MaxPF
1/2 ton status
I had a bad experience with a set of aftermarket heads. Unfortunately, it turns out the vendor isn't any better quality than their products 
First, let's have some show and tell. Here's one of the aftermarket heads next to a somewhat rusty GM head:
I threw them on a scale to see if there really is more metal in the aftermarket casting. First the GM head:
Now the aftermarket casting:
The aftermarket casting is 5lbs heavier than the GM head (I sat 4 precups on top of the GM head since it doesn't have any installed). However, a close examination reveals that all the extra mass is on the exterior of the casting. The deck is approximately the same thickness as the GM head, as are the internal passage walls.
The valve job isn't too bad either:
One intake seat is scratched, and would need to be touched with a seat stone to clean it up. You can alse see the induction hardening discoloration around the ports in that pic.
I popped a set of valves in to check out the fit:
The guides felt OK, and the seats appeared to be concentric with the guides. Not surprising since it is probably all done with one combination cutter. I should also note that the marks you see on the precup were caused by the brass rod I used to drive it in after I removed it. The material these cups are made of is very soft compared to the GM cups
Here's a pic of the precup:
If you put a magnet to a GM cup you will find the material is completely non-magnetic:
The aftermarket cups, OTOH, were as magnetic as the cast iron heads:
I have a fairly good knowledge of metallurgy, and off the top of my head I don't recall any alloys suitable for this type of high-temp service that are magnetic. There may be some that are weakly magnetic, but I don't recall any. This says to me that these cups are, at best, a ferritic or martensic stainless. Not the best material for a part that runs at a sustained 1000+ degrees in an environment that alternates between oxidizing and carburizing while being subjected to steep pressure spikes. Maybe I am wrong, but I am not going to test them in MY engine.
It gets worse. I had a machinist friend check out the fit of the cups and their bores in the heads. When I removed the one cup I found metal shavings on the seat that the cups bottom against. After measuring the diameter of the aftermarket cup, the GM cup, and the bore, he found that the aftermarket cup was .002" too big. It also had no chamfer on the seat side like the GM cup has. Apparently, when driven in the cups (even as soft as they are, they are harder than the cast iron) broach material off the substantially smaller bore. This material has nowhere to go, so it gets trapped under the cup's seat. Once I removed the cup and wiped away the shavings I could no longer get the cup to sit flush and level. The head was surfaced with the cup sitting in the bore at a slight angle atop some shavings, and this showed up when I measured the cup's seat at 4 points:
Yup, one side is .022" higher than the other. The bores have an even depth all the way around (within a thou or two), so in order for this head to be servicable it would need at least one or more new precups (depending on how many are like this one) and then resurfaced. Figure $200 just to make this one head useable I'm sure the other head isn't any better...
Now to add injury to insult: I ordered these heads from Clearwater Cylinder head after reading the favorable things folks on other forums had to say about them. Well, they basically said "What do you expect for that kind of money?". They agreed to take them back, but I would have to pay to ship them back ($75, minimum), lose the freight I paid to have them shipped to me, AND I would have to pay a 20% restocking fee. All told I would be out $225. Judging by their attitude I have no doubt they would refuse to take back the head with the now-ill-fitting precup in it, so basically I am SOL. I didn't expect AMG heads, but I DID expect the machining and assembly to be basically correct and the heads to be serviceable without worrying that an ill-fitting precup will shift on it's seat of debris and cause the loss of a $120 Cometic head gasket. I didn't want to worry that a precup of possibly inferior mettalurgy may crack apart and drop into the cylinder during operation, which is what occasionally happens with the Toyota 4-cyl IDI's.
Anyway, there you have it. I am now the proud owner of a pair of cast iron doorstops. The worst part is that I KNEW BETTER!!! I should have went with what experience has taught me, despite the good reviews from well-meaning individuals. I have seen too much garbage like these heads to have any faith in these Chinese replacement parts.
Folks, if you have cracked heads, Lock'n'stitch works. Have a pair of seats put in, surface the head, do a valve job, and keep running your GM heads. You will be better off in the long run. If you really want new heads, pony up the $1000 for a pair of fully assembled AMG heads. Yes, it is twice what I paid for these bare Chinese castings, but it is only $350 more than the Chinese heads assembled with reconditioned parts, and you get all new stuff. The only reason I didn't go that route is because I already have new valves and springs which are higher quality than the OEM AMG stuff, so I wanted a bare head, AMG doesn't sell them bare, which is why I decided to try this route. I got burned, and now I will be repairing the small crack in my GM heads and using them anyway. $550 is an expensive lesson...
First, let's have some show and tell. Here's one of the aftermarket heads next to a somewhat rusty GM head:
I threw them on a scale to see if there really is more metal in the aftermarket casting. First the GM head:
Now the aftermarket casting:
The aftermarket casting is 5lbs heavier than the GM head (I sat 4 precups on top of the GM head since it doesn't have any installed). However, a close examination reveals that all the extra mass is on the exterior of the casting. The deck is approximately the same thickness as the GM head, as are the internal passage walls.
The valve job isn't too bad either:
One intake seat is scratched, and would need to be touched with a seat stone to clean it up. You can alse see the induction hardening discoloration around the ports in that pic.
I popped a set of valves in to check out the fit:
The guides felt OK, and the seats appeared to be concentric with the guides. Not surprising since it is probably all done with one combination cutter. I should also note that the marks you see on the precup were caused by the brass rod I used to drive it in after I removed it. The material these cups are made of is very soft compared to the GM cups
Here's a pic of the precup:
If you put a magnet to a GM cup you will find the material is completely non-magnetic:
The aftermarket cups, OTOH, were as magnetic as the cast iron heads:
I have a fairly good knowledge of metallurgy, and off the top of my head I don't recall any alloys suitable for this type of high-temp service that are magnetic. There may be some that are weakly magnetic, but I don't recall any. This says to me that these cups are, at best, a ferritic or martensic stainless. Not the best material for a part that runs at a sustained 1000+ degrees in an environment that alternates between oxidizing and carburizing while being subjected to steep pressure spikes. Maybe I am wrong, but I am not going to test them in MY engine.
It gets worse. I had a machinist friend check out the fit of the cups and their bores in the heads. When I removed the one cup I found metal shavings on the seat that the cups bottom against. After measuring the diameter of the aftermarket cup, the GM cup, and the bore, he found that the aftermarket cup was .002" too big. It also had no chamfer on the seat side like the GM cup has. Apparently, when driven in the cups (even as soft as they are, they are harder than the cast iron) broach material off the substantially smaller bore. This material has nowhere to go, so it gets trapped under the cup's seat. Once I removed the cup and wiped away the shavings I could no longer get the cup to sit flush and level. The head was surfaced with the cup sitting in the bore at a slight angle atop some shavings, and this showed up when I measured the cup's seat at 4 points:
Yup, one side is .022" higher than the other. The bores have an even depth all the way around (within a thou or two), so in order for this head to be servicable it would need at least one or more new precups (depending on how many are like this one) and then resurfaced. Figure $200 just to make this one head useable
I'm sure the other head isn't any better...Now to add injury to insult: I ordered these heads from Clearwater Cylinder head after reading the favorable things folks on other forums had to say about them. Well, they basically said "What do you expect for that kind of money?". They agreed to take them back, but I would have to pay to ship them back ($75, minimum), lose the freight I paid to have them shipped to me, AND I would have to pay a 20% restocking fee. All told I would be out $225. Judging by their attitude I have no doubt they would refuse to take back the head with the now-ill-fitting precup in it, so basically I am SOL. I didn't expect AMG heads, but I DID expect the machining and assembly to be basically correct and the heads to be serviceable without worrying that an ill-fitting precup will shift on it's seat of debris and cause the loss of a $120 Cometic head gasket. I didn't want to worry that a precup of possibly inferior mettalurgy may crack apart and drop into the cylinder during operation, which is what occasionally happens with the Toyota 4-cyl IDI's.
Anyway, there you have it. I am now the proud owner of a pair of cast iron doorstops. The worst part is that I KNEW BETTER!!! I should have went with what experience has taught me, despite the good reviews from well-meaning individuals. I have seen too much garbage like these heads to have any faith in these Chinese replacement parts.
Folks, if you have cracked heads, Lock'n'stitch works. Have a pair of seats put in, surface the head, do a valve job, and keep running your GM heads. You will be better off in the long run. If you really want new heads, pony up the $1000 for a pair of fully assembled AMG heads. Yes, it is twice what I paid for these bare Chinese castings, but it is only $350 more than the Chinese heads assembled with reconditioned parts, and you get all new stuff. The only reason I didn't go that route is because I already have new valves and springs which are higher quality than the OEM AMG stuff, so I wanted a bare head, AMG doesn't sell them bare, which is why I decided to try this route. I got burned, and now I will be repairing the small crack in my GM heads and using them anyway. $550 is an expensive lesson...
