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Old 13 October 2021, 04:07   #1
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Impeller housing snapped bolt

I've ended up with a snapped bolt while removing the impeller housing.
All the other 3 bolts came out so I've been able to remove the housing, impeller and plates.
The bolt was just below the lower plate so I've removed that and there is about 3mm of the bolt showing.
Looking for advice how to remove without any further damage to the lower unit
Engine is a Yamaha 5hp 2 stroke
Thanks
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Old 13 October 2021, 04:13   #2
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Originally Posted by Tommy c View Post
I've ended up with a snapped bolt while removing the impeller housing.
All the other 3 bolts came out so I've been able to remove the housing, impeller and plates.
The bolt was just below the lower plate so I've removed that and there is about 3mm of the bolt showing.
Looking for advice how to remove without any further damage to the lower unit
Engine is a Yamaha 5hp 2 stroke
Thanks
Weld a nut on it and unscrew while hot.
If you have a dissimilar metal rod (e.g. Magmaweld or ESAB 309) that's ideal.

If it snapped flush then a cobalt drill would work, I use a pilot first. Never had any joy with screw extractors although the parallel fluted ones are best. Just tap the hole out.

Edit: Another possible method if you have a large vice with good jaws, is to invert the leg and get a really good purchase on the stump, twist and get it cracked. Repeat as required. Every case is different. For a snapped exhaust bolt on a two stroke motorcycle barrel, I used a Miller. Milling cutters don't wander. For bigger stuff I saw contractors using spark erosion. Reminiscing. All back in the day..
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Old 13 October 2021, 05:01   #3
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I too would always try MIG welding a nut onto the stub, it can be one size up so M10 on an M8 stub. I tend not to worry if its Stainless and the MIG is set for mild steel wire. It will still stick.

Mainly your getting the nut and stub really hot to break the seal.

Good luck.
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Old 13 October 2021, 06:33   #4
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Thanks chaps,
I'll try the vice first as I don't have a welder but know someone who does ,��
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Old 13 October 2021, 06:50   #5
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Agree with both of these - in fact had exactly this issue on my Johnson 5 when I bought it. I've also got a "precision" blow torch - in fact, it's one for doing the crust on the creme brulee in the kitchen - but it's a nice pencil flame. Warming the ali casting up a bit (ali expands more than steel) can also work

As above, avoid the screw extractors!

Judicious use of a cobalt drill & centre punch is my usual answer - slowly and carefully, you can even avoid having to helicoil afterwards if you get it right.
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Old 13 October 2021, 07:01   #6
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Thanks chaps,
I'll try the vice first as I don't have a welder but know someone who does ,��
Your stub's maybe a little short for that, are you feeling lucky? If it shears flush then the best option of welding is then lost to you. Alternatively your buddy needs to get the weld right first time, is he confident?

As said, best time/effort approach varies case by case also by skill level for those less experienced. Knowing when to get a workshop involved could save you money.
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Old 13 October 2021, 07:23   #7
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>>>Knowing when to get a workshop involved could save you money.

Very true. Back in the day when I needed more of that sort of thing doing I lived opp a farming engineering company. It was just a case of wandering across am accepting the abuse of "what's he broken now" and collecting after lunch all neatly sorted for a modest drop in the tea fund.

I'm lucky I've not really needed them since we moved.
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Old 13 October 2021, 10:46   #8
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Whilst it's tempting to try and DIY you're going to be better with the welded on nut.
Will get the bolt much hotter than trying a blow torch.

Other alternative is take it to an engineering company who will either weld it or use the stub to align a drill bit & use a parallel fluted extractor.

I had an inlet manifold to cylinder head bolt shear on my V8 Range Rover engine. Leaving a stub much like yours. Steel bolt into ally head. What was left in the head threads was just over 1".

Whilst I do have a lot of tools incl mig & arc welders and I've done the welded nut type removals before with this one after a bit of 'Shall I, shan't I' I took the head to a local engine rebuild company who used one of the fluted extractors and, I'm told, quite a lot of heat of the oxy-acetylene variety. Came out clean with no damage the head.

ETA. IME the carrot shaped extractors have about the same shear strength as the vegetable and when they do shear they leave a nice bit of hardened steel in the hole giving you a whole new problem!
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Old 13 October 2021, 13:30   #9
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All good advice. If there's 3mm of stud showing then I'd favour welding a bit on and trying to wind out while warm.

But the other thing to consider is doing absolutely nothing.

It's not a pressured environment and there's actually pretty good surface contact between the plastic impeller housing and the alli plate. Plus it's only 5hp. If it were me and I'd exhausted the advice above then you can either take it to a workshop or consider doing it back up with just three bolts and the thinnest of skims of gasket sealant.

Not the perfect engineering solution but sometimes issues end up not needing them.
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Old 13 October 2021, 15:48   #10
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Originally Posted by paintman View Post
the carrot shaped extractors have about the same shear strength as the vegetable and when they do shear they leave a nice bit of hardened steel in the hole giving you a whole new problem!

Made me laugh, funny.

I never snapped one, but the way around this is to switch to tipped drills. They can create holes even in hardened files, don't like interrupted cutting though.
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Old 14 October 2021, 15:43   #11
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Originally Posted by TmMorris View Post
All good advice. If there's 3mm of stud showing then I'd favour welding a bit on and trying to wind out while warm.

But the other thing to consider is doing absolutely nothing.

It's not a pressured environment and there's actually pretty good surface contact between the plastic impeller housing and the alli plate. Plus it's only 5hp. If it were me and I'd exhausted the advice above then you can either take it to a workshop or consider doing it back up with just three bolts and the thinnest of skims of gasket sealant.

Not the perfect engineering solution but sometimes issues end up not needing them.
Well I gave the lower unit to my son in law who works in the engineering department at the local university.
He had 4 options, all suggested on here too.
The welded nut failed twice, the stud extractor felt like it was going to snap so he drilled and re tapped it.
Phew.
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Old 14 October 2021, 15:51   #12
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Originally Posted by Tommy c View Post
Well I gave the lower unit to my son in law who works in the engineering department at the local university.
He had 4 options, all suggested on here too.
The welded nut failed twice, the stud extractor felt like it was going to snap so he drilled and re tapped it.
Phew.
Excellent result. Thanks for the feedback.
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