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

Doug Braun doug at silicondesigns.com
Mon Oct 6 12:51:15 EDT 2008


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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