Head Studs the real problem?

What year did they start to make short studs? ADDED: sorry I am primarily referring to the 3/8-20BSF portion

When I do a valve job the first thing I do is remove the 3 studs. I have seen as few as 7-1/2 threads (head side). I cut the threads longer since the head is about .75" deep on the front/exhaust and about .8" deep on the rear one.
If the undamaged head can take a stud of 11-12 threads then why would anyone settle for 7-1/2 or 8. FWIW my inserts (recoil) are 9-1/2 threads.
I've only ever had to fix 1 stripped stud in a head during a valve job. Never had a come-back for a stripped stud either.

Since I am taking out the OEM soft cam in my 7 mile MKIII, it will be a good opportunity to upgrade the studs and avoid a factory induced failure.

7 mile MK111? Is this a typo?

Glen

worntorn said:

7 mile MK111? Is this a typo?

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No.

Seems like a lot of work to replace a cam that could be fine! My MKIII has over 60K on the original cam with no sign of wear at this point.

How saddening refreshing even gurus suffer similar Commando fades as rest of us. I think its only 2-3 stud threads near the seam surface that carry the bulk of the tension loads but assume as they crush-shear-creep some the deeper threads engage more. Epoxy could only act as thread locker but not alu metal stabilizer as would soften or fracture to sand like state still allowing full load bearing by thin edges of brittle internal micro grain fracture alu. Would Timsert be more robust or about the same? My thinking Timeert would at least protect threads if having to check in frequently working up to detonation power limits.

milfordite said:

Seems like a lot of work to replace a cam that could be fine! My MKIII has over 60K on the original cam with no sign of wear at this point.

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In the past 20 years, I have helped many people diagnose soft and dead MKIII cams. SIr you are in the extreme minority of long life cams in a MKIII. Are you the original owner and can verify the cam has NEVER been changed?

Dynodave,
I would be interested in knowing your procedure for checking worn or wiped MKIII cams and if it can be done on an assembled engine. Is there something on this forum or your Atlantic Green site?
I have <30k on my bike and it runs fine but I would like to check for wear if possible. I am guessing there is a procedure to check for cam lift at the rockers with a dial indicator?

Thanks,
Pete

dynodave said:

the extreme minority of long life cams in a MKIII. Are you the original owner and can verify the cam has NEVER been changed?

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The late Gerry Bristow, ex of the NOC chat group, had 80,000+ miles on his Mk3,
and he'd bought it new. Only had routine servicing.
Took he and his wife all over Europe.
Being an ex-oil industry executive, swore by Mobil 1 15W/50.

Deets55 said:

Dynodave,
I would be interested in knowing your procedure for checking worn or wiped MKIII cams and if it can be done on an assembled engine. Is there something on this forum or your Atlantic Green site?
I have <30k on my bike and it runs fine but I would like to check for wear if possible. I am guessing there is a procedure to check for cam lift at the rockers with a dial indicator?

Thanks,
Pete

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Pete
As an example, at the (New Hampshire) 2002 INOA rally, a guy rode his MKIII from Michigan. Never though any thing was wrong except for a little "miss". We took both exhaust rocker covers off and one rocker went up and down and the dead side did a bit of a "quiver". He went home in the back of a pickup.
There is NO increase of valve clearance. It is a loss of LIFT and must be measured with a dial indicator for detecting the beginning of death.

Dave,

I'm just guessing at this but I assume the best approach would be:
1) Get the push rod on the base circle
2) Remove the slack with the adjusting screw
3) Zero out indicator
4) Rotate engine til I get max lift (valve in lowest position)
5) Record measurement
5) Repeat for each valve

With a standard cam and rockers what kind of numbers should I be looking for @ the rockers adjuster (I figure that would be a good to measure at). I sure I can find the cam specs but not sure about the rocker ratio's. I would need a hard number for measurement at the rocker to know if I am good or not.

Pete

milfordite said:

Seems like a lot of work to replace a cam that could be fine! My MKIII has over 60K on the original cam with no sign of wear at this point.

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My first MKIII 330046 came to me as a basket case due to a dead cam at 9400 miles. I got it as a basket case in 1995 after a very long storage. I started to learn all about MKIII and their unfortunate legacy. All MKIII cam take outs have been butter soft (RC17-21) as the article on my site documents.

I very highly suspect my new (7 mile) MKIII will have a soft cam. In my estimation I would be foolish to NOT change it. Besides it would not be smart to take a 40 year old engine with old rubber seals and treat it like it was fresh and new.....valve springs have never moved.... some compressed for 40 years?

For the sake of research, I am pulling the engine for a tear down to put an OEM NOS 1971 cam (RC58) in it.
On a good engine/bike... I have R&R, teardown/reassemble in about 10hrs.

Rohan said:

dynodave said:

the extreme minority of long life cams in a MKIII. Are you the original owner and can verify the cam has NEVER been changed?

Click to expand...

The late Gerry Bristow, ex of the NOC chat group, had 80,000+ miles on his Mk3,
and he'd bought it new. Only had routine servicing.
Took he and his wife all over Europe.
Being an ex-oil industry executive, swore by Mobil 1 15W/50.

Click to expand...

I met Gerry at the Ohio 2004 INOA rally. He was a guest speaker at one of the tech sessions I gave. Of course his talk was about OIL. Very informative and convincing. The aspect about his cam being original did not come up, or I forgot if it did.
I was very preoccupied at the time, since I had just started selling my MKIII starters then.

Timely topic. I'm rebuilding a MK3 that reportedly had ~20,000 miles on it, and the cam is perfect. However, I'm sure from looking at the inside of the engine that it has been apart before, so it could easily be a replacement cam. In any case, I'm replacing it with something else. The original is probably going to comnoz as a core.

And relevant to the topic subject, I did install Recoil inserts for the 3/8-20 studs in the head while it is apart. Not as strong as comnoz's bronze inserts, but good enough for a mild street 883.

Ken

lcrken said:

And relevant to the topic subject, I did install Recoil inserts for the 3/8-20 studs in the head while it is apart. Not as strong as comnoz's bronze inserts, but good enough for a mild street 883.

Ken

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No problem Ken, I have big enough inserts to fix pulled helicoils.

I only got one summer out of the 20 tpi inserts I installed in my streetbike many years ago. They were used with the short studs however.
That was when I switched to 3/8 -18 helicoils which did better. Jim

I got to meet a lot of my early hand holding Peel mentors at 2004 rally, like DynoDave startling me by touching his new starter w/o warning. Gerry told me he would not of been able to travel nor ride his Commando d/t knees needing joint replacement but took dr. hobot advise to heart and thanked me for being able to walk around quite far in many places over here, some at ski resort towns just prior to the Ohio rally. Peel over rev'd in early' 05 so sent Gerry her Hienz ligthened brake rotor but Gerry popped aortic aneurysm a week later in UK at BBQ lunch with his brother after a vintage ride together that day. Gerry was in almost daily contact and only other rider who would fling Phase 4 turns - catching air on sideways leap on cresting sharp turn in Italy. He helped test rod link headsteady vs swash plate for vibes a couple years before Taylor produced his design. Gerry found swash plate buzzed so sent to me but never installed d/t other crisis so gave it to another last year to test. Surprisingly Peel over tightened fastener held oil tight for 2000 more miles even after all the seams forced open far enough to jet clouds of oil smoke so thick took most a min to clear before I could even see the profile that head still on in the choking fog. Just plain lucky. though Peel's head had by cryo tempered that pushed valve seats out so had replaced. Do not cryo alu with any other alloy still attached. As comnoz demo'd best to cyro the fasteners too.

comnoz said:

I only got one summer out of the 20 tpi inserts I installed in my streetbike many years ago. They were used with the short studs however.
That was when I switched to 3/8 -18 helicoils which did better. Jim

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Yeah, I've done them with 3/8-16 Helicoils as well as Timeserts, which are clearly better at holding in aluminum than the 3/8-20. In this case, I'm trying to rebuild the bike from a basket case in time for the rally, and didn't want to take the time to make or order new studs, or maybe just got lazy. I think the Recoil inserts will hold up on this engine, as long as I don't over-torque them. If not, I can convert to 3/8-16 Bigserts (or just ship it off to you for repair :lol: ).

It would be fun to duplicate your test on a junk head with the various commercial thread inserts, but I don't see how any of them could be as strong as your inserts. On the other hand, if any of them are strong enough that the stud stretches instead of the insert pulling out, then that's as good as it gets.

Ken

lcrken said:

comnoz said:

I only got one summer out of the 20 tpi inserts I installed in my streetbike many years ago. They were used with the short studs however.
That was when I switched to 3/8 -18 helicoils which did better. Jim

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Yeah, I've done them with 3/8-16 Helicoils as well as Timeserts, which are clearly better at holding in aluminum than the 3/8-20. In this case, I'm trying to rebuild the bike from a basket case in time for the rally, and didn't want to take the time to make or order new studs, or maybe just got lazy. I think the Recoil inserts will hold up on this engine, as long as I don't over-torque them. If not, I can convert to 3/8-16 Bigserts (or just ship it off to you for repair :lol: ).

It would be fun to duplicate your test on a junk head with the various commercial thread inserts, but I don't see how any of them could be as strong as your inserts. On the other hand, if any of them are strong enough that the stud stretches instead of the insert pulling out, then that's as good as it gets.

Ken

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I also tried a couple heads with 20tpi helicoil type inserts but they were not installed by me so I couldn't vouch for how well they were done or how much previous abuse they had. Both were better than no insert but both pulled long before the stud failed. Neither made it to 700 inch lbs.
I also tried an ARP stud in a 3/8 -18 helicoil and it pulled the helicoil around 750 inch pounds.
I also tried an ARP stud in one of my inserts that had been threaded with 3/8 -18. It held 1200 inch pounds but the head started to get a bump around the insert. Jim

Jim's inserts are not my issue here...However ...Jim is the rotational device in your tests 18 TPI or 26TPI as per the normal head nut? thanks
Further info:
1949 -1951 iron heads had 3/8 cycle threads for the head stud. Plenty strong in iron.Then my 1955 aluminum head shows it had converted to 3/8 BSF, however this little 500cc engines' head stud had 11 full threads. So why did commandos get head studs that were so short of thread engagement? :shock:
Doesn't any one else see this as a problem or concern? :?:
If a better stud was used, an insert might not be needed.........

dynodave said:

Jim's inserts are not my issue here...
1949 -1951 iron heads had 3/8 cycle threads for the head stud. Plenty strong in iron.Then my 1955 aluminum head shows it had converted to 3/8 BSF, however this little 500cc engines' head stud had 11 full threads. So why did commandos get head studs that were so short of thread engagement? :shock:
Doesn't any one else see this as a problem or concern? :?:
If a better stud was used, an insert might not be needed.........

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Well I tested a long stud from an 88 and a short stud in a nearly new commando head in my video. The short one pulled at 590 inches and the long one pulled at 600 inches. It didn't seem to make much difference.

That would go along with the general consensus that only the first some many threads [there is a formula] supply the holding power and the rest do very little. Jim

Well I tested a long stud from an 88 and a short stud in a nearly new commando head in my video. The short one pulled at 590 inches and the long one pulled at 600 inches. It didn't seem to make much difference.

That would go along with the general consensus that only the first some many threads [there is a formula] supply the holding power and the rest do very little. Jim[/quote]

Have you ever tried an extended preloaded stud. I'll have to sketch one. The sample I have in mind is like on a lotus twincam head and has a extended 135 degree tip smaller than the diameter of the threads. It bottoms out in the drilling and preloads the threads engaging in the threaded part of the aluminum.