The Stovebolt Site Forums The Shop Area Engine Shop Is the Best Gasket Rope or Rubber Main Seal Advised for a '61 261?

Title says it. Does the recommendation to use the Best Gasket rope rear main seal still hold for a 1961 261? Or is the rubber seal best (or OK) for this later era Stovebolt?

Stupid question: Is there a front main seal?

Timing cover seal.

I think they offer the neoprene seal for the rear main on that late 261. I rebuilt a 1958 261 that had a neoprene seal and it worked fine. Use it if you can. Finding a good rope seal is getting harder to do.

Best Gasket will be the best rope seal you can find. I use them exsclusively when building engines and have really good luck doing so.

You ask an interesting question. 56 is when the neoprene seal was introduced for the 235 in the pass car line. I truly don't know when chevrolet began using the neoprene seal for the truck 235 and 261, or when Pontiac of Canada began using them for their passenger car 261, except to say that all of my 261 blocks (1 chev and 2 pontiac) which were 59 and 60 motors used the neoprene seal.

So with your block, do you know what was originally in the block or what was in it when you took it apart? The reason I ask is that the 54-55 261 blocks are different then the later 56 and up blocks. I dont know all the differences but they had thicker bores, used milk can lifters. The 54-55 235 pass car blocks had a rear cap where the area for the rear main seal was machined deeper for the rope seal to be packed in. My assumption is that the 54-55 261 blocks were machined similarly. If you install a neoprene seal in an early motor, and it will physically install, its too loose, sinks a bit, and thus leaks like a sieve.

If Chevrolet and Pontic followed suit with the truck motors in 56 and installed neoprene seals, and I don't know that they did, then the questions becomes if the more narrow machining of the rear main cap for the neoprene seal is sufficient to accommodate a rope seal. My gut tells me yes but I really don't know and truth be told, I have not had good luck with rope seals (old style or new) and thus avoid them if at all possible. So if its the case that your rear cap is machined for a neoprene seal, I would think you probably want to go that route.

Wally/Montana Not a stupid question!! Front main is a drive-in mtal seal in the timing cover. The rope seals (rear main ) are not as good now as when they were asbestos years ago. they made a kit to change those and it was a tuff job but you could do it. Best on a lift.but have done it on a creeper. Sounds like Joe H has found seals,and PCV helps on that with a slight suction !!

I haven't used them, but I've been told the Best Gasket neoprene seals (black in color) are not as good as the ones made by Fel-Pro for decades (the orange ones). Fel-Pro stopped making these about 5 years ago and the seals and friends familiar with both say the orange Fel-Pro ones last longer. I can tell you no matter which you choose (rope or neoprene), polish the crank surface very well. If a rope seal was used originally, the seal will be pock-marked and rough. I don't know if the neoprene seal was ever installed by GM when the engines were built. When I was young you had to have this installed by the dealership (if you had the right engine). Another good idea is to install a Speedi-Sleeve over the rear part of the crankshaft. Good luck.