Message text written by JIMMY
>jim- you really should have gone with chrome plated valve guides.
i have learned by failure that bronze guides wear faster due to carbon
buildup. sorry you went through the expence.<
I suspect that whomsoever put your bronze guides in did not use the
phospher-bronze, porous type. Perhaps they used a thin wall? If so, heat
distortion could have opened up the clearances and allowed the deposition
of the combustion byproducts that build up as carbon.
The Ph-Bronze inserts porous are self-lubricating. I looked into the
chrome and they did not meet my second design criteria (the first being
1hp/cu. in.): a 100,000 mile engine.
I agree, if I was going to pull the engine down every season and put in new
valves ( the hard chrome guides don't wear, the valve stems do) I would
have gone chrome. Since I won't be changing valves I wanted good
lubrication.
What stem to guide clearance did you run to get some oil in there? My
bronze guides are just 0.0008" (yes, 8 tenths) larger than my valve stems.
They stay lubricated, cools and do not allow oil into the cylinders. I
suspect that the clearances required to lubricate the chrome guides result
in a bit higher oil usage than I'd like. I couldn't see using
hypereutectic pistons to reduce blowby and letting oil past the valves.
The final reason that I went with ph-bronze guides is that, like the
magnesium-bronze guides, chrome plated types can seize up in a low
compression engine. I am running mid-9's compression and that may be
borderline between high and low but my exhaust temps are relatively high.
High temp exhaust is not compatiable with mag-bronze or chrome due to
luberication issues.
Believe me, I weighed every expenditure against my design criteria very
carefully.
Regards,
Jim
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