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Forums->Hot Heads Tech Talk->Rear Main Seal, AGAIN??

moparjack44
Rear Main Seal, AGAIN??


Several Questions,
I'm dealing with a 58, 392 Rear Main Seal leak, STILL mad

I have replace it twice, and still leaking. My first question, why do the 354, and 392 have different seal numbers, and what is the difference, other than what is obvious to the naked eye? The 354 rubber, has no shims, 392 has shims. However, the rope seal is same for 354 and 392.

The 426 rubber, looks like much thicker shims than the 392?

Part numbers, Best Gasket;
354 rubber, 3880 E
354 rope 5263

392 rubber 3A07
392 rope 5263 (same as 354)

426 rubber 3879 E
No listing for 426 rope

Have been told possible that leak could be because not enough ventalation? All I have is the oil filler breather in the valley pan.
This leak is driving me to drinking, like I really need a reason. lol

Thanks,
Jack
  user offline
on: Mon 29 of May, 2017 [14:03 UTC] reads: 2267

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author message
billm
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Re: Rear Main Seal, AGAIN??
on: Tue 06 of Jun, 2017 [20:04 UTC] score: 0.00
Jack,

First of all, engine oil pressure is not causing the leak. The rear main cap has vents that prevent oil pressure from directly reaching the main seal. Excessive crankcase pressure from ring blow-by can be an cause, but it would probably cause other leaks.

Although it may not be related to your problem. Please run a PCV system. The PCV system helps keep fuel and acids from accumulating in the engine. There is no downside to using a PCV system. It is good for the engine and the environment. Draft tubes are archaic and ineffective. You will need a way to get fresh air into the crankcase. Your existing oil filler breather should be sufficient, as long as it isn't clogged.

If your rear seal is leaking, and you do not have excessive crankcase pressure, there are only a few other causes:
1. The crankshaft surface on which the seal runs is worn or uneven.
2. If using a rubber seal, it may have been installed backwards. The angled lip on the seal should face towards the front of the engine.
3. If using a rope seal, it may not have been soaked in oil before installation, or may not have been trimmed properly during installation.

That's my two cents.
Bill





author message
462hemi
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Re: Rear Main Seal, AGAIN??
on: Fri 02 of Jun, 2017 [00:09 UTC] score: 0.00
moparjack44,

I'm having the same problem with the rear main seal in my 392. I don't think you will solve the problem with a PVC system. Pressure in the crankcase is not forcing oil past the seal, it's the oil pressure from the pump. If it was leaking due to crankcase pressure it'll be leaking past the oil pan gasket. Not sure what brand of rear main seal you have used, not sure if one is better than the other. I'm in the same boat as you, replacing the rear main.

Bill
Ontario, Canada


author message
moparjack44
user offline
Re: Re: Rear Main Seal, AGAIN??
on: Fri 02 of Jun, 2017 [15:10 UTC] score: 0.00
> moparjack44,
>
> I'm having the same problem with the rear main seal in my 392. I don't think you will solve the problem with a PVC system. Pressure in the crankcase is not forcing oil past the seal, it's the oil pressure from the pump. If it was leaking due to crankcase pressure it'll be leaking past the oil pan gasket. Not sure what brand of rear main seal you have used, not sure if one is better than the other. I'm in the same boat as you, replacing the rear main.
>
> Bill
> Ontario, Canada


It's a Best Gasket rubber rear seal I get from Hot Heads. Part number 3A07.

author message
Webmaster
user offline
Re: Rear Main Seal, AGAIN??
on: Thu 01 of Jun, 2017 [13:25 UTC] score: 0.00
> Several Questions,
> I'm dealing with a 58, 392 Rear Main Seal leak, STILL mad
>

Jack:
The 354 & 392 cranks are not the same diameters and use different seals. Rope seals are trimmed so they don't care. The Best Brand 392 seal is a 440 seal with a shim kit. It's been working well for the past 20+ years.
Back when we built engines, a customer brought his 392 to us saying he had changed the seal twice and it still leaked. We installed a new seal via the directions. I see him at shows every year and has never has a new leak?
Try again, be careful and good luck,
Bob

author message
moparjack44
user offline
Re: Re: Rear Main Seal, AGAIN??
on: Fri 02 of Jun, 2017 [15:04 UTC] score: 0.00
> > Several Questions,
> > I'm dealing with a 58, 392 Rear Main Seal leak, STILL mad
> >
>
> Jack:
> The 354 & 392 cranks are not the same diameters and use different seals. Rope seals are trimmed so they don't care. The Best Brand 392 seal is a 440 seal with a shim kit. It's been working well for the past 20+ years.
> Back when we built engines, a customer brought his 392 to us saying he had changed the seal twice and it still leaked. We installed a new seal via the directions. I see him at shows every year and has never has a new leak?
> Try again, be careful and good luck,
> Bob

Thanks Bob. I'm gonna put that PCV system in I got from you, just to see if that stops or helps cure the leak. I've considered putting it in my Hot Heads valve covers instead of the valley cover? I don't want to have to remove the intake.
Jack


author message
Jack
user offline
Re: Rear Main Seal, AGAIN??
on: Tue 30 of May, 2017 [00:35 UTC] score: 0.00
Should also be a draft tube.
The draft tube should be angle cut towards the rear of the car as to make a low pressure area that pulls the atmosphere from inside of the engine.
However I would remove that and put a PCV valve in its place plumbed to the intake, carb base, or T'd off of a brake booster.
A stock valley cover should accommodate that. After market valley covers may not.

author message
moparjack44
user offline
Re: Re: Rear Main Seal, AGAIN??
on: Thu 01 of Jun, 2017 [19:02 UTC] score: 0.00
> Should also be a draft tube.
> The draft tube should be angle cut towards the rear of the car as to make a low pressure area that pulls the atmosphere from inside of the engine.
> However I would remove that and put a PCV valve in its place plumbed to the intake, carb base, or T'd off of a brake booster.
> A stock valley cover should accommodate that. After market valley covers may not.

PLAN C3,idea
Would putting the PVC set up in the Valve Cover be a viable solution? As you see, I'm trying to avoid taking off the intake rolleyes

author message
moparjack44
user offline
Re: Re: Rear Main Seal, AGAIN??
on: Tue 30 of May, 2017 [15:30 UTC] score: 0.00
> Should also be a draft tube.
> The draft tube should be angle cut towards the rear of the car as to make a low pressure area that pulls the atmosphere from inside of the engine.
> However I would remove that and put a PCV valve in its place plumbed to the intake, carb base, or T'd off of a brake booster.
> A stock valley cover should accommodate that. After market valley covers may not.

Double check, but do not believe my engine has the draft tube. As familiar as I am withe the underside of this car/engine, have not seen a draft tube. I bought the PCV system from Hot Heads, but I hate to take off intake to install. Is there a plan "B"? Will breathers on the valve covers work just as well as the PCV system?

author message
Jack
user offline
Re: Re: Re: Rear Main Seal, AGAIN??
on: Tue 30 of May, 2017 [16:59 UTC] score: 0.00
I couldn't personally say that breathers in the valve covers would be sufficient as I don't go that route. However I see that a lot of guys do.
I have always figured it would make the engine dirty with oil and oil fumes.
The draft tube plugs into the opposite end of an original valley cover and HH sells a kit that puts a PCV in the same hole where the original tube mounts.
As for pulling the intake, this is one of the easiest to do as you don't have to upset the timing.
As I reread your original complaint you say that ventilation may be your problem. Positive ventilation would certainly be better than breathers or original draft system.

author message
moparjack44
user offline
Re: Re: Re: Re: Rear Main Seal, AGAIN??
on: Tue 30 of May, 2017 [18:48 UTC] score: 0.00
> I couldn't personally say that breathers in the valve covers would be sufficient as I don't go that route. However I see that a lot of guys do.
> I have always figured it would make the engine dirty with oil and oil fumes.
> The draft tube plugs into the opposite end of an original valley cover and HH sells a kit that puts a PCV in the same hole where the original tube mounts.
> As for pulling the intake, this is one of the easiest to do as you don't have to upset the timing.
> As I reread your original complaint you say that ventilation may be your problem. Positive ventilation would certainly be better than breathers or original draft system.

Thanks, I reckon I'll just have to bite the bullet, and put on the PCV system.

Do you have any answers about differences in the real main seals I questioned?

Thanks,
Jack

author message
Jack
user offline
Re: Re: Re: Re: Re: Rear Main Seal, AGAIN??
on: Wed 31 of May, 2017 [15:26 UTC] score: 0.00
I have rebuilt these engines using both the rope and the two piece rubber seal. I haven't had any trouble with either. Be sure to grease it up well on assembly.
Did you make sure that your crankshaft is clean and rust free? Grease that too.
Also I use a bit of silicon sealer on the corners of the retainer, that is usually the rear main cap. And some engines have hard seals on the sides of that retainer that get a bit of sealer.
Also a bit of silicon where the oil pan gaskets meet at the corners and if applicable the seal retainer. Again, on most engines this is the rear main bearing cap.
Important to be sure to seal any place that oil could get out.
It may not be your seal leaking but rather the area around it.
Just make sure you don't use sealer where any parts will be moving.

author message
moparjack44
user offline
Re: Re: Re: Re: Re: Re: Rear Main Seal, AGAIN??
on: Thu 01 of Jun, 2017 [14:11 UTC] score: 0.00
> I have rebuilt these engines using both the rope and the two piece rubber seal. I haven't had any trouble with either. Be sure to grease it up well on assembly.
> Did you make sure that your crankshaft is clean and rust free? Grease that too.
> Also I use a bit of silicon sealer on the corners of the retainer, that is usually the rear main cap. And some engines have hard seals on the sides of that retainer that get a bit of sealer.
> Also a bit of silicon where the oil pan gaskets meet at the corners and if applicable the seal retainer. Again, on most engines this is the rear main bearing cap.
> Important to be sure to seal any place that oil could get out.
> It may not be your seal leaking but rather the area around it.
> Just make sure you don't use sealer where any parts will be moving.

Thanks Jack. You have been very helpful. I have replaced the seal twice, and I did the things you suggested, still begins to leak immediately. Checked the crank, seems to be good. I'm going for the PCV.
I was hoping Bob or Eric would reply about diifferences with the seals. Thanks again.

Jack
Halifax, VA. 24558


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