Steve France wasn’t happy about a noise coming from his pre-unit Triumph engine and found that the engine sprocket is slack on the crank splines, causing chatter. He asks if it would be worth trying something like 660 Loctite – and if so, how difficult would it be to remove in future?
This is a difficult one. Loctite swells on curing to take up slack around a loose bearing, for example. It’s a similar principle to things seizing through rusting, but with the kind of continuous impact a sprocket faces, I’d be surprised if a chemical repair would last, and if it was strong enough I’d worry about getting it apart. Loctite does yield to heat but sprockets and cranks are heat treated so you don’t want to go too mad with the blow torch.
But any slack in this area will be a problem that accelerates, so anything that can be done to reduce the movement will help prevent it getting worse. The usual repair is to have the crank welded up and re-machined, which somebody like SRM Engineering could undertake, but it would mean stripping the engine completely.
I remember once reading an old dodge about banging fine sewing needles into worn splines to pack them out, but the wear would need to be pretty extreme before there was that much space; sounds a bit like one of those great ideas nobody’s actually tried. But a new sprocket might be worth a go; because the wear is likely to be spread between both male and female splines, renewing the sprocket may just take up enough wear to cure the trouble.
Spline wear could be the crank, sprocket or both