Rear main seal

-
B

Bob Creighton

Well-Known Member
Joined
May 7, 2009
Messages
76
Reaction score
3
How easy or hard is it to change the rear main seal on a 340 eng? Thanks.:blob:
 
Engine in or out of the car?

I'll hazard a guess that the engine is in the car. I don't have a FSM in front of me, so I'm gonna guess..........Jack the engine up as high as possible, maybe have to drop center link, unbolt pan (drain it first), lower it out of your way, unbolt oil pump, drop rear main cap. Dig old main seal out of cap and out of block, clean thoroughly, slide half of new seal up into block, place other half into cap, insure seal lip is in correct direction upper and lower, light film of oil on seal, oil on bearing bolt it all back together.
If you did it right, no leaks.

Good luck!

Be careful and don't run your distributor into the firewall when you jack the engine up.
 
If it's just an occasional drip, just make a support tray and put a disposable baby diaper in it.
 
If the crank is out and it's on an engine stand - no problem.


If it's still in the car - Good luck....


It's possible, but a pain in the @ss....
 
Its snowing out where you are so just pull motor and fix all the things on it so no issues come spring. Frost plugs/gaskets/ new oil pump/timing chaing and rear main. Total PIA to do in the car.
 
Are you absolutely, 100% sure it's the rear main..

There are several places the oil can leak, then it migrates to the back of the engine with the help of the fan,, and drips off the back of the pan..

I would clean the begeebees outta the whole area with a coupla cans of brake-clean,, then look closely at the oil pressure sender beside the distributor, check valve covers,, and gently snug the oil pan bolts, the oil filter adaptor can leak onto the pan gskt, and run to the back. dripping far away from where the leak is..

I know by experience to look everywhere else to be sure, cuz you're gonna be real dissappointed doing all that work to replace the rear main, just to find out it leaking from the fuel pump, or some such..

hope it helps
 
inertia said:
Are you absolutely, 100% sure it's the rear main..

There are several places the oil can leak, then it migrates to the back of the engine with the help of the fan,, and drips off the back of the pan..

I would clean the begeebees outta the whole area with a coupla cans of brake-clean,, then look closely at the oil pressure sender beside the distributor, check valve covers,, and gently snug the oil pan bolts, the oil filter adaptor can leak onto the pan gskt, and run to the back. dripping far away from where the leak is..

I know by experience to look everywhere else to be sure, cuz you're gonna be real dissappointed doing all that work to replace the rear main, just to find out it leaking from the fuel pump, or some such..

hope it helps
Click to expand...

Now THAT is a really good call Inertia. :)
 
If I recall you use to be able to buy a dye to put in the oil to help spot the leaks after cleaning the block and surrounding areas. May help see where the leaks are.
 
I'm going through the same thing right now with my 273 and agree with inertia I dropped my center link and pan to change the pan gasket, then it appears the leak could be coming from the oil filter adapter...and then while under the car I notice the lower back corner of the passenger side valve cover is leaking, DANG.

Now I'm under the car again and I notice a small drop of green on the bottom of the transmission. So I pulled to trans to find one of the freeze plugs all gummed up, leaking, and ready to explode!

I don't have room in the garage to pull the motor, so for now I'm going to replace as many of the freeze plugs as I can get to and I guess I'll go ahead and replace the gasket on the oil filter adapter.

I decided NOT to change the rear main seal at this time. If I still have a leak after all this I'll pull the motor in the Spring.



inertia said:
Are you absolutely, 100% sure it's the rear main..

There are several places the oil can leak, then it migrates to the back of the engine with the help of the fan,, and drips off the back of the pan..

I would clean the begeebees outta the whole area with a coupla cans of brake-clean,, then look closely at the oil pressure sender beside the distributor, check valve covers,, and gently snug the oil pan bolts, the oil filter adaptor can leak onto the pan gskt, and run to the back. dripping far away from where the leak is..

I know by experience to look everywhere else to be sure, cuz you're gonna be real dissappointed doing all that work to replace the rear main, just to find out it leaking from the fuel pump, or some such..

hope it helps
Click to expand...
 
The eng. is in the car.I hope it is not the seal and just the oil pan gasket Thanks for the info.
 
Did it 3 or 4 times with the engine in the car on a hoist though. Moved the centerlink out of the way by disconnecting bolt at idler arm, then the pan will come out by tilting the pan down if I remember correctly. The Magnum engine rear main seal finally fixed the problem. The crank rear main seal surface diameter is slightly smaller on the Magnum crank providing a tighter grip on my 69 340 crank.
 
Rocket said:
If I recall you use to be able to buy a dye to put in the oil to help spot the leaks after cleaning the block and surrounding areas. May help see where the leaks are.
Click to expand...
the 340 in the swinger I just finished up had a leak at the rear main. I used the dye kit and not only found the seal leaking, but the oil pan had a crack where the oil pump bolt had worn through. I would have never seen it without the dye kit. I did change the seal in the car and it was no problem. It turned out the crank seal surface was not in the best shape and I had to clean it up with some emery cloth.
 
Could the leak be coming from the oil sending unit hole and dripping down?
 
You must log in or register to reply here.
-

Back
Top