild in the near future.

Unlike most other engines, however, on an AMC motor, with its the high-nickel-content iron alloy in the block, the rings can retain great compression even when the bearings are worn out and the engine DOES need a rebuild.

So, I was intending to correct Craig's presumption, if there was one in the first place, that since his engine's compression is in great shape, that he didn't have to worry about rebuiding his engine.

That's all.

[Jerk]

ah.

[79cherokeechief]

i did a compression ck on mine right after i bought it and all but three had 160-170si the three bad ones had 30psi. toasted pistons and a bad (broke) pushrod.

[Jeep Craze]

Thank you Bobbarry,
So you are saying that it wouldn't be feasable to rebuild the top half of the motor in spring? I know the bearings on the lower end have a pretty good sucess rate at failing prematurely! However I don't know if there are any contributes to it or if they just get worn out at about 100,000 miles? My oil pressure is pretty good. when hot at 2000rpm it is at 40psi. At idle it is at 20. So with that in mind does it sound like the bearings are worn? Or isn't oil pressure a way of telling how the bearings are? See I know some stuff about engines and automotive in general, However I do not claim to know it all. I do ask for help ocationally. I was just trying to figure out if I could rebuild the top half of the motor (new cam,lifters,springs,valves,retainers,rockers and seals) and be able to get away w/ it for about 40,000 miles or so (there are 78,000 on it now0 if it doesn't seem worth while to do it now then do it agaoin in 2-3 years than I will just wait till this things is tired then rebuild the entire thing. Thanx Craig

[Bob Barry]

With those oil-pressure readings, it sounds like you've got a really solid motor.

Still, if you're going to pull the top-end apart, you may very well consider getting a full bearing and ring kit, and redoing the rings and bearings in the shortblock at the same time (probably no need to bore it out or do more than polish the crank). Not a whole lot more work or money, and you'll be certain that everything is in top shape.

[Jeep Craze]

Ok thank you Bob I think I might do just that w/ new bearings and rings. If im gonna take 75% of the motor apart I guess I shoudl just pull it and do it right. I also need to rebuild the T-176 it is making a wierd noise when letting the clutch out slowelly in reverse. almost like a bearing on teh input shaft or something. Thanx agian Craig