45 Engine/Gearbox Alignment

Method for aligning engine and clutch sprockets.

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old man emu
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45 Engine/Gearbox Alignment


Post by old man emu » Thu Jan 10, 2019 8:28 pm

I have to pull my gearbox out of the bike to replace a broken bottom stud (Part # 2318-26), after which I'll need to align the engine and clutch sprockets. I know the job requires the use of a straight edge.

Could someone post some pictures of how the straight edge is used to set the alignment?

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Re: 45 Engine/Gearbox Alignment


Post by Mark44 » Thu Jan 10, 2019 11:45 pm

No doubt someone will correct me if I'm wrong, but I don't think you need to align the transmission and engine. The transmission can be adjusted fore and aft, but unless the trans plate is wallowed out, it's not adjustable left and right. The straight edge is to align the rear wheel with the trans drive sprocket.

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Re: 45 Engine/Gearbox Alignment


Post by kitabel » Fri Jan 11, 2019 2:55 am

A long ruler should touch the teeth on both sprockets simultaneously with no visible gap indicating an angle. If it looks good, try the other side, there may be a gap but it will be the same width on both.
I agree, there is no adjustment provision built in. The lateral (left-right) alignment should be really close if all the parts are in good shape, no bent studs, elongated holes etc.
Most of the alignment errors I've seen:
1. sprocket not original quality, the taper may not be correctly located in the hub
2. the sprocket isn't fully seated, typically a burr on either mating surface, wrong key, or the key didn't fully seat in the shaft
3. bent frame, repaired front motor mount etc.
The transmission itself would be difficult as all of its attachment points are fixed.
Normally, if a small error is detected (chain from the engine does not accurately align with the clutch drum tooth row on both sides) it's possible to make a small adjustment using the condition of the buffer plate.
If the engine sprocket teeth are outboard (too far left) of the clutch teeth, insert a thin shim (brass or steel preferred, although aluminum has been used, roughly equal to the error) between the buffer and the clutch shell and re-attach. If need not be a continuous circle as long as all of the rivets are included and the entire width is covered, making 3 smaller pieces may be easier. Make sure they're flat.
If the engine sprocket teeth are inboard (too far right) of the clutch teeth, thin the buffer on a large piece of glass, surface plate etc. with fine paper and re-attach.

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