G: Gearbox (Twin) Cracked G4 final drive shaft

Cyborg

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I wonder if part of the story on why the other bushing materials tend to fail is because they were installed without sufficient clearance. Oilite would be more tolerant of that sort of thing? If the general consensus is that oilite is the recommended material (unless going with Viny4’s recommendation), why does the Spares Company offer a cheaper lead bronze option? Maybe they shouldn’t?

I have some NOS bushings, including a G16 that I would like to use. Is there a sure fired way to tell if it’s Oilite? It looks like it..... warm it up and see what oozes out?
 

oexing

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Oilite/porous bronce seems a bit absurd to me in a gearbox with oil filling. This type is allright for places like girdraulics with infrequent lubricating. But in a gearbox a good phosphor /tinbronce would be my choice, also easily available . Basically it would be a good idea to have some sort of circulation within gearshaft assemblies by having some scroll grooves to get oil inside and an exit as well. I tried to do so but am not quite sure about suitable philosophies to achieve this. In our case here I´d have max. 2 thou play in the bush.

Vic
 

Cyborg

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Oilite/porous bronce seems a bit absurd to me in a gearbox with oil filling.

Vic

I don’t disagree, but if absurd really bothers you, then why own a Vincent?
Same theory goes for cam bushings.... oilite seems to survive a lot better. I still think it’s a better alternative especially for the ones that don’t end up getting sufficient clearance or have questionable oil supply. There are ways to get around these things, but then you need to totally re-engineer the entire motorcycle. I think in a lot of cases, the bushings don’t get sufficient oil and some folks installing them don’t have the tools to install them properly and measure the clearance.... assuming they know that the clearance should be checked and know how to correct it. Probably lots of bushings getting the ends mushroomed over when installing, so that helps to keep oil out. Oilite is more tolerant?
 

greg brillus

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It is a clearance issue in most all cases.........The gearbox bush would fail due to either insufficient clearance and/or too tight a rear chain.........If longer rear springs are used,it is very common for the chain to hang loose..........if this is not done then the chain will be too tight in service. The gearbox oil level can drop, bleeding into the primary unnoticed.........this could be a culprit as well. I have cut a scroll into the large bush to feed oil into this cavity, but I feel it probably causes a leak from the outer bush due to the pumping action like a mini oil pump. i have heard of folk who drill a small hole though the output shaft to feed oil between the 2 bushes..........It is hard to say what is a total fix, but the modern 5 speed box tends to have small needle rollers in place of these bushes and a tiny seal between the shafts at the sprocket end.
 

john998

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Hello, Also too little clearance between the hollow shafts and the constant mesh pinion cuts off the oil. 1/16th holes drilled in the taper at the end of the hollow shafts should fix that problem.
I used phosphor bronze once but it soon failed, I think this contributed to the failure of the cam plate spindle boss in the crank case.
Best to stick to oilite to be safe, although lead bronze is an excellent bearing material for many applications. John
 

Bill Thomas

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Last time I put mine together, As well as V notches, I packed it with Copper slip,
Something we were told to do with the Mini Car, British Leyland, Primary Gear,
I was never happy with the oil supply there, As well as a lube' it was to act as an oil seal ?.
Back in the 70s.
 

TouringGodet

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I went with the Maughan G4AS, not sure what type of material is used for the bushings. I did a dry run of the assembly, and I can now shift to all 4 gears. I don't have a dial indicator, but there is a slight amount of free play for the input shaft. The large bushing has a spiral groove cut into it.



Edit - almost forgot. Greg’s suggestion in Craig’s restoration thread, about sliding the gears and cam plate slightly away from the spindle boss, worked great. First just worry about getting the cluster into place, then slightly slide the cam plate away, double check the cam plate and the shifter are in the first gear position, then slide the cam plate fully in, and bingo, the bevel gears are correctly aligned.
 
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