head bolt threads

[dogpen2]

Hi, I ' doing a head gasket replacement on a 1971 F motor and can't seem to figure out the headbolt thread size. They are bigger than a 12mm and smaller than a 14mm. When I look on some tap charts they don't list 13mm, so what size are they?
Thanks

 

[rsbcruiser]

They are 13mm X 1.75 . Toyota did that in order to keep the hole as close to 1/2" as possible. Most just modify a head bolt to chase those threads but you can special order the correct size tap. Nice of them to stick so close to the original design .

 

[dogpen2]

Thanks for the reply, I'll try to find the correct tap.

 

[rsbcruiser]

Thanks for the reply, I'll try to find the correct tap.

Might be wrong, it has happened before , but special order only. I have one but it cost me $ 100 US. Real good idea to chase those threads though. I would definitely do something there.

 

[bsevans]

Might be wrong, it has happened before , but special order only. I have one but it cost me $ 100 US. Real good idea to chase those threads though. I would definitely do something there.

This tap is off the shelf at mscdirect.com for less than $23. It is listed on page 285. You need to chase the threads in the block otherwise you will not get the correct torque on the head.

Metric Taps

 

[dogpen2]

Thanks for the source for the tap, I placed an order Sunday morning with MSC.
Jay