engine rear seal

[thrival]

Hi, I love my 85 chevy C-20 truck, rust-bucket that it is. A few weeks
ago the oil light went on, I checked the dip-stick to find it dry! Since
then, after changing filter and adding a few quarts, have noticed there
are stains on the ground at the back of the motor which I take to be a
leaky rear seal (checked valve covers and intake manifold, seems to be
coming from somewhere lower.)

Anyway, my question concerns the rear seal. Is it single or two piece?
Must I remove the entire tranny/bell-housing or can I get away just
dropping the oil pan? Again this is an 85, V6 4.3L motor. Thanks.

[VileZambonie]

Take a look at the flexplate... see if it is counterweighted.

[thrival]

Of course this is going to sound ignorant, but what is the flexplate?
If I recall, that's part of the clutch assembly. I haven't taken off
the bell-housing and tranny and hope I don't have to. Anyway would
counter-weights on the flexplate have to do with rear seals, and why
would their presence or absence indicate whether I have a one or two-
piece seal on my motor? Thanks.

[Lt.Del]

a flexplate is on automatic trannys.  YOu must have a manual trans.
If it is an 85, i think you have a two piece. Is the oil dipstick on drivers's side under the master cylinder?  i think they went to one piece in 86.

Changing the rear main is not that difficult.  I would drain the oil atleast a few hours before dropping the pan due to drops of oil conitnuously dropping on you from the crankshaft once the pan is off.

You will have to remove the rear main cap and the bottom half should be in the cap itself, the tricky part is removing the top half which is inside the block...you will have to push it on one side and with pliers, pull it out the other side....very carefully as to not touch a metal tool onto the crank shaft or you will have a scratch on the crank and you will always be dripping oil.

Same thing putting the new one back in....coat it with oil and do not touch the crank with a metal tool. it should just slide in place with your fingers pushing in on it....do not push it flush with the bottom of the block...kind of off-center it so one side is a little lower than the block surface.  Then when putting the bottom half in the bearing cap, pull one side up a little. Remember, coat the seal with oil or it will burn when first starting the engine up.   The "V" gap on the seal must face the front of the engine. 

Ensure you torque the bearing caps correctly.  If you have four bolt mains, the outer is a little different torque specs than the center. I forget what the specs are, but chiltons manual will set you straight.

[75 C20]

when u go to put it back together it will be alot easier with the oil pan gasket if you put fishiing string throught the wholes when u put it up because other wise it wil slide around and be a PITA

[thrival]

SgtDel: Thank you very much for the specifics. Yes mine is a manual shift, the dip-stick
is on the LEFT side, standing in and facing the front of the vehicle with the hood up.
The local dealer also said the seal is two-piece ($38.00-- yikes!) ...but I just wanted to
be sure with you guys. Very much a pain to start work and discover otherwise, since I'll
probably be doing it on the street.

75 C20-- How do you mean I should use the string? I guess I'm not quite clear what you
mean.

[VileZambonie]

The best way to prevent your oil pan from leaking and the gaskets from becoming misaligned when reinstalling the oil pan is to clean the block surfaces, rear cap (especially where the tabs of the rear seal sit) and the timing cover. Use 3M weatherstripping adhesive (yellow) and glue the end seals into place. Run a small bead of the adhesive on the rail gaskets and install them with bolts lightly and allow the adhesive to dry and the gaskets will be held in place. Take some RTV (use "the right stuff" in the easy cheese can - I don't use anything else anymore) and place a thin bead across the two rubber seal and over the corners where the seals and gaskets intersect. Install all the bolts then tighten them criss cross and torque to specs. Wipe any excess RTV for a neater appearance and your pan will never leak.

As far as the rear main seal is concerned when you install it, misalign the seal with the cap slightly and you will not have that seepage problem either.

[thrival]

VileZ: Thanks for those suggestions!

One last question (well, actually two.) Assuming my '85 V6 DOES have a two-piece
seal, might we assume it's the same as the V8 "mouse-motor" that the V6 is just a
shortened version of? (Same main-bearings, etc.) Point being, isn't $38.00 just a
bit high for a piece of rubber? Would the V8 seal be cheaper (i.e. more common
motor.) Does anyone know a supplier who might be cheaper than my local dealer?

Also trying to fix the problem before posting, I added some rubber swelling agent,
supposed to restore leaky seals. Well it didn't work. But my concern is that it's in
the oil now, and even letting it all drain out, concerned that any residues on upper
surfaces could cause the new seal to swell before it's fully installed.

Well I like to talk a thing to death before going to work, to be certain I don't miss
anything. Thanks again.

[Lt.Del]

I would get the part that is designed for your specific motor.  It is a lot of workto replace this thing and I would not take any chances.

Dont worry this  thing to death, just do it.  If you have a lot of miles on your engine, you may consider replacing the oil pump too, since you have to remove it to get to your mains.

If you want to see if the seal number is the same V8 vs. V6, just go to autozone.com or advanceauto website or something to plug in the different engines and see if it is the same part number.

I concur about the oil pan gasket....it is tricky sometimes lining up the holes and then trying to put the bolts through, all while laying on your back. I used the fishing string in the past.  Just tie fishing line around four bolt holes to hold your gasket onto the pan.   Then, once bolted in place, i like to take a knife and cut the line out.  Then put those last four bolts in place where the line was.  I use a one piece gasket, so i dont have to worry about the end rubber pieces.

[77c15]

Haven't you guys heard of gasket glue by Emersons?

[VileZambonie]

3M yellow snot (weather stripping adhesive) is the best gasket adhesive I've ever used. It dries fast, it's cheap and a tube lasts a long time.

[thrival]

SgtDel:

You mention using a one-piece gasket and yet that's not what the parts store wants to sell
me for my model/year ('85) which is two pieces of cork with rubber pieces (total of 4.) Are you
saying that later model/year one-piece gaskets will fit my oil pan? Note I looked up the part#
for one-piece gasket and found: GMC 10220906 GASKET. 4.3 GM 97-98 available at:

http://cgi.ebay.com/ebaymotors/NEW-GM-OIL-PAN-GASKET-
FITS-4-3L-ENGINES_W0QQitemZ250116035069QQcmdZViewItem

...and

http://www.southeast-service.com/parts/parts.php

I guess I just want to be sure it will fit since it was obviously made for different year vehicles.
Thanks in advance, --thrival

[Lt.Del]

http://cgi.ebay.com/ebaymotors/SBC-CHEVY-Reusable-Oil-Pan-Gasket-305-350-383-400_W0QQcmdZViewItemQQcategoryZ33669QQihZ020QQitemZ300114375418QQrdZ1QQsspagenameZWDVW

One piece gaskets are awesome.  I have one on my 79, should be same as 85

http://cgi.ebay.com/ebaymotors/SBC-CHEVY-Reusable-Oil-Pan-Gasket-305-350-383-400_W0QQcmdZViewItemQQcategoryZ33669QQihZ020QQitemZ300114375418QQrdZ1QQsspagenameZWDVW

http://cgi.ebay.com/ebaymotors/Fel-Pro-1-Piece-Oil-Pan-Gasket-sb-sbc-Chevy-350-383-400_W0QQcmdZViewItemQQcategoryZ33669QQihZ008QQitemZ180114399796QQrdZ1QQsspagenameZWD1V

[thrival]

OK, that's great, but again mine is a 4.3L V6. Are you saying
the lower block / oil pan / holes are the same? Parts store
says mine has the two-piece rear main seal. Thanks!

[VileZambonie]

The 350 and 4.3L are not the same oil pan gasket but the rear main seal should be the same. However it isn't listed any cheaper for the 5.7L and it's not a dealer item. In fact I believe Fel pro makes a double lip seal and an offset lip seal if the crank is scored and you think it might not seal well.