Thread: Remind me--whats involved in 305 rear main seal replacement?

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Ever since my "gasoline in the oil pan disaster" of last spring, the rear main seal in my roadster pickups 305 has been leaking a bit. Just enough to annoy me, not enough to get serious and replace it. However, with the impending 2500 mile round trip to the East coast nationals on the horizon, I'm thinking it might be wise to replace it now. Its been a while since I replaced a small block rear seal As I remember, its fairly simple---remove the pan bolts, remove the pan,---but then I kind of vague out. I can't remember just what the story is on the rear seal. I don't think I have to drop the crank, but I truly can't remember. Can somebody please give me a refresher on this. Its a 305 with turbo 350 automatic, out of an '85 Pontiac.---Brian

Brian, I know you're no beginner, but will link the procedure with photos in the event someone else with less experience than you needs to do this also.
http://www.pavementsucks.com/tech/rearmain.php

1982-85 EXC. V6-173
These engines are equipped with two-piece, helix type rear seal. A seal starting tool, Fig. 23, must be used to prevent the upper seal half from coming into contact with the sharp edge of the block. When necessary to correct an oil leak due to a defective seal, always replace the upper and lower seal halves as a unit. When installing either half, lubricate the lip portion only with engine oil, keeping oil off the parting line surface as this is treated with glue. Always clean crankshaft surface before installing a new seal.


To replace the lower seal, remove seal from groove in bearing cap, using a small screwdriver to pry it out.
Insert new seal and roll it in place with finger and thumb.
To replace the upper seal (with engine in car) use a small hammer and tap a brass pin punch on one end of the seal until it protrudes far enough to be removed with pliers.
Position tip of tool, Fig. 23, between crankshaft and seal seat in cylinder block.
Position seal between crankshaft and tip of tool with seal bead contacting tip of tool. Ensure oil seal lip is facing toward front of engine.
Roll seal around crankshaft, using tool as a ``shoehorn'' to protect seal bead from sharp corner of seal seat surface in cylinder block. Tool must remain in position until seal is properly seated with both ends flush with block.
Remove tool, using care not to dislodge seal.
Install new seal into bearing cap with tool as outlined previously.
Install bearing cap with sealant applied to the cap to case interface, Fig. 24. Do not apply sealant to seal ends. Torque rear main bearing cap bolts to specifications.

Brian, I'll let one of our more knowledgeable members give you more details, but essentially, you have a two piece rear seal in that year, as I remember. You are right about dropping the pan, and you will also remove the oil pump and the distributor drive shaft. One way is to loosen all of the main caps only slightly to let the crank drop down, just a tad. Remove the rear main cap completely, exposing the upper seal in the block. You can sometimes just turn the crank a little and the top seal will come out, or you can help it by screwing a small screweye into the end of the seal and assisting it as you turn the crank. They sell a tool that looks like a skinny corkscrew with a handle to do this too.

Once the seal is out, the new seal should come with a little plastic "slider" to put in first that keeps the new seal from getting damaged as it goes in. Lube both sides with oil to help it slide home. Once it is in place (follow the instructions about which side is out..........I think the lip goes toward the motor), then retorque the main caps and replace the rear cap with the new seal installed in it too. There is a sealant called anerobic or something like that made for rubber, and you can paint the ends of both seals with that stuff to seal the gap.

Under some cars it is a b****, but in a Model A frame you won't have much in the way of dropping the pan down. Now we'll let the good mechanics tell us the right way to do it.

Don

Hehe, Randy was typing same time as me.

Brian,you got most of it right,after ya drop the pan,drop the oil pump and pull the rear main cap,1/2 of the seal will be in the main cap.Then take an ice pick,small screwdriver or such to push on one side of the seal to roll it outa the block enough so that you can grab the exposed end with pliers and finish rolling it out.Sometimes they are stubborn but ya gotta be careful and not nick the crankshaft. When I install them I like to turn the seal halves so the parting lines on the seal do not line up with the parting lines of the main cap.
to do it you have to roll both halves of the seal into the block,I usually shoot for 1 and 7 o clock on the seal halves.

Thanks fellows---Thats a big help. I have many years of chassis design and build experience, but mostly using pre-built or "previously experienced" engines. It been a long time since I replaced a rear seal on a small block.----Brian

personally, I've never had any luck with the old 'work it out' technique on the top seal half. I've always found it easier to drop the crank, so that takes breaking loose all the main caps, but you don't necessairly have to remove the timing chain, just let the rear end droop down about 1/8 - 1/4". Makes life easier.

Brian, you are so lucky to have gotten so many excellent answers to your problem.

If it had been me, I would have advised you to go down to the nearest Goodwrench Performance Parts dealer, latch on to an inexpensive new SBC 350/290 hp crate engine and take the 305 out and put the 350 in.

But you're the builder, I'm just the accountant.

Mopar34---I so agree with you---But--so far this spring I've spent $400 on a new chainsaw, $650 on a backyard swing/play set for various grand daughters, and $200 for Lexan sidewindows for the hotrod!!! The well is dry. I have to find another contract before I can spend any more money, without cutting into the Rupnow retirement fund.

Here is my version based upon experience:

1. pull car into garage
2. jack up car using jack stands
3. block rear tires so car will not roll
4. crawl under car and loosen drain plug
5. crawl out from under car and find oil drain pan
6. crawl back under car and remove drain plug
7. reach into oil pan and get drain plug out of oil
8. crawl out from under car and get shop towel to wipe oil off hands
9. crawl back under car and loosen oil filter
10. unscrew oil filter
11. drop oil filter into oil pan
12. crawl out from under car to get shop towel to wipe oil off face
13. crawl back under car and see what size socket is used on oil pan bolts
14. crawl out from under car and find socket, extension, and ratchet
15. crawl back under car and remove oil pan bolts
16. drop oil pan bolt into oil pan
17. having remembered to bring shop towel under car, wipe off hands
18. crawl out from under car to get different socket for the 4 end of pan bolts
19. crawl back under car and remove four end of pan bolts (or nuts)
20. crawl out from under car to get pry bar to get pan unstuck
21. crawl back under car and pry pan off
22. wipe splashed oil off face
23. push oil drain pan out from under car
24. crawl out from under car with pan
25. step in oil drain pan
26. wipe off shoe and floor with shop towels
27. drive to auto supply to buy oil seal set and pan gasket
28. ......the rest is easy!!

Robot, ROTFLMAO That is all too true. Been there, done that.

Outrageous Robot!! How many of us have done that??

Ya forgot...

crawl out from under car to retrieve putty knife to scrape off old gasket.

Crawl back out from under car to wash gasket pieces out of eye.. get safety glasses..

Crawl back out from under car, cussing loudly... find a clean rag to stem blood flow from hand, caused by putty knife slipping off stuck gasket.

Wife comes out to investigate loud cussing. Cuss wife.

go in house to get ice pack for head... which has the impression of a high heel...

Originally Posted by glennsexton

Outrageous Robot!! How many of us have done that??

NOT ME

Awright!!!--Had to go all over town this morning on business, so thought,"What the Heck---I'll stop at the Chevy dealer and see what their flat rate is to replace a rear main seal in a chevy smallblock."---Can you believe $407.55! That includes a new rear seal and a pan gasket.--but $300 of the cost is labour. I guess I'll be spending some time laying on the concrete floor under my roadster pickup.