[ROVERNET - UK] P6/ pinto

Vern Klukas vern at inkspotco.com
Sun Dec 9 18:52:10 GMT 2007

>  I have
>>  one question. What is
>>  the difference of a free running design and a
>>  interference design?
>A free running or free wheeling engine has enough
>clearance between the valves (when open) and the
>pistons (when at Top Dead Center) that they don't
>collide if the timing chain or belt fails and the
>valve timing gets out of sync.
>An interference engine can bend valves or worse if the
>chain/belt breaks.
>I believe the original P6 engine is free wheeling.

That is correct. A know failure was for the camshaft to break just 
forward of the last cylinders, and the engine would continue to run 
merrily, albeit roughly.

The root cause for the breakage was repeatedly abruptly reving the 
engine to speeds far higher than 3500 rpm  with no load in quick 
succession. The cam would wind up and release torsionally with each 
cycle, and I guess the casting couldn't take it after a few cycles. 
Happened to me twice in quick succession, once on my car and once on 
a customer's car, and it was common enough that Rover warned about it 
apparently. I learned that after getting royally reamed by my boss 
for breaking the customer car.

Speeding the engine smoothly and allowing it to return to idle for a 
few seconds before repeating eliminates the risk, but the reality is 
doing it to high speeds is pointless anyway.


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Vern Klukas                             I'm a little . . .
Inkspot Type & Design
vern at inkspotco.com

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