Hewland draw bolt woes

[MrJackson]

I recently went into my Hewland Mk8/9 gearbox and had a rough time getting the cotter pin out of the layshaft. When I went to put it all back together, I saw that the drawbolt goes too far in to allow access to the cotter pin hole. It would have to be backed out about five or six full turns to get a cotter pin through it. It also won't go in quite far enough to put the cotter pin behind the head of the drawbolt like the former owner tried to do. Any thoughts?

[MrJackson]

So here's what I've figured out so far. Upon looking at the bolt head through a magnifying glass (I do that a lot lately), it appears that the previous owner ground a little off the underside of the head in an attempt to get it to fit further into the layshaft so they could put a cotter pin BEHIND the head of the drawbolt instead of through the hole in it. SO.... I took the bolt out (again) and counted the threads that engage the input shaft at the other end. Of the 15 or so turns it takes to thread the bolt until it bottoms out, it would take five complete turns counterclockwise to align the cotter pin holes in the bolt and the layshaft, leaving 10 threads engaged in the input shaft. Is this enough? Or do I need a new drawbolt?

[DanW]

So here's what I've figured out so far. Upon looking at the bolt head through a magnifying glass (I do that a lot lately), it appears that the previous owner ground a little off the underside of the head in an attempt to get it to fit further into the layshaft so they could put a cotter pin BEHIND the head of the drawbolt instead of through the hole in it. SO.... I took the bolt out (again) and counted the threads that engage the input shaft at the other end. Of the 15 or so turns it takes to thread the bolt until it bottoms out, it would take five complete turns counterclockwise to align the cotter pin holes in the bolt and the layshaft, leaving 10 threads engaged in the input shaft. Is this enough? Or do I need a new drawbolt?

The long bolt threaded in until it "nips up" snug. It is then slackened by one full turn before the cotter key is reinstalled. It is not pulled up tight. If you line up the holes of the drawbolt with the shaft, you're good.

[tlracer]

If the previous owner has ground off the underside of the the head (ie. the bolt is still the correct length) then the number of threads will be fine.

My only concern is whether modifying the bolt will have weakened it where it's been ground away. I realise it's not under tension but could shear and, as the head would be retained, the break wouldn't be obvious. This might not be a problem though, until you needed to take out the drawbolt.

[Bobsy SR 6]

David
I would definitely replace the bolt, it’s not that expensive. My reasoning is the draw bolt holds the clutch shaft engagement into the layshaft (rather losely). If the head of the bolt has been shortened this would allow the shaft to walk in and out of the layshaft more causing accelerated spline wear of the clutch shaft. The clutch shaft is way more expensive that the draw bolt. I’d say cheap insurance.

Best
Tom

[tlracer]

David
I would definitely replace the bolt, it’s not that expensive. My reasoning is the draw bolt holds the clutch shaft engagement into the layshaft (rather losely). If the head of the bolt has been shortened this would allow the shaft to walk in and out of the layshaft more causing accelerated spline wear of the clutch shaft. The clutch shaft is way more expensive that the draw bolt. I’d say cheap insurance.

Best
Tom

When I posted earlier, I wondered how much movement it would allow (especially if it broke). I guess it may be possible to sleeve it (to make up for the removed part) but only if the modified area isn't ragged up.

[MrJackson]

Many thanks to all. I'll run this one until I can source a new draw bolt.

[Roland V. Johnson]

Since it does not run with the shoulder against the countershaft I do not see any issue running it as is. The cotter pin is holding it into position . Just make sure you have a good cotter pin installed through the hole in the drawbolt, not behind it.

[stonebridge20]

Many thanks to all. I'll run this one until I can source a new draw bolt.

https://www.sy-gearboxes.com/

[MrJackson]

Since it does not run with the shoulder against the countershaft I do not see any issue running it as is. The cotter pin is holding it into position . Just make sure you have a good cotter pin installed through the hole in the drawbolt, not behind it.

I think you're right. So do several others I've spoken to about it.
Thanks!