Small end bearing question

[tippo88]

I'm building my engine using a go crank with Yamaha rid and an SR 185 kit.
As per photo the Yamaha small end bearing is approx 17 mm wide whereas the gap in the piston is approx 24 mm wide. Guess I need a wider bearing it some spacers? How much play should there be between the small end bearing and the piston ?
Thanks in advance.



Cheers
Tippo


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[garry inglis]

mb has 22mm bearings

[hendy]

This is conjecture rather than knowledge but......

The bearing will be able to drift off to one side allowing the roller ends to run in the small end eye, which I think is a bad thing. So, shouldn't the correct solution be 22mm bearing plus 2 x 1mm small end shims?

[Donnie]

Does anyone use small end shims anymore??? isn't the percieved wisdom to ensure your big end on the cranks shimmed and then simply use the wider small end bearing as sold by several suppliers?

[hendy]

Does anyone use small end shims anymore??? isn't the percieved wisdom to ensure your big end on the cranks shimmed and then simply use the wider small end bearing as sold by several suppliers?

I think that's a sort of separate issue which is more about restraining the rod. I'm suggesting that the small end bearing should be restrained. A "normal" piston has a gap about 0.5mm wider than the bearing; I'm talking about reducing the gap to about the same width.

I've seen them for sale recently but I'm not sure where; maybe torbay lambretta?

[Velo Merde]

Suzuki man. I orderet at http://www.motorcyclespareparts.eu.
It was this one i could found for my yamaha conversion, did over 10k.km with it and its all fine!
09263-16008 16x20x23.8 HX0310A HX
https://www.motorcyclespareparts.eu/suz ... aring.aspx

[HxPaul]

Scooter restorations sell piston shims.

[Rich_T]

Best to use a wider small end bearing rather than shims.

GT small end bearings are 22.5mm wide and are identical to DT175 SE bearings. These bearings have the same roller width as 20mm wide SE bearings, it is just the cage that is a little wider to stop end float.

You can get a DT175 bearing from Ebay or I've got GT ones if you need.

[hendy]

Best to use a wider small end bearing rather than shims.

GT small end bearings are 22.5mm wide and are identical to DT175 SE bearings. These bearings have the same roller width as 20mm wide SE bearings, it is just the cage that is a little wider to stop end float.

You can get a DT175 bearing from Ebay or I've got GT ones if you need.

Rich, it makes sense to use a wider bearing but he has a 24mm gap. Isn't that too much float for a 22.5mm bearing?

The reason I'm asking is that I had an SR185 kit that I abandoned before I tried to start it and one of the things I was nervous about was the slop the small end bearing had.

I ended up buying a gt186 kit

[Rich_T]

Provided the bearing needles don't hang out of the end of the rod you should be fine.

RD rod is 16mm wide, gap is 24mm and bearing is 22.5 so bearing end float is +/-0.75mm

The effective contact width on a DT175 rollers is 14.5mm so if the bearing floats +/- 0.75mm in either direction the rollers will come to the edge of the rod.

GT kits typically float +/- 0.5mm so not a country mile off. I would have thought it OK.