interference engines... all makes...

[Cody Forbes]

E. Roy Wendell IV wrote:
>>> So are the MC turbo motors. "Generally speaking" they are not
>>> interference
>>> engines at idle, but are at higher opperating speeds. That's not
>>> always
>>> the case, though.
>>>
>
> Nope, don't buy that theory. I was asked by a friend to diagnose a non
> running MC1 engine after a timing belt change done by a monkey lad. No
> compression on at least three cylinders, engine ran fine before
> preventative belt change. Investigation revealed that the cam was
> about 90 deg. out of time because the monkey lad couldn't follow
> simple instructions. Said monkey of course put everything together
> and twisted the key rather than turning engine over by hand first.
> For some reason the engine cranked quite unevenly after the first
> rotation and never ran again. As far as I know, the engine had never
> been apart but of course I can't rule out a previous head resurfacing
> operation that may have affected clearance.
>

I know this much, when cruising at ~2500rpm in 5th gear and the main 
crankshaft keyway shears, this is what happens:

http://pics.jcforbes.com/11-20-03

My theory on why it can be interferance up high, but not at lower RPM would 
have to do with oil pressure to hydraulic lifters. At low RPM (near idle) 
and therefore lower oil pressure the valve lift is not as much because the 
lifter isn't fully pumped up, at higher RPM the lifter is at its proper 
pressure and the valve will open farther. Just a theory.

-Cody Forbes
http://www.5000tq.com
'86 5ktq
'86 5ktq
'86 5k-t-q
'87 5ktq - Fast.