[DeTomaso] Venting crankcase to valve cover (wasOilpangasketrecommendation?)

Tue Oct 7 23:15:05 EDT 2008

So, having forgotten about the pushrod holes, I went out to the garage to
study the four engines I have in various states of disassembly.  It sure
seems like there's enough total area for case gasses to get into the valve
covers without impeding oil drainage.  Now I can't well explain my previous
oil volcano experiences.  There has to be something more complicated
involved, like crank windage creating serious flow dynamics throughout the
engine.

A couple of interesting observations:
Because of the head angle, the pushrod holes are way up higher than the oil
drain holes.  If the oil drain holes are ever impeded, you're going to
collect a lot of oil before it drains back into the pushrod holes.
The dogleg portion of the dogleg drain hole is nearly horizontal as
installed on the engine.  That probably explains why stuff settles there and
often results in a plugged passage.
The oil drain passages in the front of the block are horizontal too.
It sure looks like the cam gear could sling a lot of oil up the one of the
front oil drain passages and up to the valve cover.

-----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 6:52 PM
To: detomaso at realbig.com
Subject: Re: [DeTomaso] Venting crankcase to valve cover
(wasOilpangasketrecommendation?)

I thought the question centered around what would happen -if- you
vented the valley.  I have to admit it was an interesting thought, one
which began to make a lot of sense until I started examining all the
holes between it and the valve covers which to me indicate there is
plenty of space.

So, if the valve covers start blowing smoke, it probably means there
is a lot of blow by increasing the block pressure, which in turn
probably helps suspend oil in the air.  If the valve covers fill with
oil, there are eight more drainbacks to get it back in the valley.

Maybe the valley would be a better place to vent from, as the vent
could be placed even farther from any oil source.  But where would you
tap it?

Asa Jay

Quoting Doug Braun <doug at silicondesigns.com>:

> Thomas,
>
> 	I misunderstood and didn't read your posting carefully enough.  I thought
> you were implying that the lifter valley had a means of venting to the
> atmosphere other than through the valve cover cap holes.  And in my
attempt
> to point out that the valve cover holes are the only exit, I made two big
> blunders.  I forgot to mention the pushrod holes (as Asa Jay pointed out,
as
> did you in your posting) and I got it wrong about where the drainback
holes
> return to.  I'm sorry, I just created more confusion here.
>
> Doug
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> [mailto:detomaso-bounces at realbig.com]On Behalf Of Tomas Gunnarsson
> Sent: Monday, October 06, 2008 11:18 AM
> To: DetomasoList
> Subject: Re: [DeTomaso] Venting crankcase to valve cover (was
> Oilpangasketrecommendation?)
>
>
>
> ----- Original Message -----
> From: "Doug Braun" <doug at silicondesigns.com>
> To: "Tomas Gunnarsson" <guson at home.se>; "DetomasoList"
> <detomaso at realbig.com>
> Sent: Monday, October 06, 2008 6:51 PM
> Subject: Re: [DeTomaso] Venting crankcase to valve cover (was Oil
> pangasketrecommendation?)
>
>
>> 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).
>
>>> I'm with you here.
>
>> 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.
>
>>> I have looked at pics I've taken and ones found in the Tom Monroe
rebuild
> handbook. To me it seems like the head drains don't exit into the lifter
> valley. The oil drainback holes are actually outboard of the outermost
> headbolts.
>
>  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.
>
>>> I see this differently. Oil primarily runs down the drains. Crankcase
> gases can pass up those drains too unless they're filled with oil. Should
> they be filled with oil, gasses can pass up into the lifter valley past
the
> camshaft through the four 1/2" or so holes above the camshaft. I
understand
> that there's also a certain amount of oil flow from the lifters going down
> these holes at the same time. From the lifter valley there are eight
pushrod
> holes (~1/2") to each valve cover that are only partially filled with
> pushrods.
>
>   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.
>
>>> This is the way it's supposed to be as far as I can tell. The hose
> connected to the intake could never handle much gas flow.
>
> Tomas
>
>
>> -----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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