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Stripped Thread on a DuraForce Block

1779 Views 13 Replies 7 Participants Last post by  2cycled fruitcake
Fun times at GC's garage!

I was reassembling the good DuraForce from my donor 10323 to the 10550 mounting plate yesterday morning. Assembly was going well when low and behold one of the bolts from the mounting plate seemed to turn too easily. I removed the bolt with thread debris on the bolt.

It must have been corrosion that seized it. I didn't use any PB Blaster during disassembly as the bolt came out normally, but I didn't check the threads after removal.

Needless to say I am pretty miffed. It appears that all the threads came off with the bolt during disassembly. Now I have good DuraForce with one bad mounting bolt thread.

What do you think I should dö:


Ideas anyone. I want to get this 10550 assembled.
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I'm going the helicoil route. It's an SAE 5/16" thread on a 9/16" head bolt. I'm not keen on drilling out the bad thread, but I want to fix it right. This 10550 is going for sale after I finish.

I didn't realize how much of a hassle it was going to be taking the motor from a steel to aluminum deck. First the exchange of the mounting plate, then this stripped thread thing.

Taking the plate off again I decided to replace the exhaust and muffler gaskets since they both could take another disassembly. No one has the gaskets. Hopefully, one place does, but it's closed today.

Has anyone else had this problem with the mounting plate bolts? I thought cadmium plated bolts wouldn't freeze in aluminum threads. Hmmm. I will use PB Blaster next time.
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What about drilling it one size larger and tapping it for new threads? Since it's aluminum, a slightly larger bolt might just cut the treads for you.
I went ahead and bought the helicoil. I want it to last. Tapping the thread for a bigger bolt would require drilling the mounting plate as well.

Thanks to all for the advice!
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Update on my junked 10324 donor to the junked 10550 that I got for free.

10550 transplant completed. Did the helicoil, and it worked great. changed all of the exhaust gaskets, de-coked the port, etc.

Put the whole thing together, and after one pull, I have a great running 10550. Actually, it runs better than mine! It starts without a prime warm in low speed! One interesting note: this DuraForce surged bad when I first got it running in August. Now it runs better than any other DF in the stable? The only thing I did was the above plus a little carb cleaning.

If anyone in the southeast Texas area is looking for a 10550, it will be on craigslist by lunchtime.

First major LB repair completed with 100% success.
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Here's the finished product.


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looks sharp!!!!!!!
got a question,
on the 10323....
which holes bolt the exhaust plate to the deck?is it the ones with the sort of nut embedded in the plate?
going outside to mess with this unit later
That's the one, although mine were threaded and had no nut in them. Furthermore, the bolt only entered about 3/4" into the flange.

I just threaded one helicoil into the flange(mount) It works great. The mower is running fantastic with no undo vibration or weaknesses.
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