Commando Head stud thread.. (2016)

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biker_smith

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Hi all,

One of my of the three head studs was threaded, so I pulled apart my Roadster '72 this afternoon. When I extracted the all three studs from the head to replace them all with new items, one came out with all the ali from the head!

So - my question please - what thread is in the head for the stud?

I can see it is course and when I measure the OD of the stud just under 3/8ths - is it 3/8th whitworths?

Thanks - Paul.
 
biker_smith said:
I can see it is course and when I measure the OD of the stud just under 3/8ths - is it 3/8th whitworths?
Click to expand...

No, it isn't Whitworth. The thread on the head end of the stud should be 20 TPI so is 3/8 BSF.
 
Hi.
I have the same problem on the front left head stud of my Atlas.
But there is not oil leak from the head gasket still.
I know i shall replace this thread, but i hope to ride all the summer without problems.
Is the Helicoyl the best choice?
Ciao
Piero
 
pierodn said:
Is the Helicoyl the best choice?
Click to expand...

I think Jim's bronze insert mod is probably the best choice, as the BSF Helicoils have been known to pull out of the head.
 
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B+Bogus said:
I've heard Time Sert are better but haven't used them:

http://www.amazon.com/TIME-SERT-8-24-Thread-Repair-0382/dp/B001JK0YXI

but I've had good results from heli-coils, although V-coil seem more readily available and are pretty much identical.

All much better than the factory original, as Peter says.
Click to expand...

Unfortunately, Timeserts are not available in 3/8-20 thread, only 3/8-18 and 3/8-24.

I don't know of any off-the-shelf solid inserts that are readily available in 3/8-20. That doesn't mean there aren't any, just that they aren't common.

Like L.A.B. said, custom inserts like Jim does are the strongest technique.

Ken
 
The 20 pitch thread is a poor choice in an aluminum head. The 20 pitch helicoil insert is only slightly better. The fine thread just does not have enough strength in aluminum.

The best repair short of sending your head for the custom bronze inserts is to use a 3/8-16 helicoil and a custom stud. the coarse thread is much stronger.
You can take an old head bolt and cut it off slightly longer than the original stud and use a dye to cut a 3/8th- 16 thread on the end. This works pretty well as a custom stud. Jim
 
The 3/8" BSF thread can be a problem even on new heads. My very expensive Fullauto head suffered the same fate. I machined up three inserts 1/2" x 16 BSF outside & 3/8" x 20 BSF inside & screwed these into the head using high temp. Loctite, much the same as Jim does. This should hopefully fix the problem for good.
 
Matchless said:
The 3/8" BSF thread can be a problem even on new heads. My very expensive Fullauto head suffered the same fate. I machined up three inserts 1/2" x 16 BSF outside & 3/8" x 20 BSF inside & screwed these into the head using high temp. Loctite, much the same as Jim does. This should hopefully fix the problem for good.
Click to expand...


I got to the point several years ago that I don't even install a head unless it has inserts -new or old.

Nothing like that sinking feeling you get when your finishing up an engine build and the head stud just keeps on turning. Or your out on the road and oil starts blowing out of the breather because combustion is finding it's way into the pushrod tunnel.
 
Sinking feeling indeed Jim. When you were reworking my head I was tempted to get you to do the thread inserts, but, as it was a brand new head I thought it unnecessary. Shows what I know!!
As a matter of interest, what is the material spec. for these heads?
 
comnoz said:
The 20 pitch thread is a poor choice in an aluminum head. The 20 pitch helicoil insert is only slightly better. The fine thread just does not have enough strength in aluminum.

The best repair short of sending your head for the custom bronze inserts is to use a 3/8-18 helicoil and a custom stud. the coarse thread is much stronger.
You can take an old head bolt and cut it off slightly longer than the original stud and use a dye to cut a 3/8th- 18 thread on the end. This works pretty well as a custom stud. Jim
Click to expand...

Based on your suggestion while conversing my pulled studs, I put 3/8-16 Helicoils in the head (thanks for tapping those), then installed 3/8-24 Helicoils in the deep nuts. You were right; the metal used on those is also rather soft, and I remember a recent post where a stripped nut was causing someone's head gasket oil leak. 3/8-16 X 3/8-24 studs in Grade 5 are easy to come by, and being slightly longer, give even more grip area in the nut.

Nathan
 
Matchless said:
Sinking feeling indeed Jim. When you were reworking my head I was tempted to get you to do the thread inserts, but, as it was a brand new head I thought it unnecessary. Shows what I know!!
As a matter of interest, what is the material spec. for these heads?
Click to expand...

I believe it is a356 or similar. Similar spec to the original casting -as good as you can get for the purpose.

The casting methods on the new heads have improved so porosity and voids are no longer a problem -but they are still gravity cast aluminum. Jim
 
Nater_Potater said:
comnoz said:
The 20 pitch thread is a poor choice in an aluminum head. The 20 pitch helicoil insert is only slightly better. The fine thread just does not have enough strength in aluminum.

The best repair short of sending your head for the custom bronze inserts is to use a 3/8-18 helicoil and a custom stud. the coarse thread is much stronger.
You can take an old head bolt and cut it off slightly longer than the original stud and use a dye to cut a 3/8th- 18 thread on the end. This works pretty well as a custom stud. Jim
Click to expand...

Based on your suggestion while conversing my pulled studs, I put 3/8-16 Helicoils in the head (thanks for tapping those), then installed 3/8-24 Helicoils in the deep nuts. You were right; the metal used on those is also rather soft, and I remember a recent post where a stripped nut was causing someone's head gasket oil leak. 3/8-16 X 3/8-24 studs in Grade 5 are easy to come by, and being slightly longer, give even more grip area in the nut.

Nathan
Click to expand...

That works very well. I used that same setup on my bike for many years.

Of course Matt now has 3/8th-24 long nuts so it's no longer necessary to helicoil the original nut....

When I install the bronze inserts I give a choice or 3/8-20 or 3/8-16 so you can use the fancy ARP hardware or the original stud. The 3/8-20 stud has no problems in the hard bronze insert. Jim
 
Here is what happens when the bike is used for a while with a stripped stud. This head had BS helicoil inserts.

This picture was after I had taken a .009" cut. It was still not enough to clean up the channel that had been cut into the pushrod tunnel.

It's your head -Glenn. Jim

Commando Head stud thread.. (2016)


Commando Head stud thread.. (2016)
 
Wow.. How long or how many miles do you think it burn the groove? I road it less than 50 miles after I noticed the oil leak and tried retorquing the bolts. It must've been this long before I knew about it. So glad to have someone like you in our camp. Thanks for doing your magic on it. Glenn T. Suneson
 
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