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Stripped Threads

Dave Jackson

Forum Website User
Non-VOC Member
Hello there

I have a 49 B Rap HRD with the old style 3.5 inch dynamo cradle. The dynamo strap is held on one side by a 1/4 Whit "T Bar," which has been pulled out consequently stripping its threads in the alloy crankcase.

It seems to me the best repair for this if feasible is to make a steel insert threaded 1/4 whit on the inside and 3/8 whit on the outside. I can drill the existing hole out and tap it.

Can anyone re-assure me that there is enough material in the crankcase to do so, I imagine yes, but can't see from the pictures / diagrams I have and someone out there may either know or have an early twin crankcase to inspect.

Many thanks

Dave Jackson
 

clevtrev

Well Known and Active Forum Website User
VOC Member
Hello there

I have a 49 B Rap HRD with the old style 3.5 inch dynamo cradle. The dynamo strap is held on one side by a 1/4 Whit "T Bar," which has been pulled out consequently stripping its threads in the alloy crankcase.

It seems to me the best repair for this if feasible is to make a steel insert threaded 1/4 whit on the inside and 3/8 whit on the outside. I can drill the existing hole out and tap it.

Can anyone re-assure me that there is enough material in the crankcase to do so, I imagine yes, but can't see from the pictures / diagrams I have and someone out there may either know or have an early twin crankcase to inspect.

Many thanks

Dave Jackson
Plenty of depth for a 1 1/2D insert.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
PLENTY OF CRANK CASE THICKNESS,, GET A HELICOIL TAP AND GO STRAIGHT IN, PUT A LITTLE GREASE ON IT TO SAVE SWARF INTO G/BOX THEN PUT A COIL IN,, THE BROKEN OFf TAG WILL DROP TO THE BOTTOM, AND THE JOB IS DONE AND WILL BE STRONGER THAN the ORIGINAL.
bananaman
 

timetraveller

Well Known and Active Forum Website User
VOC Member
Sorry Marcus but I think this is bad advice. About three years ago I was building a twin racer for a local chap and at one stage we had to take the engine/gearbox unit out of his Prince and use it for tests in the racing chassis. On return from race testing the bike would not wheel back and forth in gear with the clutch held in. Dismantling showed two wrecked gears and the cause was a very short length (6 - 7mm) of the original dynamo holding down stud which some previous ahole of an owner had allowed to fall into the gearbox when he had done a similar repair. I know the tag from a helicoil is smaller than a bit of studding but if it goes through the gears it will be a very expensive job. Dave might not want to hear it but it is better to take off the primary drive and the gearbox end plate and make sure that whatever falls in is recovered. With care and luck he might be able to manage it without taking all the gears out.
 

ogrilp400

Well Known and Active Forum Website User
VOC Member
G'day Dave,
Hmmm, all the above seem to have partly relevant points. But lets have a look at things. First, are all the threads in the hole stripped out? If only say the top half are then make up a longer T bar going right down to engage all the threads. Thread so that the taper cut portion the die has made is in the stripped portion of the hole, tighter fit in the stripped section. Clean and use super strength loctite. 2 If all the threads are gone then you can get a longer helicoil to put in it. That way you don't need to break off the tang. It can remain in place, just make sure that you don't screw the T bar past the point of breaking off the tang. Again loctite in the T bar.
 

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
Use a bit of light fishing line and a tiny dab of superglue on the middle of the tang.I was shown this trick by an Inuit in the Klondike in 1898. I think her name was Nell-----
 

Dave Jackson

Forum Website User
Non-VOC Member
I've already tried the old dervish tribesman sticky toffee paper trick, but it only works if you get your bit of string really sharp.

Thanks for your advice. Isn't it a blind hole? If not I've probably already got loads of debris in the gearbox. The T bar hasn't snapped off, it has actually been yanked out of the hole pulling the threads with it. My mistake, perhaps when I fitted my alternator last time I didn't engage enough threads. It then went back in and far deeper with loads of locktite, and its now stripped the rest of em as well. Nice.

If it is a blind hole its worth trying a helicoil or insert with the gear cluster in, if not I'll have to take it all out and do it, as I don't fancy going anywhere knowing all that crap is lying around in there.

Dave
 

Bracker1

Well Known and Active Forum Website User
VOC Member
Take the gears out, it's an easy proposition and make sure it is derbris free. Use your insert or helicoil, but size properly. Loctite isn't a gap filling repair. Leaving bits of metal in your engine/box is like the surgeon leaving a bit of gauze in you after your surgery and hoping you don't get a complication. Hope in one hand as they say. Good luck. Dan
 
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