Small end spacers, H6 and VB.

[farmer58za]

Hi All
There's some small end spacers shown in  the parts manuals for both the 360 H6 and 250VB.

360H6 - Part No. 6660.149010E410, E430, E450 and E470

250VB - Part No. 6660.14900E370430, E390 and E410

I don't seem to have any on my bikes.

What are they made of and how significant are they?

Regards
David

[Montynut]

they are critical as the bottom end has no thrust washers. Montesa use top guided conrods people will say convert to bottom guided there is good and bad in both. Never had a problem with top guided.

It is difficult to get the correct size little end bearings these days. so flat thrust washers may not do the job. I use current model KTM 250/300 2T little end bearings which are slightly wider (1mm) than the original and get a thrust washer machined up with 0.4 - 0.6mm clearance total on both the rod and bearing. This means a stepped thrust washer.

The originals are hardened steel and that is what I use.I have heard that people use aluminium and mild steel but both of these would have high expansion when heated. I actually use material from a high temperature fastener with very low expansion.

[farmer58za]

Thanks for the advice.

In the meantime I found the spacers for the VB: Those are the hardened steel thrust washers, 1.9mm thick.

But then I checked the new small end bearing supplied: It's longer than the original bearing and the new rod small end width. That means I might have to look at stepped washers there .
 

Regards
David

[cappra]

Almost impossible to find a rod bearing with the correct width of the original 6660.011 bearing.

[farmer58za]

Okay, I have to work with the available (larger) small end bearing. The "stepped" washers will work but I just need to confirm the clearances:

The crank, as re-built, has a big end side clearance of 2.4mm.   The piston bosses are 25.0mm apart. Less the overall width of the small end of 16mm gives 9.0mm. The minimum small end spacer washer width would be (9.0 - 2.4)/2 = 3.3mm thick. At this thickness, the big end would just touch the crank.  How much more must I add to each washer to give the correct running clearance at the big end?

Thanks all
David 

[Montynut]

Mate you only want a 0.4-0.60mm of float at the big end. PM me your email address and I can send you a drawing of the ones I used in my VG414.

Unfortunately I have found that the pistons vary in journal spacing so new washers are sometimes needed when rebuilding.

You do not want the big-end to floating anywhere near the crank wheels. The conrod should be centralised at the big-end by the little-end thrusts.

You don't need to worry about measuring the big-end clearance just centralise the little-end within the piston with 0.4-0.60mm clearance to both the rod and the bearing. You need to measure the piston and L/E of rod etc very accurately. I have never had nice values like 25 & 16mm, last one I measured was 24.8mm & 16.1mm which makes a difference.

25 - 16 = 9 - 0.5mm (ideal clearance) = 8.5mm total. 8.5mm / 2 = 4.25mm +-0.1mm width of thicked part of stepped washer.

25 - 19.7 (width of KTM L/E bearing) = 5.3 - 0.5mm (ideal clearance) = 4.8mm total. 4.8mm / 2 = 2.4mm +- 0.1mm width of thinner part of stepped washer