Checking out a used motor

[jacktoad]

i hope i have posted this to the appropriate forum. if it is better placed elsewhere, i'll understand

i recently bought a used 3.4 liter SFI motor out of a 1994 camaro. it also came with the automatic transmission, which i have sold already. tranny worked out fine for the guy i sold it to(i.e. no problems in his camaro).

i was initially told, by the husband, that this motor had 35K miles on it. when i got to the sellers home, i asked again how many miles on it. this time, the wife said it had 'less than 100K' on it. the husband agreed. the family i bought it from had pulled it out of a car that they had bought for the body parts. they seemed trustworthy enough. but, then again, i dont know them personally. there place was very organized and well kept. and the motor looked genuine... not like it had been steam cleaned or even 'touched up' in any way since removal from the car.

my question: what, if anything, can i do to the motor while it is out of the car that would help me determine its integrity/condition?

my plan is/was to put this motor into my 92 Rodeo as a replacement for the original 3.1 liter. but i would really like to have a bit more confidence in the motor's condition before i go through all the work.

thanks for any help anyone can offer on this.

rb

[bszopi]

Depending on how much you want to spend, I'd recommend tearing the engine down to the short block and replacing all the gaskets (head gaskets up basically). With the engine torn down that far, you can inspect the heads and pistons for any potential issues. I'd also pull the oil pan and rotate the engine over by hand making sure everything appears to be rotating without any issues.

The above would probably run you about $300 (just an est, I haven't had to replace all the gaskets in several years), but it might be a worthwhile $300 to get everything cleaned up, all new gaskets, and all the nuts and bolts torqued correctly.

[SappySE107]

If you don't want to go that far, you can pull the spark plugs and turn it over by hand. Pull the pan for sure and check out the block for sludge or metal shavings.

[gectek]

compression test and cyl leakage while the engine is still together.

[SappySE107]

How do you do that with the engine out of the car?

[gectek]

use a good batt.(maybe hook a charger up to it) hook up the pos wire to the starter, and neg to a ground, then jump the pos to the s term on the starter, and use the starter button to turn the engine, hold the throttle plate open with a screwdriver, and thats it, turn 4 revs and check pressure

we do it in class all the time

[SappySE107]

Hmm, guess you gotta have it on the stand for that then. Never really considered it out of the car before:P

[gectek]

stand or pallet, or just braced up, you could do it on a lift also

[alainman15]

you dont need a batt 4 the cyl leak down test the cyl. just have 2 be at tdc and on the end of compression listen 4 were the leaks r coming from. if its coming from the intake than intake valves are leaking. exhaust, exhaust valves.

if you are doing a compression test i would suggest cranking until the pressures won't go any higher on the gauge. that way u know u got it

[gectek]

yah, well i didnt say u need a batt for the leakage test, and service manual says 5 to 6, because if you keep cranking you can ruin the seal of the rings on the wall

[alainman15]

yah, well i didnt say u need a batt for the leakage test, and service manual says 5 to 6, because if you keep cranking you can ruin the seal of the rings on the wall

no you dont need a bat 4 the cyl leak down test, if u turn it manualy. the motor doesnt need 2 spin. u gust have 2 test each cylinder at tdc and at end of compression when valves are closed in that cylinder. you need an air compressor 4 this test. as i can remember there u need a guage 2 so u know how much presure u have in the cylinder. check what the spec. should be

both leak down and compression tests should have the motors at operation temp ( but my car manual say taking the spark plugs out of a hot head can damage the head. check yours)

i never knew that u could dmg the rings. if there is oil in it ,I dont see a problem. i usually put a squirt of oil in the cylinder before i do the compression test. does the manual tell u to do that?

do what u want its your motor anyway. i didnt build the motor

[gectek]

ok u have a wet compression test switched with a dry compression test. you are supposed to do the dry first, then the wet if you dont get good readings. secondly, i agreed that you dont need a batt for the cyl leakage, and yes you def have to have a source of air supply, and a cyl leakage gauge, you should pump the press up to 100 psi and watch it leak, i think about 12 - 15% is the max it should leak, if its more than that then you have a big proble, but any engine i have seen that was in good shaped showed only 10 max. when it starts leaking, look/hear for where it is leaking from, intake hissing is valves, manifold is valves, and put a steth in the dip stick, thatll be the rings. and yah if you keep cranking, itll ruin the walls and the rings, because there is no lube being put on the underside of the pistons. and you dont have to have the engine at op temps, but your readings will be more accurate at the op temp.

you only put the oil in after a dry test to see if the rings will seal then, if they do, then you have a ring problem, but you dont do that one first. that is only after you get a reading that isnt 20% of the highest reading with the dry test, IIRC, but the compression tester will have that data. Sears has a real good compression test kit for about $60, good money spent

[alainman15]

nicely put gectek

[prophiseer]

I would recommend smoke testing the cooling system of the motor, but the equipment to do that is kind of pricey.

If the motor still has the old oil filter on it - pull it off and cut the top off the filter, remove the filter media and inspect it for metal shavings and other bits of junk.

You might also want to yank the valve covers and inspect the top end for anything odd looking with the rocker and valves assemblies; also depending on how much hard carbon or sludge buildup is in the top of the motor, it might necessitate further tear-down just for cleaning purposes.

probably, it wouldn't be a bad idea at all to replace the front and rear crank seals while it's out - especially the rear . . . although, 95% of GM's v-blocks leak from the rear main sooner or later

[alainman15]

ya I agree with the rear main i think mine is leaking slowly.