[rohrt]

I was told when I was still a kid the sarrations on a stock crank were to scuff the rope seal and keep it from glazing. Is this true?

Do the aftermarket cranks have the sarrations? I was thinking they didn't.

That being said, I know a lot of people are in there camps on their favorite seal but does anyone use one type of seal for a stock crank and a different seal for the after market cranks?

One last question if a crank is turned does that makes the surration usless?

[nUcLeArEnVoY]

The serrations are there to permit a scant amount of oil through to lubricate the rope seal. There has been only anecdotal evidence regarding the serrations chewing up the one and two piece viton rubber seals. Some people say they're fine, others say they're not. BOP recommends polishing down the serrations.

The one and two piece viton seals are technically a way better and more modern design but their efficacy depends a lot on installation technique. As for the crank serrations, if I'm not mistaken, Scat cranks don't have the serrations and would be better suited for the viton seals. I would fear that completely milling out and polishing down the serrations would wear enough material away that the viton lip seals would no longer even make a seal. Maybe just polishing up the serrations to smooth the edges would work, or finding a crankshaft that doesn't have them.

[Formulajones]

Most of these 60 year old cranks have so many miles on them already running a rope seal for decades that they are already somewhat polished up. That's been my findings anyway.

I put viton Seals on every Pontiac I build stock or aftermarket crank and just to be safe I still have the factory cranks polished up on the seal area to remove any sharpness they may have. I've never had a leaker.
I haven't seen serrations on any aftermarket cranks Ive dealt with but that doesn't mean they all dont.

[Sirrotica]

The serrations are angled so that they tend to pull oil back into the crankcase as the shaft is turning. If they serrations were there to keep a seal from glazing they'd, be straight cut.

Pontiac isn't the only manufacturer to use serrations, some older engines used rope seals both front, and rear, many have serrations. All the ones I have seen are angled so that oil is pushed inward towards the sump.

The problem with rope seals are originally they were used on low speed shafts, and the packing could be tightened with a gland nut (think faucet packing), or collar to allow for wear. In an engine application there is no way to adjust tension to allow for wear, it's also being used on a high speed shaft. Obviously a less than desirable situation. It's going to leak eventually, lots of things will affect how long before a rope seal starts to leak, crankcase pressure etc.

I worked in a GM dealership when the 5.7 olds diesels were still under warranty, (mid 80s) also used a rope seal. If the rings were worn, or the PCV system was neglected, there was no way whatsoever that you were going to seal one of those engines. The rope seals don't hold pressure well, and they barely are able to hold oil back when everything is right. Add a compression ratio of 22 to 1, and you have instant crankcase pressure.

There are better engineered seals now, but 50 years ago rope was one of the common seal types used in many engines. Getting a rope seal to be oil tight is, much luck, and voodoo, there's not really any science, or skill involved. No matter how much care I used installing rope seals, you get leakers right from the get go.

As far as lipped seal being used on a Pontiac shaft, I would want the serrations polished level with the rest of the shaft. Machining the main bearing journals has nothing to do with the seal surface, as it's rearward of the main bearing surface on it's own journal, behind the slinger..

[Schurkey]

Rope seals have characteristics that make them "just right" for certain applications. Unfortunately, those advantages are not of use in an automotive crankshaft seal, except one.

1. They're cheap. Well, they used to be cheap, when they could use high-temperature-compatible asbestos in the manufacture of the rope. Now that's impractical. The labor required to install the seal was not a big deal decades ago, but labor costs have increased tremendously. So the rope seals are NOT "cheap" any more, but they used to be.

2. They can be somewhat "universal". The rope could be packed into any device that the length of rope would fit.

3. They're forgiving of seal-groove-to-shaft non-concentricity. And this is apparently an important consideration on some Pontiac engines, where the seal groove is not concentric with the crankshaft saddle machining. The rope seal can be packed "thicker" where needed, and "thinner" where there's less room between the crankshaft and seal groove.

4. They tolerate abrasion better than lip seals. Rope seals are still used in applications where they're keeping slurry inside the plumbing. But if you've got abrasive engine oil, the rear main seal is the least of your worries.




Yes, the serrations in the crankshaft are intended to "pump" oil back into the crankcase. You'll find out how effective they are if you mistakenly put a "marine" reverse-rotation crankshaft (which has serrations in the opposite direction) into a regular-rotation engine.