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#4479817 - 08/05/17 11:25 AM rope rear main seal
zrxkawboy Offline


Registered: 11/30/04
Posts: 1761
Loc: SD
I'm rebuilding my '57 Plymouth 230 flathead. I've rebuilt newer (60s-80s) engines but never rebuilt a flathead before, and it's my first time installing a rope-type rear main seal. I've read the basic procedure (roll into the groove with a pipe, etc and trim flush with a razor blade) but would appreciate any tips/tricks for success. Thanks!
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#4479826 - 08/05/17 11:32 AM Re: rope rear main seal [Re: zrxkawboy]
Chris142 Offline


Registered: 06/05/03
Posts: 16825
Loc: Deplorable in apple valley, ca
Do any gasket manufacturrers make a neoprene seal for it?
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#4479834 - 08/05/17 11:38 AM Re: rope rear main seal [Re: zrxkawboy]
zrxkawboy Offline


Registered: 11/30/04
Posts: 1761
Loc: SD
Doing a lil research on that right now. My Felpro set came with the rope.
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#4479854 - 08/05/17 11:52 AM Re: rope rear main seal [Re: zrxkawboy]
turtlevette Online   shocked


Registered: 12/24/13
Posts: 3568
Loc: Massachusetts
With a rope seal you want to get a tight fit. I compressed the ends down to get as much rope in as possible. Didn't end up trimming anything. When together I couldn't turn the engine with a breaker bar.

I did it with the engine in the car and the crank in place. Its a Pontiac engine.

Retrofit neoprene seals have their problems too.




Edited by turtlevette (08/05/17 11:56 AM)
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#4479878 - 08/05/17 12:17 PM Re: rope rear main seal [Re: zrxkawboy]
Kestas Offline



Registered: 06/04/02
Posts: 12340
Loc: The Motor City
I went with a split seal for my 1971 Oldsmobile 350 rocket engine. This was per recommendation from the Oldsmobile community. Ten years later and it's still sealing just fine.

I think the seal was specified for a 1957 Ford. Maybe you can find a similar recommendation.

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#4479908 - 08/05/17 12:59 PM Re: rope rear main seal [Re: zrxkawboy]
zrxkawboy Offline


Registered: 11/30/04
Posts: 1761
Loc: SD
Thanks for the replies. Looks like I jumped the gun, though. Here's what happened: This was one of those deals where I tore down the engine nearly 2 years ago and am just now getting around to reassembling it. (Fortunately, I took a lot of pics during disassembly.) I opened my Felpro gasket set today and it had the rope rear main seal. After posting my question, I got to thinking about it, and couldn't remember removing a rope seal. Pulled up the pics, and sure enough, it was a rubber seal. After some searching, looks like this may work: http://www.bestgasket.com/pop_up_picture.asp?PartNumber=3675
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#4479914 - 08/05/17 01:07 PM Re: rope rear main seal [Re: zrxkawboy]
BrocLuno Offline


Registered: 09/06/15
Posts: 5519
Loc: Kalifornia Kollective
Rope seals work. They did for about 75 years. There are two keys to success. 1.) minimize blow by. You do not want any vapor pressure in the crankcase. So cylinder wall prep and good ring seat is critical. 2.) As mentioned, they need a bit of compression at installation. So get it in tight. Find a PVC pipe close to the diameter of the crank journal and clamp it in place with the seal in the groove. Take a piece of decent hardwood and make a tapered square end that will fit the seal/groove. Trim seal on one end maybe 1/8" above mating surface. Use square hardwood to tap end down flush. If that went OK, do other side. Remove "fuzz" from tapping.

Vaseline is all I ever used on the seal face against the crank. Nice film of Vaseline and the crank should turn by hand, but not easily. There should be some drag with the caps snugged down. If all goes OK, you can do the rods and other mains. By the time it is all together, you will have a hard time turning it with a breaker bar.

I can't remember for sure, but I seem to recall that there is a slinger collar on the crank just ahead of the seal area ... Some old fattie I worked on years ago had a pressed-on slinger collar that was left out. It lost a fair amount of oil before we figured it out ...

Those old Chrysler flat-heads are tough. They actually run pretty good. Richard Petty won a lot of races in the early days with that little six. They can go. And I've seen one with a turbo on it that is actually quite entertaining. Won't knock a BBC down, but it runs well laugh

There is a cooling water distribution tube that needs to be in the block to get proper cooling to the rear cylinders. The exhaust exiting through the block adds to the heat load on the cooling system, so gotta pay attention to that. Many that were run on straight water will have the cooling tube rusted away and they will all overheat ...
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#4480472 - 08/06/17 07:04 AM Re: rope rear main seal [Re: zrxkawboy]
GMBoy Offline


Registered: 11/22/04
Posts: 7703
Loc: Texas
Rope seals were a huge issue on Buick Grand Nationals right from new. They all leaked including mine.I had 2 warranty rear main seals fixed on my 1987 GN until the dealer agreed to try a replacement 1 pc neoprene style that an aftermarket Buick performance place marketed (ATR was their name). That was in 1988 at 17k miles. Today, I still have this carand it has 50k miles and still no leak. The OEM rope seal just didn't handle the pressure from a turbo well at all.

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#4480533 - 08/06/17 08:20 AM Re: rope rear main seal [Re: zrxkawboy]
Kestas Offline



Registered: 06/04/02
Posts: 12340
Loc: The Motor City
How does a turbo place pressure on a rope seal?

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#4480562 - 08/06/17 08:44 AM Re: rope rear main seal [Re: Kestas]
Scdevon Offline


Registered: 09/07/09
Posts: 325
Loc: Rockies
Originally Posted By: Kestas
How does a turbo place pressure on a rope seal?


It doesn't.
Not on an engine with 17k miles on it in 1988 with no blow-by and a healthy PCV system anyhow. The original rope seal was likely botched at the factory when installed and another rope seal was botched again by a flat rate dealer tech trying to beat the warranty time to replace it. Many dealer warranty rope seal "replacements" were done by packing the upper seal tighter with a hammer and a punch, cutting a small piece of new rope seal and stuffing that into the upper groove to take up the newly created void and then just replacing the lower rope piece. Just because the rope seal was "replaced" under warranty doesn't mean that it was done properly.
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