462624 Heads - Stick with them, or move on?

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Hi Duke,

Thanks for the information and taking time to point me in the right direction. Here are the answers to your questions in the order asked:

1. L48
2. Automatic
3. I run 93 Octane in all of my vehicles.
4. I do not plan to have it judged.
5. Being a 1978 it should be exempt from emissions testing in Massachusetts.
6. I do not have a chassis service manual and chassis overhaul manual for '78. I do have the Technical Information and Judging Guide.
7. I have downloaded copies of your two articles and will dive into them in the near future.

Thanks again. Love the red SWC by the way.

Regards,
Mike

[Duke W.]

Re: 462624 Heads - Stick with them, or move on?

Your L-48 was designed to operate on 91 RON unleaded fuel (similar anti-knock properties to current 87 PON unleaded fuel) and shouldn't need 93 PON. Even though you don't plan on judging, I would recommend keeping it close to OE without major modifications. A set of smaller chamber heads will cause a useful increase in compression and the OE inlet manifold and Q-jet are fine. The important part will be finding smaller chamber heads that have all the bosses/tapped holes for accessory mounting, temperature sensors, etc.

Aluminum heads will require a composition gasket, which is thicker than the OE shim gasket, which will offset the increase in compression due to smaller chambers. Cast iron heads can be installed with the thin OE shim gasket as long as the surfaces are flat. I believe the OE shim gasket is .015" thick and assuming yours are OE can you measure them?

Once the heads are off you can measure for bore taper and make a determination if the block needs to be rebuilt. BTW, how many miles does it have? If the bores are in good condition the only thing I would recommend is replacing the timing chain set. An OE replacement only costs about 25 bucks. I think your engine should have a cast iron cam sprocket, but if it has one with the nylon teeth, DEFINITELY replace it.

Your engine is basically a stroked version of the 327/300 with lower compression to run on regular unleaded fuel. It would be a good candidate to convert to a Special 300 HP configuration with massaged heads, McCagh Special camshaft,t and at least 10:1 compression, but there is one major issue that must be "corrected" if you're interested in going this route, and that is the exhaust system.

The single bead bed catalyst exhaust system has WAAAAAY too much backpressure to significantly increase top end power no matter what you do inside the engine, so don't bother with any internal modifications other than optimizing the spark advance map unless you're willing to convert to a full dual exhaust system.

A neighbor has a '77 L-48/automatic Coupe, all stock with about 150K miles. It's had a lot of issues that I've helped him with brakes and the rear axle, but the engine appears to be sound, and it passes California field emission testing. In normal driving it's torquey and responsive... not a top end screamer, but he just likes to cruise around the beach in it and go to cars and coffee meets. He's the second owner, but bought it decades ago when it was only a few years old.

Duke

[Joe L.]

Re: 462624 Heads - Stick with them, or move on?

Your L-48 was designed to operate on 91 RON unleaded fuel (similar anti-knock properties to current 87 PON unleaded fuel) and shouldn't need 93 PON. Even though you don't plan on judging, I would recommend keeping it close to OE without major modifications. A set of smaller chamber heads will cause a useful increase in compression and the OE inlet manifold and Q-jet are fine. The important part will be finding smaller chamber heads that have all the bosses/tapped holes for accessory mounting, temperature sensors, etc.

Aluminum heads will require a composition gasket, which is thicker than the OE shim gasket, which will offset the increase in compression due to smaller chambers. Cast iron heads can be installed with the thin OE shim gasket as long as the surfaces are flat. I believe the OE shim gasket is .015" thick and assuming yours are OE can you measure them?

Once the heads are off you can measure for bore taper and make a determination if the block needs to be rebuilt. BTW, how many miles does it have? If the bores are in good condition the only thing I would recommend is replacing the timing chain set. An OE replacement only costs about 25 bucks. I think your engine should have a cast iron cam sprocket, but if it has one with the nylon teeth, DEFINITELY replace it.

Your engine is basically a stroked version of the 327/300 with lower compression to run on regular unleaded fuel. It would be a good candidate to convert to a Special 300 HP configuration with massaged heads, McCagh Special camshaft,t and at least 10:1 compression, but there is one major issue that must be "corrected" if you're interested in going this route, and that is the exhaust system.

The single bead bed catalyst exhaust system has WAAAAAY too much backpressure to significantly increase top end power no matter what you do inside the engine, so don't bother with any internal modifications other than optimizing the spark advance map unless you're willing to convert to a full dual exhaust system.

A neighbor has a '77 L-48/automatic Coupe, all stock with about 150K miles. It's had a lot of issues that I've helped him with brakes and the rear axle, but the engine appears to be sound, and it passes California field emission testing. In normal driving it's torquey and responsive... not a top end screamer, but he just likes to cruise around the beach in it and go to cars and coffee meets. He's the second owner, but bought it decades ago when it was only a few years old.

Duke

Duke-------


I can virtually guarantee that the engine will have a nylon-toothed cam sprocket. I've never seen a 1966 or later PRODUCTION small block that did not come with a nylon-toothed sprocket. In SERVICE, GM discontinued the nylon sprocket MANY years ago and replaced it with a cast iron piece. I suppose they want an engine used in PRODUCTION to be as quiet as possible. In SERVICE quietness is not so important as the vehicle is already sold by then. Even SERVICE long blocks were supplied with nylon-toothed sprockets.

ALL PRODUCTION big blocks used in cars or light trucks had nylon-toothed cam sprockets; no exceptions.

Nylon-toothed cam sprockets are actually hard to find if one happens to want to use one. Many years ago I purchased about 20 each of all variants of the nylon-toothed sprockets directly from Cloyes. Why did I do this? I have no idea as I'd never use one. However, I think it was because they were so hard to find, when I finally found a way to get them I went "whole-hog". There were 4 variants-----small block wide, small block narrow, big block wide, and big block narrow.

[Duke W.]

Re: 462624 Heads - Stick with them, or move on?

I thought that at some point later in Gen 1 SB production that GM went back to a cast iron cam sprocket.

In any event I always recommend the OE replacement truck roller chain. I believe it's actually manufactured by Cloyes and costs about 25 bucks for the set.

Duke

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

I couldn't agree more. I'm a big "stock" fan. So I definitely want to keep it as close to stock as possible and I wouldn't even be considering changing out the heads if it wasn't for the fact that I have to address the crack in one of them, and I have read many horror stories about the heads I currently have. So regarding the block, I purchased the car 4 years ago with 11,000 miles on it. Yes, I know 11,000 or 111,000 how can I be sure? I am the third owner. The guy I purchased it from bought it from the original owner and was just flipping it to make a few bucks. I have spoken to the original owner, who owes me nothing, and had no logical reason to lie to me, especially since it was obvious that he didn't really care for the guy he sold it to. He assured me that the car only has 11,000 miles on it. It looks like a hard 11K but that's because he lost his indoor storage 4 years earlier and had it sitting in his driveway with a tarp over it. So the frame has some surface rust, no rot, the body will need a paint job, the birdcage, floor boards, pillars, window frame etc. are like new, and all of the components appear to be original including the exhaust system and tires that look new that have 20 year old date codes. So I'm inclined to believe the mileage. So back to the block. I'm no expert but the cylinder walls look great. I did do compression and leak down tests before pulling the engine and everything looked really good. The engine ran great, very tight and responsive. So I think other than new seals and gaskets, addressing the head issue, and now maybe the timing chain, I should be fine. If you could point me to information regarding the bore taper measurement you mentioned I would be interested in doing that as well. I'm pretty much in line with your neighbor. Just looking for a nice cruiser with this one. Will likely be in the market for a C2 next year, and have a couple of Harley's, boats, and jet skis to satisfy the speed addiction for now. Once Again.... Thank you for the excellent information and hospitality here on the site. I should have joined years ago. - Mike

[Joe L.]

Re: 462624 Heads - Stick with them, or move on?

I couldn't agree more. I'm a big "stock" fan. So I definitely want to keep it as close to stock as possible and I wouldn't even be considering changing out the heads if it wasn't for the fact that I have to address the crack in one of them, and I have read many horror stories about the heads I currently have. So regarding the block, I purchased the car 4 years ago with 11,000 miles on it. Yes, I know 11,000 or 111,000 how can I be sure? I am the third owner. The guy I purchased it from bought it from the original owner and was just flipping it to make a few bucks. I have spoken to the original owner, who owes me nothing, and had no logical reason to lie to me, especially since it was obvious that he didn't really care for the guy he sold it to. He assured me that the car only has 11,000 miles on it. It looks like a hard 11K but that's because he lost his indoor storage 4 years earlier and had it sitting in his driveway with a tarp over it. So the frame has some surface rust, no rot, the body will need a paint job, the birdcage, floor boards, pillars, window frame etc. are like new, and all of the components appear to be original including the exhaust system and tires that look new that have 20 year old date codes. So I'm inclined to believe the mileage. So back to the block. I'm no expert but the cylinder walls look great. I did do compression and leak down tests before pulling the engine and everything looked really good. The engine ran great, very tight and responsive. So I think other than new seals and gaskets, addressing the head issue, and now maybe the timing chain, I should be fine. If you could point me to information regarding the bore taper measurement you mentioned I would be interested in doing that as well. I'm pretty much in line with your neighbor. Just looking for a nice cruiser with this one. Will likely be in the market for a C2 next year, and have a couple of Harley's, boats, and jet skis to satisfy the speed addiction for now. Once Again.... Thank you for the excellent information and hospitality here on the site. I should have joined years ago. - Mike

Mike------


If you wish to go stock and are willing to use the 462624 heads, here's an answer:

https://www.ebay.com/itm/NOS-1974-84-Chevrolet-350-5-7L-SBC-Engine-Head-Corvette-Camaro-Truck-GM-464036/153569939655?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Dc8151918ab3a401ebfc9c0995cc7d21d%26pid%3D100675%26rk%3D12%26rkt%3D15%26mehot%3Dnone%26sd%3D253635167574%26itm%3D153569939655%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Ab9862011-666f-11eb-b910-5a8a8d25222c%7Cparentrq%3A6a06b4ed1770ada186e03f3cfff32062%7Ciid%3A1

Another option: if the cracked rocker stud boss is your primary concern, depending on how extensive the crack is, you might be able to have the boss machined down and a threaded stud installed. In fact, I HIGHLY recommend replacing all of the studs with threaded studs. I would use the flanged type that require the stud bosses to be machined down. If the crack only extends the length of the boss that needs to be machined away, your crack problem is fixed.

I've always thought that pressed in studs were a dumb idea.

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Joe,

I clicked on that link but it brought me to a 464036 head rather than a 462624. Are they equivalent?

I went back and forth with the decision to go with pressed in vs. threaded studs. Here again I figured go stock if possible. A buddy who owns a machine shop let me borrow the tools so I decided to go ahead with the pressed in version. Thus only having to replace one stud rather than all of them. And, well you already know the rest of may sad story. I will investigate the extent of the crack. But I expect its a bit more then just the top surface of the boss.

Thanks,
Mike

[Tom P.]

Re: 462624 Heads - Stick with them, or move on?

I scan the discussion topics occasionally, but rarly participate.
But your concern about 624 heads got my attention.
In 50+yrs of building engines (MOSTLY small blocks), here is what I have observed, as well as observations from my machinist.
The LAST year for a GOOD production small block head was 1974. After production of 74 model year SB engines, the amount of metal in a typical SB head was reduced-----------------AND WORST OF ALL, a second exhaust cross over passage was added in the center of the head----------------MORE HEAT, GREATER TENDENCY FOR CRACKS TO OCCUR!!! Just for the heck of it, I placed some 76-78 variety SB heads on the bathroom scales and then some late 60s-very early 70s heads on the scales. The later 70s heads were about 3lbs lighter. Thus, they saved 6lbs per car and sacrificed what had been a good, long lasting head!
Thus, when I build a SB engine, it either gets nothing but 74-earlier heads, OR, aftermarket heads, such as DART for example.

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Tom,

Thanks for taking the time to bring your experience and perspective to the discussion. Great information and much appreciated.

Mike

[Joe L.]

Re: 462624 Heads - Stick with them, or move on?

Joe,

I clicked on that link but it brought me to a 464036 head rather than a 462624. Are they equivalent?

I went back and forth with the decision to go with pressed in vs. threaded studs. Here again I figured go stock if possible. A buddy who owns a machine shop let me borrow the tools so I decided to go ahead with the pressed in version. Thus only having to replace one stud rather than all of them. And, well you already know the rest of may sad story. I will investigate the extent of the crack. But I expect its a bit more then just the top surface of the boss.

Thanks,
Mike

Mike------


GM #464036 is the finished part number for the L-48 head using the 462624 casting. Cylinder head casting numbers are rarely, if ever, the same as part numbers. Part of the reason is that more than one finished part number may be manufactured from the same casting. That's the case here, too. The L-82 head using the 462624 casting was GM #464045.

If you zoom in on the ebay head I linked you will note that it is a 462624 casting.

As far as the machining of the stud boss goes, in order to install the flanged base threaded studs the boss has to be machined down by a large amount. In fact, all of the stud boss through which the pressed-in stud contacts. It's very likely that the crack will be eliminated after this machining.

Originality is fine. However, for valve rocker studs I would gladly deviate. There's just no point in going that far with originality. If you are ever 500 miles from home and have a rocker stud failure, you'll appreciate the merits of the threaded studs. As a matter of fact, the L-82 version of the 462624 casting is factory machined for threaded studs.

[Duke W.]

Re: 462624 Heads - Stick with them, or move on?

With only 11K miles doubt if the block has any measureable taper, so it should be good to go with a proper cast iron cam sprocket timing chain set and gaskets/seals.

Mike, I think you should consider Joe's idea. Can you post a good photo(s) of the crack? Maybe just machining them for screw in studs is the way to go, and just lap in the valves and assemble with new valve stem seals as the originals are probably deteriorated from old age, and install the heads with the .015" Felpro 1094 shim gasket.

Even with a more aggressive/optimized spark advance map it should run detonation free on 87 or 89 PON fuel.

Duke

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Okay. Here's a picture of the crack. I just brought the head outside to get more light on it, so hopefully you can get a sense of what I have here. IMG_9952.jpg

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Ahh. That makes perfect sense Joe. Thanks!

If I'm reading it correctly it looks like it even has a 78 date code.

This is very tempting as it's a quick way to get me back to where I was before the crack.

Mike

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Duke,

Where can I get copies of the chassis service manual and chassis overhaul manual that you mentioned in an earlier post. I have looked on line there are a few different versions. I'm sure you know which one is best, and where to purchase it.

Thank you,
Mike

[Mike H.]

Re: 462624 Heads - Stick with them, or move on?

Joe,

What are you referencing for the original GM Part Numbers? I have been unable to locate anything on-line. I would like to get my hands on a copy of whatever it is that you have. I think it would be quite useful.

Thank you,
Mike