Has anyone ever drilled and tapped the 6 bolt holes to switch from a 350 2 bolt to 4 bolt by themselves? My machine shop quoted me at $700 for the work which I think is too much for my budget build. I bought billet steel splayed main bearing caps with 10 degree angles on the outer bolts and I work at a shop with a good supply of drills and presses with experienced workers that are willing to help me with the project. Has anyone ever done this on their own and could give me some advice?

 

Actually, it can be done by hand. If the main cap is bolted into place and moderately torqued, a drill bushing and aircraft drill can be used to pilot the new holes. The drills can be stepped up in increments as long as a drill bushing of correct size can be inserted into the clearance holes in the new main caps. The drill size can be increased until the available drill bushing size is no longer useful. At that point, careful hand drilling to follow the pilot holes and careful tapping can finish the job.

Of course, if a LARGER press or mill is available with an indexing fixture on the table, exact angles can be drilled and the tap can even be started in a floating tool holder (like ER) to remove a lot of the margin for error. If you have access to a large tap table with enough room for an indexing fixture AND your case casting, that is also an option, but would probably be a rare find. It would also be a lot of extra setup labor.

 

Don't forget you will have to line hone and maybe line bore the mains after they cut the caps.

What is the power goal??

 

I presumed that was a given. $700 seemed high for mounting drilling/tapping saddles, but that's what was asked.

 

Power goals will be over 500hp in the hopefully near future and I want to spray 100-150 shot. I just can't wrap my mind around spending $700 for 6 bolts to be drilled and tapped. I've heard of guys doing it I just wasn't sure if they had special equipment available at their use. So you are saying if I put the caps on and slightly torque the middle two bolts I can use the angled holes on the caps as a guide to make pilot holes and slowly increase drill size until I am at the required width. This may be a stupid question but what are these drill bushings you mentioned? I have little knowledge of machine work that's why I am getting helped from some experienced gentleman at my work

 

You can drill the holes but there is a little more than just drilling that the machine shop is doing. (Id bet)
Every cap/block is a little bit different and will require a fit and finish to the main size once on.
You won't be able to drill/tap 6 holes, bolt the mains on, have perfect bearing crush and go..

 

TT - You're probably right that the cost quote was for the installation, cap parting line machining, and an align bore (or at least hone). That still seems a bit steep to me, since it is about 1/2 of the way to a complete and ready to build Dart 4-1/8 bore Little M or similar casting, and only $75 less than a brand new GM 4-bolt block, caps and all.

 

No such thing as a stupid question, unless it's a question that isn't asked when information ins needed.

Enter "Drill Bushing" and interwebs search engines will get you all kinds of information.

 

I plan on sending the motor to the machine shop to get the works done on the block for my 383 stroker set up so I wanted to get the main caps drilled and tapped and then send it in to have it all aligned