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#740497 07/02/18 12:58 pm
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Les P Offline OP
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I need to do a few things to the Norton 850 cases, one being replace the cam bushes.
I have two of the short Mk3 type (T/S) bushes (06-5428) but some googling suggests staying with the Mk2 long type (06-3020) with flange because the short version can move having less contact with the tunnel in the case. ?

Photo courteous of Old Britts.
[Linked Image]

The journals (used but good cams) on two camshafts measured around .874" so was going to get a 7/8 (.875") ground shank helical flute reamer over a straight flute.
I thought a helical/spiral flute cut smoother over a straight but do not know it for a fact in bronze ???? maybe it makes little difference ?

[Linked Image]


Last edited by Les P; 07/05/18 10:12 pm. Reason: .874/875" not .824/825"
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Can't see the material making any difference as the smoothness is coming from a fully round contact rather than threepenny bit type contact once you have some depth of cut. Make sure the reamer is long enough to cut both bushes at the same time or can be piloted in some way which is what I did.

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Les P Offline OP
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Thanks for the reply, I ordered a reamer today.
Machine ground shank OD 3/4"
OL: 10"
FL: 2 3/4"

Once it arrives in the post some form of pilot system can be constructed.

[Linked Image]








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You may have to reverse the reamer in to cut the first bush in the timing side with the long extension inside the uncut drive side bush, then once you have a start and the reamer bottoms out in the driveside bush turn the reamer round and finish the cut.

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Les P Offline OP
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I was tempted to try and do it by using the toy mill starting on the D/S fixed to the table then bolting the T/S case to it to ream that bush, it would take a lot of clocking and a dry run to see how the two bores compare to each other before hand.

Some form of reusable fixture is still top of the list, it looks like no reamer until after the weekend.

One small job out of the way in the meantime.... ( 12 mm ball nose )

[Linked Image]

[Linked Image]


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As my 850 is not apart I went to a flexible tube with enough give to clear the web which I will change for the solid tube if the crankcases ever need splitting. Best possible place for the breather.

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Les P Offline OP
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The mod got the nod from Mr Comstock. (I wanted to avoid cutting the tube)

I had some time last night so milled the D/S bush until it could be collapsed easily (and carefully) and all but fell out.
The blind D/S will be a little more tricky.
I wonder why Norton did not use sintered bronze.

The picture is not clear enough but the machining marks were still visible from when the case was bored, to the right of the oil feed hole is raised alloy from when the bush was installed cold and raised the surface as it went in.
The replacement bush will have the engine case heated and the bush will have the outer face of the hole chamfered to avoid that.

[Linked Image]

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Les P Offline OP
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Done, now a waiting game.

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