Engine pin bolts (measurements inside)

[beta250rrowner]

I recently found a snapped off engine bolt when I pulled the skid plate for something else.

The bolt cost £16 from Beta UK so I decided to measure the thread pitch and length for next time so that I can buy a cheaper alternative.

For some reason, it is thin in the middle, but the thickest part is m10 in diameter.

Using a leaf thread pitch gauge, I measured the thread pitch, which is 1.25mm

I also measured the length at 12cm

IMG_20211010_122827_914 by a a, on Flickr

I don't see why a generic bolt matching those measurements wouldn't fit and it would probably do a better job as it won't have a thin part in the middle.

[mtdirtbag]

I believe the reason for the smaller diameter in the middle is due to dissimilar metals so the bolt does not seize to the aluminum of the engine.

[beta250rrowner]

I believe the reason for the smaller diameter in the middle is due to dissimilar metals so the bolt does not seize to the aluminum of the engine.

Wow, I never thought of that! Surely some copper grease would do the job just as well, though!? As long as grease provides a barrier between the two metals.

[Hurky]

One issue is that those bolts normally are a high tensile strength, say 10.9 grade for example, and those are normally only available in pavonated black finish, that in a dirt bike starts to rust soon and is not pretty. I find it hard to impossible to find higher grade bolts in a good finish.

Another thing with most motorcycle bolts is that they have smaller hex heads than the industry standard, for example an motorcycle M8 bolt can be a 10mm hex head, but the industry standard available bolts are using 13mm hex heads...

Regards.

[F5 Dave]

How often are you expecting this to happen? Especially for only 16 squid for the proper bolt.

Make sure they are all tight and it is unlikely to happen again.