Export thread

somehow i managed to ruin the threads in the blade shaft of my walk behind mower (7/8" shaft). The blade comes loose by itself. it looks like i need to re-thread the shaft somehow with a larger bolt size. i've never done this before but i'm pretty sure i can handle it. just need some direction...or maybe a how-to.

any help is greatly appreciated

Buy a helicoil kit from a auto parts store. Everything you will need will come in the kit but the power drill driver.

yes...i was just researching and helicoil came up as an option. but i'm a little concerned about it....is that better than using a tap & die set? i'm looking at videos that show how to use a tap to rethread a hole. some show that you have to drill out the hole first, then use the tap and some just show using the tap. Would this be better than the helicoil?

cadman, May be a risky way to learn basic machine skill. Try a local machine shop if the mower is worth ?$50.

The only thing with going the next bigger bolt is you are going to have to make your blade hole bigger. I personally never had a problem with a helicoil coming out. I would prefer to keep the same bolt to hold the blade on. Just follow the directions on the kit and you won't have problems.

i was able to 'repair' the threads of the shaft using a 3/8-24 tap. picked up a set from harbor freight. I also repaired the bolt with a die from the same set...worked out pretty good. working great so far.

Thanks for all your help.

Helicoil is a repair for a bolt that will not be removed and reinstalled hardly at all.
Your application does not apply for that since you will need to remove your blade to replace it, sharpen, and clean your deck.
Need to go up a size on the tap.

Glad you got it fixed. Tapping it like you did should be the strongest method, besides a timesert kit (similar to a helicoil but MUCH stronger.)

I'm not sure I would want to trust a helicoil to hold on a blade that is spinning in the vicinity of where I am standing.

Blaine B. said:

Glad you got it fixed. Tapping it like you did should be the strongest method, besides a timesert kit (similar to a helicoil but MUCH stronger.)

I'm not sure I would want to trust a helicoil to hold on a blade that is spinning in the vicinity of where I am standing.

Click to expand...

You will find that a helicoil is stronger then the original threads. They are made of spring steel. I have never had one pull out yet. Just taping the old threads you are just removing metal making it much weaker. Just make sure you can torque it to specs to be safe. Yes there are other brand thread repair kits that work just as well on the market as Helicoil. If your blade comes off and hits you I am sure you will be the only one hurting and it would of been a lot cheaper to repair it right.

Tapping to the next size does remove material, but that's why you use a bigger bolt. How does that make it weaker?

We aren't getting to the point where the wall behind the threads is getting too thin. I don't think there is any concern about removing material. And tapping to the next size or two is barely any difference at all...

Blaine B. said:

Tapping to the next size does remove material, but that's why you use a bigger bolt. How does that make it weaker?

We aren't getting to the point where the wall behind the threads is getting too thin. I don't think there is any concern about removing material. And tapping to the next size or two is barely any difference at all...

Click to expand...

Thread #6 the OP said he used a 3/8 -24 tap and die. You will find that is the original size not oversize. If the threads were bad then he would be removing metal. Not that it matters to me, I wouldn't feel a thing if the blade comes off and hits someone. I suggested he makes sure he tightens the bolt to specs.

Putting in a helicoil would require removing metal, in order to accommodate the insert, but you still use the original fastener, and is a great repair, stronger than the
original. Also, going to a larger bolt might mean you have to enlarge the blade hole as well..

Fish said:

Putting in a helicoil would require removing metal, in order to accommodate the insert, but you still use the original fastener, and is a great repair, stronger than the
original. Also, going to a larger bolt might mean you have to enlarge the blade hole as well..

Click to expand...

Yes, yes and yes :thumbsup:

Good advice IMO. If a "clean out" was done on buggered threads a good test is to torgue the bolt to the upper range of the scheduled value (torque) with a torque wrench. Bad threads will not allow that value to be reached and the force will pull out threads . Then oversize or helicoil. Better that than risk runaway windmill. :2cents:

edit, threads steel/steel