Rebuilt the 5.0 but it's got an oil leak

65-Fstbk

Active Member
May 20, 2007
276
13
29
Vancouver, B.C. Canada
#1
Ok so I was getting all excited as things are getting nearer to completion. Two winters ago I rebuilt the motor (out of an 87 Fox GT). All new seals, bearings in the motor and I was pretty careful to check and torque everything properly. Heads are new aluminum ProComp.

Fired up the engine and it sounds really great with a fairly big cam in it (Comp 281HR, 512 lift, 220 duration). After running for awhile and a few tweaks of the throttle to rev it up I notice oil after shutdown. Coming off the bottom of the trans spacer plate and the oil pan. So I'm thinking is there some possible way I did not put the one piece rear main seal in right. I don't think so but there it is, something is leaking.

Do any of you think this could be a case of crankcase pressure being too high and blowing oil past rear main? Engine had everything new except I reused the forged pistons and the block did not need to be bored, just honed/crosshatched which was done by a machine shop.

I really don't want to have to break apart exhaust, pull drive shaft, tranny etc to replace a rear main seal but I'm thinking that may be the case.

Any thoughts?
 
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tos

Founding Member
Apr 27, 2001
815
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49
Cincinnati Ohio
#2
I would rule out the high crankcase pressure. Usually that high of a pressure will push oil out of the dipstick tube or valve cover vent before a rear main. I would first make sure your pan gasket is not the problem or even the intake or a valve cover leaking in the back and running down. If those look good then either your seal got damaged or is in backwards?
 

65-Fstbk

Active Member
May 20, 2007
276
13
29
Vancouver, B.C. Canada
#4
Thanks guys.

I would say the leak is fairly bad (a spot about 8" x 4") under the trans spacer and there seems to be oil on the pan bolts near the rear as well. Last night I removed the pan and found a couple of fairly large gobs of cured RTV right at the corner by the rear cap. I'm hoping this is the cause so I have removed the old gasket and cleaned everything out of the old application. Just to be sure I checked the torque on the rear caps that hold the main seal and they were 70 ft lbs so that's perfect. Bought a new Fel-Pro one pc pan gasket which has now been installed completely dry. Felpro says there is no need for any additional RTV with these new gaskets so that's how I installed it. Completely dry.

I was also wondering if there was a chance I had put the rear main in backwards but I don't think so. I was very careful when I installed it. Not saying 100% no way though. If this doesn't cure it I guess I'll have to dive deeper which I really don't want to do.

Rear seal was lubed with oil prior to install.

I will fill with oil and run tonight and update. Thanks for chiming in.
 

65-Fstbk

Active Member
May 20, 2007
276
13
29
Vancouver, B.C. Canada
#5
Ok so I ran the car again last night. Was dry for a while then a drip down below followed by another but wasn't coming off trans spacer area. Shut down and had a good look up from underneath and I could see the rear corner of the pass side head was wet with oil. I removed the valve cover and re-torqued the head to 70 ft lbs which I was surprised the wrench/bolt turned before clicking at 70ft/lbs. I guess new gaskets compress a little over time and the heads need re-torquing. Will do drivers side next to be sure they are both down good (I did use ARP head bolts).

Cleaned up what I could see under and fired again and ran it for a while. Other than some small residual oil it seems to be dry now so that may have been my problem. Left overnight with clean paper under and no drops this morning.

Fingers crossed that was the issue.

If anyone would like to see/hear how it sounds I have put a link here to YouTube. Hopefully the link works. Turn your volume up ;^)

www.youtube.com/watch?v=LJQV-1it_FU
 

tos

Founding Member
Apr 27, 2001
815
50
49
Cincinnati Ohio
#6
Yes after a rebuild you do need to retorque due to heating up and expanding then cooling down things move and stretch and become loose. Make sure you do the other head too.
 

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