TheSamba.com :: View topic - Understanding engine breathing w/a sand seal

Thu May 02, 2013 5:44 pm

If i understand correctly, the Type 1 engine w/a stock style crankpulley pulls fresh air into the block via spiral rings on the pulley hub and this helps to maintain a negative internal pressure which inturn aides in scavaging of the crankcases internal combustion by product gases through the oil filler vent and out of the engine.

It would seem that installing a sand seal will disprupt this much needed drafting.

Question, does the sand seal effect proper engine venting and if so, what or where is the fresh air introduced?

Thu May 02, 2013 6:10 pm

the stock pully has grooves ( Oil Slingers ) to keep the oil pushed back inside , you wouldnt want dirty getting pulled in throught the grooves .

installing a sand seal will not hurt , as the pistons move back and forth the pressure difference is what the breather is for it pushes out and pulls in air as needed .

Thu May 02, 2013 6:14 pm

I may be wrong, but I was under the impression that the spiral was designed only to move any accumulated oil back into the case. Also, I believe the pulley end of the case is just another vent for the pressure.

Also, I believe slightly more adequate venting is required if changing to a sand seal.

Fri May 03, 2013 6:14 am

Interesting, being an ACVW novice, I try to research as well as I can before I act, you know measure twice and cut once and theres quite a bit of conflicting info when one uses the 'net :D

I found this site awhile ago: http://www.vw-resource.com/crankcase_ventilation.html and by trail and error I've been able to determine that their explaination on the volume mixture screw on a 34PICT-3 was incorrect (a member here on the samba proved otherwise w/a broadband in which direction leans or richens the mixture) so it's possible their discussion on the crankcase ventalation could be off also. Hense my question here......

My 72 AE 1600DP of unknown mileage and quality of rebuild is leaking oil from behind the pulley. I've put it up on jacks, cleaned the area, run the engine w/the stock style oil filler cap off and soon discovered a small trail of oil coming from the area behind the pulley. The pulley is a chrome aftermarket stock type w/the grooves on the hub just like the warped stock one it replaced. Being a novice I didn't check to see if I could see an oil slinger washer installed nor if the case was cut for a sandseal. I just replaced the stock pulley that was on it w/a chrome similar type. The engine wasn't running when I got it in a 72 Ghia.
The engine doesn't smoke, has plenty of power, runs like a sewing machine and there was no smoke or excessive blowby from the open oil filler tube when I was testing it so I tend to think that blowby isn't the leaking issue. It has the stock style oil bath air cleaner and the filler is vented to the air cleaner.
I'm looking at replaceing that pulley w/a Berg or CB degreed wheel -or- a sand seal kit that doesn't require machineing.
From research here, a sand seal seems to cure leaks like this and cause no adverse engine breathing issues. But I'd like some more info, if anyone else wants to come out and play cool, if not, well I'll carry on anyways :D
Dave

Heres a pic when I had the engine out.

Fri May 03, 2013 6:38 am

I'd try a good quality stock or aftermarket pulley (CB or BERG) before I resorted to a sand seal. Most of the time the cheap chrome/aluminum pulleys leak because the grooves suck.

Fri May 03, 2013 8:25 am

Bashr52 wrote: I'd try a good quality stock or aftermarket pulley (CB or BERG) before I resorted to a sand seal. Most of the time the cheap chrome/aluminum pulleys leak because the grooves suck.

X 2 ^^^ I bet the chrome pully is the issue ..

My Grandfather always said Son Chrome dont get you home it only causes problems ..

Sun May 05, 2013 7:39 pm

You do have an oil slinger in there. Also, an engine with enough blow by to get out past the pulley can still run and sound decently well.

Tue May 07, 2013 6:13 am

Volfandt wrote: If i understand correctly, the Type 1 engine w/a stock style crankpulley pulls fresh air into the block via spiral rings on the pulley hub and this helps to maintain a negative internal pressure which inturn aides in scavaging of the crankcases internal combustion by product gases through the oil filler vent and out of the engine.

It would seem that installing a sand seal will disprupt this much needed drafting.

Question, does the sand seal effect proper engine venting and if so, what or where is the fresh air introduced?

To clarify, air isn't pulled in through the crank pulley. POSITIVE pressure builds up inside the case due to blow by past the piston rings. Air is then vented out via the breather. The oil slinger on the pulley is to keep the oil in. Sand seal seals up this spot to keep dirt out (oil in as a side effect), oftentimes increasing the need for crankcase venting.

Tue May 07, 2013 9:17 am

kme9418 wrote: Volfandt wrote: If i understand correctly, the Type 1 engine w/a stock style crankpulley pulls fresh air into the block via spiral rings on the pulley hub and this helps to maintain a negative internal pressure which inturn aides in scavaging of the crankcases internal combustion by product gases through the oil filler vent and out of the engine.

It would seem that installing a sand seal will disprupt this much needed drafting.

Question, does the sand seal effect proper engine venting and if so, what or where is the fresh air introduced?

To clarify, air isn't pulled in through the crank pulley. POSITIVE pressure builds up inside the case due to blow by past the piston rings. Air is then vented out via the breather. The oil slinger on the pulley is to keep the oil in. Sand seal seals up this spot to keep dirt out (oil in as a side effect), oftentimes increasing the need for crankcase venting.

Bob Hoover wrote:
The VW engine was designed in the 1930's. It’s crankcase ventilation system consists of pumping the air in around the pulley hub and using a road-draft tube to suck it out, along with whatever it happens to pick up such as water vapor, oil vapor and combustion products.

The late great Bob Hoover had an excellent blog that is still available here:
http://bobhooversblog.blogspot.com/2007/02/blow-by.html

Fri Jun 06, 2014 7:22 am

Volfandt wrote: Interesting, being an ACVW novice, I try to research as well as I can before I act
I found this site awhile ago: http://www.vw-resource.com/crankcase_ventilation.html.jpg[/img]
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Not good info. The spiral cut on the pulley does not pull air into the engine case but helps keep the oil in. Unless there is a vacuum hose hooked up to the breather / filler tube the blowby from the rings produce positive pressure inside the engine crank case which will force oil past the pulley. If the little nipple is not on the end off the "road draft tube" you no longer have a closed system for the vacuum so you will have an oil leak at the pulley or the valve covers at high rpm.. In stock applications that vacuum hose is connected to the air cleaner

Fri Jun 06, 2014 7:41 am

To clarify, air isn't pulled in through the crank pulley. POSITIVE pressure builds up inside the case due to blow by past the piston rings. Air is then vented out via the breather. The oil slinger on the pulley is to keep the oil in. Sand seal seals up this spot to keep dirt out (oil in as a side effect), oftentimes increasing the need for crankcase venting.[/quote]
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the above is correct
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Bob Hoover wrote:
The VW engine was designed in the 1930's. It’s crankcase ventilation system consists of pumping the air in around the pulley hub and using a road-draft tube to suck it out, along with whatever it happens to pick up such as water vapor, oil vapor and combustion products.
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THIS is totally incorrect. The "ROAD DRAFT TUBE" had a little rubber nipple at the end of the tube with a split in its end so when you had excessive crank case pressure the split would open up to help more pressure relief in conjunction with the vacuum from the air cleaner. The rubber nipple is nothing more than a check valve. Most people don't seem to know that the rubber nipple is important to the ventilation of the crank case pressure because the rubber nipple is usually gone by the time they get and engine..

Fri Jun 06, 2014 5:07 pm

Yes, Bob Hoover was smart and figured a lot of things out, but this is an area he got wrong. While he thought the "road draft" tube would pull air from the engine, if the little nipple was missing it would actually encourage the gases to vent to the air filter, along with oil mist - hence the popular belief that correct venting will clog up your carbs.

Oh, and making up your own abbreviations without defining them just confuses people - w/a = "wild-arsed?"

Sat Jun 07, 2014 3:19 am

On a slightly different note , don't high rpm race motors have vacuum pumps that purge the internal of the motor- to create a negative pressure.

Sat Jun 07, 2014 3:19 am

On a slightly different note , don't high rpm race motors have vacuum pumps that purge the internal of the motor- to create a negative pressure.

Sat Jun 07, 2014 9:52 pm

The V8 Supercars do - it decreases windage, but the main reason they do it is that without air to keep it in the air or cause foaming, the oil settles to the sump a lot quicker. The power loss to drive the vacuum pump would outweigh the benefits for most of us, though.

Sun Jun 08, 2014 1:38 am

what about an evac system (i think its called) where you have a tube going in the the exhaust at an angle using venturi effect to pull a vacuum...

have seen a couple vw's with it

Sun Jun 08, 2014 7:45 am

It won't pull a hard vacuum.

Sun Jun 08, 2014 8:15 am

Neither will a belt driven vacuum pump, what's your point?

Sun Jun 08, 2014 9:49 am

Quokka42 wrote: It won't pull a hard vacuum.

the reports i've seen seem to think it works well, pretty sure i saw a youtube video of a baja with it?

you don't need crazy vacuum in the engine anyway, just a little apparently....?

Sun Jun 08, 2014 4:41 pm

Ah, you are meaning to stop oil blowing out your breather or crank snout? I'm sure you could pull enough vacuum for that, but be aware if the seal at the snout isn't good you could be pulling more dirt into the engine. I imagine you would want this because the oil separation in your breather isn't effective, so be aware you might be blowing oil out your exhaust as well, which will probably end up as smoke.