Machine shop advice - 71 LT-1 rebuilding heads

[Dan H.]

I pulled my heads off because I have to get my valve guides replaced. They have .004 - .005" play. I am a rookie/newb and want to get these heads rebuilt so that they last a long time. I do not want to hot rod these, more like repair them and use any modern technology that makes sense. My car is a NOM 71 LT-1 with 49k miles.

Took my heads to two different shops today and got two different methods of repair. Now I am confused and could use/appreciate some advice.

Shop #1 - machine shop servicing many local repair shops
pressure test heads to look for cracks
replace all guides with new guides, not a thin sleeve
cut top of guide so a seal can be attached to it
replace all exhaust valves
Insert new exhaust valve seats - said this was needed to run unleaded (i already do)???
cut both valve and seat to match
check all spring pressures and heights - replace whats needed
NOT replacing intake valves
.010 cut across the bottom of the head to true the surface
clean & paint
price: $860
reco'd a thick fel pro that would lower compression.


Shop #2 - Guy builds race motors - full shop in his garage.
Drill guides and put in thin bronze sleeve
replace all valve, intake and exhaust
replace all springs
grind valve seats to match valves - without inserting new material/seats
no milling/cutting of the base
clean
price: $375

My confusion is the valve seats. Why is shop #1 putting a new valve seat in when shop #2 is grinding the valve seat? I was under the impression these heads didn't require leaded fuel. Is one of these guys overlooking something or wrong? Shop #1 warned me several times that when replacing the valve seat that he "could hit water and ruin the head". He said it rarely happens, but it is a possibility due to how the head was cast, that there could be a sand pocket......

casting # on heads - 3973487

Would like to know your opinions

[Timothy B.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Dan,

For me it's definately shop #2, no valve seats and no milling of bottom of heads. What is he planing to do with valve seals as I would keep the original valve guide height and o rings. Make sure the springs meet OEM replacement specs and nothing more.

If these are original heads they should have the screw in studs and pushrod guides, also, have him check your rocker arms to see if they are wore and need replacing and if so just use the stock stamped rocker arm, no need for anything more.

[Joe L.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

I pulled my heads off because I have to get my valve guides replaced. They have .004 - .005" play. I am a rookie/newb and want to get these heads rebuilt so that they last a long time. I do not want to hot rod these, more like repair them and use any modern technology that makes sense. My car is a NOM 71 LT-1 with 49k miles.

Took my heads to two different shops today and got two different methods of repair. Now I am confused and could use/appreciate some advice.

Shop #1 - machine shop servicing many local repair shops
pressure test heads to look for cracks
replace all guides with new guides, not a thin sleeve
cut top of guide so a seal can be attached to it
replace all exhaust valves
Insert new exhaust valve seats - said this was needed to run unleaded (i already do)???
cut both valve and seat to match
check all spring pressures and heights - replace whats needed
NOT replacing intake valves
.010 cut across the bottom of the head to true the surface
clean & paint
price: $860
reco'd a thick fel pro that would lower compression.


Shop #2 - Guy builds race motors - full shop in his garage.
Drill guides and put in thin bronze sleeve
replace all valve, intake and exhaust
replace all springs
grind valve seats to match valves - without inserting new material/seats
no milling/cutting of the base
clean
price: $375

My confusion is the valve seats. Why is shop #1 putting a new valve seat in when shop #2 is grinding the valve seat? I was under the impression these heads didn't require leaded fuel. Is one of these guys overlooking something or wrong? Shop #1 warned me several times that when replacing the valve seat that he "could hit water and ruin the head". He said it rarely happens, but it is a possibility due to how the head was cast, that there could be a sand pocket......

casting # on heads - 3973487

Would like to know your opinions

Dan-----


I would not recommend installing new exhaust valve seats. You don't need them.

I prefer thick wall valve guides over the thin wall type.

I do not understand how shop #2 can do the work for $375 if they replace all the valves and valve springs. They must be using pretty cheap parts.

[William P.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

# 1 is giving you the complete head rebuild , # 2 is repairing your head . If you can afford it , go for #1 , less the re-surface unless it is absolutley necessary .

Bill

[Patrick H.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

I agree with Joe. Don't have valve seats (inserts) installed unless you have significant valve seat recession and it's the only way to fix it.
At 49k miles, I doubt this is your problem.

Patrick

[Dan H.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Can I install new valves without installing new seats? Can the seats that are in there be machined to match the new valves?

I don't want to say money is no object when talking to these shops, but the cost isn't a factor. I just don't want to be taken advantage of. I'm not opposed to spending 800-1000 to get this done correct.

[Timothy B.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Dan,

IMO, I don't think the bronze thin wall valve guides will cause any problems, these things are installed using a pilot drill bit that centers inside the original guide so everything stays lined with the original valve seat. The bronze guides I have seen are approx .404 OD and .375 ID and are reamed after installation for valve clearance.

You can install new valves using the original seats and after seating the valve pay attention to the valve stem height as this affects rocker geometry. Use all OEM specs and it will be fine, your shop should have these measurments.

[William C.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Take shop # 2

[Terry M.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Unless there is something wrong with your exhaust valves (unlikely with that mileage unless it was 1/4 mile at a time) you do not need new exhaust valves. Shop 1 is recommending that because with the new thick wall valve guides one loses the center of the valve in relation to the seats, but then he should replace the intakes as well.

Hardened valve seats are not necessary unless there is already significant valve seat recession (As Joe said, unlikely at your mileage.) or you intend to tow heavy trailers with your Corvette. They are just a way for the machine shop to run up your bill needlessly. They are as useless as corn alcohol in our gasoline, but that is another story.

Shop 2 sounds like they know what they are doing. If you feel confident in them after your conversation with them -- go for that.

[Edward J.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Dan, along with all the advise given, Did the machine shops give you this advise after they had disassy'd the heads? sometimes the guides may not even be worn, with a new set of valves everything tightens up with the new valve stems.Since the valve stems are the easiest part to check and commonly wear with years and miles also.

Shop 1 did give some good advise on cutting the top of the guides to acceppt the umbrella type seals which is a must have to keep the oil from running down the guides, this is a common problem with small block chevys.( smoke on start-up).

I am a believer of do it right the first time and spend the money needed to do a job correctly , you'll know this once you have been bitten. On the other hand I would put the job in the hands you trust. get some referels from some of the repair shops locally and even some of the parts stores.
good luck,Ed

[Edward C.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

If the engine is NOM the heads may not have the hardeded seats. Ed

[Joe L.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

If the engine is NOM the heads may not have the hardeded seats. Ed

Ed------


The GM #3973487 cylinder head (including later SERVICE heads of this casting number) did not have hardened valve seats. Although all 1971 and later engines were designed to operate on unleaded fuel, hardened valve seats did not begin until the 1973 model year (or, possibly, very late in the 1972 model year for some applications).

[Dan H.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

I appreciate everyones feedback. You've given me a lot to think about and a ton of useful information. It is very much appreciated

[Clem Z.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

Ed------


The GM #3973487 cylinder head (including later SERVICE heads of this casting number) did not have hardened valve seats. Although all 1971 and later engines were designed to operate on unleaded fuel, hardened valve seats did not begin until the 1973 model year (or, possibly, very late in the 1972 model year for some applications).

unleaded gasoline was not mandated till 1975 when cat convertors came out. 70 big block heads had induction hardened valve seats.

[Larry M.]

Re: Machine shop advice - 71 LT-1 rebuilding heads

In April, 1988 I bought two service heads PN 464045 for our '72 LT-1. The listed applcation was for 1971-1979 LT-1 and L-82 engines. I recall a label on the boxes that each head was packaged in, and my strong recollection was that the label stated that the heads were manufactured with hardened seats to operate safely on low/no-lead fuel.

Larry