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Stud replacement advice

11 Jan 2020 18:49
Art
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Stud replacement advice #1
I need to replace a cylinder hold down stud. I've got good threads to work with, should I heat the case or stud prior to attempting to double nut it and unscrewing it. The engine is in the frame and I don't want to screw up somthing and have to split the case to complete the repair. I have the new stud on the way but any ideas would be greatly appreciated.
first attempt at attaching photos, hope it works.
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11 Jan 2020 19:07
MarkT
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Stud replacement advice #2
Nice photo!

Normally I'd say it's good to heat but with it assembled, I probably wouldn't.

Actually, I'd probably clean up what you have and use it... the first thread that's engaged in the nut takes the majority of the load and after just a few threads engaged the rest don't add any strength... from the "staining" it looks like the nut has several threads engaged before it gets to the damaged part.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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11 Jan 2020 20:03
Art
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Stud replacement advice #3
The cylinder hold down nut is aluminum and about 1 3/4" long with a lot of thread engaged , I could cut off the damaged part of the the stud and proceed as you suggest. Not real sure how strong aluminum nuts are, i have never seen one of these before and i plan on torquing to the spec. in the manual. The photo is of the remains of the removed hold down nut as well as the drill guide i used to center it thru the cylinder fin hole. It was tough getting the nut off, I've got new nuts on the way, wish they were steel, alo ng with new studs. I'm hoping i'm at the point of reassembly not more tear-down.
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11 Jan 2020 21:27
MarkT
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Stud replacement advice #4
It's an engineering thing... when you have "enough" threads, first thread handles about 35% of the load... then the remaining threads handle less and less load each until after not too many threads any additional threads aren't loaded at all.

"Enough" depends on the size of fastener and thread pitch... A regular nut is designed to have at least "enough" threads... from memory it's usually about 5 or 6 threads for common fasteners. Beyond "enough" threads, adding additional threads by using a longer nut doesn't add any significant strength.

I'm making the percentages up but the load on each thread for a nut with 8 threads is something like 35% - 25% - 20% -15% - 5% - 0% - 0% - 0%....

The additional threads won't hurt anything... they really won't help either. If you have a good 5 or 6 threads engaged and the threads strip at a certain torque, adding 5 more threads or 10 more or 100 more won't make a difference... threads will still fail at pretty much exactly that same torque...

Failure is like a "chain reaction". Since first thread handles the most load of the engaged threads... ~ 35% of the load... it fails first... then the second thread effectively becomes the first thread and now has to handle the 35% of the load and it's the same strength as the first thread so it fails... then the third thread fails... and so on until you run out of threads.

Looks like about 10mm studs... rule of thumb I was taught is that if you have 15mm of good threads engaged you'll be more than fine.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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11 Jan 2020 21:31
MarkT
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Stud replacement advice #5
Oh... and nice tool and job at removing the seized nut! Those can be nearly impossible to get apart. :likey

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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12 Jan 2020 08:32
Art
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Stud replacement advice #6
Thanks for the feed back, your mechanical engineering description makes a lot of sense. From the look of the remaining threads below the damage I'm thinking i will be fine in using what is left after I cut off and clean up the stud. I think this is safer than trying to extract the stud while the engine is still assembled.
Onward with the cylinder machining and piston replacement.

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12 Jan 2020 19:10
JGersh
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Stud replacement advice #7
Not to minimize good mechanical engineering but I have had good success with penetrating oil and a vice grip on the stud below the threads. Just thought I’d throw it out there...

‘68 DT1
‘70 CT1-B
‘70 HT-1
‘12 Triumph Scrambler
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13 Jan 2020 04:08
RT325
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Stud replacement advice #8
I'v got a set of stud removing things that are just a one way locking roller clutch. Think i can use it for fitting studs as well as removing. works a treat on a parallel stud but not on a wasted undersize stud. Think i still have pretty brutal one too that has a moving central serrated bit that swings around & locks onto the stud. Works on any size stud although only ever used it on large ones on car head studs on my old cars i used to have in my youth. [think was head studs--big ones]. I'd try it without heating. Should be ok unless someones loctite'd them in.

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13 Jan 2020 04:21
MarkT
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Stud replacement advice #9
Yeah... I might be too cautious... Saw the corrosion and remember some nightmares removing stuck studs from aluminum.... breakage... threads coming out with stud...

It wouldn't hurt to *try* to use penetrating oil to remove it and if it comes out easily just replace it.

:Buds

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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13 Jan 2020 08:54
mdscott
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Stud replacement advice #10
I have the same roller type stud remover as RT325, they work well. Personally I would and have used heat to get that stud out, propane only, no acetylene torch. Kroil penetrating oil works great. The drill type stud removers are good but have to be drilled straight, the remover does tend to break if too tight, I know this very well.

Thanks Mark
Roseville, Ca.

'76 Bultaco 143 Frontera
'06 GL1800
'01 KDX200
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