Burman 4th Gear Selector Meltdown

[oexing]

When buying oils or grease it should be shown that these lubricants are OK for copper materials like in gearbox bushes or synchro rings . Most of the modern recipes should be allright today. In doubt do the copper strip corrosion test as described in this PDF:
Link:
https://www.panamlubricants.com/wp-content/uploads/2016/11/Copper-Corrosivity-ASTM-D130.pdf

Vic

 

[BigEd]

GL-4 Specification gear oil seems to be the safe one to use with bronze bushes as it does not have the sulph.ur additive

 

[nkt267]

https://www.morrislubricants.co.uk/golden-film-ag140-classic-gear-oil.html

this may work instead

 

[brian gains]

terrifically useful thread having had the gearbox in / out and apart at least 1/2 dozen times this summer and having to go in again after 4th wouldn't engage again yesterday.
After all replacement parts there are only two options left, spacer behind main drive gear and on starter end of selector cam shaft/ At present the end play is 0.9mm which is excessive and by working in and out by hand seems to be the difference between gear engaging or not.
My question is what is the minimum end play that should be aimed for?. I thought I had seen this figure somewhere 5 thou'?, but can't find.

 

[Bill Thomas]

Have you done the work, Without taking the Box out Brian, Only years ago, I lost top gear, On the road,
And found the case had split and the big bearing next to the drive sprocket had moved out a nats.
I stripped it out and had the end of the box alloy welded,
He welded it with the circlip in, So as not to lose the groove, So I had to replace that,
Been OK since. Cheers Bill.

 

[tatty500]

Brian,
The figure is in Richardson. Minimum camshaft end float 2 thou. But if you are using gaskets you need to check after it gets compressed....when its too late!
I presume you have checked the selector face and its peg that fits in the cam groove.
Happy hunting
Tatty

 

[brian gains]

Thanks, I was sure I had seen a figure somewhere. I'm not running an inner gasket although there is a part # specified I have read that there are those that do and those that don't, I shall be in the latter camp.
Yes, checked the selector and did replace the pegs despite the action still being smooth and minimal wear apparent.
I replaced the output gear just because the dog teeth looked to have minimal wear, however the teeth on the replacement seem marginally more substantial.
The inner selector cam bush was worn and had two 'split' shims in place by PO, had replacement bush made up in silver steel.
End play on mainshaft seems within tolerance at 0.0245" taken from Aeriel owners site.
Will take the inner cover out this arvo', if the outer cam selector shaft bush appears worn and a replacement will bring it back into tolerance I shall go that route otherwise I'll have some shims made up. I'll deceide on that when I'm satisfied that any fitted shims will not be torn up by snagging on the shaft.

 

[tatty500]

Brian,
Like Bill says, there must be something else to blame. The cam moves the double gear into the final drive gear by about 2.5mm. Even with 1mm (40thou) cam end float there should still be engagement with your new parts.

Check that the distance from the joint face of the shell to the face of the output gear down inside the box is not more than 110mm.

The KS end cam bush flange is 6mm. It is a difficult place to shim because of the undercut on the cam shaft. If the bush is easy to remove put the shim/spacer on the bush(think there's an undercut in this corner too). This can keep it away from 3rd gear's teeth better.

Tatty

 

[brian gains]

points taken and the suggestion that if a shim should be needed place it between the outer cam bush flange and the inner cover is a good one.
Having removed the inner cover it is apparent that the outer cam bush has had a step 'machined' into the flanged end by the action of the gear change cam shaft, this would account for the excessive end play so as you (tatty) say I will need to take into account the gasket thickness. Having run the box for thousands of miles with no gasket from the PO's rebuild does not mean that this was good practice.
Bill: I haven't pulled the box out this time but when I did at the start of the summer I found the drive sprocket retainining nut loose and the bearing / oil seal circlip not seated. Having replaced the circlip I am satisfied the bearing is in the correct position and did not notice any damage to the casing. What I did do was measure the depth of the casing from the sprocket end to the face of the mainshaft bearing in consideration of putting an up graded oil seal as per the Draganfly site suggestion but it appears that there is insufficient depth as they say can be the situation in some cases. Now considering the replacement gear change bush in the inner cover and whether to have one made up or buy standard replacement. I trust new parts aren't NOS as I am not impressed at all by the quality of the material of the existing part. Once again a consequence of Burman boxes being sourced on financial considerations and also quality materials being in short supply?

 

[brian gains]

"Check that the distance from the joint face of the shell to the face of the output gear down inside the box is not more than 110mm."
I make the measurement 111.30mm which makes me a consider that the shim behind the output gear is necessary. What I don't understand though is where the wear has suddenly occurred, the bearing does not appear to have moved and nothing is apparent on the gear despite this having been replaced on an earlier strip down during the summer.