[DeTomaso] Venting crankcase to valve cover (was Oilpan gasketrecommendation?)

[Doug Braun]

Asa Jay,

	My bad! Of course you're correct that the pushrod holes provide additional
paths for venting the crankcase via the valve covers.

Doug

-----Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of asajay at asajay.com
Sent: Monday, October 06, 2008 10:58 AM
To: detomaso at realbig.com
Subject: Re: [DeTomaso] Venting crankcase to valve cover (was Oilpan
gasketrecommendation?)


Doug,

What about all the pushrod holes in the head that lead directly to the
valley?
http://www.351c.info/gallery2/v/asajay/351C_Build_2001/head_id.jpg.html
http://www.351c.info/gallery2/v/asajay/351C_Build_2001/topend2.jpg.html

With the pushrod holes at the top and the oil drainback holes at the
bottom, it seems to me you should have plenty of room for venting to
the valve covers, in fact, as the pressure goes up it might actually
help force oil back through the drainback (unlikely I know but the
theory is sound).  My point is, the oil drainbacks are -not- the only
path into the valley.  With that said, it is possible to fill the
covers such that all the pushrod holes are draining back oil as
well... but that would be a helluvalot of oil.

Unless I missed something.

Asa Jay




Quoting Doug Braun <doug at silicondesigns.com>:

> Thomas,
>
> 	Yes there is an issue.  The valve cover openings are the ONLY crankcase
> vents to the atmosphere in a 351C (as long as the engine doesn't leak
oil).
> Vent-wise, the lifter valley lies between the crankcase and the valve
covers
> so oil from the heads drains into the lifter valley and then to the
> crankcase.  Crankcase venting gasses and head oil drain back are both
> fighting for passage (in opposite directions) through the heads' two each,
> 3/8" diameter or so, drain passages.  Any blowby that the lowly PCV can't
> handle gets shoved into the air cleaner assuming the stock type emissions
> hose is present between the oil filler cap and the air cleaner.
>
> 	One of the head's drain back holes is straight while the other (as Jack
so
> often cites) is doglegged.  But it's only a single dogleg which can be
> easily drilled from both ends, meeting at the angle in the middle, to
> completely clean out this passage (of course this assumes that the head is
> off the engine).  On my 160K mile 351C-4V quench heads I found these holes
> to be about 50% blocked with sludge.  I also recommend chamfering the
valve
> cover side entry to each drain hole to promote oil flow.
>
> Doug Braun
> blue 73L #5505
>
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> [mailto:detomaso-bounces at realbig.com]On Behalf Of Tomas Gunnarsson
> Sent: Friday, October 03, 2008 12:02 PM
> To: DetomasoList
> Subject: [DeTomaso] Venting crankcase to valve cover (was Oil pan
> gasketrecommendation?)
>
>
> Is there really an issue with venting the lower part of the engine to the
> valve covers? I'd have thought that even with the head drains completely
> filled with oil returning to the crankcase there'd be enough combined
> passage area through the lifter area floor and pushrod holes to vent
> whatever blowby there is.
>
> Tomas
>
> ----- Original Message -----
> From: "Barry Seib" <oldwheel at mts.net>
> To: "Drew, Mike" <MikeLDrew at aol.com>; "DetomasoList"
<detomaso at realbig.com>
> Sent: Wednesday, October 01, 2008 11:01 PM
> Subject: [DeTomaso] Oil pan gasket recommendation?
>
>
>> Mike
>> I think Larry may be right on with his suggestion. If there is no leak
>> except at high RPM, that's a very strong indication that no matter where
> the
>> leak is, excess crankcase pressure is likely causing it. I suspect the
>> factory PCV system is totally inadequate for sutained very high revs. You
>> might try the same run with extra NASCAR or circle track type breathers
to
>> see if the problem is solved.The other issue is making sure that the
>> crankcase can breathe to the valve covers (if that's where the extra
>> breathers are). If the heads and drainbacks are all flooded with oil so
> that
>> can't take place, you will have to remedy it first - or put a breather
>> directly to the crankcase by some other route to stop the leak. MD must
> have
>> dealt with this issue a long time ago.
>>
>> Dawg? What say you?
>>
>> Barry
>>
>>
>>
>> [DeTomaso] Oil pan gasket recommendation?
>> Larry - Ohio Time Corp larry at ohiotimecorp.com
>> Wed Oct 1 12:54:55 CDT 2008
>>
>>
>>
>> Hi Mike,
>>
>> You may want to check you venting / PCV system. At high RPM the blow-by
is
>> at its highest. I have seen crank cases pressurized and blow oil out a
>> normally good seal. If your heads are full of oil the venting system may
> not
>> be working to well.
>>
>> Larry (no, tarter sause) - Cleveland
>>
>>
>>
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