GT40X heads, Drill/tap one of the accessory bolts holes

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GT40X heads, Drill/tap one of the accessory bolts holes

Post  HorsinAround on March 21st 2017, 9:29 am

Putting a 302 together and noticed that one of the accessory bolt holes is smaller then the other 2. Can I just drill and tap it to match the other 2? I need them all the same to bolt the oem accessory brackets on.
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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  rmcomprandy on March 21st 2017, 10:17 am

You do realize that one side of the head has different sizes than the other side, correct ?


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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  HorsinAround on March 21st 2017, 12:04 pm

rmcomprandy wrote:You do realize that one side of the head has different sizes than the other side, correct ?


I looked at both ends and they both seemed to have the same 1 different than the others, but I will look again tonight. If I was wrong, then I'll pull the heads and flip with new head gaskets. Would be just my luck if I did them wrong.

thanks.
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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  HorsinAround on March 21st 2017, 2:04 pm

Ran home at lunch and took a picture of each end of one of the head. 2 are the same size and one is different. Is there enough meat to drill/tap so they are all the same or should I machine a step bolt?



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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  dfree383 on March 21st 2017, 3:08 pm

Don't the large holes use a reducing insert on those heads
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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  dfree383 on March 21st 2017, 3:09 pm

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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  HorsinAround on March 21st 2017, 3:37 pm


Thanks for the link Dave. I think these heads just have allen plugs deep in the thermactor holes. I have the E7 iron heads that came off this block, so I can compare them and the cast brackets.
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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  dfree383 on March 21st 2017, 4:26 pm

The inserts are a combination plug and accessory hole
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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  HorsinAround on March 21st 2017, 7:03 pm

dfree383 wrote:The inserts are a combination plug and accessory hole

Yep. Got home and checked these heads and they just had allen plugs in there. Took them out and will order the inserts from your link. (thanks for that btw)

Alan
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Re: GT40X heads, Drill/tap one of the accessory bolts holes

Post  gt350hr on April 3rd 2017, 2:40 pm

The small tapped hole is for the clamp that holds the smog crossover tube in place on stock ( smog equipped) applications.

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