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| | | | Joined: Aug 2015 Posts: 17 'Bolter | | 'Bolter Joined: Aug 2015 Posts: 17 | Somewhere, I read a thread which I can't find now, that stated if you mill .100 inch off a 3836850 head from a 261 and recess the valve the same amount, you would have the same thing as the most desirable "848" head. Can anybody verify or has anybody ever milled a head this much? I'm building a 261 and I have not been able to find a usable 848 head. My machine shop is skeptical of cutting a head down this much. Your help, opinions, and or insight will be greatly appreciated | | | | | Joined: Feb 2004 Posts: 29,869 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,869 | Yes, it can be done, and was one of the ways hotrodders tried to improve performance before the 848 head came along. Recessing the valves is an absolute must, as is putting shims between the rocker arm stands and the head to restore the proper geometry on the rockers and prevent the pushrods from being so long you run out of adjustment. Since the exhaust rockers and valve stems are at an oddball angle, there might be some geometry problems there that simply shimming can't correct.
It sounds like your "machinist" might not be qualified to analyze and correct all the problems the milling job might create, so it's going to be up to you to make it work.
Measure everything, and don't assume anything is going to work right without checking it, repeatedly.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2007 Posts: 210 Shop Shark | | Shop Shark Joined: Dec 2007 Posts: 210 | I have a head on mine that I had cut .100" and sunk the exhaust valves the same. It is on a 235 with solid lifters.They seem to adjust without any problem. I have turned the engine by hand but am not far enough along with the truck to start the engine yet. I agree with what Hotrod said. | | | | | Joined: Feb 2004 Posts: 29,869 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,869 | One of the tricks I used to use on the claimer engines I built for the local round track involved angle-milling 76CC small block Chevy heads .100" on the spark plug side and ending up with 60CC combustion chambers. With 1.94" intakes and 1.6" exhaust valves, I had a higher-compression head than the illegal 64CC camel-hump heads everybody wished they could run, a "legal" casting number, and the intake manifold still fit with very little tweaking. A blind tech inspector could have discovered the modification by running his fingers along the edge of the head under the spark plugs, but they obviously didn't know what to look for. A few more "Smokey Yunick" tricks like that made my engines consistent winners.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jan 2014 Posts: 3,690 'Bolter | | 'Bolter Joined: Jan 2014 Posts: 3,690 | Ought to be able to find a usable 848 head without too much trouble. Might even put a post in the parts wanted forum if you haven't already.
1951 3100
| | | | | Joined: Feb 2004 Posts: 29,869 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,869 | I have a head on mine that I had cut .100" and sunk the exhaust valves the same. Since the exhaust valves are at least an inch away from the piston crown, what was the reason for recessing them? It's the intakes that are in danger of touching the piston. If the rocker shaft is shimmed to correct the intake rocker geometry, it might be necessary to add a lash cap to the top of the exhaust valve stems. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2007 Posts: 210 Shop Shark | | Shop Shark Joined: Dec 2007 Posts: 210 |
Since the exhaust valves are at least an inch away from the piston crown, what was the reason for recessing them? It's the intakes that are in danger of touching the piston. If the rocker shaft is shimmed to correct the intake rocker geometry, it might be necessary to add a lash cap to the top of the exhaust valve stems.
Jerry
[/quote]
I was mistaken when I posted that, I believe it was the intakes valves that I had sunk .100". I may be wrong in this but if I remember correct. The intake valves are located such,that they are over the engine block and are not over the piston or cylinder .
| | | | | Joined: Feb 2004 Posts: 29,869 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,869 | The intake valves are located such, that they are over the engine block and are not over the piston or cylinder Those are the exhausts, which you said were recessed in your post. The intakes are positioned straight down, toward the piston and they are the ones which need to be moved deeper into the head. Nothing that I'm aware of needs to be done to the exhausts. It would be a good idea to install shorter pushrods for the intakes only, or shim the rocker stands and add a lash cap to the exhausts to retain the proper geometry for the rockers. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2007 Posts: 210 Shop Shark | | Shop Shark Joined: Dec 2007 Posts: 210 |
Those are the exhausts, which you said were recessed in your post. The intakes are positioned straight down, toward the piston and they are the ones which need to be moved deeper into the head. Nothing that I'm aware of needs to be done to the exhausts. It would be a good idea to install shorter pushrods for the intakes only, or shim the rocker stands and add a lash cap to the exhausts to retain the proper geometry for the rockers.
Jerry
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I tell my wife I have some timers. Some times I remember and some times I don't.
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