Inliners International Forums General Discussion Hi Performance Modified rear main seal early chevy

I have heard that there is a way to machine the rear of the block on a 235-261 to take a different type of rear main seal. Does anyone know how this is done or any of the details?

It used to be here, but it looks like most of the article is missing. I'll keep looking.

http://www.enginebuildermag.com/2007/12/old-iron-sealing-stovebolt-chevy-engines/#

urgh! its the webrodder thing. I guess I was not paying attention but at one time they had a pretty cool series of articles on using a 292 rod and offset grinding the crank to stroke a 261? maybe a 235? Now it appears you have to purchase the articles. The link on the rear main seal appears be more of the same. Darn.

Its really pretty easy to convert to a more modern rear seal. You have to bore out only the rear portion of the rear main area of the block and cap for the one piece rubber seal. I've seen a write up before of the procedure.

Easy when you know how, right, lol. CNC, I envy the ability to have access to good machinery and machine work. Machine shops are dropping like flys around my parts, not to mention no one wants to tinker anymore. If I had the knowledge and machinery, I would love to do it myself, alas, I am stuck relying or others. Someone must have that article as well as the 292 rod and offset ground crank article.

Well, you did a good job on your other mods with access to a lathe, if you can use a Bridgeport mill for about 30 minutes, you can do this mod pretty quick and easy.

I was lucky, I have a friend with a lathe who helped me make up a tool and to cut down those bearings? He also has a Bridgeport but it is very old, the ways have not been maintained, is not all that accurate any longer and is used primarily for notching tubing for roll bars. That being said, I have got to beat the bushes for that article. This rear main seal business is starting to get out of hand with the current shortage and high price of neoprene seals and the challenges attendant with the new manufacture rope seals. There has to be another way to deal with the rear main seal.

I'm still looking for the article. I think I have it somewhere. I found these notes. It's a cut and paste from someone that had it done.

Here's the finished product awaiting the installation of the seal. I'm planning to slide the seal on the crankshaft prior to placing the crank in the block. The rear main cap will then be fitted over the seal and torqued in place. First step is thoroughly washing the block again to assure no metal shavings are hiding in oil passages. The seal part number for this application is CR38649 if using a Chicago Rawhide seal. CR is now part of SKF Bearing Company. My supplier crossed referenced to a #N0046762001 which is about $15 less expensive. The Speedi Sleeve (Shaft Eze) part number is 99386. If you plan to do this modification, check the diameter of the crank flange closely before ordering the sleeve kit. There are two sleeves that are very close in diameter and either may work for your crankshaft. Speedi-Sleeve pdf catalog can be found on line.

Here is the blog that this came from. Almost all the way down the page.
http://41chevystreetrod.blogspot.com/

The new Best Gasket rear main seal kits work great. Just pillow the directions.

Does this involve sleeping on the directions?

Yea, For it to work really well you have to put it under your pillow until the Rear Main Seal Fairy comes and puts it in for you. It has always worked for me.
I think that should be in the Tech Tips.

Thanks for posting the info. I really appreciate it. I am going to start obtaining the parts to do the conversion. I appreciate the effort in trying to locate the article. Unless the gasket manufactures start making more of the neoprene rear seal, the rope may be it, and I have never been all that successful in using a rope real main seal and I am getting too old to keep crawling under the car to drop a pan and replace a seal, lol.

I wish I had known about the RMS Fairy before I did all that tedious trimming and fussing with a rope seal . . . I could have just slept in . . .

You've got my vote for a Tech Tip.

You know, I should have given more detail. This seems to be only a west of the Mississippi service. I'm not sure why but it may be connected to the observation that the farther west you travel the more fairies you actually see, and the more fairies you see the greater the chance you have of seeing one doing something worth while. i.e. installing a leak free rear main seal. Some actually specialize in rear ends.

I came across a very lengthy post and how to one day about installing the one piece seal. The general consensus was it was lots of expensive work for something that seemed to also fail and leak lots.

I am not saying your wrong but are you 100% sure its the rope seal leaking all the time and not the rear pan seal? Lots think its the rope just because the leak is at the rear crank area. That aside The one piece that people are using is Cr-38649 and I think I recall you just machine the depth of the seal. This however can be an issue if you don't get your machining dead center it will leak worse that the improper installed rope.

Lots of opinions between the rope vs the neoprene. My rope has yet to leak one drop. The installation and the trimming of the ends is key to getting it to seal correct. Mine was installed with the crank fully removed so i was able to roll it in. Some say if you try to do the install with the finger trap pull around method when the crank is installed it actually can stretch it out a bit causing it to later slightly retract and form end gaps. Lots also cut the ends perfectly flush with the main halves because it so easy to do so with the razor blade.

The Best Gaskets 'Graphtite' rope seal comes with a small cardboard template that one lays on the block before trimming with the supplied razor knife:

The result is just enough excess protruding above the block.

The installation still requires a second trim as some of the rope ends got squished in between the bearing cap and the block during first torque - creating excess clearance. Removing the cap and trimming the flattened bits from the block surface is easy enough.

I am not on the road yet so I cannot say how well this going to seal long term. But I have pressurized the crank with an electric drill-in-a-dizzy-body so that I could set initial valve lash and verify top end oiling. So far so good.

There is also a 2 pc. neoprene seal upgrade for these engines as well to eliminate the rope seal seal.

Several things that make the 1 piece seal a little more involved is that not all articles show the entire process. Since these engines do not have main caps that index into place, they basically just float around and center on the crank journal, its difficult to affix them to the block with the crank out of the block. So a centering ring needs to be made to locate the cap on the block to act as the crankshaft to center it correctly, or the pocket you machine for the seal will be off center from the flange on the crank and be a potential leaker. Also, if the block has main shims, they need to be installed during the machining process as well or the hole for the seal will be out or round when you assemble the engine with them in place. A lot of little secrets that a seasoned machinist will know that a hobbyist or DIY person may not realize. And these little things can add up to a not so successful engine mod.