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Re: SVO: Rich running, will it toast the guides or what?



With the SHO you also have a piston clearance problem. The failed thermostat
not only cause's a over rich mix. The colder then normal water temps do not
let the  cylinder walls expand at the same rate as the piston. The piston will
reach its normal temp well before the clyinder will, so the piston will expand
faster then the walls do. This can casue the pistons to scuff. In the marine
engine world you need to increase the piston to wall clearance by 50% to
compensate for this. Most motors that are converted automotive motors run
anywhere from 150-180 degrees. If the pistons clearance is kept to automotoive
specs the pistons can scuff. We built a few APBA speed boats, they run in the
283/ 305 chevy class. We have to set the piston to wall clearance at .005, if
the same motor was in a car it would be about .0025.

If you run a high lift camshaft you run more valve spring pressure. This means
you have more load and more pressure on the valve train. With the greater
loading you need everything running at 100%. If you are running very rich with
a 2.3 turbo you will damage your valve guides well before you damage your
rings. This is because the fuel and boost will wash the oil right out of the
valve guide. While under boost some pressure gets passed the valve stem seal
at the top of the guide. This would be no problem with a good fuel mix, it
would be dry and not wash the oil. Lack of good oil will cause metel to metel
contact between your valve guide and valve stem. This will then gall {sp} the
stem of the valve. When this happens the valve stem will act more like a file
and eat the inside walls of the valve guides.  When the boost is filled with
fuel you have a great pressure washing of the valve guides. When this happens
the valve stem acts like a file and eats the guides.  I have seen this before
and it does not take long to happen, how long can you run your motor without
oil? This is what the guides are seeing. Any and all valve guide failures have
been in engines that are running very very rich. Anytime I have been told of a
valve guide failure, it has been with a motor that was running very very rich.
They also had the big valves installed in them. As for the stuck valve, he was
also running the Motorsport type big valves. This would mean that the
retainers are sitting much higher and could never hit the seals. How does a
rubber seal that mat or may not be hitting the top of the valve guide smash it
over? How does this cause a motor to lock up and not turn over until it cools
down? Why would you not send it piston back for inspection if it means you
would not have to pay for a camshaft. Thanks again



Later....Nick