My Comet let me down a few days ago. Just like Vic Youle's did a few years ago. The fault was exactly the same, a melted selector on the 4th gear side.
I was beating myself up for using the wrong lubricant which could be oil or grease depending on what you read. However the real reason is far more serious.
So what I'd like to determine for all Burman users is if this is a manufacturing problem that applies to boxes made in March 1951 or if all are the same.
For those who don't know, the model number and date are stamped on the outsde of the inner cover. G97 is the Comet BAP model and in my case C51 is the date using letters A to M for the months from Jan to Dec with I not used.
The meltdown occured because when the mainshaft sliding gear is in the direct drive 4th gear position its 26 teeth only overlap the dogs inside the 33 tooth output gear by 1.2mm and some of this was on the lead-in chamfer! (When in third gear, the overlap at the other 20 tooth end of the sliding gear is 4mm.)
Having spent most of its life in top, this little contact patch slowly wears the corners away so that now the selector has to provide a force to hold these teeth in position.
This force produces wear in several places......the gear groove, the selector face, the selector pin, the groove in the camshaft and last but not least the inboard end of the camshaft bush where there is steel to soft steel contact.
As the wear increases the force increases and as the force increases the wear increases until the lubricant breaks down and the selector melts from one side.
My question is this. Is this a design fault that can affect all BAP boxes, OR is it a manufacturing fault that occured for a few days or months? So if your Comet has suffered like this what is your gearbox production date?
Also, will everyone with lots of Burman bits go and look at the shiny contact patch caused by the dogs on the tooth ends of the sliding gear and reassure us all by finding lots with a good 4mm at both ends.
Now where can I buy a new selector from?
Good hunting,
Tatty
I was beating myself up for using the wrong lubricant which could be oil or grease depending on what you read. However the real reason is far more serious.
So what I'd like to determine for all Burman users is if this is a manufacturing problem that applies to boxes made in March 1951 or if all are the same.
For those who don't know, the model number and date are stamped on the outsde of the inner cover. G97 is the Comet BAP model and in my case C51 is the date using letters A to M for the months from Jan to Dec with I not used.
The meltdown occured because when the mainshaft sliding gear is in the direct drive 4th gear position its 26 teeth only overlap the dogs inside the 33 tooth output gear by 1.2mm and some of this was on the lead-in chamfer! (When in third gear, the overlap at the other 20 tooth end of the sliding gear is 4mm.)
Having spent most of its life in top, this little contact patch slowly wears the corners away so that now the selector has to provide a force to hold these teeth in position.
This force produces wear in several places......the gear groove, the selector face, the selector pin, the groove in the camshaft and last but not least the inboard end of the camshaft bush where there is steel to soft steel contact.
As the wear increases the force increases and as the force increases the wear increases until the lubricant breaks down and the selector melts from one side.
My question is this. Is this a design fault that can affect all BAP boxes, OR is it a manufacturing fault that occured for a few days or months? So if your Comet has suffered like this what is your gearbox production date?
Also, will everyone with lots of Burman bits go and look at the shiny contact patch caused by the dogs on the tooth ends of the sliding gear and reassure us all by finding lots with a good 4mm at both ends.
Now where can I buy a new selector from?
Good hunting,
Tatty