[DeTomaso] Exhaust Valve Not Closing?

[Asa Jay Laughton]

I'll have to let the more experienced brains on the list jump in at this 
point.  But if the noise is there one minute, then you let the car 
breath for a while by not going anywhere, and then it stops.... it 
sounds like a lifter is starving.

Yes, hydraulic lifters pump-up, but that doesn't mean they -stay- that 
way.  At high rpm, you might be getting some bleed back which is 
allowing the lifter to collapse.  My bet would then be a slightly bent 
pushrod.  Follow my on this.

At high oil pressure when the lifter is pumped up, the clearance on the 
pushrod is taken up and you have no noise.  As the oil warms with high 
rpm, you get just enough bleed down on the lifter to open the gap on the 
pushrod and you start to get some clattering, or ticking.  You let off 
and the process reverses.

Of course, I honestly could be all wet on this idea too.  I've not 
built, trashed or have quite enough experience to know for certain.  But 
I enjoy learning from everyone on this list.

Let us know what you find,
Asa Jay

Asa Jay Laughton, MSgt, USAFR, Retired

& Shelley Marie
Spokane, WA

1971 Mach I Mustang  [ASA JAY]
1973 Pantera L 5533  [ASASCAT]
    
******************************     
http://www.asajay.com
http://www.teampanteraracing.com
  



Art Stephens wrote:
> Asa Jay,
>     It's not backfiring.  In fact I was hoping it was just an exhaust 
> leak, which it kind of sounds like. (Probably just wishful thinking).  
> The last time it did it,  I pulled over while it was still making the 
> noise.  I got out and looked it over with the engine running.  I 
> couldn't see any obvious problem so I got back in the car and drove  
> home.  As soon as I drove away, the noise stopped.  I'm pretty sure it 
> has the original hydraulic lifters though it appears that the heads 
> had been off at one time.  Aren't hydraulic lifters supposed to work 
> like solids after they are pumped up?  A lifter can't grow can it,  
> beyond its full normal height?  I wonder if I just slightly bent a 
> valve when I missed the shift and maybe that valve moves fine thru its 
> guide until it gets hot from the heavy load of accelerating hard?  
> Perhaps the additional heat is enough to make things expand to the 
> point that the spring can't pull the slightly bent valve all the way 
> down to the seat?  Maybe it starts running ok again because I slow 
> down and let things cool off at which point the clearance between the 
> guide and valve increase?
>
> Thanks,
> Art
>
>
> ----- Original Message ----- From: "Asa Jay Laughton" <asajay at asajay.com>
> To: <detomaso at realbig.com>
> Sent: Sunday, May 31, 2009 4:00 PM
> Subject: Re: [DeTomaso] Exhaust Valve Not Closing?
>
>
>> Art,
>>
>> Is it backfiring out the exhaust?  If not, then the valve is probably
>> okay.  Something in the valve train though?  Maybe.  It might be you
>> stressed a lifter, are they hydraulic or solid?  Maybe bent a pushrod?
>>
>> Seems to me if it's running fine until you run it hard (presuming higher
>> rpm), then I'm betting a lifter problem, one that can't keep up.
>>
>> Asa Jay
>>
>> Asa Jay Laughton, MSgt, USAFR, Retired
>>
>> & Shelley Marie
>> Spokane, WA
>>
>> 1971 Mach I Mustang  [ASA JAY]
>> 1973 Pantera L 5533  [ASASCAT]
>>
>> ******************************
>> http://www.asajay.com
>> http://www.teampanteraracing.com
>>
>>
>>
>>
>> Art Stephens wrote:
>>>      A couple weeks ago I missed a shift and surely over revved the 
>>> engine.  The engine was making all kinds of racket for a couple 
>>> minutes and then the noise stopped.  Hmmm?  The engine runs fine 
>>> till I run it hard and then it sometimes does the same thing again.  
>>> It sounds to me like an exhaust valve is not completely closing?  
>>> Any ideas as to what is going on?
>>>
>>> Thanks,
>>> Art
>>>
>>>
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