340 Rear Main Seal Replacement

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DustyEd

DustyEd

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Getting ready to replace the rear main seal on my factory, stock '70 Duster 340. The engine has not been tampered with and has about 82k miles on it. I will also be replacing the oil pump and pickup tube/screen and possibly the pump driveshaft while I'm in there. Thinking about checking the connecting rod bearings, too.

Just asking for opinions (from those with experience) for things to watch out for and types/ brands of parts, gaskets and sealant to use for this project, so I can do it right the first time.
 
I’ve never really met a crappy gasket. I’ve met some crappy installations and prep work! I even seen high school friends use thin cardboard. Stick with the known brands and you’ll be fine. Detroit gaskets, FelPro, Mr.Gasket, etc...
 
I think there's a procedure where you cut the tabs off the rubber two piece seal, and apply silicone to the ends, butt it together where the seam of the seal is offset to where the main cap butts to the block, in other words the seal butt, and the main cap butt isn't lined up. If you guys already know this, disregard.:)
 
I'm a Felpro fan for gaskets, Mopar or Melling on the oil pump, and Permatex Ultra Black RTV for sealer on the main seal ends. Mahle/Clevite if you have to change the bearings.
 
Are you sure that you do not want to overhaul it? Get hardened seats installed for the valves etc etc. I just tore down my '72's 318 with about the same mileage, very glad I did, it took .030 to clean the cyls up. Cam was flat, rod bearings were into the copper, sloppy timing chain, bad valve guides, leaking freeze plugs, it was time even though it ran fine.
It was hemorrhaging oil.
If you decide to go your way, when you put your main cap back up, skim or smear a very thin coat of silicone across the back of the main cap or block saddle. My 418 seeped in that area, had to redo it because I had not done that. There have been numourus threads in the past about leaky rear mains and why they may leak. Odds are, your oil pump, and drive gear are probably fine. There will be more advice!
Good luck!
 
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rumblefish360 said:
I’ve never really met a crappy gasket. I’ve met some crappy installations and prep work! I even seen high school friends use thin cardboard. Stick with the known brands and you’ll be fine. Detroit gaskets, FelPro, Mr.Gasket, etc...
Click to expand...

Have you or anyone else used Milodon 40600 crushproof oil pan gaskets?
 
rumblefish360 said:
I’ve never really met a crappy gasket. I’ve met some crappy installations and prep work! I even seen high school friends use thin cardboard. Stick with the known brands and you’ll be fine. Detroit gaskets, FelPro, Mr.Gasket, etc...
Click to expand...
I have. I've seen many off brands with thin bare cork gaskets that would deform and crack REAL easily.
 
cudamark said:
I'm a Felpro fan for gaskets, Mopar or Melling on the oil pump, and Permatex Ultra Black RTV for sealer on the main seal ends. Mahle/Clevite if you have to change the bearings.
Click to expand...

Are you familiar with new Clevite bearings not be same as the OEM in regards to the oiling holes/grooves?
 
No, I haven't. I put in a set of rods and mains yesterday and they fit perfectly. Plastigauged out just right. What have you seen that didn't meet specs?
 
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Buy the red viton rear seal. Don’t trim it. Cut the head off a tooth brush and use it to push the old one out. The worst part of the job is getting the steering linkage out if the way.
 
DustyEd said:
Have you or anyone else used Milodon 40600 crushproof oil pan gaskets?
Click to expand...
Sorry, no.

cudamark said:
I have. I've seen many off brands with thin bare cork gaskets that would deform and crack REAL easily.
Click to expand...
Actually, I just remembered one. I don’t remember the maker, but it was an oil pan gasket crazy thin and did tear before the torque load was reached. I thought it odd to see in the kit since it was name brand. Dang shame I remember saying. Oil pan gasket torque load is very light. But your right, there is some garbage out there.
 
CRUZE 418 said:
Are you sure that you do not want to overhaul it? Get hardened seats installed for the valves etc etc. I just tore down my '72's 318 with about the same mileage, very glad I did, it took .030 to clean the cyls up. Cam was flat, rod bearings were into the copper, sloppy timing chain, bad valve guides, it was time even though it ran fine.
It was hemorrhaging oil.
If you decide to go your way, when you put your main cap back up, skim or smear a very thin coat of silicone across the back of the main cap or block saddle. My 418 seeped in that area, had to redo it because I had not done that. There have been numourus threads in the past about leaky rear mains and why they may leak. Odds are, your oil pump, and drive gear sre probably fine. There will be more advice!
Good luck!
Click to expand...

Where was you major oil leakage coming from? You certainly make me wonder about an overhaul. However, I did all that just over a decade ago with a B-body 383 HP. That ran me $12k with parts,machining,etc. Plus, I really would like to drive it this summer after this Covid-BS.
Do you have a picture where to apply the silicone on the main cap? Hate to get the location wrong. Thanks.
 
cudamark said:
No, I haven't. I put in a set of rods and mains yesterday and they fit perfectly. Plastigauged out just right. What have you seen that didn't that didn't meet specs?
Click to expand...

My Nephew was replacing connecting rod bearings in his '73 340 Challenger and Clevite told him they changed the design and the old style are not available. He seemed concerned the oiling would be less efficient with the new style.
 
I don't know what to say. I just got mine from Summit last week. Mine are just the standard performance ones, not for a race car.
 
There was a High Tack or a glue type sealant for the cork gaskets. I have steered away from cork for various reasons, valve covers, I like rubber, they can be reused if need be. The Intake ends, I use silicone ,oil pan same I like a rubber gasket when possible. I think Mopar has rubber oil pan ends with a gasket for the sides, I have used one piece oil pan rubber gaskets on fords.
 
The old reliable fel-pro gasket set is good for the money. I do stay away from the cork valve cover gaskets and oil pan gaskets.
Plan on doing freeze plugs while your at it. Last summer I pulled my original 340 and found two freeze plugs had holes in them. They had rust crud sealing the holes and they were not leaking!! Simply amazing that they didn't leak. Spend a few extra dollars for the brass plugs.
Luckily, mopar small blocks don't have a lot of rear main leaking problems like some engines do. Chubby and Ferds leak out the rear main like they were designed to do it.
 
DustyEd said:
Have you or anyone else used Milodon 40600 crushproof oil pan gaskets?
Click to expand...
Yes I use those every time. They are excellent. I usually glue them to the oil pan using Edelbrock Gaskacinch. I’ve never had an oil pan leak, but the damn rear main seal yes, and I’m currently battling that issue in a rebuilt 360. I use the Victor Reinz JV1610 seal for the 360.
 
What's the torque for the main cap bolts and the oil pump? Should I get NEW bolts?
 
No reason to get new ones unless they've been abused, or, you're building a race engine. Main caps get torqued to 85 foot pounds.
 
DustyEd said:
Have you or anyone else used Milodon 40600 crushproof oil pan gaskets?
Click to expand...
Yes, and it is reusable so long as you put it on dry....which I found out a few years ago when my new engine had a rear main leak after 1 mile of use....1 frickn mile.....I had a race the next weekend so I quickly pulled the engine back out and replaced the rear main seal (just barely got the engine back in the car the night before the race, lol). Was thankful for 1 less gasket to re-purchase on a new build. Still works great, no leaks.
 
I find that you normally dont need a new pickup tube either. Flush it out with some carb cleaner and they are usually good as new.
 
Well, everything is dismantled. Double thinking on the type of rear main seal to use. I have the Cometic black Viton on hand, but the contact surface appears it would be very small compared to the factory rope seal and the knurling on the crank is still very visible. Does anyone know where to find the rope style for the 340. I have searched and found Mopar big block (Best Gasket brand), but NOT small block.

What's the vote....Viton or Rope (if I can find one)? Last call.
 
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