Small end bush

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JoshJ
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Small end bush

Post by JoshJ »

Lad’s,

Just after some info on the small end bush for a 350 single. Existing bush I’m about to remove has three lube holes drilled into it, I will need to drill a hole/holes in the new bush once installed and before reaming. Should I be drilling three new holes as per the existing bush or just the one hole?

Pics below of existing bush showing the 3 x holes.

Cheers

Josh
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nevhunter
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Re: Small end bush

Post by nevhunter »

You could mill a slot if you wanted to. It doesn't matter much as long as the clearance doesn't close up when it gets hot. You need a good bronze in the small end bush and check the rod alignment. Twist bend and offset. Nev
Simon.Gardiner
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Re: Small end bush

Post by Simon.Gardiner »

Factory would have had a slot that matches to the slot in the rod eye. I've seen plenty with a variety of holes in though, and some also with a lengthwise groove at the top of the bush.
As Nev says, I don't think it's critical, as long as some provision is made for lubrication.

HTH

SG
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'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
JoshJ
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Re: Small end bush

Post by JoshJ »

Will slot it out to match connecting rod, cheers guys.
Simon.Gardiner
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Re: Small end bush

Post by Simon.Gardiner »

Looking closely at the first pic, it's got a spiral groove in the old bush too?
I haven't seen that in a small end bush - again probably harmless but I don't think a spiral will draw oil into the bearing particularly. The bearing doesn't rotate, it oscillates.

SG
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'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
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cmfalco
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Re: Small end bush

Post by cmfalco »

nevhunter wrote: Sun Sep 17, 2023 6:09 am You need a good bronze in the small end bush
FWIW I used PB1 for the bush I made for my 1928 Ariel, with a clearance of 0.0005", and it survived the 3000-mile Cannonball without issue.
nevhunter
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Re: Small end bush

Post by nevhunter »

The interference fit in the rod eye can result in the bush closing up a bit when it all gets hot. Soft extruded bar is not good enough. A gudgeon pin dia around .680' can run .0008' to 001" if the finish is good. You won't hear any noise from that fit. Nev
JoshJ
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Re: Small end bush

Post by JoshJ »

Cheers for all the info. I have a replacement bush from Draganfly which I’ll be installing.

Simon, you are correct, there is a spiral in the old bush but funnily enough it only runs half length of the bush. The new Draganfly bush isn’t spiralled and will be staying that way.

The existing bush also has a significantly thicker wall then the new Draganfly one, the engine didn’t come with a piston so not sure what brand it was, something with a smaller diameter gudgeon pin then the NOS piston I’ve received from club spares.

I spent a bit of time cleaning up the new piston I’d received from club spares yesterday to confirm that the gudgeon pin and new small end bush would be compatible (which they will be). Upon getting it all cleaned up I found the bottom ring to be broken, not sure how that could have happened as they are pretty well protected with all the corrosion protection that’s been applied. Anyway I’ve emailed Alan at club spares and am in the process of tee’ing up a replacement set of rings.

Cheers

Josh
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