Helicoil Question

One of the bolt holes where the lower unit attaches is stripped out on my Yamaha 30. The bolt is an M10x1.25 with 40mm thread length. What length helicoil insert should I look to buy for this job? I've only used one once before and it was a thu hole scenario so I didn't have any worries about breaking off the tang. I am not sure if I need a shorter insert than my oem bolt thread length in order to allow a gap at the bottom for breaking the tang or if I can get a full length one. Most of the kits I've seen are 10mm length inserts with a few in 20mm.

Yeah, you will need space in the bottom of the hole to break the tang.

But before that, is there any chance you can tap the hole deeper and use a longer bolt?

Current thread engagement is probably close to 10mm so I'm sure you're good with that length.

RaisedByWolves said:

Yeah, you will need space in the bottom of the hole to break the tang.

But before that, is there any chance you can tap the hole deeper and use a longer bolt?

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I actually didn’t think of that. I will have to check. For whatever reason my tap and die set doesn’t have a m10x1.25 in either tool so I do plan on getting one in case I go forward with that.

MrGiggles said:

Current thread engagement is probably close to 10mm so I'm sure you're good with that length.

Click to expand...

Thanks!

wmk0002 said:

I actually didn’t think of that. I will have to check. For whatever reason my tap and die set doesn’t have a m10x1.25 in either tool so I do plan on getting one in case I go forward with that.

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A tap is probably cheaper and rethreading is a much more durable fix than a helicoil.

After a couple years that helicoil will most likely destroy that hole. Above the waterline it would be fine but on a lower unit it’s not so great.

RaisedByWolves said:

Yeah, you will need space in the bottom of the hole to break the tang.

But before that, is there any chance you can tap the hole deeper and use a longer bolt?

Click to expand...

^^^I've done this ^^^ Worked just fine, and that tap has come in handy several times since.

Have you considered a time-sert? This is a pretty good video on the install details and why/when/where to use one....





What's the difference between a TIME-SERT and a helicoil?

Helicoil inserts are held in by swedging the top by hitting a spreader tool with a hammer. Time Sert is held in by using a threaded install driver which finishes the bottom threads by cold rolling and expansion of the bottom portion of the insert.

Also, there is no tang that needs to be removed.

Tin Man said:

Have you considered a time-sert? This is a pretty good video on the install details and why/when/where to use one....





What's the difference between a TIME-SERT and a helicoil?

Helicoil inserts are held in by swedging the top by hitting a spreader tool with a hammer. Time Sert is held in by using a threaded install driver which finishes the bottom threads by cold rolling and expansion of the bottom portion of the insert.

Also, there is no tang that needs to be removed.

Click to expand...

Im aware of them but don’t know much about them other than they aren’t very cost effective. I guess I could check with my local machine shop and see if they install these and what they charge.

Tin Man said:

Have you considered a time-sert? This is a pretty good video on the install details and why/when/where to use one....





What's the difference between a TIME-SERT and a helicoil?

Helicoil inserts are held in by swedging the top by hitting a spreader tool with a hammer. Time Sert is held in by using a threaded install driver which finishes the bottom threads by cold rolling and expansion of the bottom portion of the insert.

Also, there is no tang that needs to be removed.

Click to expand...

The problem with Timeserts, Keenan inserts and the like is the kit to do a single hole will cost far too much unless you have a shop dedicated to this work.

Even a simple helicoil kit is 4-5X the cost of a good tap, and you don't even need a good tap to thread cast aluminum.

RaisedByWolves said:

The problem with Timeserts, Keenan inserts and the like is the kit to do a single hole will cost far too much unless you have a shop dedicated to this work.

Even a simple helicoil kit is 4-5X the cost of a good tap, and you don't even need a good tap to thread cast aluminum.

Click to expand...

I checked today and there is plenty of room in the boss locations to tap more threads or even drill and tap. Grabbed an $8 tap from NAPA today so gonna see what I can do.

Drilled and tapped it last night with no issues. Strangely though, the flat and lock washer on the factory bolts would not come off. I had to knock them off by catching the washer edge in my vise which damaged the threads. They won't fit on the longer bolt I bought at the hardware store either. It's not a big deal; I can go get matching washers for a few cents but I feel kinda dumb for not knowing what I'm missing here.

Many times a manufacturer will have special bolts made for their particular product to meet there own specs! Was more common in years past.

airshot said:

Many times a manufacturer will have special bolts made for their particular product to meet there own specs! Was more common in years past.

Click to expand...

I went to the hardware store and grabbed some M10 washers today and the fit like they should on both the new bolt I bought and the ones that were already on the outboard. I think the M10 bolts that were holding my lower on actually have 3/8" washers for some reason. This motor had a busted lower unit on it when I got it and had some iffy redenck engineering done to it to try to fix it so in a way it's understandable that someone may have used what they had laying around there as well.

Oh well...tap job was successful and I'm back in business after that and resealing it. Prob give it a new coat of paint when I get some more time and move on to the next project.

Glad you got it fixed !!

wmk0002 said:

Drilled and tapped it last night with no issues. Strangely though, the flat and lock washer on the factory bolts would not come off. I had to knock them off by catching the washer edge in my vise which damaged the threads. They won't fit on the longer bolt I bought at the hardware store either. It's not a big deal; I can go get matching washers for a few cents but I feel kinda dumb for not knowing what I'm missing here.

Click to expand...

Tolerances on washers are all over the place, no real set standards. I often take a bolt along and try various sizes until I get the fit I want, irregardless of what size it is supposed to be!!