How to install bevel gear and woodruff key

junglepig

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Joined
Oct 30, 2018
Messages
218
I almost hijacked another thread where key/keyway problems were being discussed, but decided to post my own.
Note, I also originally posted in 2-stroke engines instead of Transmission / drivetrain. I just deleted old post and reposted before anyone responded.


On the HT engines, the bevel drive gear from the crank fits on a keyed, tapered shaft.
It is secured by a thin lock washer and screw.

What is the proper assembly technique? Qualitatively, what should the clearances be like between the gear keyway and the key?
How much are we allowed to "tap" the gear onto the shaft without damaging crank seals and bearings?

Can't put much force into turning the screw without buggering the head on it, so I assume it is not intended for pulling the gear down much.

I figured we seat it onto the shaft with a few light taps, and then tighten the screw as much as possible. And then the torque is primarily transmitted by the taper-fit, not by the key, right?

Or wrong?

Thanks guys!
 


junglepig

Active Member
Joined
Oct 30, 2018
Messages
218
I almost hijacked another thread where key/keyway problems were being discussed, but decided to post my own.
Note, I also originally posted in 2-stroke engines instead of Transmission / drivetrain. I just deleted old post and reposted before anyone responded.


On the HT engines, the bevel drive gear from the crank fits on a keyed, tapered shaft.
It is secured by a thin lock washer and screw.

What is the proper assembly technique? Qualitatively, what should the clearances be like between the gear keyway and the key?
How much are we allowed to "tap" the gear onto the shaft without damaging crank seals and bearings?

Can't put much force into turning the screw without buggering the head on it, so I assume it is not intended for pulling the gear down much.

I figured we seat it onto the shaft with a few light taps, and then tighten the screw as much as possible. And then the torque is primarily transmitted by the taper-fit, not by the key, right?

Or wrong?

Thanks guys!
Alright, I didn't get any help from the forum on this one :cry:, but that's OK. I got a pretty great set of answers in this video from CR machine / Fred.
Mine sits about like the one in his video now, i.e. not allowed to move far enough up the taper to fit 100% flush with the clutch gear, but it looks like the important part is that it is aligned correctly and that the end of the crank is not "proud" from the surface of the gear where the screw should be applying pressure to keep it jammed on the taper. I need to pull my screw out once more and double check this since this has been a trouble spot for my engine from the beginning (it came without a key, and the gear would come loose during deceleration. I've since installed a key. I think I'm almost done with the issues here.:giggle:)
 

Will'smotobikes19

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Apr 9, 2018
Messages
1,653
I saw this as well I think If the small gear was heated and the engine cooled it would go on better. I learned this with the bearings. As for the bolt, it is most likely a low grade and could be replaced with a 10.9 if you could find out what size it is. I’ve heard it’s some type of furniture bolt.
 
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LewieBike

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May 21, 2014
Messages
501
Note that a better retaining bolt for the pinion gear is a 3 piece, square tapered bicycle crank bolt.

This is not the nutted spindle one, but for the better quality crank spindles that are internally threaded to fit the 8X1 crank bolt. They can be found in both 15 mm head and 8 mm Allen key sizes. I'd look into getting the washers Fred makes just in case your pinion's inner taper dimensions is stretched more than acceptable limits.
 

junglepig

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Joined
Oct 30, 2018
Messages
218
Note that a better retaining bolt for the pinion gear is a 3 piece, square tapered bicycle crank bolt.

This is not the nutted spindle one, but for the better quality crank spindles that are internally threaded to fit the 8X1 crank bolt. They can be found in both 15 mm head and 8 mm Allen key sizes. I'd look into getting the washers Fred makes just in case your pinion's inner taper dimensions is stretched more than acceptable limits.
I'm going to look for one of these. I'm not happy with the shallow slot drive on these bolts. Hard to put any torque to it without buggering it. Thanks for the info!

EDIT:

So like these?
1542689902959.png

Do you recall are these fine threaded M8-1.0mm? or M8-1.25mm? I can check in the morning...

EDIT: I went ahead and ordered a pair (different from above) from AliExpress for $1.30 shipped from China.
M8x18mm
"
ZTTO MTB Road Mountain BIke BIcycle BB Bottom Bracket Waterproof M8*18mm Socket Head Bolts For Square Tapered Spindle Crankset
"
1542691522659.png

I'll let you know how it works out when I eventually get them.
 
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LewieBike

Active Member
Joined
May 21, 2014
Messages
501
I'm going to look for one of these. I'm not happy with the shallow slot drive on these bolts. Hard to put any torque to it without buggering it. Thanks for the info!

EDIT:

So like these? View attachment 84656
Do you recall are these fine threaded M8-1.0mm? or M8-1.25mm? I can check in the morning...

EDIT: I went ahead and ordered a pair (different from above) from AliExpress for $1.30 shipped from China.
M8x18mm
"
ZTTO MTB Road Mountain BIke BIcycle BB Bottom Bracket Waterproof M8*18mm Socket Head Bolts For Square Tapered Spindle Crankset
"
View attachment 84657
I'll let you know how it works out when I eventually get them.
I hope there's enough clearance under the clutch cover for those Allen bolts, their head is a little tall.
 

junglepig

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Joined
Oct 30, 2018
Messages
218
I hope there's enough clearance under the clutch cover for those Allen bolts, their head is a little tall.
I'll try to revisit this thread and document it either way when they come in if I remember.
I could always drill a hole in my clutch cover for clearance and then cover the hole with a domed freeze plug or something :)...
 

junglepig

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Joined
Oct 30, 2018
Messages
218
I'll try to revisit this thread and document it either way when they come in if I remember.
I could always drill a hole in my clutch cover for clearance and then cover the hole with a domed freeze plug or something :)...
Funny that I said this. Take a look at this Grubee "Drill Start" engine. I'll be damned if it doesn't look like that's exactly what they've done.
LOL. I might have a "drill start" option on my motor soon y'all!!

1542863690577.png
 

junglepig

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Joined
Oct 30, 2018
Messages
218
Anybody have one of these? Wouldn't starting it with a drill require spinning it counterclockwise and tend to spin the hex-head bolt off?
How do they keep that from happening?

EDIT: I found their instructions page for using the overrunning clutch tool on a drill. There they say to remove the allen head screw and apply blue Loc-Tite. I suppose that might be sufficient. The compression on my little motor seems pretty high to start it this way. But I may give it a try. Cool.
 
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