Moparts
318 rear main seal question....
Posted By: tpabayflyer
318 rear main seal question.... - 09/02/08 07:47 PM
I finally managed to pull the stock pan off my 390 stroker.
I had a fairly bad leak from the rear main seal area and I think I found the problem. I bought a new fel-pro seal and it has the extensions that fit into the cap while the other seal did not. Was this the proper that I installed the first time??? I have a nice milodon pan going in now and I wanted to get some input on this seal and make sure I get it right this time.....
I have about 6 hours run time so far on the engine and I am going to run the shell rotella synthetic oil.
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/02/08 07:49 PM
I wonder if I should have filled the channels next to the seal with silicone???? Here is a pic of the upper seal...
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/02/08 07:53 PM
lower end looks nice and clean...
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 07:54 PM
yes, that could definetly be a problem.
My 340 has a leak too that I think is the oil pan gasket. it squished out when I bolted the pan down and I used a torque wrench.
On my 340, the cap has the grroc extending out from the rear main seal as well BUT it doesnt go all the way to the edge of the cap. The ends of the cap are flat. so I cut the additional extensions off the seal at that lip where the groove ended and used permatex on the flats.
USE PERMATEX ON THOSE EXTENSIONS. And put a slight dab on the ends of the seal where they meet.
btw, that orange rear main looks odd. it doesnt have the triangulaly lip like Id expect. could it be in backwards?
use some brake clean and the seal with the ears
brake clean will help the rtv to stick and seal
and yes,it does look nice and clean
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/02/08 07:59 PM
Thanks.. I think it was installed correctly as the larger lip was pointed in towards the engine. Are you saying that I should trim the rubber seal portion that extends out past the upper cap area???
The bottom of my car has a nice coating of oil on it now so I don't think I will ever have to worry about rust! I was a total pain to get the old pan off as I had to remove the pax side header and jack the engine up as well... Car is an 83 J-body with hooker super comp headers 1 3/4" TBF
Posted By: RapidRobert
Re: 318 rear main seal question.... - 09/02/08 08:09 PM
Quote:
It was a total pain to get the old pan off as I had to remove the pax side header and jack the engine up as well... Car is an 83 J-body with hooker super comp headers 1 3/4" TBF
You definitely dont want to have to R&R the pan again.
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 08:11 PM
Quote:
Thanks.. I think it was installed correctly as the larger lip was pointed in towards the engine. Are you saying that I should trim the rubber seal portion that extends out past the upper cap area???
no, dont trim that. just add rtv to it.
See how your groove extends all the way from the seal to the outside of the cap past the ledge there? My #5 didnt have groove extending all that way. the groove (or more like a nitch) stopped at the ledge so the outside edge was flat.
Not sure why that is but it was.... Maybe its a 340 thing???
Posted By: Posest
Re: 318 rear main seal question.... - 09/02/08 08:14 PM
What did you do to make a 390 stroker. Lemme know the ingredients please.
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 08:21 PM
Quote:
Quote:
Thanks.. I think it was installed correctly as the larger lip was pointed in towards the engine. Are you saying that I should trim the rubber seal portion that extends out past the upper cap area???
no, dont trim that. just add rtv to it.
See how your groove extends all the way from the seal to the outside of the cap past the ledge there? My #5 didnt have groove extending all that way. the groove (or more like a nitch) stopped at the ledge so the outside edge was flat.
Not sure why that is but it was.... Maybe its a 340 thing???
scratch that comment. I just looked at my pics and I DID have the groove extending all the way out.
What I did was cut the ears off the rear main so I could rotate the seal in the block and cap so the seal's parting line didnt line up with the parting line between the cap and the block. After I cut the ears off, I RTV'd them into the groove butting them up against the seal edges.
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 08:32 PM
btw, I did not put RTV under the seal itself where it fit into the round groove around the crank. Just rtv the flats where the ears are.
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/02/08 08:34 PM
Quote:
Quote:
Thanks.. I think it was installed correctly as the larger lip was pointed in towards the engine. Are you saying that I should trim the rubber seal portion that extends out past the upper cap area???
no, dont trim that. just add rtv to it.
See how your groove extends all the way from the seal to the outside of the cap past the ledge there? My #5 didnt have groove extending all that way. the groove (or more like a nitch) stopped at the ledge so the outside edge was flat.
Not sure why that is but it was.... Maybe its a 340 thing???
O.K. gotcha.... I wonder if the original seal was for a magnum engine and would that even make a difference???
Short block is very basic and cheap too...
Eagle cast 4.00" crank 318/340 main $330 delivered
Eagle sir rods $250 delivered
K/B forged pistons .030 over $395 summit
So for less than $1,000 you can turn a plain jane 318 into a torquey 390.... If you figure in the cost of a used 318 engine is usually free it makes alot of sense to build one of these. I should also mention that the lower end balanced out real good with only drilling the counterweights for a perfect balance. The sir rods are very light as are the kb forged pistons. They are only 3.940 in diameter and pretty short as well. I won't spin this over 6,000 but it makes great power and is by far the smoothest engine I have ever built. I ran a 13.75@102mph with 3.23 gear and ran 13.81 @92 with the new 3.73 gear letting off after the 2-3 shift.
It should run a 13.30 as it sits with the trans shifting properly now and maybe I can touch the 12's with my drag radials as my 60 foot is 2.1. Car is an 83 cordoba... TBF
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/02/08 08:36 PM
Quote:
Quote:
It was a total pain to get the old pan off as I had to remove the pax side header and jack the engine up as well... Car is an 83 J-body with hooker super comp headers 1 3/4" TBF
You definitely dont want to have to R&R the pan again.
Yes... I want to get it right this time.... TBF
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 08:47 PM
how tough was it to get the old rear main seal out with the crank in place? i figure it should be somewhat easy to remove
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/02/08 09:10 PM
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 09:17 PM
maybe we need a new post entitled "HOW TO REMOVE A REAR MAIN SEAL WITHOUT REMOVING THE CRANK"
Posted By: MoparforLife
Re: 318 rear main seal question.... - 09/02/08 09:54 PM
If you aren't going to use the 'wings' on the seal turn the seal off center 3/4 of an inch or so to offset the parting lines of the seal from the parting lines of the block and retainer. Use some silicone in the grooves.
Posted By: Neil
Re: 318 rear main seal question.... - 09/02/08 10:23 PM
Quote:
If you aren't going to use the 'wings' on the seal turn the seal off center 3/4 of an inch or so to offset the parting lines of the seal from the parting lines of the block and retainer. Use some silicone in the grooves.
Yup. 
Posted By: Posest
Re: 318 rear main seal question.... - 09/02/08 11:17 PM
Where did you order your crank and rods. This sounds like a setup I would like in my dakota. Converted to a teen w/ 727 and 8 3/4 with 4:10 gears. Sorry not trying to steal your post. Just had a few questions.
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/02/08 11:18 PM
mancini has good prices and the ultimate in customer service. I cant believe how many times Ive called them and changed my orders. they never had a bad attitude
www.manciniracing.comask for WES. theres a moparts discount too I believe
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/03/08 03:33 AM
I thought my leak was the pan gasket as well but it looks like it was the seal. I am not going to cut the gasket and rotate the seal as others have suggested. I am going to install it with the rubber tips inserted into the cap as designed. I will use a dab of rtv on the parting line area of the seals. It just looks to me that the seal is in fact designed to be installed just 1 way....... TBF
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/03/08 11:33 AM
also rtv the tabs that extend out in the notch in the cap.
let me know how easy it is to get that old rear main seal out
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/03/08 02:12 PM
i am installing a rear main in my 318 tonight and i am scared to death i will have to pull this motor again if its not right. i just want to stop my james bond smoke screen.
any tips on a flawless install? i will be working on it hanging from the engine crane.
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/03/08 08:07 PM
Let us know how it goes... I won't be able to get back to my project until saturday... good luck... TBF
Posted By: ap6valiant
Re: 318 rear main seal question.... - 09/06/08 09:54 AM
was original seal out of detroit gasket set as i had same problem with mine years ago then put new fel pro in and no probs
Posted By: tpabayflyer
Re: 318 rear main seal question.... - 09/06/08 02:05 PM
I think I bought a gasket set for a 318 magnum engine as I was putting magnum heads on my LA block. It looks like the rear main seal is different and was the cause for the leak.
I also did get a fel-pro seal for a 70 318 so hopefully it will work.... TBF
Posted By: 69Cuda340S
Re: 318 rear main seal question.... - 09/06/08 08:48 PM
Quote:
also rtv the tabs that extend out in the notch in the cap.
let me know how easy it is to get that old rear main seal out
The upper half will come right out without loosening all the main caps. You just push on one side and the other side comes out then just pull it out.
Clean block and main bearing mating surfaces with Brake Parts Cleaner and clean paper towels then put a small film of RTV on that area before assembly.
Put a small film of oil on the seal lip so it doesn't get burned up on initial start up.
I run a Fel Pro rear main in my 340 and it has not leaked one drop in years.
Posted By: Anonymous
Re: 318 rear main seal question.... - 09/08/08 11:44 AM
turns out my rear main seal wasnt the reason for the leak in my motor. it was the rubber pan gasket at the back of the pan. I am running a milodon 7 qt pan and the gasket there sits up much too high. I figured it would smush down when I torqued the bolts but it apparently split.
I put a new seal on and trimmed it with a razor blade even with the side gaskets and it seems to have worked.
