What is the correct true size of bolt holes in head?

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Model T Ford Forum: Forum 2017: What is the correct true size of bolt holes in head?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Wednesday, August 23, 2017 - 12:17 pm:

I am using a Model T head as a drilling guide for my adapter plate. I need to know if the 29/64"(.4375) I am reading is correct? I can find the counter bore's that have that size pilot or they jump to the next size, 15/32" (7/16 + 1/32, .46875). I am doing this part on my drill press and have made a centering guide and drilled 1/4" centering holes at this point. I am ready to go to the next step and drill the thru holes then remove the head and do the counter boar but need to find out the correct counter bore pilot size for the socket head cap screws.
Thank you;
MarkG


Top of pagePrevious messageNext messageBottom of page Link to this message  By Warren Henderson, Dunbarton, NH on Wednesday, August 23, 2017 - 05:23 pm:

Mark, I am working on replacing the head gasket in my '26 touring and the head bolt size is 7/16 x 14.

Hope this helps,

Warren


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Wednesday, August 23, 2017 - 05:42 pm:

A 29/64 bit just fits in the hole. 15/32 is too big.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison - Rice, Minnesota on Wednesday, August 23, 2017 - 05:56 pm:

Isn't 29/64 closer to .452? I think back when I was machining .4375 was 7/16. It makes sense that the hole would be .015" over the nominal bolt size of .4375 (7/16)". Or have the darn progressives messed that up now too? :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison - Rice, Minnesota on Wednesday, August 23, 2017 - 06:00 pm:

Actually, I'd be willing to bet a nickel that 15/32 (.46875) is closer to what one would expect for head bolt hole size.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Wednesday, August 23, 2017 - 06:12 pm:

According to this old thread, Mark Chaffin has a copy of the Ford factory drawing for the high head:

http://www.mtfca.com/discus/messages/257047/318941.html?1351372221


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Wednesday, August 23, 2017 - 10:43 pm:

Mark's numbers are for the height of the head, not the size of the bolt holes. Again, trying two drill bits in the holes on a high head, a 29/64 bit JUST FITS and a 15/32 is TOO BIG.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Wednesday, August 23, 2017 - 11:21 pm:

I am going with the 29/64 bit to drill the next stage in the plate. 15/32 is no go for the holes. Thank you everyone. :^{) The counter bore with 15/32 pilot seems more common but I will work it out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Thursday, August 24, 2017 - 08:52 am:

Yes, but if Mark has the drawing, maybe he can look up the size of the bolt holes. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison - Rice, Minnesota on Thursday, August 24, 2017 - 09:07 am:

Yeah, well, you notice I only bet a nickel.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, August 27, 2017 - 11:59 pm:

Got the counter bore with 29/64" pilot on it's way. The 29/64 holes are all drilled. :-)After I do the counter boar I will check for fit, then do the holes for the Chevrolet head. While I am waiting for the tool I guess I will do the valve holes and start doing the water passages. Might be getting my steps out of order because I plan on doing the cylinder holes last.


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