Hardened Valve Seats
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Joined: Nov 2011
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Hardened Valve Seats
Going to pull the heads on my 73 L48 and replace the valve seals. Don't know the condition of the valves. I have no indication that there is any problems other than worn out valve seals. Motor has never been apart w/46000 miles.
My question is if a valve job is in order, should I replace the seats with hardened ones.
My question is if a valve job is in order, should I replace the seats with hardened ones.
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
Going to pull the heads on my 73 L48 and replace the valve seals. Don't know the condition of the valves. I have no indication that there is any problems other than worn out valve seals. Motor has never been apart w/46000 miles.
My question is if a valve job is in order, should I replace the seats with hardened ones.
My question is if a valve job is in order, should I replace the seats with hardened ones.
This is something you could just wait and see the condition of your heads now. Most of this hype on hard seats is just that! If your heads are good now after 39 years you add it all up and see if you really think it is worth the effort. Cost wise when you add the false seats to the equation you my be better off buying some better heads for better performance.
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Joined: Nov 2011
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I dont really know when the hardened seats were introduced. I know it was in the early seventies. The reason I am pulling the heads is two fold. Valve seals and engine detail. The valve seals just give me a good excuse to pull the heads!
Le Mans Master
Joined: Jun 2004
Posts: 6,231
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From: Seattle WA
St. Jude Donor '14
This is something you could just wait and see the condition of your heads now. Most of this hype on hard seats is just that! If your heads are good now after 39 years you add it all up and see if you really think it is worth the effort. Cost wise when you add the false seats to the equation you my be better off buying some better heads for better performance.
I've seen very, very few cases of seat recession in old heads fed a steady diet of unleaded for decades.
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Race Director
Joined: Jul 2001
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It turns out that the hardening of valve seats on Corvettes or similar cars was unnecessary- the engines never run hard enough for long enough to create the conditions required for valve seat recession. There are some that still believe it to be required despite 40 years of evidence to the contrary.
Drifting
Joined: Jun 2010
Posts: 1,781
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From: Oxford Ohio
If in doubt lay a straight edge across the valve stem tips and see if any are taller than others. Open the valves about 3/8ths an inch or so and see if there is any lateral movement to check guide wear. If there is lateral movement of a fair amount, do the valve job and guide attention. otherwise change the seals.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
That's correct- all '73s came from the factory with hardened seats. The change was a precautionary measure purely for the upcoming removal of lead from fuel, not directly associated with the reduction in compression ratio.
It turns out that the hardening of valve seats on Corvettes or similar cars was unnecessary- the engines never run hard enough for long enough to create the conditions required for valve seat recession. There are some that still believe it to be required despite 40 years of evidence to the contrary.
It turns out that the hardening of valve seats on Corvettes or similar cars was unnecessary- the engines never run hard enough for long enough to create the conditions required for valve seat recession. There are some that still believe it to be required despite 40 years of evidence to the contrary.
I was in business as a professional engine builder for over 30 years. I am still doing head work. It was all hokus pokus... The Sky Is Falling... from the contingent opposed to unleaded fuel. Recessive valve seats are -typically- the result of an unskilled mechanic getting over ambitious with the seat cutter.
Drifting
Joined: Jun 2010
Posts: 1,781
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From: Oxford Ohio
I don't want to get a debate started on this thread, but I've torn down sbc engines for the first time, having soft seat heads, and found the exhaust valves into the chamber roof completely below the surface. Not often, but I've seen it never the less. Never seen intake issues, only the exhaust. So it would indicate a heat related issue.
I think stainless valves would benefit the a soft seat head rebuild.
I think stainless valves would benefit the a soft seat head rebuild.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
I don't want to get a debate started on this thread, but I've torn down sbc engines for the first time, having soft seat heads, and found the exhaust valves into the chamber roof completely below the surface. Not often, but I've seen it never the less. Never seen intake issues, only the exhaust. So it would indicate a heat related issue. I think stainless valves would benefit the a soft seat head rebuild.
Drifting
Joined: Jun 2010
Posts: 1,781
Likes: 15
From: Oxford Ohio
It's like most things, I have publications from an Engine Builder publication I subscribe to that explains the micro welds that take place and lift small particles from the seat and in time, erase the seat to depth. So, I think it's what ever expert one chooses to believe. There is a reason new heads have hard seats. The auto industry wouldn't spend the cash for hard seats if there were not a reason.
Race Director
Joined: Jul 2001
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It's like most things, I have publications from an Engine Builder publication I subscribe to that explains the micro welds that take place and lift small particles from the seat and in time, erase the seat to depth. So, I think it's what ever expert one chooses to believe. There is a reason new heads have hard seats. The auto industry wouldn't spend the cash for hard seats if there were not a reason.
Dad and his fully loaded Vistacruiser pulling the Airstream trailer over the Rockies in July might have a problem.
