KOHLER K91 Exhaust Port Threads

[rmaynard 16,301]

While disassembling one of my recently acquired K91's, I discovered that the exhaust port threads are not in the best shape. There appears to be enough remaining threads to hold the nipple securely, but is there a proper way to repair this or should I just let it go and hope that it doesn't break any more? I've rebuilt many engines, but not one this old, and have never had this issue. I'd like all you engine gurus to chime in here with your thoughts.

 

[Racinbob 11,947]

I'm not one of the gurus you're looking for but I'm thinking I would run a bottom tap in to allow you to thread the nipple a little further and I think it would be OK. I had to tap the K-91 on my 400 and I finished up with a bottom tap and I got a real good bite on the nipple.

[rmaynard 16,301]

The threads go about as deep as they can already, but I will chase them with a tap before reassembly.

 

[Racinbob 11,947]

To me that looks like it would work fine. The only thing I was thinking about the bottom tap vs a taper tap is that it would remove the taper until the very end allowing the nipple to run in further before it snugged up.

 

[rmaynard 16,301]

Good idea.

[Shynon 7,482]

3 hours ago, rmaynard said:

The threads go about as deep as they can already, but I will chase them with a tap before reassembly

Bob I broke some threads out of my block on a K301 and chased them out so I could turn the nipple in farther, that cleaned up the rust and corrosion in the threads.

[buckrancher 2,694]

Bob as long as the nipple goes in beyond the break you should be fine

 

Brian

[rmaynard 16,301]

Thanks. Looks like I may just be able to get both K91's working again. 

[6bg6ga 272]

I'll go with others on chasing the threads to clean them. Looks like your going in far enough and if not and you have access to a threading machine for threading pipe you can play with the setup a little and be able to max the pipe's depth in the block. If it were mine and I'm sure no one will agree but I would thread a piece to go into the hole that is long enough to accept a coupler. I would then weld to fill the broken area. This way it is a finished look without metal missing and will surely provide life to the project.