Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Stripped thread in the cylinder

Stripped thread in the cylinder

Post Tue Jul 03, 2012 7:12 am

Posts: 72
Location: South Australia
Hi Folks, just putting the finishing touch's to my stroker motor, but when i was doing the torque for the head studs, before i got to 30Ft pound, the thread in the cylinder barrel turned to S**t, and has stripped out, I have looked on the net for helicoil repair threads, but can't find any 7/16 x 16tpi sets. How do others over come this problem??
Regards Rod
Last edited by ozihotrod on Wed Jul 04, 2012 5:47 am, edited 1 time in total.
" The more I learn the less I know"

Post Tue Jul 03, 2012 8:06 am

Posts: 67
7/16-16 is called a special Harley helicoil. It is available. You may find that others start to pull. Sometimes it's easier to just do them all, on a drill press, so they'll all be perpendicular. Sometimes you just get lucky and one repair is enough.

Post Tue Jul 03, 2012 11:34 am

Posts: 152
Location: Carver, MN

The Helicoil part number for the kit is 5540-7 if that helps. Also, both V-Twin and Eastern Motorcycle Parts carry the kit, though I don't know that will be any help to you in Australia.

Post Fri Jul 06, 2012 1:55 pm

Posts: 767
Location: Pa. , USA
The head bolt may have bottomed out before seating on the head causing the threads to break, this happened to me ONE time , after that I measure them individually, shorten if needed, and number them so they will always go back in the same slot, this should especially be done when installing new head bolts or racing applications not using a gasket... my 2% Tim
Vintage roadracing, Class C, AHRMA # 335

Post Sat Jul 07, 2012 4:06 am

Posts: 176
Location: Carmarthen, Wales, UK
Was it one of the long studs that holds the head steady? If you weren't aware this is a fairly common problem, due in the main part to vibration I suspect. Had both of mine go; not particularly high-use barrels as they were both on standard bore. I had them drilled and sleeved, as they were pretty well gone.
72 Ironhead, goes better than it stops!



2005 XL1200R.... well ya gotta have a rat-bike!

Post Sat Jul 07, 2012 10:56 am

Posts: 51
I've had the same problem 2 years ago. Then I cutted the threads to a metric M12 and took some M12 bolts. Than torqued them to 90 ft and everything was perfect till today.
Regards, Thomas

Post Mon Jul 09, 2012 11:58 pm

Posts: 1
Hi Rod try repco if they still stock Recoil products. I got a 1/4-24 kit a long time ago part no 34040-24. Recoil still list 7/16-16 on there website part no 34070-16 do a search for harley and they both come up. Hope this helps regards johnno

Post Sat Jul 21, 2012 7:01 am

Posts: 202
Location: Middle England UK
Sorry to be pedantic,but they're head bolts,not studs,unless an early model with 3/8" threads.
The "best practice" when building any engine,is as follows.
Run a standard tap down the holes to check they are clean.
Screw the bolts down just snug,without and washers,brackets etc.
Use the washers etc as "feeler gauges" under the heads.they should not slip in by some margine,if they do,or even come close,you won't get the clamping force on the bolts when tightened,the torque could be from bottoming,not clamping.
90 FT/LB may be ok on 12mm quality bolts,for the standard 7/16" bolts the figure is 60-65 FT/LB.
Early models with 3/8" studs 40-45 ft/lb.
Head bolts will age with heat cycles and stretch,but if replacing,I will always look for plain headed NOS ones.
Just my opinion,but the plain head screw cut ones give more thread engagement,than the CP drop forged or cold headed ones.

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