Drive side main bearings.

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Re: Drive side main bearings.

Postby SPRIDDLER » Fri Jan 01, 2021 6:51 pm

Iron Head wrote: am unsure about the theory that crank end float can somehow be taken up by tightening the drive sprocket nut and thereby somehow sliding the crank through the inner races or by the outer races moving in the drive side crankcase housing.

My understanding is that the end float is required to avoid end loading the timing side bush. Manuals advise that to achieve that end float it may be necessary to machine the inner face of the t/s bush. I have never had to do it on rebuilding.
The end float isn't felt after the drive axle shock absorber assembly and sprocket have been fitted as tightening their retaining nut draws the axle through the main bearings' inner races.
I poke badgers with spoons.....from 2 metres.

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Re: Drive side main bearings.

Postby Iron Head » Sat Jan 02, 2021 3:11 pm

Hi Spriddler agreed about avoiding end loading the timing side bush and ways to ‘set’ a new bush correctly (my old timing side bush was fine) but what I am not understanding from reading the old manuals etc is how the tight to crank and crankcase main bearing system permits any end float/movement of the crank left or right. The new mains I fitted nipped up darned tight on the crank once cooled. I did a test with the old race and you need some heat and a puller to get ‘em off again. Also setting the bearings to perhaps allow some future drive side take up likely means the crankcase halves won’t meet properly. If there was a single race and perhaps more of a sliding fit on the crank the original instructions on taking up end float etc might work. As always just my thoughts.

Iron Head

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Re: Drive side main bearings.

Postby SPRIDDLER » Sat Jan 02, 2021 4:36 pm

Iron Head wrote: am unsure about the theory that crank end float can somehow be taken up by tightening the drive sprocket nut and thereby somehow sliding the crank through the inner races or by the outer races moving in the drive side crankcase housing.


I think the end float requirement is only relevant during assembly and is just a check to ensure that there is end float, thus avoiding pre-load on the t/s bush.

What I am not understanding from reading the old manuals etc is how the tight to crank and crankcase main bearing system permits any end float/movement of the crank left or right.

As with your method I've also always fitted the mains in the the heated c/case and then installed the flywheel and shaft assembly. The correct end float has been there without any need for further attention although I've not found that the axle has been immovably tight (or loose) in the bearings and generally the whole assembly goes together with a satisfying 'clack' from the axle as it hits home on the inner race.
I may be having a geriatric moment but ISTR that somewhere in the depths of the manuals there's reference to the inner main bearing being a looser fit in the c/case than the outer one to facilitate moving it to obtain the required end float. On the other hand it's suggested in manuals to achieve the end float by machining the face of the t/s bush. :?
Anyway, just as long as there is some end float before the rest is fitted (s/absorber etc) it'll be fine. My only thought is that if there was too much end float the scroll on the t/s axle might not mesh 'nicely' with the oil pump plunger although if the drive axle and bearings are to spec'n and correctly installed that wouldn't happen.
I poke badgers with spoons.....from 2 metres.

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