We have a 300 six we just put into a 1976 F100. While the engine was out we replaced the bottom end gaskets, oil pan, rear and front main seals. After we got it running, it is leaking from what looks like the rear main area. Not a full blown gusher but it's leaking enough to be noticable. It's not the tranny. Is there a trick for sealing the rear main seal?

 

Do you recall what year block you are dealing with?. (to determine whether it was a 2 pc rear main or one pc). Also, did you use a new style 1 pc oil pan gasket?. I'm not an expert on these rear mains but I know there are different styles of seals for different blocks.

If I had an engine out I personally would not have replaced a rear main seal w/o replacing the main bearings as well. ( Or at least checked all the rods and mains for wear.) A new seal is not going to help a sloppy main bearing issue, not completely at least.

We used to say "one of the tell-tale signs of a bad bearing is a leaking seal"..

Just some extra info for you to chew on.

 

We got the engine and from the looks of it she looks like it had been gone thru recently as the block and everything is clean and all painted red. I got the engine from a friend who wanted it moved because it was in his way in his shop. The PO pulled the engine because he was putting a 302 into the truck he had and didn't have any use for the 300. My son, the presant owner checked and by the numbers he saw it's a 1969. There was a bottom end gasket set with the engine, with front and rear seals and from the info my friend had we redid all of the bottom end seals and gaskets while the engine was out of the truck. From what I remember, the rear seal was a one piece seal.

 

Well hopefully it's not leaking to badly, but more importantly running well and doing it's job.

These days most guys elect to use the more modern 1 pc pan gasket that is used in the EFI version of this motor from the 90's by Felpro. If you search here you will find info on this. (The oil pan needs a little grinding is all, nothing too special) This gasket is a "1 piece" wonder in solving the trials of a 4 pc pan gasket set. Maybe this is something you may consider soon and it may solve your seep at the rear.

If in fact the rear main seal needed a 2 pc and 1 pc was used I don't think that mistake could be made but I haven't worked on one of the older blocks myself. Usually the rear main caps are designed either one way or the other so mistakes can't be made, yet each seal needs to be installed carefully and correctly of course and hopefully by someone with experience.

Best wishes..I'm sure others will chime in with perhaps more experience.

 

The good news is that it's possible in theory to change a 2 pc seal w/o removing the trans I believe.

This should be fixable with the engine in the truck along with the changing to the new 1 pc oil pan gasket while you're at it.

 

Might have found the problem. Denny went to a JR for some other parts including the oil dipstick as it was plain to see the dipstick wasn't the original. There was some obvious differances between the two dipsticks and the dipstick that came with the engine had a red mark which we assumed was the "full" mark because the dipstick was cut at some time or another and nothing made sense. Looking at the newer stick it looks like the oil level needed to be lower than the red mark. How much oil did the 300 take?

 

6 quarts with a filter change.

 

Rear main could be a lil sloppy...on the other hand...there could be another culprit. regardless if the seals were all replaced. The one piece gasket is super handy, but over time if the gasket mating surface on the outside of the crank flange has a lof miles on it...might need to sleeve it. the journals can be ground down and polished but the rear seal surface isn't touched. a repair sleeve might be just the ticket if its not a snug fit. may be another option to look into next time you have access to replacing the seal itself...its a pretty simple procedure.

 

All 240 / 300 sixes use a one-piece seal.
If you want a little more insurance you can use a seal from a Modular V8 - it has a "two lip" seal (actually a dust cover in front of the spring loaded seal).

Another possibility for a leak is if the flywheel bolts were installed without using thread sealer. These bolts pass thru the crank flange and into the crankcase area.

Check all the usual suspects - side cover, valve cover, oil filter, oil pressure fittings - to be sure oil isn't seeping down into the seal area from some other source.

 

Excellent info..actually makes me a little embarrassed to suggest it may have a 2 pc seal. (Untill I had some mid 70's Pinto 2.3's apart while fiddling with turbo's versions I hadn't had seen the pan off of a Ford product since y-blocks) I know my 86 and newer blocks don't for sure..well sorry about this mis-info I had shared..