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Old 10-03-2012
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Advice on removing snapped s/s bolts from alu block

Last night a bolt holding my Yamaha 6hp 2 stroke's lower unit to the cylinder block snapped on me. Upon removal of the block I found a second stripped one.

How should I go about removing two snapped s/s bolts in aluminium? They broke almost flush. They are size M6. They appear to be well corroded into place.

Both bolts are either side of the waterway, so it leaks cooling water like a sieve without these two bolts tightened.
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Re: Advice on removing snapped s/s bolts from alu block

Do you have access to drill a pilot hole and use a bolt extractor? If so, I'd soak them in pblast for a day, then hit it with the drill and reverse-thread bolt extractor.
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Re: Advice on removing snapped s/s bolts from alu block

your best bet would be to try easy outs, then drilling if that fails....worse case is dremeling them out completely

either way you are likely going to have to retap, If that is possible - I would look at using studs - you may have to use a larger section in the AL that switches to M6 through the housing, else drill it out if you can.

stainless and AL can be problematic, as you are seeing, in a marine environment with out insulating or large mass....and especially crevice corrosion as you are up against....

not sure I would replace them with stainless, I would do a bit more research on, else make sure your fasteners are top quality..then there is the fact that stainless really can't stretch in AL like you would want a bolt to do, and you need the correct anti-seize if you ever want to take them out without destroying the AL threads....

more to this than you would think....Yamaha should know better

Last edited by kd3pc; 10-03-2012 at 12:59 PM.
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Re: Advice on removing snapped s/s bolts from alu block

Almost impossible?

But there might workarounds. Depending on the casting shape you might be able to mill (or dremel) a flat for a nut and drill out the offending bolt. You could epoxy fill any holes to the inside. You will need to drill it out anyway. You could try helicoils (sp?) and larger bolts too.

Have fun.

Gene
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Re: Advice on removing snapped s/s bolts from alu block

I would NOT use easy-outs for anything small like this. Break an easy-out and forget drilling. You can drill it, use a coil or insert, put in a stud, or mill space for a nut. AND do not use stainless. Use hardened steel and paint it.

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Re: Advice on removing snapped s/s bolts from alu block

Easy outs are almost useless in most cases. If the easy out snaps you are going to have a much harder time with any other method since easy outs are so hard.

Best way that works for me is using a tig welder to build the broken bolt up high enough to then weld a nut of the same metal type to it. This works about 90% of the time when a bolt that is broken is a different metal that the surrounding metal.

Also as was already mentioned take in to a shop with a drill press to make sure the bit goes in straight and then use a helicoil.
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Re: Advice on removing snapped s/s bolts from alu block

Use a dremel and cut a groove for a flat head screw driver, soak it in PB Blaster or the lube of your choice then back them out with a hammer drill.
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Re: Advice on removing snapped s/s bolts from alu block

I have done (tried) a number of these things, messy. If I had to do it again I would take it to a good machine shop and have THEM drill and re-tap. Use lots of never-seize, or equivalent, on re-assembly. If you can get the rest of the bolts out without breaking them, suggest you clean the bolts and re-assemble with never-seize. I have also used silicone head gasket seal paste and been able to remove the bolts later. I think never seize may be better however.

Paul T
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Re: Advice on removing snapped s/s bolts from alu block

Quote:
Originally Posted by Gene T View Post
Almost impossible?
(snip)
I agree. Removing broken bolts is difficult in larger sizes, but with anything less than 3/8" it's downright ugly. I have seen the tig-weld-a-nut-to-it approach work, again with larger sizes. When corroded, the difficulty goes way up and the chances of success go way down.

There are some good extractors on the market - they are NOT "easy outs". The Alden "Drill Out" works well: http://www.drill-out.com/how1.html
You'll want to heat the broken bolt red hot with a torch. Search Youtube for video demos. Hell, it's worth a try.

Personally, I would just shop eBay for a good used block, or another putt-putt.
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Last edited by Brewgyver; 10-03-2012 at 05:08 PM.
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Re: Advice on removing snapped s/s bolts from alu block

Bring it to a machine shop where it can be fixture d and drilled out with a diamond point bit.
You will probably have to go with a helix for your new screws.
Dick
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