Square Four main bearings-line boring.....

[Knud.Degnbol]

You can support it in the bearing at the other crank case half. But you will have to clean the bearing afterwards. Or you can do, as I did. turn a temporary bush to insert in the outer ring.
I aggree, that white metal is more difficult to work on with a reamer.

[ken summerton]

Hi, does anyone have a drawing of the original main bearing (timing side) for a Square Four 4G MKII, Dowelled type, also for the camshaft bearing.

Thanks
Ken

[roger.fellows]

I can photograph mine if that's any good Ken. They were put together by somebody who should know.

Is the camshaft bearing not held in by a circlip? Or do you want the drive side for that?

[ken summerton]

Hi Roger, thanks very much for the offer of the pictures, I do have some pictures but I was after some drawings really, re the camshaft, sorry my mistake, I need the bush side not the bearing side, I have new bearing for this. thank you anyway, it is appreciated

[paul.jameson]

So far as I can see, the drawing for the timing side main bearing bush no longer exists. The good news is that Draganfly supply excellent examples of this bush so you should have no problem in getting your bike back into working order. The Draganfly bushes are white metal lined so if you insist on a phosphor bronze surface - buy a Draganfly white metalled bush and work from that.

[keith wainwright]

Hi Bob I made up a line boring jig using a redundant king pin adjustable reamer. A turned up extension shafts on each end of the reamer. Made up four plates that can be bolted to the existing crankcase halves. Using the plates

[keith wainwright]

We go on pressed the wrong button?
Fixing the other two plates with spacers and holes bored to clear reamer diameter. Using flange bearing on the outer plates and locating the reamer in line with the roller bearing OD and mainbearing OD with tampered OD bushes to locate the reamer on centre line of both bearing housings. Clamping up with flange bearings on either side to support reamer in line with bearing housings. Do not line bore from one half of the crankcase. The engineering tolerances in those days was not very good. I could carry this jobs out for you but I am in Surrey close to junction 11. Keith

[keith wainwright]

Also do not attempt to line bore without supporting each end of the reamer, you will end up with rifling in the bore. Keith

[nevhunter]

Or something resembling a shallow spline, if you are unlucky.
White metal (babbit) runs with much less clearance than Bronze (or copper lead) needs.. The normal boring of these white metal bearings is done with a sharp fine pointed tool with a very small rate of feed.( Like the finest thread you could imagine).. Bronze and copper lead need to run on a hardened shaft for best results.( Carburized, nitrided or hard chromed.) Those metals are also in need of a greater oil flow rate to keep them cool as their coefficient of friction is worse than Babbit. In my view there's a good case for sticking to the original. and keep the thickness of the babbit to a minimum as it then fatigues less and lasts longer.. Nev