Clutch bolt thread and pitch

[Redbeard]

Steve, I agree. If the Yamaha bolt is in fact metric, it's such an obscure thread pitch that must be exclusive to Yamaha, and match the US bolt.

By all means, contact Terry for his expertise!

...and beers are on me at the Half Pint this winter!

 

[Winderallday!]

Interesting how close these threads are, could be attributed to the difference in thread class and allowable tolerances. Based on Machinery's Handbook, the class and grade of threads are endless based on application.
The thing to consider if one were to entertain actually using a 1/2"-20 bolt instead of OEM, I would be very cautious that the 1/2"bolt grade was the same or greater tensile strength than Yamaha OEM. Would think you would want to be at least grade 8 bolt.
You would be surprised at how much a lower tensile strength bolt will stretch under torque, which for this application, I would go with OEM.
Cheers fellas!

 

[Redbeard]

The reason I brought up the thread/pitch question, revolves around my purchase of an aftermarket primary clutch for my aging Vector: CV TECH Power Bloc 80. This clutch is supplied with a longer-than-stock, 1/2-20 grade 8 bolt, as the PB 80 is slightly taller than a stock Yamaha clutch. I thought there had to be a mistake, but the bolt fits and had me scratching my head. I do appreciate everyone's feedback and I apologize for not mentioning the clutch sooner.

If you guys would have any interest in seeing pictures of the clutch etc, I will post them up. Otherwise, I'm ill prepared to give any real word feedback until I get some time on the snow.

The booklet supplied with the clutch says to torque the clutch bolt to manufacturers specs.

 

[cannondale27]

The reason I brought up the thread/pitch question, revolves around my purchase of an aftermarket primary clutch for my aging Vector: CV TECH Power Bloc 80. This clutch is supplied with a longer-than-stock, 1/2-20 grade 8 bolt, as the PB 80 is slightly taller than a stock Yamaha clutch. I thought there had to be a mistake, but the bolt fits and had me scratching my head. I do appreciate everyone's feedback and I apologize for not mentioning the clutch sooner.

If you guys would have any interest in seeing pictures of the clutch etc, I will post them up. Otherwise, I'm ill prepared to give any real word feedback until I get some time on the snow.

Dang you for making us think! Like I said before the initial torque is the biggy and second torque it really is the tapered shaft holding clutch on. The gauges I used say its a fit so that's good enough for me and every machine shop I have worked for.

 

[sledjunk]

Here are pics of the two threads meshed as best they can. Silver is a Yamaha Clutch bolt and the gold is 1/2 - 20

 

[Redbeard]

You're posting incorrect information!

 

[skidooguy]

A 1/2-20 fine series thread may well thread just fine into a M12.5 x 1.25 threaded hole, they are very close in size, and with manufacturing tolerances this could be the reason it will thread into your clutch mount without an issue.

*M12.5 diameter equals 0.492"
*Metric 1.25 pitch equals 0.049" thread to thread

*1/2" nominal diameter equals 0.500"
*20 threads per inch equals 0.050" thread to thread

So the difference between the two is minimal.
Also, measuring the body of a bolt may be different than the threads, depending on how they are manufactured, they could be rolled threads instead of machine cut threads, this could account for a slightly different body diameter vs diameter measured over the threads.

If I were a betting man, the threads are metric on a Yamaha sled.

Cheers.

This has stumped me. I am changing the motor in my kids 2001 Yamaha Mountain Lite 500. The very last step, installing the primary clutch, the threads would not even start. I looked at the crank and the first few threads are mushroomed, assuredly from a clutch puller. I've tried to fire what size tap or thread chaser I need. I purchased a 12x1.125 as I had read that, but it is too small. I took my bolt and it threaded into a 1/2 x 20 nut. When I rake a 1/2 x 20 tap it threads into a nut, but not perfect. So seemingly it is 12.5x1.25 but I cannot find a tap or anything that size. Stumped. Part number for bolt is 8V0-17647-10-00. Even the local Yamaha dealer could not really help

 

[Trussman]

I'd be tempted to take a die grinder to it and remove the 1st thread or 2.....carefully that is......

 

[skidooguy]

I thought of that too. Though to get a good angle on it. Engine is fully installed. Ideally I should have checked it on the bench when I fixed exhaust y pipe threads etc. Not wanting to remove it again. I'll tinker when I have some daylight