Fastener Torque Conversion After Changing From 17mm Bolt to 8mm Allen?

[Milo]

I didn't know where to ask this hopefully someone with knowledge will chime in. I've replaced my drain plug (actually it's on a motorcycle) to a recessed allen plug which will be less venerable. An 17mm socket is used on the stock plug and torques at 20 ft lb. The new recessed one takes a 8mm allen and my thinking is being turned by a smaller diameter wrench some compensation should be made. If so is there any conversion? It's almost 1/2 the diameter but certainly it wouldn't need to be doubled would it?

 

[The Fred]

No compensation 20 ft-lbs. is 20 ft-lbs. Torque is applied to the threads so what size threads? Guessing 16mm x 1.5 or so?

I would believe in replacing your drain plug seal with every oil change would be the best practice and don't over-tighten.

Regards, Fred

 

[Raised on a Deere]

The torque requirement is for the threads of the plug. It is independent of the length of the wrench, of the diameter of the socket or anything else like that. If the new plug has the same thread size the torque would probable be the same although plating and type of material might call for a different torque. If the plug seller did not establish a torque setting for your application then I would just proceed with caution using the torque you already have been using.

On edit, The Fred said it better. We were both posting at the same time and I did not see his until after I posted.

 

[ericm979]

Is that from a Yamaha, and the new plug from a Mazda? I have the same waiting for the next oil change on my FJ-09. Then I'll sand down the protective fin on the oil pan that sticks out too far and can bottom out, breaking the oil pan. The new plug should be the same torque. It's in the same threads, and made of the same material.

My FJ-09 manual calls for 31 ft-lbs.

 

[Milo]

OK Fred and Deere thank you for explaining it for me, it makes sense now.

Yes Eric it's on my FJ-09, I just sawed off the fin, changed oil, then installed the new Mazda flush fit drain plug torqued to 20 ft lbs. (previous oil change I did 25# which seemed really tight). I know Yamaha says 31 pounds but I'm thinking that is a dry spec for assembly and with oil on the threads it's too much. A number of people on the FJ-09 forum have stripped the aluminum sump threads with the recommended 31# and suggest no more than 25 maximum. One person uses 15# and never had it loosen. Same size oil plug on a BMW motorcycle I have calls for 20#.

It sure is a fun motorcycle.