Seeking advice for misaligned head stud

Hi folks,

I am finally back to rebuilding my MKIII engine and have hit a situation that has me a bit stressed. It looks like I have two courses of action and I don't like either of them, so I wanted to see which choice people think is the wisest.

I had my valves and guides redone and helicoil inserts put into the three stud locations as this is a known weak point on these heads. Well, I just went to dry fit the head onto the barrel and the head studs don't quite align with the jug holes. I don't believe its off by much, but its enough that it absolutely won't fit. So a helicoil must have been drilled misaligned. I spoke to the gentleman who did the work and he suggested either opening up the hole in the cylinder barrel with a rat tail file or drill press, OR send the head back to get the helicoil reinstalled.

I hate to risk damaging my cylinder barrel to fix my damaged head, and don't have much experience with cast iron but feel I shouldn't have drills or files around a freshly decked gasket surface unless its absolutely necessary. And I'm not sure how a cockeyed nut would fare in holding things tight. So I'm not thrilled about the idea of modifying the jugs. But I'm also not confident a helicoil insert can be "redone" without compromising the integrity of the connection. I'm not a machinist and I don't have enough experience with what is and isn't possible. Given this situation, what would you guys do here?

Thanks,
Anthony

No easy answer, if the helicoil was installed incorrectly then it has to be removed, the hole redrilled and tapped correctly for a bigger insert such as a Timesert. I would not be sending it back to the original guy as he could get it wrong again. Other option is to get bronze inserts fitted, but I believe there is a long wait for that.

That's an unfortunate predicament, There is a MKlll head for sale right now on ebay for 879 bucks (385231093814). seller is parting out a '75 mklll seller is Mach lV motors. today is 19 july '24......you could keep going with your rebuild and get you current head sorted out at a later time. (I know ...I know, its easy for me to spend your money & it's not something you probably want to do, but the darn thing is on ebay at the moment and would be a 3rd choice or option)

This is odd, I just went through a similar problem this past Sunday.
All new studs and new 5/16" studs on the Barrell.
the difference being no new machine work was done. So I knew it should fit.
Played around pulling studs till I found the issue.
It was the new 5/16" barrell studs. One stud was a couple thou over.
Replace with original, all is good.
Studs were not A/N..

I just had my head gone through and repeating that with a replacement head is not a viable option for me. So is there consensus that the head needs to be addressed versus modifying the cylinder barrel?

If the stud is the only issue then fix the stud by having the helicoil corrected. But first check that the stud is straight itself or not oversize.

A quick and easy 'fix' would be :
Tighten the stud and mark the deviation.
Remove it and give it a slight bend.
Take care not to damage the threads (use nuts).
re-install it in the same position.
I know it's a bodge but it will work, and studs are cheap.

The head needs correcting. The stud has to be true for it to pull down properly, any misaligned stud, because its is at an angle will be bent when the nut is tightened, leading to premature failure.

Invest in a small (machinist) square, or make one. Don't try to use a carpenters square. Place it on the head and examine all the studs from different angles and see how much they are out and if it is more than one. I'd want to know for sure whether I was reeming a few thousandths off the holes in the cylinder or a millimeter before I considered it. Regardless of the course of action, it should be good information to have.

There is an old thread on the studs how not are all made equal, and one reputable dealer had the best threads , but the studs had a very slight bend , but could be straightened , they had the same problem as you , but managed to sort it without any major equipment .

As others have said , you may be able to tweak the stud . I would take an old stud and cut it short so that only a small portion extends beyond the head , then dry fit and see if the shortened stud will enter the barrels. This way you can check if the problem is caused by the helicoil being installed at an angle versus
mis located. If the helicoil is mislocated but square no amount of tweaking will fix it .

The head gasket goes on and looks fairly well centered when against the surface, so I suspect its just a little cockeyed and not mislocated. With a machinist square it looks like its the rear stud very slightly off. I believe the original studs were put back in, but I'll have a check to see if anything is bent or out of spec. Bending the stud slightly sounds like the least risky course of action available, and I suspect it would not be any sort of failure point since the nut will be sitting properly flat. Thanks guys for this suggestion.

If I go down the path of attempting to get the helicoil corrected, it sounds like it will have to be with a larger insert. Is this possible to do? I don't have anything in front of me but in photos it looks to me like time serts might be a bit narrower than helicoils.

If you go the bending route index the stud with a marker on the stud and head then remove the stud and do the tweaking in the bench vise . Forgive me if I am stating the obvious but a caution nonetheless.

It is essential that you identify the offending stud.
It will not take much "out of square" to create interference.
Assuming the interference is not excessive, bending the stud or oversizing the hole are both options.
Bending the stud to square has the benefit of creating a better clamping force under the nut.
The stud could be bent in a vise as Richard points out.
Bending the stud in place will allow you to start with the stud bottomed out. Which is always preferable.
If the out of squareness is excessive, re-doing the helicoil will be required. Do-able, but you are probably in for some custom machine shop work.

rvich said:

Invest in a small (machinist) square, or make one. Don't try to use a carpenters square. Place it on the head and examine all the studs from different angles and see how much they are out and if it is more than one. I'd want to know for sure whether I was reeming a few thousandths off the holes in the cylinder or a millimeter before I considered it. Regardless of the course of action, it should be good information to have.

Click to expand...

And further...If you find the offending stud...great. Determine if the stud is the problem or the threaded hole is catywampus. If the threaded hole is 90 degrees you have less of a problem. Now remove it and fit the head with only two studs. Does it go on like it should? Or is there a further issue. If it is not obvious which stud is the problem remove all of them and roll them on glass. You might get lucky and one has a wobble.

You might try taking a 3/8" drill to the 3 cylinder stud holes. Try to fit the head. If one is slightly off center but 90 degrees to the head then I would take a drill 1/64 over size and drill the offending hole in the cylinder.

The hard way is to drill the hole in the head oversize, thread, and put in a bronze slug which can be drilled and tapped for the stud.

Anvill said:

I just had my head gone through and repeating that with a replacement head is not a viable option for me. So is there consensus that the head needs to be addressed versus modifying the cylinder barrel?

Click to expand...

A consensus would be a first in an interweb forum.

Do all the threaded and unthreaded holes in your barrels have a very shallow countersunk edge at the deck to help start the bolt in the threads or stud through the holes? It can help get the head studs started. Disadvantage is the head can be difficult to remove once the studs are pushed through the holes.

I have a factory untouched early Norton Commando 750 head that does not like to drop onto a set of pre-Commando 750 barrels. I had to dig through sets of studs until I found a set that could be pushed through. It is a bear to remove the head though. I wouldn't have a problem making the holes slightly larger as mentioned by seattle##gs. I don't need to use the head or barrels, so have not done it yet.

Thanks for your input everyone, these are a lot of good perspectives to get me started. I realized I actually had replaced the original studs--the originals read at ~.371" whereas the replacements sit right at ~.375" . Not sure if that's enough to cause the problem alone but its good to be aware of. Next I'll pull the current studs to check to see if any are bent and I'll also try to put the originals back in for a fit test. I used a vice grip to remove the originals but they got a little chewed up so I'm currently waiting for a set of thinner Whitworth nuts to come in--better to do it right this go around as I might still use these ones.

Schwany--Out of curiosity, did Commando barrels originally have a chamfer at these holes or is this an improvement you're suggesting? Mine show no sign of it, but it was recently decked and that detail may have been lost.

Anvill said:

Thanks for your input everyone, these are a lot of good perspectives to get me started. I realized I actually had replaced the original studs--the originals read at ~.371" whereas the replacements sit right at ~.375" . Not sure if that's enough to cause the problem alone but its good to be aware of. Next I'll pull the current studs to check to see if any are bent and I'll also try to put the originals back in for a fit test. I used a vice grip to remove the originals but they got a little chewed up so I'm currently waiting for a set of thinner Whitworth nuts to come in--better to do it right this go around as I might still use these ones.

Schwany--Out of curiosity, did Commando barrels originally have a chamfer at these holes or is this an improvement you're suggesting? Mine show no sign of it, but it was recently decked and that detail may have been lost.

Click to expand...

The small diameter difference adds up with all three studs. Likely has a lot to do with the issue.

"Chamfer" that's the term that would not pop into my memory yesterday. Another false neutral brain fart.

I think it is a common thing to do today. I'm not actually sure if the factory did it. When I had the iron barrels I have bored over +.040 the machinist asked if I also wanted the bolt holes chamfered. I declined and did it myself when I got home. I turned a 11/16" drill bit in my fingers over the tops of all the holes. Did the trick.

There are some old threads here about lengthening the head studs in order to get full thread on the nuts. The back stud particularly discussed because the short nut has fewer threads. I only mention it now because manufacturing your own studs might be a good option. As I recall the idea presented was to use old head bolts as they already have the cycle thread on one end. It's not my idea, but I have used it. It gives some extra courage when reaching for specified torque.

Highly suggest to get a proper stud removal set.
I have this one.
Amazon has it also.