Scooterotica

shims or no shims ,its clearance that will cause early failure 0.3mm clearance is too tight but often seen on lamby cranks ,2 stroke mx /road race/kart etc run 0.5 to 0.7 mm with or without shims allowing the rod to float and be adequately lubricated on a film of oil the same film of oil that lubes the alloy piston to bore ,the ring to bore ,the balls and cage ,the needle rollers and crank/gudgeon pin
often cranks built with different rods end up at different widths due to wider rods in use and or shims added that reduce clearance ,extra wide cranks then sit off centre in the case placing side load pressure on the crank web or shim causing problems too if not shimmed or machined
just stripped a yamaha fs1e motor 27,000 miles of teenage abuse thru to adult 1 owner from new crank as built by yamaha in 1973 guess what !!!!

'guess what' no shims no doubt.

The engineer that did my Yam 110 SIL crank conversion, told me at the time, 'you don't need shims', this was good because the crank fitted without any extra gasket packing on the mag housing side and the scoot is still running great and very smooth. Anyway, I just been out to the garage to measure the clearance on another Yam 110 SIL crank conversion he did for me and guess what..... he put the shims in.

I'll tell ya....I take Mark's word (and work) in the highest regard. And yeah, I saw (and responded to) his FB msg! haha. If my crank were a 22mm straight pin, there'd be shims on it without question...but having used the reverse stepped pin, it seemed like a proper question. Sure, I could machine the shims to fit over the 22.9 part...but then where are they gonna run? Got concerned they might end up on the verge of that lip between the two and perhaps self-destruct.

Rebuilding cranks where I'm at is no problem at all, provided I can find the correct parts kit to fit. Honestly, just trying to get the best possible quality.

if shims can be fitted without the expense of losing clearance or making the crank too wide id use them ,its just in most applications it cant be avoided without milling deeper pockets in the crank web but that means reduced meat grabbing the crank pin so more chance of twisting

Ok so Y fitted no shims so what can y do t cool and lube it t keep rapid wear to a minamum, Anyone know or is y rebuilt crank fooked?

Lamaddict wrote:'guess what' no shims no doubt.

The engineer that did my Yam 110 SIL crank conversion, told me at the time, 'you don't need shims', this was good because the crank fitted without any extra gasket packing on the mag housing side and the scoot is still running great and very smooth. Anyway, I just been out to the garage to measure the clearance on another Yam 110 SIL crank conversion he did for me and guess what..... he put the shims in.

check the width across the webs approx 40.4 - 40.6 mm from memory and slide a feeler down side of shims to check clearane
if 41.4 (+1mm) it will push over 1mm towards mag so a 0.3 -0.5 clearance will be lost if u use a shimmed piston or a piston with a narrow opening/small clearance and a rod eye/bearing with a wide section might only have 1mm float
using a wide small end as yamaha do will allow full float without the piston rocking over and running on 2/3 like it does on a narrow bearing in a wide gap
for example a 24mm wide small end with 1mm clearance to piston (25mm gap) on a rod small eye thats 22 wide will allow the rod at the base to float without side load being applied
not saying im right just the logic i apply and how i choose to check

Muppet wrote:no shims so what can y do t cool and lube it t keep rapid wear to a minamum?

the fuel/oil mix thru a big clearance 0.5-0.7mm just following what have seen on many production motors from big manufacturers get away with for many years ,there engineers/r+d departments must have done the calcs and be happy although development has seen all cranks progress to shim use so preferred when possible to fit without loss of clearance/increased web width

good option use the yam rod ,narrow each side on its width to std 15mm ,use a good lamby sized bearing and run shims with 0.5+ clearance should make for a good crank

and 4% oil ,as we do on the race scoot

Tis all swings n roundabouts cramin a wider rod to 41mm webs; kawasaki rod is poss with shims on 22mm pin injun webs

Muppet wrote:Tis all swings n roundabouts cramin a wider rod to 41mm webs; kawasaki rod is poss with shims on 22mm pin injun webs

What Kawasaki rod is this?