Piston pins/gudgeon pins

[e3steve]

Can anyone tell me the difference between 13111-251-000 & 13112-251-305 please? Both are in the parts manual and on the fiche with no reference notes.

Also, there appears to be no small-end bush, so does this mean that the rods need re-working at an engineering facility or that I need to source rods or crank ass'y?

Thanks in advance and regards to all,

Steve

[LOUD MOUSE]

The 305 has a small amount larger diameter than the 000. Some folks/shops use reams to clean and enlarge the hole in the little end of the rod and the hole in the piston. If the little end can't be made to fit the 305 pin (to much damage) it will be necessary to replace the rod. Here in the US that usually means get a replacement crank because we weren't supplied spare rods or crank pins and finding a shop to do the job is tough. .....................lm

Can anyone tell me the difference between 13111-251-000 & 13112-251-305 please? Both are in the parts manual and on the fiche with no reference notes.

Also, there appears to be no small-end bush, so does this mean that the rods need re-working at an engineering facility or that I need to source rods or crank ass'y?

Thanks in advance and regards to all,

Steve

[e3steve]

Many thanks for that info, Ed. I was afraid that would be the answer. I think I'll get the larger pins and some new circlips on hand ready for when I drop the motor. I don't suppose you happen to know the exact diameter of pin 305, do you? I'd really like to be able to source the correct reamer beforehand.

You may remember that I posted, back in March, that I thought the top-end clatter was the carb slides chattering, as I had come across this before, although not on a CB77 but some old 2-stroke a pal had. Well, I'm now guessing that it's the little ends -- or could it possibly be the advancer mechanism? --; if it turns out to be little ends, I'm surprised that the clatter is only apparent when on a feathered throttle, as I'd have expected it to manifest itself when under load. I bought a pair of very low mileage, serviced carbs ready for swapping out in order to alleviate the noise. Imagine my disappointment when, after finally getting the old girl running again, I fingered the (older) carb slides 'down the throats' whilst the clatter was omnipresent only to find the bloody noise didn't shut up! Still, live & learn. The newer carbs are lovely and will make a real cosmetic difference when I get the barrel & head fins blasted over the coming winter. I may even get the newer carbs bright anodised or chromed!

Regards,

Steve

[davomoto]

Steve, yeah either the advance mechanisms rivets have loosened up, or small end are worn, the latter more often the culprit. Depending on milage, piston slap, or rod up and down movement are other possibilities.

davomoto

[wombat200]

Std pins are 15mm, over-size pins are 15.1mm, from memory.......

[e3steve]

Many thanks Rob. 0.1mm seems a minimal difference for small end take-up. Then again, maybe that's all it takes to make the 305 motor sound like a diesel..... I may need to bush the rods there.

[wombat200]

Just thinking out loud here.......... It would be expensive, but you might be able to find a little-end roller bearing from a 2-stroke engine that would suit the pins & then over-bore the rod end to suit......

Or, I can't see any reason why you couldn't have larger over-sized pins made up - say, 15.2 or 15.5, etc.....

Rob.