[Fot] Oil pressure and tolerance on valve clearance

[Duncan Charlton]

I've seen anywhere between 70 and 100 psi on our racing engine when 
warmed up and on the track but never as low as 50.  I have read that 70 
to 80 is best but I never had any leaks of the engine or the oil cooler 
with 100 psi.  By the way, where are you measuring the pressure?  The 
oil line to my gauge was tapped into the oil gallery on the left side of 
the engine rather than the stock location to get the most accurate 
reading of what's going on in the oil passages.

I don't think it's unusual to see a range of valve adjustment although 
it most often seems to be stated thus: "0.010 to 0.012".  I looked at a 
list of specs for Briggs and Stratton small engines and most of their 
engines are given an allowance range of 0.002" to 0.004": 
http://tinyurl.com/m2vynmd

I understand it can make a difference in power if you set valve lash at 
the small end of the range since the valve opens earlier and closes 
later but the amount of time the valve sits on it seat is shorter, so 
there is a tradeoff in loss of time for heat transfer.

Duncan

On 6/2/14, 9:54 PM, Tim Murphy wrote:
> What oil pressure is typical or desired for the TR4 engine?  When the engine
> is up to temperature, at 3000 to 6000 RPM (typical racing revs) we are
> running 50 PSI.
>
> I was just checking the valve clearance and again I've wondered why a
> tolerance is never given for the clearance.  The only time I've ever seen a
> tolerance given was for a 1975 Honda Civic 1200cc engine I rebuilt and the
> clearance was +0.010 /- 0.001.  that made sense but it's the only time I've
> seen it in a manual or any place else.  Does +0.001/-0.001 really make a
> difference or am I missing something here?
>
> The questions are mainly an engineering curiosity.
>
> Thanks,
>
> Tim Murphy
>
> 1961 TR4 #317
>
>
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