The Stovebolt Site Forums The Shop Area Engine Shop Oil is coming out at the back of the engine

I've got a question. In my pickup with a 235cui engine, a lot of oil leaks out on the gearbox side. The following similar seals are currently installed: https://bestgasket.com/rear-main-seals/4519S - Rubber Rear Main Seal What do I have to do so that I can change the two seals? Do you have to dismantle the complete engine and the gearbox for this, or is it enough if I remove the oil pan and the two blocks where the seals are located?
Can someone send me detailed instructions so I know how this works?
Wolfgang

From reading early post of yours, I believe you have a ‘54 235. I believe the early 235’s (pre ‘56) were not machined to accept a rubber seal (neoprene) and may not seal correctly.

Maybe some of our experts can confirm this.

Any engine with shimmed mains will not except or work well with the rubber seal.
The shims hold the ends of the seal apart creating a oil leak path.
Shims were used until mid 1955 on 235s.

Hello Phil,
and may be that this is right, how did I get them out and change it?
Wolfgang

Best Gasket "rope" rear main seal
considered to be the best

Installation instructions for the Best Gasket "rope" rear main seal.

Good info just in time for my 261.

The problem with the Best rope seal is it is not like the original rope seals that were used by GM and the aftermarket. Unfortunately, there are not any better new replacements. If you can find an original type seal (they used asbestos as a component) that is still pliable, I think they are the better call but finding decent asbestos based rope seals is getting harder all the time. The current crop of seals is fiberglass based and will work but it appears not as durable or effective as the original.

The neoprene seal was introduced for the 56 model year. The announcement can be found in the shop manual. So you can find a block date coded 55 that will use the neoprene seal but it will be for the 56 car and truck line. I have a 55 dated block, September 55, with the neoprene seal so that is 56 model year. The June 55 block I have is rope and shims for 55. The June block is machined differently then the September 55 block at the rear main cap. On the June block its cut deeper to accommodate the rope seal. You can physically get the neoprene seal in but its not a firm fit, sinks and separates and then leaks.

Over the years I have tried a couple of things to see if there is a a way to use the neoprene seal, spacers, cut down rope seal as a packing so to speak, a piece of thin spring seal to impart pressure, none of it worked and I got tired of pulling motors and taking them apart.

So short of swapping over to a 56 and up block, you will have to see if you can get the main cap off, sneak the upper seal out and fish a new seal in, and replace the old seal in the lower cap. I myself have never been very successful in getting an in car re seal completed and have it work. that is not to say you can't. Just not me. We have had a couple of threads on this issue, search around because I know a couple of the fellas here have done it successfully.

I have had great success with the Best gasket rear seal in both my 216s. The secret for me was to get the rear main bearings down to minimum clearance.

Wokri Be sure your oil level is right,had one that would leak setting because dipstick tube too tall ! Got it right for 5 quarts leak stopped, especially with PCV,slight suction . Be sure its vented if you install positive crankcase ventilation. Otherwise it can suck your gaskets out of place,or worse.

Dragsix Did you see where MACHINE SHOP IN cOSTA mESA PUT IN A truck hub seal to fix that leak ? Would take some careful assembly work but should solve it ! Since we can't get asbestos rope seal anymore it is tougher to fix. Isuppose best bet is 56 up block.

I just completed the Best Gasket graphite type rope seal in a 1955 235 with the engine out of the truck on a stand. I found it somewhat difficult getting the upper rope pulled through with the sneaky pete cable tool. I slacked all the bearing caps except the front to produce about a 1/8+ inch gap on the front cap. I then lubed the seal with vaseline and with steady pressure pulled the seal along WHILE rotating the engine at the harmonic balancer, slowly walking the
upper seal in. This took three tries as the seal pulled free from the sneaky peat claws. Go slow and steady as it is a tight fit especially at the rope ends. While it may be possible to do this under the vehicle with the oil pan off I found it challenging enough with full access but worth a try. Forget the FEL Pro seal its just too fat too work . Good luck.

Swami29,

Did you rotate your 235 while on the stand? If so, how did you get it upside down?

My stand was just the inexpensive wood engine cradle (stovebolt tech tips ) fitted with some angle iron mounts allowing me to support the engine with the oil pan off. It was not ideal working height but did allow me to complete the job. I have since began fabricating my own tubular steel run stand which I will fit with a radiator for test running .