crack in cumbustion chamber
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crack in cumbustion chamber
I just obtained a pair of 1948 panheads with a fresh valve job completed and spark plug helicoils installed. I noticed that there is a small hairline crack in the combustion area running between the new metal valve seat and the sparkplug helicoil. I brought it to a machine shop for inspection and the guy said that it would be OK in that the crack ends at two solid metal points--ie the helicoil and valve seat. Essentally , the crack has nowhere to go and can't progress or get any worse. Any opinions on this? I'll post a picture soon.
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Re: crack in cumbustion chamber
I wouldn't run them if it were me,,,they expand with heat...Any kind of edge is a burn or melt point. Try a good welder with head experience...
Dave
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Re: crack in cumbustion chamber
You may get some leakage around the plug, try an air test with soapy water to see...Mike
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Re: crack in cumbustion chamber
More Panheads have been ruined by botched hardened seat installation than by chroming, O-ring conversions, double-plugging, and three foot cheater bars all combined.
Just like the aluminum vs steel pushrod adjustment story, steel inserts and aluminum head castings expand differently with heat.
In other words: The hole gets bigger than the seat gets.
So the seat must be pressed in disastrously tight, because at running temperature the interference is reduced to a fraction of what it is at room temperature.
If a crack results, the squeeze that holds the seat is uneven, Not only will the seat distort out of round, there is little to keep it in.
Even "successful" installations can fall out if there is a spike in temperatures, such as from points follower wear advancing the spark, contaminated fuel, or the the old nemesis of the Evil Manifold Leak. The materials hardened seats are made from shrinks when it hits a critical temperature that is much too easy to reach.
If all other alternatives have been exhausted to bring the valve geometry of a sunken seat into serviceability (including spray-welding the original seat), then a soft seat such as bronze should be installed at a much safer interference.
....Cotten
Just like the aluminum vs steel pushrod adjustment story, steel inserts and aluminum head castings expand differently with heat.
In other words: The hole gets bigger than the seat gets.
So the seat must be pressed in disastrously tight, because at running temperature the interference is reduced to a fraction of what it is at room temperature.
If a crack results, the squeeze that holds the seat is uneven, Not only will the seat distort out of round, there is little to keep it in.
Even "successful" installations can fall out if there is a spike in temperatures, such as from points follower wear advancing the spark, contaminated fuel, or the the old nemesis of the Evil Manifold Leak. The materials hardened seats are made from shrinks when it hits a critical temperature that is much too easy to reach.
If all other alternatives have been exhausted to bring the valve geometry of a sunken seat into serviceability (including spray-welding the original seat), then a soft seat such as bronze should be installed at a much safer interference.
....Cotten
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Re: crack in cumbustion chamber
You might give a call to Creekside Welding and machining or HeadHog. Bothe offer services that will fix the spark plug holes as well at the cracks.
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Re: crack in cumbustion chamber
Head Hog (Don )told me last year he was close to perfecting a way to repair heads with the( so called )unleaded seats installed & put them back to stock condition . Give him a call ,he does not do well with e-mails , he will call you back. He is always busy. He repaired my 65 heads and they had the same problems ,except my heads were still in stock condition. He does great work .
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Re: crack in cumbustion chamber
If you do talk to Don, let lus know how far backed up he is. Last I checked it was at least six months.
Joe
Joe