Socket head bolts US engines

[Dennis Toth]

What is the source for engine socket head bolts for US engines? I think they are 1/2" 4-40 carbon steel.

Best,     DennisT

[bob whitney]

  RTL Fasteners at  www.rtlfasteners.com  or MSC

[Tim Wescott]

Or MicroFasteners, or if you live in a metropolitan area that has any semblance of high-tech, your local bolt store.

Note that you probably need more lengths than 1/2 inch, and if the engine is small, large, or old enough you may need more threads than just 4-40.  (Cox 049 reedies, for instance, are put together with 2-56 screws with 5-40 prop screws).

[James_Mynes]

And sometimes the socket head is larger diameter than the Philips head and won't fit between the cooling fins.

[Allan Perret]

McMaster Carr,  MSC,  Grainger,  Fastenal.  The last 2 have local branches.

[Don Hutchinson AMA5402]

I just go to the Ace hardware store near my home. Take the engine with you to make sure the bolts fit.

[Steve Helmick]

Ace Hardware stores are good places, but I usually go to Hi-Strength Bolt, a local industrial fastener store. If I really want 10 screws, it's usually almost as expensive as buying a whole box of 100, so I get the box. You may find that the case if you go to a good industrial fastener store.

I went in one time to get something oddball, they had it, I only wanted one, and they didn't want to do the paperwork, so gave it to me! But I've been going there for a decade or two. Sometimes, it pays to patronize one particular store...  Steve

[Dennis Toth]

Jim brings up a point that I have been having on the Fox 35's. When I've tried to use the socket bolts the head is just a few thousands bigger then the Philips bolts. This causes binding on the fins/head which distorts the case and causes binding of the piston/cycl. What I've done is to take the small Dremel end mill and mill the bolt area fins larger to accept the larger head size. I also drill out the holes one drill size larger to give a little more room.

Is there a size designation for smaller socket head diameter?

Best,       DennisT

[Allan Perret]

Jim brings up a point that I have been having on the Fox 35's. When I've tried to use the socket bolts the head is just a few thousands bigger then the Philips bolts. This causes binding on the fins/head which distorts the case and causes binding of the piston/cycl. What I've done is to take the small Dremel end mill and mill the bolt area fins larger to accept the larger head size. I also drill out the holes one drill size larger to give a little more room.

Is there a size designation for smaller socket head diameter?

Best,       DennisT

You could also chuck the screw in a drill motor and grind or file on head diameter while spinning it.  I machine on small parts all the time in a drill motor.  I usually turn part with the drill and grind on it with a Dremel tool.

[bruce finley]

What is the source for engine socket head bolts for US engines? I think they are 1/2" 4-40 carbon steel.

Best,     DennisT

RSM Distribution, one of our vendors here...that's where I get mine

[Dennis Toth]

Allan,
I had thought about girding down the head and after your post I tried it. Worked great, thanks. The socket head diameter is 0.178", the normal Fox philips head is 0.173". I simply took the bolt, put it with the head extended about 1/32" below the jaws in the chuck of the drill press. I used a fine flat file held against the head for about 15 sec then measured the reduction. I repeated this until I got the head down to 0.172". These fit very nice (even better then the Fox philip heads). After doing a couple you get a feel for how long to hold the file and can get it in two shots.

Since I have a whole box of these I think I will make a simple measuring tool by drilling a No. 17 (0.173") hole in a piece of 1/8" by 3/4" by ~3" plate (from Home Depot). Using this I can just chuck the bolt and grind down the head a check with the gauge.

Best,          DennisT

[Motorman]

You can get Du-Bro hardware from Tower Hobby. I think it's better to counter bore or grind the head than to weaken the bolt on a Fox 35.


MM

[Dennis Toth]

MM.
I tried opening up the bolt landings in the head, I also open the hole one drill size. This will work if you have access to a milling machine so you get the landings flat and on plane with the seal ring of the head. I tried to do it with a drill press and simple head mount jig and got all but two flat using a Dremel 3/16" end mill. The two that are off caused the head to be pulled down uneven (putting a bending force on the edge). This cause the case/cylinder to distort every so slight and resulting in a bind as the piston started the compression stroke.

The amount I removed from the diameter of the bolt head was 0.005" ish, the socket head is pretty robust. Doing this allows the bolt head to fit down into the bolt landing and not rub against the side of the head which causes the head to distort and the piston/cycl to binding. It is surprising how little a side rub causes the binding to occur. When you do this you need to check for bind free rotation with the plug out, so you can feel the bind. The bind causes the engine to get hot and destroys the 4-2-4 run (similar to what happens if you get a castor varnish build up).

Best,    DennisT 

 

[Gerald Arana]

I use socket heads from "microfasteners" and don't have to do anything 'cept screw them in!   
Jerry

[Dennis Toth]

Jerry,
Do you have the stock # for Microfastners  4-40 socket heads? Have you measured the head diameter, the stock Fox Philips head bolts have a head diameter of 0.173" the 4-40 socket heads that I have are 0.178".

On some Fox heads that 0.005" difference causes the bolt head to rub against the side of the recessed bolt landing area in the head and puts enough pressure to cause the piston/cycl to have a slight bind.

Some heads are on the up side of the tolerance and don't bind at all. You need to check the smoothness with the plug out. You may think it will just wear in but for my Foxes it cause them to run hot and inconsistent. Also the third party heads are setup for the socket bolts and have better tolerance on the landing recess.

Best,       DennisT