** updated ** re-threading a bolt hole - need some ideas, please.....

[jtexas]

I have an out-of-production prestolite starter motor with a problem.

The housing is held together by 2 long bolts running the length of the motor, screwing into threaded holes on the top end. Starter failed yesterday, one of the bolts was loose, on disassembly found the inside threads broke off - little metal rings just fell out in my hand. My idiot mechanic (myself) must have overtightened it last time.

There's enough thread left in the hole to hold it tight - reassembled, reinstalled, tested, works fine now, but I'm wondering, how long before the bolt threads break off.

Replacement parts not available (prestolite is long gone), and using a larger size bolt is just out of the question - too specialized of a part to find one in a bin somewhere.

I was thinking that Marine-tex or JBWeld or a similar epoxy might work, if there were some kind of "release agent" that can be put on the bolt, so the epoxy would adhere to the hole but not the bolt.

I'm grasping at straws here.......any ideas?

 

[F_R]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

Heli-Coils. The life saver for marine mechanics. One will restore your threads to like new, same size.

If you only need one, it is probably cheaper to get a shop to put one in for you than to buy an installation kit. Automotive machine shops can do it, or any decent outboard shop. I could do it for you if you were here.

 

[luckyinkentucky]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

+1 In addition to what he said. I went ahead and bought the whole kit of Heli-Coils since you never know what you might need them for. I bought the complete set of several different sizes for $25 at Auto Zone.

 

[mikesea]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

are you talking about the brush cup?if so,I have a feeling if you do some internet searches you just might find one,there were a couple electric companies that made replacement brush cups,in fact I worked in Brooklyn NY for a industrial complex and one of our tenents made them PREFFERED ELECTRIC,dont know if they are still around or same name but 15 yrs ago I worked at an outboard shop and we had tons of them,I doubt many people knew these parts were avail.or maybe a electric motor rebuilder can help,now if thats not a winner,how about drilling through the housing and putting a nut on the outside if possible,using a piece of all thread rod,or,use the one bolt,try your epoxy on the other,then perhaps a large hose clamp to add support.I do hope Im thinking right here,if not,give more detail if you can

 

[angus63]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

Helicoils are great, but here is some caution from a frequent user in aerospace applications.
Be sure to purchase the "tanged" version and not "tangless".
To do it "right", you'll need the proper twist drill size (may be fractional, letter, or number so you'll need a complete drill index).
I suggest having the installation tool (winder) and tang removal tool (spring-loaded punch). If you don't have or can't borrow, they are expensive to use once. A skillfull person can improvise a winder using a small screwdriver that clears the id of the insert and adding a slot to the tip with a dremel (for example).
The tang removal can also be improvised using a drill blank or even a twist drill inserted backwards and tapping the pointy end with a hammer. Be careful to recover the broken off tang for they end up in the worst place and cause havoc sometimes.
You'll need a helicoil tap. Be sure it is the proper tap for your insert.
Be certain you have at least 1/8" of cross section left around the new hole before attempting this , for the tapping stress can easily crack the casting and propogate until the bracket assy is trash.
Use plenty of tapping oil, make sure your tap is straight, and only advance less than one turn at a time, and back out at least two turns each time to prevent chip build up and possible cracking.
I'm not a big fan of "repairing" threads with "permanent" epoxies. Great for temporary fix though. And remember, they're only as good as the cleanliness and surface texture of the mating parts.
I hope this helps and post back if you have any questions...
Good luck

 

[Chris1956]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

JT, Can you use a longer bolt? Sometimes the way a starter is mounted, leaves enough clearancve for thru bolts with nuts.

 

[BF]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

If you go to a GOOD specialty fastener store (not a consumer Home depot type place), ask about "Keen inserts". I think Keen was a guy's name. They are along the lines of a helicoil, but you don't need any specialized tools. They're steel (?) inserts that are threaded both on the outside and inside. You buy one with the inside threads to match your current bolt, and they'll tell you what size to drill and tap the old hole. Then you screw in the insert (with locktite on threads), and tap in a locking pin that comes with it. Google "Keen inserts".

The place I went to also sold heli coils and kits, but they suggested I try the Keen insert which worked pretty slick. The inserts were a couple dollars each and I could use drill bits and a regular tap which I already had. For the size I was using, the helicoil needed a specialty tap that was > $20 if I recall correctly, or I would've had to buy a whole kit (more $$).

 

[yorab]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

Heli-Coil or a longer bolt would be the best method. However, you may have trouble locating a longer bolt as it is about 1/4" and about 10" long. The cheapest way would be to go Mikesea's route and use all thread. Quick and simple and cheap.

 

[angus63]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

Keenserts are excellent fasteners, however, the new th'd size for the insert is very large compared to the original size. For example, a 1/4-20 original hole will require a 3/8-16 new tapped hole. They also only come one length only (1.5x dia). If you have the depth and plenty of room around the original hole, BF is correct in my opinion to recommend.
Jtexas - I have helicoils and keenserts in front of me at work. If you pm me with what you need, I think I could send you a few wayward pcs. and help you thru.
Good luck

 

[Chris1956]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

JT, If a longer bolt will work, but you cannot find one, use a threaded shaft, cut to length and two nuts.

 

[R.Johnson]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

That starter is heavy for it's size, and mounted off to the side of the motor. One reason for a starter to strip thread's, or break the mounting bolt's is a damaged, unbalanced prop. That can shake part's loose in a hurry.

 

[jtexas]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

thanks for all the ideas - the bolt comes through *maybe* enough for a nut on top - *if* I can find the right one, and *if* it's enough threads for it to hold - the all-thread was one of those slap your forehead "why didn't I think of that".

I hadn't considered prop damage, RJ, did some DIY grinding on minor prop dings a couple years ago, didn't cause any *perceptible* vibrations - .........a trip to the prop shop might be in order. Appreciate the feedback.

 

[jtexas]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

well, it didn't hold very long - broke again midmorning Saturday. Had to rope start 70hp the rest of the day (couldn't leave fish biting).

got around to looking at the manual...there are supposed to be nuts on those bolts - whether I lost 'em a few years ago or a prior owner left 'em off I don't know. All thread with lock washers & nylock nuts seems to be holding pretty well.

 

[angus63]

Re: re-threading a bolt hole - need some ideas, please.....

Re: re-threading a bolt hole - need some ideas, please.....

Outstanding!!!!! Love those easy fixes......