To grind or not to grind...

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gradymotorco

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I'm getting ready to do a Head Gasket replacement on my '75 Corvette, and I'm trying to figure out whether or not I should have the heads done. It has 155k on it, was last rebuilt at around 100k. I really do not want to do a rebuild on the bottom end right now, and before the HG went out, the engine seemed tight. My dilemma is, I've heard several old timers say that having a valve grind done without rebuilding the bottom end is asking for trouble, since compression will be higher with the refurbished heads than before. Is there any truth to this? The engine is a 350 SBC which is basically stock.

Thanks!
 
Depends on what was done to the heads during the last rebuild.

If the heads were done with new bronze guides/valves and they are still tight, run as is. If they are still stock iron guides/stock valves I would have them checked/fixed. Regardless I would pull the valves to ck for cracks between the intake and exhaust seat while the heads were off.
 
I don't see any problem with re-doing the top end and leaving the bottom end, provided the bottom end is in good shape.

I did a full top end (new heads, cam, etc) on my Jeep at 119k miles. The bottom end is completely stock and untouched. It still had cross-hatching on the cylinders when I had the heads off, as well as good compression, so I wasn't concerned at all. 7500 miles later, it's running great with no issues or excessive blowby.
 
Well I intended to take it to the machine shop to be checked for cracks and put a new set of valve stem seals in; but I just don't want to cause there to be more trouble than I already have by trying to fix something that isn't broken.
 
If you have accumulated quite a bit of mileage on your lower block (e.g. cylinder walls, piston rings, etc.) then it's better not to touch the valve/valve seats if head gasket is all that you want to do...

Otherwise, if you just do the top end (valve grind, valve-seat refacing, etc.) w/o touching the bottom end, you'll ended up with an oil burning issue due to "tighter" upper end (valve seats now seal properly, but the vacuum is now pulling oil from the lower end into your combustion chamber).

Q.
 
Honestly...I would use the stock heads as doorstops and get a pair of L31 Vortecs. They are much better than ANY other factory casting, a pair will run about $600 from Scoggin-Dickey (first place I checked, you might find them cheaper)...it is tough to get old heads reconditioned for less than that.

Also, the mid-70's heads tended to crack, especially if overheated.
 
As far as the oil burning thing, I saw the opposite. I've dropped from burning a 1/2 quart in 6k miles to just over an 1/8th of a quart in 6k miles. And the last 6k included a good bit more long-distance highway running than normal (that's the only time I've seen the level drop). I'm pretty sure having new valve stem seals, etc, helped out a good bit.
 
Originally Posted By: Jarlaxle
Honestly...I would use the stock heads as doorstops and get a pair of L31 Vortecs. They are much better than ANY other factory casting, a pair will run about $600 from Scoggin-Dickey (first place I checked, you might find them cheaper)...it is tough to get old heads reconditioned for less than that.

Also, the mid-70's heads tended to crack, especially if overheated.


That may be true, but Vortec heads require a different kind of intake manifold than what earlier versions of the SBC used. Also, the Vortec head used center bolt valve covers instead of side bolted ones, so new valve covers would be needed too.

The other problem is that the car might need to be numbers matching if it has any collector's value.

If you don't mind buying non matching heads, maybe you could buy some Dart or AFR cylinder heads, or something like that. There you have the option of keeping your intake manifold, valve covers, and still have a superior product at a decent price.
 
If the valves aren't leaking now there will be no increase in compression when reinstalled, if valves are leaking the heads should be rebuilt, simple... As for the 55K miles since the last rebuild that's nothing, if it had 155K and not rebuilt then I'd say it was time to go through the engine fully...
 
Well I do want to stick to the stock heads, because its a numbers matching car, and although I don't ever see myself selling it, (my dad bought it in '87 and its been in the family ever since), if I did that would be a plus. So I guess I'll just make sure the block and heads are indeed straight, and then bolt her back together. I'm planing to use the composition (blue) Fel-Pro head gaskets, along with new head bolts, and of course replacing all the other gaskets that get pulled off along the way.
 
Before disassembly the OP just needs a few minutes with a vacuum gauge and a compression tester to determine whether or not the bottom end or the top needs service.

Personally, if I'm removing the heads already I'd go through the whole engine. NOTHING wrong with those stock heads, have them machined by a good shop and even ported a bit, then port match everything when you reinstall them.

Keep it original. Just another opinion.
 
Originally Posted By: punisher
Depends on what was done to the heads during the last rebuild.

If the heads were done with new bronze guides/valves and they are still tight, run as is. If they are still stock iron guides/stock valves I would have them checked/fixed. Regardless I would pull the valves to ck for cracks between the intake and exhaust seat while the heads were off.


+1 These cracks have led to the demise of many SB Chev heads including V6 versions. BTW a '74 exhaust will bolt right on, true duals and no cats. IIRC '75 was the last year for the fiberglass floor pans. Went to steel in '76 due to heat from converter cooking the polyester resin out.
 
Originally Posted By: SteveSRT8
Before disassembly the OP just needs a few minutes with a vacuum gauge and a compression tester to determine whether or not the bottom end or the top needs service.

Personally, if I'm removing the heads already I'd go through the whole engine. NOTHING wrong with those stock heads, have them machined by a good shop and even ported a bit, then port match everything when you reinstall them.

Keep it original. Just another opinion.


Nothing wrong with them...except that they are poor-flowing, crack-prone doorstops.
 
Quote:
75 would have hardened seats from the factory.

What year did that happen?
In Germany for the most part only the cars for export had hardened seat even in 86, very few had them for the domestic market, only the seldom G Cat equipped models had them and they were hard to find non leaded fuel for.
 
It is good advice to have the heads looked at/inspected by someone you trust. And maybe more than one source!
Don't tell them the miles that are on them. Let the parts speak for themselves.
 
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