C15F layshaft bush pin woes

Tigerfeet · 27 March, 2025, 15:16:03

The layshaft bush securing pin was missing from my C15F project. As the photo shows, it seems to have departed sideways. The replcement pin that I have sourced simply falls out. Does anyone have any suggestions for how to proceed with this? I'm surprised that the pin is under enough load to rip it out of the casing - maybe this is related to the engine disaster that killed this engine several decades ago.

MadPete · 27 March, 2025, 15:44:19

Did the gearbox run without oil and the layshaft seized the plain bearing? Difficult to imagine what caused that otherwise. A very strong rotational force, without a doubt!

Not sure what best to fix it without stripping. Maybe alloy build up, re-drill correct size hole and punch in pin. The simplest option would be to drill it out to the "next size up" and fit a larger pin made up for the job. However I do not know the alloy wall thickness - so any drilling would have to be done ultimately carefully.

Not sure building that hole up with epoxy would be very viable for any prolonged amount of time. Maybe remove the whole bush and Loctite it in to prevent rotation? Or rotate the bush appropriately and drill an entirely new pin hole (careful!)

neil1964 · 27 March, 2025, 18:00:39

I'd measure it and tap in a pin next size up.
Is the new layshaft broken sh a good fit in the casing?

scifi · 27 March, 2025, 21:19:55

Did you position the bush in that position for the photo..? As it looks like the bush is in the correct position anyway. Maybe a solution would be to drill the hole out, and then tap a thread with a bottoming tap to take a short pin. Problem is, how thick is that casting, as it could leak oil, if you drilled straight through.
I take it any carnage was caused by the loose pin floating around in the gear box. maybe use lots of Red Loctite next time.

iansoady · 28 March, 2025, 09:59:42

I understand th pin is to prevent the bush from rotating in the casing. This makes me wonder whether loctite bearing fit may be a suitable alternative. There's so much damage that I can't see an oversize pin solving the problem.

Stubaker58 · 28 March, 2025, 10:26:50

Would it not be possible to simply drill a brand new hole and rotate the bush accordingly?

rhyatt · 28 March, 2025, 11:12:54

Obviously check for depth of existing hole.
I'd be sorely tempted to put an appropriate tap in there and screw a new "pin" in with loctite.
Is the bush itself a good fit on the shaft or does it need renewal.
Is the pin in there to ensure the bush does not rotate and cut off a lubrication drilling ?

iansoady · 28 March, 2025, 12:11:38

Quote from: Stubaker58 on 28 March, 2025, 10:26:50Would it not be possible to simply drill a brand new hole and rotate the bush accordingly?

That sounds like a good idea. You'll be replacing the bush anyway. Won't you?

TTJOHN · 28 March, 2025, 13:42:33

Try using Loctite 510 Flange sealant, looks like the shaft has seized causing the bush to spin. make sure oil holes line up when fitting the new bush.

Tigerfeet · 06 April, 2025, 17:54:23

Thanks for all of the replies on this. I processed the suggestions... and took a trip to see my pal who is a horologist. (He makes watches by machining down lumps of metal. So has a well equipped workshop, and precision skills.) As you can see, we put the new bush in about 90 degrees rotated from the original, and used a Triumph retaining pin that fitted the bush cut out nicely. The pin is an interference fit into the casing, with a drop of loctite for good measure. I am a very happy bunny.