Ok don’t blame Jim Goods, but there he is on page 42 of “Jaguar XJS” by Rivers Fletcher, tapping in a valve seat. The workbench and hammer might be older than ol’ Jim himself.
Nice technique in use!
many shops still do it that way, i know i do, many many times ,never dropped a seat!
its all how the machining operartions are done , and Jag V12 HE are notoriuos for dropping seats , VERY HOT combustion temps, Pre he has cooler combustion temps!
ron
Yeah, but the combustion temps aren’t the problem. The problem is steam pockets in the head. Poor coolant flow (due to whatever) is a major contributor, but it’s possible that the redesign of the head to create the H.E. combustion chamber may have increased its proclivity to forming steam pockets.
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My 63 “Forward Control” Corvair camperized van developed a habit of running on 6 at most of the time, but dropping to 5 at times. I chased the miss for a long time. At last it was on 5 in my drive!!! Did a compression test and found 0 in one hole!!!
Pulled both heads. I was much younger and not all that hard to do in my garage. SOG. A floating valve seat. Clear, a times, the insert would seat in the head, and at times not !!
A talented local machine shop had the battered seat in the head welded. then cut a new seat and according to them forced a tighter seat by the col insert vs hot head technique. He shoed me some examples of other failures. One included dimpling around the seat to tighten it in place. Not the best, but n old tech fix to tighten s fit!!! Similar to knurling…
With a fresh valve job on each head, the full 98 HP was back full time!!
Carl,
you just said it , high temp combustion is the major problem!
simply put , HE chamber is in the cylinder HEAD, PreHE chamber is in the piston???
so heat of combustion HE goes into coolant in the head!
PreHE heat is distributed in the piston and block coolant, little goes to head coolant!, that is why PRE engines need effective OIL cooling!
case in point most dropped seats are HE High Efficency heads , terrible design, good for light throttle street driving, USELESS for a serous Hi-performance engine!
Ron
HI Carl , the GM Corvairs never had STEAM pockets in the heads ,Correct? LOL.
another vehicle that was ahead of its time , I owned many of them , just sold off a 4 Carb. engine RARE!
i been studying these forum guys, they mostly seem caught in THERE generation BOX, outside there box doesnt compute , like you Carl, are ahead of my time, and most others are behind my generation , i guess thats the way they are educated!
ron
Ron:
Do you suppose that getting old has it’s benefits !!!
AKA experience. So, log as we learn and keep what we learn along the trail of time.
Alloys and cast iron and steels contract and expand at different rates. Hmm the valve seat is a form of steel. Seated in an alloy head, Jag, Corvair or any other. heat must be accounted for.
But, steam pockets can be a cause. No coolant in the vicinity of the seat to carry away the heat of combustion. Localized expansion of the alloy greater than that of the steel seat. So, in spite of the valve hammmeri8ng on the seat, it drops
OTH, a side valve engine. Again an alloy block and steel valve inserts. Over heat generally or locally. Seat loosens. Stays in place/ Gravity?
I dunno. Such an engine configuration rare if it exists at all. Not on my experience.
Carl
Carl latest tests have shown what is really happening to valve seat dropping,especially with aluminm heads!
when the engine combustion gets extremly hot the exhaust valve starts to change shape and MICRO WELDS to the seat pulling it loose , once it loose its down hill from there. like HE engine do runs very high combustion temps.
of course expansion rates of dissimular metal doesnt help, altho later metalurgy tech. has changed much of that concept!
ron
And that would mean unleaded gasoline is the problem. The lead in gasoline effectively coated the contact surfaces between valves and seats so they don’t jam or microweld.
Ron and Kirby:
Thanks. makes sense to me.
And reinforces my decision to lump my car with an all iron engine!!!
Carl
All iron is even worse. Iron is relatively soft, so without lead in the gasoline the valves will eat up the seats. Hence, modern iron heads designed for unleaded fuel STILL have valve seat inserts! Ya can’t win!
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OK Kirbynerd, we aint never gonna have Leaded gasoline anyway,Jeez.
course we could have screwin valve seats , like the old days!
ron
I’d be happy with aluminum heads with steel valve seat inserts if only they were designed with a positive retention scheme rather than simply pressed in. Considering the differential expansion issues, I’m not sure how they ever concluded that pressed in was an acceptable assembly scheme.
I’ve read that copper-infiltrated seats have helped in the expansion differential issue
I would think that copper would also help the microwelding issue.
Well, always been a puzzlement to me, but as evidenced by the hundreds of millions of ali head/steel inserted engines that have been made, with few to no issues, they figured it out, somehow!
OK, im0precise language. Iron head LT1 chosen over the alloy head version.
And, GM took care of preparing it to do non lead and ethanol based gas.
Carl
I didn’t know there was a iron head version of the LT1!
GM hardened the exhaust seat cast iron , a form of induction hardening, seems to work quite well with no lead fuels, and ethenol
technology sleeps for no one!!
ron