Weird Honda Bolts

[Eggbert]

The mystery is now partially solved. When they say 8 x 20 they mean 8mm dia. and 20 mm long. For the foot-peg bolts, it turns out to be M8 x 1.25. Did you know that SAE 20 and Metric 1.25 are the same, at least over the length of the thread pitch gauge. Oddly, the broken off piece looks to be 5/16 x 18. Too many measurements and not writing things down caused me to confuse myself. Ever happen to you? I was able to successfully chase all the 8mm threads, so that slightly smaller 5/16 bolt didn't ruin the threads. Wasn't that long either, so more threads downs deep I suppose.

The exhaust seems to still be a mystery. It ought to be a M6 x 1.25, however I'm not sure if that is a common size. M6 x 1.0 is. What came out could be the remains of the correct bolt or it may be 1/4 x 20 (remember that 1.25 and 20 are the same - well, 1.27 vs 1.25) that someone substituted. I'll probably re-tap both holes for 1/4 x 20 studs.

I think I'm on the right track..... hopefully!

[Eggbert]

I bought a used Honda S90 engine that had two bolts broken off. Wasn't difficult to remove them, but when I went to measure them so I could chase all holes with a tap, I became confused. Looking up the bolt part numbers, I got 8 x 20 for the bolts holding the foot-peg assembly on. Yep, 8mm diameter and 20 threads per inch.

For the exhaust stud, it came up as 6 x 20. What's going on with these bolts that have a metric diameter and an SAE thread pitch?

...and what about taps? I guess I could re-thread the exhaust studs for 1/4" x 20 (slightly larger), but what about the foot peg mounts? 8 mm isn't just shy of any SAE diameter bolt.

Comments, thoughts, etc.