66 SB Exhaust Valve Recession

[Michael A.]

Heads are off my 327/300 and the report is that all looks pretty good except for #4 exhaust valve has receded. I'm trying to understand the options and pros and cons of the choices.

AS background the heads are original however they've been involved in one rebuild. The original owner had the engine overhauled in 1990. They did not install hardened valve seats at that rebuild. I've owned the car for 18 years and drive it regularly. It has a little over 50k miles since it was last rebuilt. After the heads are done, I want to continue my regular driving of the car so I'm most interested in long term solutions that allow me to hop in the car for a long weekend of top down motoring with the bride!

I have some flexibility as my brother is doing the R&I work. He's very experienced, having built engines professionally for years. He uses a trusted machine shop with lots of small block experience. Thanks in advance for your input!

Cheers,

[William C.]

Re: 66 SB Exhaust Valve Recession

how badly receded? Why only one cyl?

[Gene M.]

Re: 66 SB Exhaust Valve Recession

Hardened seats not a good idea in 461/462 heads. Also do rebuild with new valves, ground down old valves just makes valve position worse. Is entire valve train OEM design or after market? Seems odd only one cylinder as Bill questioned.

[Michael A.]

Re: 66 SB Exhaust Valve Recession

Here's what I've learned in answer to Bill and Gene's questions. Definitely OEM valve train. The one valve is sunk about .060 compared to other exhaust valves. The sunk valve is one of the center siamesed ports that always run way hotter than the rest. My brother believes it may be from our trip on Rte 66 a few years back. 6 days of 400 miles per day going out and 3 days of 800 miles a day coming back.

Right now I'm waiting to hear the machine shops suggests on what to do. I'm just trying to get my thoughts together on this ahead of that. Definitely planning on new valves and trying to understand if a valve seat will work in the receded exhaust port.

Thanks for the questions and keep the ideas coming.

[William C.]

Re: 66 SB Exhaust Valve Recession

Why just one head? '462 heads are pleantiful. why not find one that is a date match and swap it out. Used on every 327 pass car with a 327 in '66.

[Joe L.]

Re: 66 SB Exhaust Valve Recession

Here's what I've learned in answer to Bill and Gene's questions. Definitely OEM valve train. The one valve is sunk about .060 compared to other exhaust valves. The sunk valve is one of the center siamesed ports that always run way hotter than the rest. My brother believes it may be from our trip on Rte 66 a few years back. 6 days of 400 miles per day going out and 3 days of 800 miles a day coming back.

Right now I'm waiting to hear the machine shops suggests on what to do. I'm just trying to get my thoughts together on this ahead of that. Definitely planning on new valves and trying to understand if a valve seat will work in the receded exhaust port.

Thanks for the questions and keep the ideas coming.

Mike------


My guess is that the valve seat in question was excessively ground during the previous rebuild. Why I do not know; possibly just a mistake or an attempt to "grind out" some imperfection noted on the seat.

I don't think it will be any problem if you use new valves.

[Michael A.]

Re: 66 SB Exhaust Valve Recession

Why just one head? '462 heads are pleantiful. why not find one that is a date match and swap it out. Used on every 327 pass car with a 327 in '66.

Bill - you just gave me a good reason to thumb through the Driveline which just arrived. I'm awaiting the results of a magnaflux on the current head but may need to have a backup plan just in case.

Cheers

[Michael A.]

Re: 66 SB Exhaust Valve Recession

Mike------


My guess is that the valve seat in question was excessively ground during the previous rebuild. Why I do not know; possibly just a mistake or an attempt to "grind out" some imperfection noted on the seat.

I don't think it will be any problem if you use new valves.

Joe - I doubt there's much more diagnostic that can prove the cause of 1 valve receding on a previously rebuilt head. Your guess may well be the cause. For now we just have to deal with it. Hopefully the head looks good in the magnaflux and we can use it. But as a back up I'm going to look at the Driveline for a possible replacement.

Definitely going back with new valves!

Cheers,

[Joe L.]

Re: 66 SB Exhaust Valve Recession

Joe - I doubt there's much more diagnostic that can prove the cause of 1 valve receding on a previously rebuilt head. Your guess may well be the cause. For now we just have to deal with it. Hopefully the head looks good in the magnaflux and we can use it. But as a back up I'm going to look at the Driveline for a possible replacement.

Definitely going back with new valves!

Cheers,

Mike------


If the head is determined to be cracked in some way, then you definitely need to find another head. In many cases, a cracked head can be repaired but the cost of doing so usually exceeds the cost of purchasing another head. The only exception would be a very rare and valuable head which your head is not.

If the head is not cracked and you wish to repair the valve seat recission, this could be done by installing a valve seat insert. However, I really don't think you would need to do this

[Michael A.]

Re: 66 SB Exhaust Valve Recession

Mike------


If the head is determined to be cracked in some way, then you definitely need to find another head. In many cases, a cracked head can be repaired but the cost of doing so usually exceeds the cost of purchasing another head. The only exception would be a very rare and valuable head which your head is not.

Joe
Any suggestions on sources for a good donor head hear in Illinois? I know JT Piper's had a huge supply of items like this but heard he had a big fire some year's back. I will be checking with him. Any other suggestions are appreciated. Just in case!

Cheers,

[William C.]

Re: 66 SB Exhaust Valve Recession

Keep in mind that the exact same head was used on passenger cars in '66 with the 327 engine. Go to any salvage yard that has some vehicles from the 60's and see what you find there. It is NOT a Corvette specific item, used on every 327 pass car in '66

[Michael A.]

Re: 66 SB Exhaust Valve Recession

Keep in mind that the exact same head was used on passenger cars in '66 with the 327 engine. Go to any salvage yard that has some vehicles from the 60's and see what you find there. It is NOT a Corvette specific item, used on every 327 pass car in '66

Thanks for the reminder Bill.

Cheers,