Shaft wear

[saltyrob]

Hi Folks,

With a one inch shaft with cutlass bearing in a P bracket how much wear is the recommended maximum before renewal is necessary .I think our shaft may have wear as there was a small amount of movement when new bearing was fitted at beginning of last season.

Many thanks


Rob

 

[Neil_Y]

New our bearings are 0.13mm clearance and we suggest changing when they get near 0.63mm. As you can only size the bearing to slide over the good bit of shaft you can't make up for the worn part so starting with a larger than 0.13 clearance will just mean it will get to 0.63 quicker. if the shaft was skimmed down we can make bearings to suit 25.00 or whatever the shaft ends up being.

 

[Tranona]

Hi Folks,

With a one inch shaft with cutlass bearing in a P bracket how much wear is the recommended maximum before renewal is necessary .I think our shaft may have wear as there was a small amount of movement when new bearing was fitted at beginning of last season.

Many thanks


Rob

Not clear whether you are talking about wear on the shaft or play in the bearing which could be either shaft wear or bearing wear. Neil has suggested the sort of clearance you would expect and how much additional is tolerated. Unusual for a cutless to wear that amount in a season so suggests a more deepseated problem such as a worn shaft. poor alignment or failing mounts. Wear on the shaft at that point can only be measured by drawing the shaft, so if the movement is excessive you need to do some dismantling to find the cause.

 

[HunterWanderer]

Mine is the rubber fluted bearing and there is at least 1mm of movement and the bearing hasn't been changed for years. There is no vibration or any problem.

These bearings need clearance as they are water lubricated. In fact they need to be loose so that if the rubber swells up with being in the water the shaft doesn't get tight and overheat.

 

[Neil_Y]

The details of variables in bearing clearances are known and as an example for a 25.40mm shaft the basic running clearance is 0.03mm, to this you add clearance for moisture change in bearing ID (as it is constrained you get closure) 0.042mm and finally the biggest factor is unscheduled thermal change at 0.06mm. So total 0.13mm new, as the bearing will wear there is no point in starting at anything but the minimum clearance.

These figures are for a composite not rubber but there will be similar attention to detail and figures should be available from suppliers.

You are right in saying they shouldn't run tight and that is why so much time and research is spent looking at the detail of what happens over time so that we start with the minimum safe clearance.