Longstroke timing gears v standard gears

[CheeserBeezer]

If this information has been on here before I won't be offended if one of the Moderators pulls it!. A few people have made kind remarks about my 'valve timing -time saver' thread. So, if you're using a slave idle pinion, I would strongly advise you check it is correct for the engine you're building! Indeed, check all the gears are correct! Please be aware that, whilst longstroke gears are (roughly) the same shape and size, their timing marks are in different positions so they are not interchangeable unless you remark them. I have come across the occasional longstroke gear amongst supposedly standard A7/10 gears. I've attached a drawing, which I did a few years ago, which shows the difference. When building an engine I always refer to this drawing to double-check I'm not mixing up the various gears.

[Peter in Aus]

I have used this many times, very useful, thanks for putting it up again 
Peter

[Brian]

I wasnt sure just where to put this topic, I'll leave it up to Musky to shift it to wherever is appropriate.

This is a follow on from CheeserBeezer's post on timing gears.

I think it was me who originally started this back in 2009, 14 years ago, with my experience with a longstroke Star Twin I was restoring at the time so I thought I would re-visit what happened for the benefit of members who have not come across this.

I restored a 1950 Longstroke Star Twin, full rebuild including magneto etc etc. After the resto the bike started first kick, idled perfectly and ran perfectly but would only do about 55mph. I knew it should perform better than that so after a couple of days of thinking about possibilities I checked the valve timing and found it was considerably out. All marks lined up correctly and this is when I first found out that the longstroke and shortstroke gears are identical except for the marks stamped into them. As is now know there is four tooth difference. My bike had the wrong gears in it and that was backed up by two previous owners I was able to talk to. Both said they liked the bike but were very disappointed with its performance. Even when you have been working on these bikes for many years you can still get caught out although this was the first Longstroke I had worked on.