Drill and tap my head or find conversion bolts?

[thegreatjustino]

And my 351 debacle continues...

I am in the process of doing the Explorer serpentine conversion to a 351 I recently installed.

According to the tech article on the swap, it's rare to come across a set of heads with the incorrect bolt holes in them. Well, I've managed to do so.

The passenger side head has the correct one large two small hole layout, but the driver side head has three 3/8" holes instead of the required 7/16"

Am I better off trying to drill out and re-tap or finding conversion bolts with a 7/16" shank and 3/8" threads?

 

[KAllen]

my vote is conversion bolts. drilling and tapping would be a last resort for me. hope this helps

Kallen

 

[Apogee]

I would drill and tap unless there is a such a conversion bolt/stud already in existance. The nominal pilot drill size for a 7/16-14 would be a "U" drill bit measuring .368", however most would just use a 3/8" [.375"] instead if you don't have a lettered/numbered/fractional drill bit set. Alternatively, if you chose to run 7/16-20 fine thread fasteners, then you could just pilot drill it 25/64 [.391"], tap and call it a day.

Cast iron is very easy to drill and tap IMO.

 

[ntsqd]

Drill & tap.

Do so in cast iron dry, no cutting fluid. Cast iron dust is very abrasive and cutting fluid turns it into something like valve lapping compound.

If you can, use the bracket to guide the drill bit.

 

[Bajabrewer]

Just a thought but are the holes the same on both ends of the heads? you may be able to swap heads side to side & end up with the right hole in the right place? I know this means new gaskets & some more work but what the heck it's still a thought.

 

[Viperwolf1]

Just a thought but are the holes the same on both ends of the heads? you may be able to swap heads side to side & end up with the right hole in the right place? I know this means new gaskets & some more work but what the heck it's still a thought.

Might also look close to make sure there isn't an insert in those smaller holes.

 

[Nickm1024cobra]

Might also look close to make sure there isn't an insert in those smaller holes.

I would follow this advice and clean it really well and verify there isn't a thread insert. If there isn't..no way would I flip the heads (bolt holes correct on other side) and do new gaskets...fluids, etc. I would drill and tap personally. Conversion bolts...never seen 'em.

 

[thegreatjustino]

No sleeves inside. Even on the passenger head it looks as if the one larger bolt hole was drilled and tapped larger.

Not interested in taking off the intake and heads. Even if I could find the bolts, I would imagine they would be idiotically expensive. Drilling and tapping is free as long as I don't screw anything up...

 

[DirtDonk]

I wonder if that oddball power steering bolt would be the correct length?
http://www.wildhorses4x4.com/category/s?keyword=power+steering+bolt
Just search "power steering bolt" if you forget the number.

If you want, I can measure it for you tomorrow. I know you're not that far away, but if it's wrong you might as well save the trip.

Let me know.
Otherwise... Seeya tomorrow!

Paul

 

[thegreatjustino]

Nice thought Paul. The funny thing is I just packed one of those up to drop in the mail tomorrow for someone who bought it from me here on the board.

 

[Broncobowsher]

Just put the 3/8 bolts in and be done. It doesn't change the belt alignment.

 

[Rustytruck]

I would use 3/8 bolts too. The weak spot is the cast Iron threads in the head. The bolts are stronger than the head material.

 

[ntsqd]

The strength point is moot. There's no real load on any of it. You could use Grade Zero bolts and more than likely be fine for the application.

Alignment is an entirely different story. If the bracket aligns properly with all 3/8"s bolts then that would work. If it/they do not align correctly, then drill and tap is easier than turning a reducing bushing with that thin of a wall.

 

[drock]

Did you ever come up with a good soultion? I'm still rounding up all the parts to do the Explorer serpentine on my 351W with a Saginaw pump.

 

[SHX669]

My 5.0.L had a " conversion bolt" - actually more of a "stud" for the PS pump bracket - 3/8" on one end x 7/16" on the other. Didn't need it for the 351w that replaced the 5L.

 

[DirtDonk]

I bet you could also find an appropriate sleeve at McMaster Carr or some place like that.
I got some to allow me to use the existing smaller bolts for the stock brake caliper mounting bracket, with my new larger diameter Camaro calipers going on the Buick.

Might just be the ticket.

Paul