Modifying a 250 Head at Home

[nickstewartroc]

Has anyone attempted to modify a 250 head for a 2bbl at home? I can't seem to find many engine shops around my area, and the only one I really found will do the milling, but they don't feel comfortable milling it for a 2bbl. Thanks,
Nick

 

[wsa111]

Nick, you need to purchase new valves from Mike @ classic inlines. He has the correct performance valves at a reasonable price.

If you want a direct mounted 2 barrel, do not do any other machine work done till the low areas of the intake log are filled in by brazing. I recommend having an experience welding shop preheat the head to 400F then do the brazing.
If you want to install the 3-4 exhaust port divider it can be welded in at the same time.

After that is the time to get it to a qualified machine shop to check the head for cracks & clean up the bowl area of both the intake & exhaust. They will then install the hardened exhaust seats & maching the seats for the new valves. Lap in the new intake valve to its seat & then back-cut the intake valves with a 30 degree angle for improved flow.

Maybe some member in your area can recommend a qualified machine shop for you.

I would call Mike & see if his machinist still does all this work. The key element is proper brazing of the log so it can be machined to the same 16 degree angle as the original 1 barrel carb mounting surface.

The performance gain with all matched componets will result in double the original HP.

Do a search of this forum on this topic. Bill

 

[thefurnacedude]

Nick,

I see your in Longwood. I used a shop in Jacksonville who did the 2 barrel conversion. Let me know if you want
nore info.

 

[nickstewartroc]

Would love some more info! Thanks!

 

[CZLN6]

Howdy Nick:

What is the casting number on the 250 head you're working on?

Much of the grinding and detail fitting can be done at home, but it will take a pretty sophisticated home shop to do the machining and weld fill-in required for the two barrel conversion. While I appreciate DIY and homebuilt, it is good to know when you need help and where to get it. You might want to make a decision on if you intend to use an exhaust port divider on the center exhaust ports as it requires welding to properly fit it. There are differing opinions on the performance value of the divider. Do a search and decide for yourself. My only advice is that if you're going to add it do it right and have it welded in.

It is a good idea to get all of the milling, fitting and welding done prior to any detailed finish work because cracking can occur during welding and/or grinding. And, distortion/warping can occur during the heating and cooling process of welding. You would not be happy if you do hours of detailed hand work only to find a fatal crack.

Bill hit the high point on building a performance head- all good stuff. Enjoy.

Adios, David