My understanding is that 351W blocks had 2 piece rear main seals until 1984 and that beginning in 1985, the blocks switched to the 1 piece rear main seal. Is this correct?
rear main seal question
- Thread starter jerry S
- Start date
Bueller? Bueller? Any one? Any one? If I order an oil pan gasket for a 69 351W block, I want the 2 piece rear main seal, correct?
302 coupe
Founding Member
If you want a leak free one, order the Felpro one piece gasket made for the early mustangs. It's around $50 but well worth it IMO. It is a rubber composite with a steel core and leak free performance. Reusable too and no RTV required! 
Also, the type or rear main doesn't affect the pan gasket. BUT, the year of pan does. The early pans had ribbing in the pan flange to prevent the cork from squeezing out. The later 5.0/5.8 engines had flat flanges, thus the gaskets are different. Felpro makes a specific gasket for the early pans (early i mean pre 5.0) and is available at autozone. I know you aren't running a 5.0 pan (cause it is rear sump) but they may try to give you a 5.8 pan gasket.
Also, the type or rear main doesn't affect the pan gasket. BUT, the year of pan does. The early pans had ribbing in the pan flange to prevent the cork from squeezing out. The later 5.0/5.8 engines had flat flanges, thus the gaskets are different. Felpro makes a specific gasket for the early pans (early i mean pre 5.0) and is available at autozone. I know you aren't running a 5.0 pan (cause it is rear sump) but they may try to give you a 5.8 pan gasket.
jbuening said:If you want a leak free one, order the Felpro one piece gasket made for the early mustangs. It's around $50 but well worth it IMO. It is a rubber composite with a steel core and leak free performance. Reusable too and no RTV required!
Also, the type or rear main doesn't affect the pan gasket. BUT, the year of pan does. The early pans had ribbing in the pan flange to prevent the cork from squeezing out. The later 5.0/5.8 engines had flat flanges, thus the gaskets are different. Felpro makes a specific gasket for the early pans (early i mean pre 5.0) and is available at autozone. I know you aren't running a 5.0 pan (cause it is rear sump) but they may try to give you a 5.8 pan gasket.
Well that is an eye opener. I am ordering a new pan by Moroso and I thought that the rear main seal dicatated what oil pan gasket you needed to get.
jbuening said:
I am ordering a new Moroso pan from summit for my 351W and will need a new oil pan gasket. The descriptions for the gasket provide that they are either for one or two piece rear main seals. For example:
FPP-1827
Brand: Fel-Pro Performance Gaskets
Product Line: Fel-Pro Performance Oil Pan Gaskets
Gasket Material: Rubber with steel core
Rear Main Seal Style: 2-piece
One Piece Gasket: No
I just want to verify before ordering and shipping here that I need an oil pan gasket for a 2 piece rear main seal style.
thehueypilot
Active Member
Isn't the rear main seal for a 351W a bigger diameter than a 302? So the pan gasket should be ordered for a 351W and not just for a small block Ford like "Jegs" advertises. Aren't the pan gaskets different between a 351W and 302, but the rear main bearing cap is the same Outside diameter on a 351W between a one piece seal and a two piece seal?
dennis112
15 Year Member
thehueypilot said:
Crank and the rear main seal for a 351w is larger than a 302. Needs a 351 specific part, a 302 won't fit. Doesn't matter it you are talking 1 pc or 2 pc seal--both are larger than the 302 counterpart.
The rear main cap is also physically larger than a 302, so a 351w will only work with a 351 pan specific gasket. Even the oil pan is 351w specific to clear the larger rear main cap needed to clear the larger crank.
I had both my old 69' block and 89' block setting side by side during my build. jbuening is correct that the block sealing surface has not changed over the years. I believe that 1983 is when the 1 pcs seal appeared in a 351w.
I used an SCE 1 pc rubber oil pan gasket that Summit sells to install my 69' 351w oil pan (original 2 pcs seal block) on my 89' block (1 pcs seal.) Seals perfectly, no issues. It is very pliable rubber and I know it would be hard to install from under the car, but on an engine stand it was a piece of cake. Had I know then the differences of the pan, I would have went with a 1 pcs oil pan seal for a 2 pcs seal block.
To sum it all up for Jerry, if you are truly concerned, choose a pan gasket (any pan gasket) made for a 2 pcs seal (such as your 69' block) and install it. It will work an your later year block and be the best choice for the oil pan that you have. The 1 pcs pan gasket has an edge over the "multiple" pcs ones for sealing.