The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: bikerbob on 05.11. 2014 16:30
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Have got the A7 dismantled and am just checking. Am I correct in thinking that the early A7 swinging arm does not have the removable tube in the sludge trap, and the end float at the moment is .012 and should be a max of .005. Also the left hand small end bush has turned in the con rod but must have still been getting enough lubrication as there is no visible scoring and both gudgeon pins are the same size. but I will replace both small end bushes.
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G'day Bob.
I don't recall the A7's having a tube, I thought they were only in the LJ A10 cranks.
A 10thou shim behind the drive side roller will fix the end float, but if the timing side bush is if'y it should be replaced and end float calculated afresh.
I'd ask why did the little end bush rotate? A few things to check there before a new one is pushed in. Alignment of big and little ends, rod twist or bend, fit of bush in the rod.
Cheers
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yep ,no sludge trap tube in my 61 a7.
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The previous owner had a problem last year when the timing side bush turned and cut off the oil supply this was repaired along with the camshaft and cam followers and I think the small end bush must have turned then and was overlooked on the strip down I would not have known till I removed the pistons there was no play on the small end bushes. I have removed the sludge plugs and there was very little sludge in there cleaned it out and refitted the plugs and there was no tube in there am now waiting for new shims. I was reading an old service sheet and it said max .005 for A10 and .005-.010 for A7 but on rechecking the service sheet was dated 1948 so must be for the first A7 and A10 not for the swingarm models.
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The previous owner had a problem last year when the timing side bush turned and cut off the oil supply
*????* *????*.....I think I suddenly know less than I thought..?....that the T/S bush has locating flats that prohibit it from turning... *????*
.....and an oil groove around the outside to feed no matter how it's orientated........*dunno*
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HI Dutch bikerbob is probably referring to the two part bush where the inner metal bush is pinned to the outer part that has the flat on it , the pins do apparently sometimes shear allowing the inner to revolve with the shaft, not good, I never did like that idea although BSA and many others find it sound enough, I always use the one part bush, get it oversize and have it bored to suit the crank ( should that be undersize?}
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Yep, that would do it, but if the t/s bush cut supply to the big ends the oil should be diverted to the cam and the little end gets fed with splash from it. *dunno*
Cheers
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the two part bush where the inner metal bush is pinned to the outer part
Thanks Bill, forgot about them...,and yep I think you mean ' undersize and bore it out'...
get it oversize and have it bored to suit the crank ( should that be undersize?}
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The offending timing side bush was the type with the steel outer and bronze inner but it had not been pinned and had turned I don't know if it caused damage to the camshaft and followers only that on strip down they were found to need attention and were built up and reground to the correct profiles.