Need advice on fixing the threads again. - Ducati.ms

grendels_arm · May 23rd, 2006, 10:26 am

OK I've mentioned this before but I messed up the threads on the little bolt hole underneath the mesh filter. The little plug sorta you never mess with. Anyway I had the guy who sold my track bike to me look at my 996 to see if he could fix it. Here's what he said. What should I do here?

"Threads are definately stripped and only one good thread exists at the top of the hole but the bolt doesn't contact this thread. It leaked a good bit of oil over the last couple of days as well!

Anyway, not an easy fix as the bolt is not a standard size at 15mm with 1mm pitch.

The only option I can think of is to drill the hole out, tap to a larger size standard bolt, install new bolt and seal with permanent thread sealant.
Due to the size of the bolt required, all the components will be costly. A standard hex head bolt will not work due to the limited work space. A socket cap bolt is the best option and even this will need to be machined down to fit the machined opening where the crush washer sits.

The bolt (stainless), drill bit and tap will be roughly $60 and machining the bolt head will be roughly $40. I've got about an hour into it already and figure it will take about another hour and a half to finish it off once I get the parts. Your looking at roughly $200 for the fix. I know its high but this isn't an easy fix like I thought it would be."

Gallep · May 23rd, 2006, 11:25 am

@ first I thought you were saying that the forum threads were messed up

I'd let him do it and why I say this is from my past experience...

When I was a land rover tech, we had to take off the exhaust down-pipes from the headers all the damn time when fixing oil leaks. 95% of the time 5 of the 6 studs/nuts rusted together, snapped, bent and broke off resulting in many hours of applying heat, drilling, installing inserts and new hardware. It’s just a headache I'd prefer not to mess with and depending on the application; you can only mess up once. Hope this helps.

grendels_arm · May 23rd, 2006, 11:31 am

Well I do know on my car when the dealer replaced the head gasket a few of the head bolts busted taking them off. Requiring expensive bolt replacement. But that's a different story because those are head bolts and I guess that happened due to rust or whatever. The thread in my cause was due to my ignorance about tightening too much on aluminum threads. So it's tough to stomach this if I give the go ahead. I guess I figured he'd be able to use the same bolt, since the bolt was fine and use a Helicoil or something. Therefore a somewhat cheap fix.

deerharb · May 23rd, 2006, 11:36 am

The bolt (stainless), drill bit and tap will be roughly $60 and machining the bolt head will be roughly $40.

$40 for machining seems over the top to me. Shouldn't take more than 5 minutes. For what it is worth, send me the bolt and the dimension and I will machine it for nothing and send it back. I am on the left coast, but the price is right.

Gallep · May 23rd, 2006, 11:39 am

Yeah I know what you mean about personal ignorance and how it can cost you 10x what you thought something would cost you... I overhauled my clutch last month with new basket, steels and fibers, springs, and hardware...and eventually a new hub. My old hub was good until I tried sliding a breaker bar between the spring perches and brake lever to hold the hub and basket in place while I broke free the 146 ft lbs. hub nut. I broke 2 spring perches off the old hub...so 186$ for a new hub, 85$ for a clutch holding tool from eBay and I was back in business

Desmo_Demon · May 23rd, 2006, 11:59 am

Quote:

Originally Posted by Gallep

My old hub was good until I tried sliding a breaker bar between the spring perches and brake lever to hold the hub and basket in place while I broke free the 146 ft lbs. hub nut. I broke 2 spring perches off the old hub...so 186$ for a new hub, 85$ for a clutch holding tool from eBay and I was back in business

LOL.....I did the same thing on my Harley a few years ago. I'd taken it apart probably 4 times and never had a problem, but this time I dissasembled it out of order and improvised. That perch/stud just snapped off as easy as could be. I had it tig welded, decided against it after I had it done, then went and bought a new hub. Turned out the hub was a poor design and that part of it was redesigned for better strength, so....I have the *better*, upgraded hub, now. The old design was known to snap the perches off under hard acceleration with guys who had the 100"+ engines.

grendels_arm · May 23rd, 2006, 12:20 pm

So does $60 sound about right for the bolt, tap and the drill bit? I guess if I took it to a Ducati shop they would have the drill bit already. And then another $100 from somewhere, which I've asked about, I guess in labor.

deerharb · May 23rd, 2006, 1:41 pm

Quote:

Originally Posted by grendels_arm

So does $60 sound about right for the bolt, tap and the drill bit? I guess if I took it to a Ducati shop they would have the drill bit already. And then another $100 from somewhere, which I've asked about, I guess in labor.

When you are talking about drilling out damaged threads with the part in a vise and the drill in a drill press and everything locked down so nothing can move and the drill running nice and slow, this is the optimum situation. Actually, drilling slightly undersize and finishing the hole to size with a reamer is the best, but drill only will work.

If you are doing it by hand, it is very difficult to avoid the drill catching and making the hole oversize. It is also easy to engage the tap so that it is not square with the surface that it will be seating and sealing against.

That said, I have never seen a motorcycle shop that had mechanics with machine shop experience. I am not saying that there aren't any. If the shop stands behind their work, meaning they will replace what they screw up for no more than the cost of the repair, then you might be better off going with them. If you are confident of your own abilities then go for it.

I do not think that $60 sounds like too much for the parts.

I hope this advise is helpful without being overbearing.

grendels_arm · May 23rd, 2006, 3:45 pm

Thanks, didn't sound overbearing at all. Ok here's what he said. Sound about right ?

"Due to the odd size of the bolt (15mm w/1mm pitch) a Heli-coil is not available. A 14mm bolt and Heli-coil could be used but the hole is already too big for the 14mm Heli-coil. Going up to a 16mm bolt will mean drilling the case out and using a tap to cut threads for the 16mm bolt. The drill bit is ~$20, the tap is ~$20 and you can either go with an untreated bolt at ~$8 or a stainless bolt at ~$20. The untreated bolt will rust very quickly which is why I quoted a stainless bolt. The head of either bolt is too large to fit the recess machined into the case and will require the head to be machined down to fit. The local machine shop charges $65 an hour and there minimum is $40. The bike will need to be put on its side to allow access to the bottom of the case for drilling. I have large foam pads so there is no worry about damage to anything externally. The passages within the case will be blocked so that shavings from drilling will not enter the motor. I figure this will take about an hour and a half more than the hour I have into it already. I'm relatively cheap at $40 per hour."

paulo57509 · May 23rd, 2006, 6:27 pm

My experience/observations in doing what you're proposing....you probably know all this already.

Drilling the hole oversized and tapping to the next larger size is probably your only course of action at this point, short of new cases. We won't go there. the good thing about this repair is that it's not a load bearing fastener. You just want it to leak when your finished.

Before you start, make sure that there's going to be enough "meat" around the socket of the socket head cap screw you're going to be modifying to fit the case recess.

In my experience, drilling an already existing hole is fairly straight forward. To minimize getting the hole crooked, drill in small steps; don't drill to the tap hole size all at once. I've found that the existing hole kind of acts as a drill bushing, guiding the drill bit fairly straight. Start as straight as you can, though. Use a good drill motor. Using a drill that has a worn out spindle will make oversized holes.

Once the hole is drilled, starting the tap straight is your next task. Get yourself a few taps of the correct size; a taper and a plug tap. Start with a taper tap. It's a bit more pointed and will allow you to start the tap in straight before you begin to cut some serious threads. Try to get some kind of "cylinder" that you can use as a guide. The cylinder will help keep the tap straight; kinda like a drill bushing. If there's not enough clearance to get the taper tap all the way thru the hole, go to the plug (or a bottom tap) to finish up. Use aluminum-specific tapping fluid and don't be shy about using it. 1/8 turn and back off to clear the chips. Go slow and you'll get some nice threads. Don't side-load the tap - removing a broken tap is no fun.

As for machining down the head of the bolt....sometimes if you find the right machine shop, they'll turn down the head for you for a nominal fee or perhaps free. It's not a lot of set up time and they'll have the cutting tools at hand. Just be sure to return with sandwiches and beer!

Wait! Have you considered this?

http://www.midwayautosupply.com/deta...ption.asp?2379