T3/LM2 engine breather valve

Can anyone give me the size of the ball bearing in the crankcase breather valve. The one in mine is 10.28mm in diameter which is only 0.07mm (0.0025")larger than the bottom of the hole in the breather valve.It do’es not look right to me.The ball sticks very easily on it’s seat.I would have thought the ball should be 11 or 12 mm in diameter.

Will see if I have one in the shed.Could you go from bore of the valve minus a clearance figure say 0.5mm? This would take account of the wear in the bore.Just a thought,All the best,Steve

Thanks i dought that the bore of the valve is worn ,i just think the ball is the wrong size.The bore of the valve is 12.87mm so 11 or 12mm would look better.

From memory the ball does not totally block the hole as such …but I will check for you mate

Guzziology has a fair bit on this i will see if i can dig it out

looks like … you may have to order a nuvver one then compare and send the duff one back ?

ok ok gettin my coat …

Ahh older ones were redesigned as they did have problems…

the only place that is likely to have one to measure is a spares emporium, just DON’T ask Baldrick cos I can guess the reply …

You is getting scary Ralph you will be going around counting nuts and washers and how long the bolts threads that should be showing soon

Not a member of the VMC are you?



Is the ball a black round ball? If so I might have one in the drawer of bits and pieces.This is the detail from Guzziology

Yes it’s the check ball. All the ones i have had previously were steel ball bearings. I think someone has put a smaller one in for some reason ( probably dropped it on the floor and rolled away never to be found again). It’s far to small for the seat. All i need is the ball diameter i think it should be 11-12 mm.so it sits on the seat correctlyralph2012-04-28 08:33:23

Tried doing this ?

xtheone&onlymin2012-04-28 09:35:19

The one in my drawer of bike bits and pieces is about 18mm diameter so is probably a red herring!

if you put a red herring in it won’t it start to smell?

Depends where you plaice it!

Bangs head against the wall in despair.

Suggests to me hole in the bottom is wearing oversize, get a whole new unit. Hope this isn’t a new one!

I got a new new-style one somewhere, ball does not stick in hole. (Yet…!)

The note about the old style having problems is true, the square hole in the top plate tended to get hammered until it was round, then the ball would block the hole so no venting. (Crankcase pressurized!) Or, literally hammer the top plate off, I was shocked when I clocked the state of (one of) my Spada’s one, shocked I tell you (top plate hole was perfectly round and had started cracking)

PS: the ball can’t be too large coz air has to blow past it easily don’t forget

I have replaced the old undersize ball bearing which sticks on it’s seat with a 12mm diameter one it looks right sits on the seat of the valve correctly do’es not stick and there is still room for it to vent.My valve body is the one with the removable circlipralph2012-05-14 16:36:18