Breather Banjo Bolt

cinquecento

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Got back after a cold ride yesteday and checking over the machine for loose bits and oil leaks I found that the breather banjo bolt had obviously partially stripped its threads and had been silicone sealed in position.

I've not taken the part off yet but am guessing it's a 50/50 that treads in the case and the bolt are stripped. As there seems to be plenty of 'meat'in that area I was thinking I would drrill and re tap for next size up, using pleanty of grease on the tap to catch swarfe.

Can anyone see any obvious consideration i've not given to this straight forward fix?.
 

greg brillus

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If it is one of the original type alloy banjo bolts, they will often start to shear off across the holes drilled through them. If is a stainless one you may be in for your said repair. You can fit a helicoil repair of the original size without too much difficulty, and plenty of grease on the tap should avoid swarf down the hole.....thread is a 1/4 BSPT from memory, that is a parallel thread, not tapered...........Greg.
 

roy the mechanic

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The "easy" fix would be a longer banjo bolt ,the original does not take advantage of the depth of thread available. Even if this does not work you may save all sorts of swarf + nastiness entering your motor. Be lucky.
 

chankly bore

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Tapping oversize would only increase the problems for the next owner and force you to make a non-standard banjo- which is only permissible if you live in the Appalachians and have polydactylism. I would helicoil it.
 

cinquecento

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Thanks for the points to ruminate on, the Heli repair would return things to near standard and would justfy my recently acquired ratchet T drive tap holder, now just need to find pipe thread heli insert.
 

chankly bore

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Gotcha there, Max. Tracy Tools have the kit for about 55 pounds. I think there should be enough metal to take a standard 1.5x diameter insert. If this is a Comet, do the job with the piston at B.D.C. and pressurize the crankcase interior with an air nozzle, a bit of rag and a series ''D'' breather cap. this should blow out any swarf the grease trap misses. Let us all know how you get on.
 

Kansas Bad Man

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In the US try Grainger or McMasters. Most tool specialty stores will have it or will be able to order it, it wont be that hard to find. On the swarf thing, if you stuff the hole with a little bit of cotton , after taping , vacuum the swarfs , remove cotton with wire hook. One other thing , it is easy when taping ,to start the tap crooked in the hole to be taped. A long something in the hole will give you a reference position of the tap . No problem chanky.
 

paulpackman

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Drill it out and Hellicoil it. Put a good dollup of high melting point grease on the end of the drill and tap and the swarf will stick to it and not fall in the engine.
 

Magnetoman

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..., the Heli repair would return things to near standard and would justfy my recently acquired ratchet T drive tap holder,
If I'm correctly inferring from this that you don't have much experience with taps and dies this particular repair is not the place to practice your skills. First, you will have to drill the hole to the proper size for the special Heli-coil tap, and it is very easy to drill it at an angle. Slathering the drill bit in grease will trap some of the swarf, but remember a drill bit is designed to push swarf out of the hole and grease will stop this from happening. So grease will gain you something, while also losing you something, in terms of the amount of swarf left behind in your engine.

Next, even if the hole is straight it is very easy to start a tap at an angle and just as easy to leave engine-damaging swarf behind despite using grease. Finally, installing the Heli-coil deep enough, but not too deep, and removing the installation tang without screwing things up and so it doesn't wind itself out later also is something a first-timer should get experience with on a less critical job than this one.

The right way is to disassemble the engine to do the repair, but I realize most people wouldn't do that. However, ask yourself it you would pay someone to do this to your Vincent who has your level of skill. If your answer is 'yes,' then proceed. Otherwise, you really should find someone with the necessary expertise to do it for you. No matter what, drilling and tapping in situ is the wrong way to do it, so you want someone who has the skills to do it the least wrong way possible.
 
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