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Valve seat / Valve work info needed

BlueCorvette

Active member
Joined
Feb 13, 2016
Messages
29
Location
Florida
Corvette
1985 two tone blue Z51 4+3
I am rebuilding my 1985 C4 L98 143k miles. No prior valve work done on it and it ran great before disassembly. I need some advice on Valve seat / Valve work.

The intake valves appear to be in good shape. Very minor imperfections on the valve contact area that are only apparent under a magnifying glass, no visible wear. They have a ~30 deg backcut that I am guessing is stock.

The intake and exhaust seats have very slight pitting only visible under a magnifying glass. The condition seems good for the mileage. Stock angles should be 46deg/45deg seat/valve.

The exhaust valves show a little more wear. Minor pitting of the contact area. Some show barely visible wear of the contact area. Given the extra heat load on the exhaust, they also seem to be in pretty good shape for the mileage. I think it would be best if they could be recut as they show the most wear.


I'm not sure what my options are.

I read that valve lapping is a bad idea, but that would be the easiest for a minor refresh.

How much would it cost to have a machine shop clean up the valves and seats? I'm talking about a basic valve and seat cleanup to remove the imperfections back to stock specs, and add a 30deg backcut on the exhaust valves.

I don't want to put much money into head work as these are the original iron heads. They weren't leaking oil down the stems, but I'm sure they have some guide wear after 143k.

I live in the Jacksonville Florida area and don't know of any shops that have a reputation for reasonable, quality SBC work.
 

Robertwav1

Well-known member
Joined
Jan 7, 2003
Messages
821
Location
Ocala, Florida
Corvette
1993 Blue
143K on cast iron heads in my opinion are broken in well. I just did a few heads on another vehicle with 250K. Couldn't find a machine shop that does that kind of work except for NAPA. I decided to recondition them myself. Had some pitting on the valves themselves but followed a video on youtube about refinishing. I checked the springs for specs fully extended as well as the valve stems and was surprised that they were indeed within the tolorence. Again cast iron heads seem to hold up pretty good. Valves are really no big deal to reseat as long as they are in good shape otherwise. Again NAPA will do the job but you have to find one that has machine equipment. Your valve guides have no leaking so I'll bet the stems are in spec as well. I cleaned up the chamber and valve faces with a brass brush in a dremel. I only did these heads cause of the mileage, I had the vehicle since new and always took good care of it, careful oil changes, regular tuneups etc....it seems to make a big difference as the vehicle ages. Anyway, very satisfied with the job, vehicle very quiet and runs strong. Good luck on your decision.
 

DonB

Well-known member
Joined
Mar 25, 2015
Messages
339
Location
Chicago
Corvette
2019 ZO6 in Elkhart Lake Blue
I had the aluminum heads on my L98 done by Windy City Engine Machine Shop here in Chicago. They have been around since the early '70s servicing the needs of professional engine builders and Hot Rodders alike. They did a remarkable job with my heads and engine block. I noticed quite an increase in power and the engine just seems to breathe much better, run smoother. The heads were dipped & magna-fluxed, straightened & decked, plus had the full comp. valve job with 3 angle seat cut, ported, relieved, new guides, seals, rocker studs, springs, retainers and titanium keepers. Then vacuum tested. The block was dipped and resealed, cylinder & lifter bore honed, decked. Crank journals were line-bored and new cam bearings were installed too. They did this all at a very reasonable price.


They are in an older part of town that isn't the best of neighborhoods anymore, but they (as always) were well worth it. If anyone is familiar with Chicago they are at 7700 S. Stoney Island Avenue. Phone (773)721-7373 Components are shipped to them from all over the country.

If anyone needs some awesome head or block work, look them up. You will be glad you did!
 

Kevo

Well-known member
Joined
Sep 10, 2013
Messages
46
Location
Hampton Va
Corvette
1993 torch red stripped automatic coupe
Generally when one rebuilds an engine that would include the heads, a valve job and new seals would be the norm. I do understand the part that these the less than desireable iron heads. Although I don't recommend it you could clean chambers and lap valves in and replace valve seals. You would be surprised what happens to valve and seat faces after refacing tool makes first pass. What might have looked round was actually oval with high and low spots. If you decide to get your heads redone I don't recommend "Knurling" guides. It doesn't last; replacing guide is the best way to go. Myself I would look for some quality reconditioned later model aluminum heads. Honestly you don't want to put engine together to take it apart later to do an upgrade or repair of something you tried to get by with. To me rebuilding drivetrain assemblies are "Do It Right The First Time"thing. It's no fun having to take it out and apart a second time.
 

kpic

Well-known member
Joined
Mar 29, 2014
Messages
2,292
Location
Columbus, NC/NE Georgia
Corvette
1997 boosted silver coupe
A couple of things I do personally. Be forewarned, I am absolutely anal with my "babies."

I use a very fine lapping compound to check the seal width on newly machined seats. I see it as everyone makes mistakes. The cost of some machinist blue and fine lapping compound is small. As a good carpenter will tell you, measure twice and cut once.
If that makes any sense. :D

I also shim the valve springs. Rather than my boring over detailed blah blah blah. ;) Lunati offers a very nice article on the subject.
Valve Spring Tech - Lunati Power

Springs have a value in PSI. However, if the distance between coils at maximum lift is all over the place so will the spring force.


 

DonB

Well-known member
Joined
Mar 25, 2015
Messages
339
Location
Chicago
Corvette
2019 ZO6 in Elkhart Lake Blue
Generally when one rebuilds an engine that would include the heads, a valve job and new seals would be the norm. I do understand the part that these the less than desireable iron heads. Although I don't recommend it you could clean chambers and lap valves in and replace valve seals. You would be surprised what happens to valve and seat faces after refacing tool makes first pass. What might have looked round was actually oval with high and low spots. If you decide to get your heads redone I don't recommend "Knurling" guides. It doesn't last; replacing guide is the best way to go. Myself I would look for some quality reconditioned later model aluminum heads. Honestly you don't want to put engine together to take it apart later to do an upgrade or repair of something you tried to get by with. To me rebuilding drivetrain assemblies are "Do It Right The First Time"thing. It's no fun having to take it out and apart a second time.


I couldn't agree more Kevo(especially about knurling the guides...waste of time.) I can't think of anything on a Vette I'd relish doing twice or more,.. besides driving it!
 

BlueCorvette

Active member
Joined
Feb 13, 2016
Messages
29
Location
Florida
Corvette
1985 two tone blue Z51 4+3
Thanks everyone.

I found a local machine shop that had SBC experience with drag racing builds and good equipment for valve work.

I was able to get a multi angle valve job for $150 because I had disassembled and cleaned the heads before delivery.

They said the valve seats were slightly worn out of round, so I am happy I had the work done. I am reassembling the engine now, so wish me luck.

Also they strongly advised against any kind of valve lapping. They said you should always recut to the exact angles you want with good quality machines.
 

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