Rear main seal is leaking pretty bad, before I change out the rope/wick seal that's in it now, I thought I'd ask...
Anyone recognize this neoprene/rubber seal ? (see attachment) I can't seem to find anything online anywhere, I don't know anything about it, it's what was in my engine when we torn it down for the rebuild. The only identifying marks are...SCI 8 500855, and other half is...SCI 21 500855.
That's the lip seal that was designed to replace the rope seal. On some engines they're interchangeable. What's the condition and oil clearance of the rear main bearing? If the crankshaft can bounce up and down on a loose main, no seal is likely to hold for long. The lip seal also works best on a very smooth seal surface- - - -if there's a groove worn in the crankshaft or any roughness, you're probably better off using the rope. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Tim, Bestgasket #6100 is what I'm planning on going with. The other link you posted, and everything I've found on the internet is for SBC & BBC'S I just didn't understand why (when we opened it up), it had this rubber seal.
Jerry, I hoping I don't have some other issue (other than the rope/wick) install. It's a reconditioned (-.010) Crank and new bearings, just over an hour run time.
There is a good reason that your '53 full pressure 235 was "leaking pretty bad" with that style of main seal. That engine came with shimmed main bearings. The lip seals will not work on that engine. They cannot be easily trimmed to fit without a gap for oil to spew. Once GM tidied up their block machining routine so that shims were no longer necessary (1955?), the 2 piece lip seal became a nice option in place of the rope seal.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
All of my 55 motors have had rope seals and shims with the exception of the early 56 motor (date coded late 55) I am currently redoing which had the neoprene seal installed. GM changed the bearing style in 56 so 55 motors still used a dowel style main bearing, shims, and a rope seal but 56 and forward used tanged bearings, no shims and neoprene. I cant remember whether the neoprene seal was first identified in the shop manual, 56 or 57 so I will check that. The rear main cap in the 55 and earlier blocks are not machined for a neoprene seal, specifically not machined accurately enough to use the seal. The did not need to be and the rope filled the area. That being said, the neoprene will physically fit but will not work. As for the rope seal, the most reliable sold today is the Best Gasket version but there is a rub. The older rope seals had an asbestos component to them. They were a little trouble some as there was somewhat of an art to installing them but even by 53/54 they were really obsolete, designed for the earlier low pressure or splash oiling motors, and not really all that effective for the later full pressure motors. In other words, the rope sealed motors still dripped a bit. Todays rope seals use a fiberglass graphite product. Its ok, I have gone down the middle on two motors (a 54 and a 55). The 54 did fine with the Best Rope, still drips here and there (Its in a buddy's 54 pickup) but the 55 leaked within 1000 miles and we had to redo it. I used a older rnos felpro that I had (the instructions were dated to the early 70s) and that seems to have done the trick. My opinion is that older rope seals work a little better. So you might consider kicking the bushes for a real GM seal or an older Felpro, victor, McCord or like rope seal.
Don, yes you can. You may have to loosen a main bearing or two but it can be done. I did it on my 50 pickup several years ago with the rope seal. It was still holding up when I sold it. Today many are using a different type seal than the original.
Hello, I’m having trouble installing the new seal. This is the third seal and it is still leaking. I would like to get some information from someone who has done this many times. Do you just beat it as much as possible into the groove? I tried best gaskets and last one was felpro rope. I have the manual but I tried that method also. How is this rope seal suppose to be installed? The correct way. Silicone at ends? Thank you.
Thank you for the reply and yes we have tried that. I’m just looking for info on how to set it to the cap. Top seal I replaced and it’s not leaking. It’s the bearing cap seal I’m having a hard time with. The last one I did I installed the new seal and installed the cap. Torqued it down to 105 + - 5 and I could not turn the crank by starter or hand. So I had to loosen it a bit.
The diameter of the seal surface on a stovebolt crankshaft is 3 7/8 inches. Back when we were changing a couple of those seals a week, GM had a tool that was used to pack the rope into the groove in the cap, simply a half circle of steel with a handle on it. I made a similar tool out of an old 4" piston, turned down to 3 7/8" diameter with a piece of wooden dowel rod through the wrist pin hole. Use it to pack the well-oiled rope firmly into the groove and trim the ends off flush with the cap. Silicone sealers weren't even thought of 50 years ago when I was installing rope seals, and they didn't leak. The seal I installed in a 261 we rebuilt six months ago isn't leaking. It's all in the technique you use. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thank you Jerry, I’m going to look for a piston I have laying around. Now you mention you “well oiled seal”. So you soak the seal before installing it? This is the info I’m looking. Thank you. I have read not to soak the seal, to leave it sticking out Not cut it even, but somethings make sense and some don’t. So I’m asking from experienced people. Keep the suggestions going please.
The Best Gasket seal is the closest thing to the ones we were using back in the 1950's and 60's. It's not identical, due to the elimination of asbestos in the rope, but it's pretty close. I usually soaked rope seals in clean 30 weight oil, then packed them as snugly as possible into the groove in the block and the cap. OTC used to make a seal installation kit that included a "Chinese handcuff" puller to coax the upper seal into place and a shield to avoid scoring the crankshaft as the rope was cut off flush with the block. If any seal material is left protruding above the cap after packing it into place, make it VERY short, like 1/32" or less. Best recommends putting a 1/16" roll pin into a hole drilled in the cap to prevent seal rotation, but I'm nor entirely sure that's necessary if the seal is installed right. It was not done that way back when these engines were daily drivers.
I'm working on a machining fixture to allow the back of the block and the main bearing cap to be machined for a full circle lip seal that will eliminate the rope seal altogether. Once that's finished I plan to write a tech tip on the procedure. It involves using a cylinder boring bar instead of requiring lots of setup time on a Bridgeport mill. If it works the way I expect, the job should require less than an hour working on a bare block during a rebuild. The picture thread from the homecoming shows the fixture setup, but I didn't have a main cap available to complete the demonstration. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
That would be great once the lip seal project is complete, I’m definitely interested. I did use the sneak Pete method for the top and it worked pretty good. The cap is the one giving me issues. Hopefully I get some time this Friday and drop the pan.
