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MONTAC Enterprises
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Azle, TX 76020



Engine Block Fastener Sizes


One of the steps in properly preparing a block for build-up is to clean/chase the threads in all the various threaded bosses.  While making a list of bottoming taps required to accomplish this little task, I decided to take some pictures and write up a short article.  Here you go!

Click for larger version...

Starting at the top...  This is the easiest one to remember.  All you have are the head bolt/stud holes. They are all 12mm x 1.75.

Click for larger image...To the bottom...

Oil pan bolt holes are 6mm x 1.00.  The oil pump mount bosses are 8mm x 1.25, and the main bearing cap bolt holes are 12mm x 1.75.

Click for larger version...Front...

Cylinder cover, aux shaft retention plate, and aux shaft cover are all 6mm x 1.00.

The water pump bolt holes are 8mm x 1.25.

And the two plugs are 3/8" NPT.

Note the block fill... for a little extra strength.

Click for larger image...... to back.

Sorry for the crappy image, but I didn't have the time or inclination to remove the block form the stand for one picture.

The 4 tapped bell housing to block holes are 10mm x 1.50.

And again, the two plugs are 3/8" NPT.


See what leaving your block on the deck will do for/to you?  A whole lot of extra cleanup.

Click for larger version...Here's the driver's side of the block.

The fuel pump block off plate holes are 8mm x 1.35

Alternator/Power Steering, motor mount, distributor hold down, et al. purple are 10mm x 1.50.

The coolant sensor and ?? yellow one are 3/8" NPT.

What is that lower yellow hole for?  Is it just plugged?

Click for larger image...And finally, the passenger side...

A/C bracket, motor mount, et al. purple holes are 10mm x 1.50.

The turbo coolant port is 1/4" NPT. In my case, this port is blocked off by the block fill. Thus, I will just plug it with a Loctite covered plug.

The turbo oil return is 1/2" NPT.


Well, that's pretty much it... So the bottoming tap list includes a total of 4 pieces:

6mm x 1.00
8mm x 1.25
10mm x 1.50
12mm x 1.75

They should all be bottoming taps even though some of the holes are through holes.  You need to make sure you chase the threads as close to the bottom of those blind holes as possible.

Hope this helps,



Copyright (C)2003 MONTAC Enterprises.  All Rights Reserved©
Revised: March 03, 2006 .