moper
Well-Known Member
I thought I'd stick this up here. I've had to change the shop I source most of my machine work to due to unforeseen events. It got me thinking while I was looking at places..Why go thru the trouble? Cant anyone do this work? I see a lot on various sites that most people have trouble seeing what is "good" or "right" in terms of automotive machining. These are pics from two different big block heads. I am friends with both machinists. One is leaving the business, one has a brisk business in central CT. This head is cracked from just being real old and possibly from freezing. I am replacing it for a customer with a core head I have done similarly. The following are examples of what not to want to see. The head that cracked is off a rebuilt and running 383 Road Runner, that has run a best of 13.97 with mild bolt ons and an engine rebuilt by "Shop 1". It has, from what I can gather, about 5000 miles since a complete "good" performance rebuild, which included unleaded seats, guides, new exh valves, and Comp springs for the XE268 cam. I'll stay with just head work for this thread.
First pic is the chamber showing the exh bowl area, and the huge step left by installing the unleaded seat without "fixing" the bowl. This is fine for your John Deere or flathead. It has no place in a modern performance engine.
Second pic is an intake valve bowl/seat. You can see it had a 3 angle valve job. However, see the edge hanging down from the guide boss? That's the new liner that was not installed squarely. That's a sign the hole wasnt the right size when they pressed in the liner. Also note you can see how much oil was getting past the new guide. Not a good result.
Third is a close up of that same stepped exh bowl. Here (sorry its blurry) you can see the one angle they cut on the new seat. Should be 3 if you paid for 3 angle, right? Youcan really see how bad the short turn gets as a result of the improper installation here too.
Fourth is an intake valve. You can see from the stem finish it was run thru a tumbler to clean it. That's a no no. It mars the surface, so the seal and guide cant control oil. It also weakens the stems with the nicks it creates. Also note the oil coaked up on the back side. All that does is fowl plugs and lower octane.
Last...Here's a true performance job, on a similar head. The correct seat rings installed properly, 5 angles, made using a straight pilot and cutters. Correctly installed guide liners, proper seat widths and placement for intake and exhaust (they are not the same...), basic unshrouding of the chamber walls and a cut that does 90% of the bowl hogging and blending for you. This is performance work. Know what you are looking at. Make sure your shop is capable of doing what they charge you for. These jobs cost within $300 of each other. So now you know....
First pic is the chamber showing the exh bowl area, and the huge step left by installing the unleaded seat without "fixing" the bowl. This is fine for your John Deere or flathead. It has no place in a modern performance engine.
Second pic is an intake valve bowl/seat. You can see it had a 3 angle valve job. However, see the edge hanging down from the guide boss? That's the new liner that was not installed squarely. That's a sign the hole wasnt the right size when they pressed in the liner. Also note you can see how much oil was getting past the new guide. Not a good result.
Third is a close up of that same stepped exh bowl. Here (sorry its blurry) you can see the one angle they cut on the new seat. Should be 3 if you paid for 3 angle, right? Youcan really see how bad the short turn gets as a result of the improper installation here too.
Fourth is an intake valve. You can see from the stem finish it was run thru a tumbler to clean it. That's a no no. It mars the surface, so the seal and guide cant control oil. It also weakens the stems with the nicks it creates. Also note the oil coaked up on the back side. All that does is fowl plugs and lower octane.
Last...Here's a true performance job, on a similar head. The correct seat rings installed properly, 5 angles, made using a straight pilot and cutters. Correctly installed guide liners, proper seat widths and placement for intake and exhaust (they are not the same...), basic unshrouding of the chamber walls and a cut that does 90% of the bowl hogging and blending for you. This is performance work. Know what you are looking at. Make sure your shop is capable of doing what they charge you for. These jobs cost within $300 of each other. So now you know....
