Score marks from timing chain Norton 7

Slack off magneto nuts, pull magneto back until chain correctly tensioned, tighten nuts. You might need to lever magneto with suitable implement. If it won't go back far enough, the chain is clapped out. Get a new one. Good luck.

Previously wrote:

I have recently taken my timing cover off and noticed score marks on the top of the Oil Pump and also on the crankcase from the timing chain. The Timing chain does seem loose but I dont see any way of adjusting it. Does anyone know what the cause is and how to cure it. The engine itself seems to run well with no timing issues.

Craig Murphy previously wrote on Saturday Jan 8th 2011. 14:39hrs:

I have recently taken my timing cover off and noticed score marks on the top of the Oil Pump and also on the crankcase from the timing chain. The Timing chain does seem loose but I dont see any way of adjusting it. Does anyone know what the cause is and how to cure it. The engine itself seems to run well with no timing issues.

Hello Craig,

Alan's solution is correct.

There is an aspect of Norton twin cam chain & magneto chain adjusting (alsothe loosening & tightening of the sprockets) which isoften overlooked.

The intermediate gear spindle, at the centre of the timing case is supported at its outer end by a boss in the timing cover. Because the timing cover screws need to have plenty of clearance in the cover, accurate alignment of the spindle by that coveris provided by two dowels. One under the magneto sprocket and one under the cam sprocket.

The inner end of the spindle should be a slight interference-fit in the crankcase. You'll only achieve accurate chain tensions by using a modified timing cover (see my photo attached). When this cutaway cover is used it keeps the spindle in line and prevents it being levered sideways, which will damage where it fits into the crankcase. It's useful to keep a couple of spare dowels handy with your cutaway cover.

A few years ago, every Norton owner's box of bits contained a few spare timing covers. Now they are squirrelled away to be sold on eBay. If you can track one down, they are very easy to modify with a 2 1/4" hole cutter in a pillar drill and some files. Some of the cutaway covers I've seen on Fleabay just have the cam & magneto areas hacked off leaving no dowels so, with the sloppy fit of the remaining screws, you'd be defeating the object.

A tool made from a Dommie timing cover will fit all the twins (Mod 7 - Mk111 Commando); but the boss in the 20M3S-onward Commando covers would need milling down about 3/8" to fit a Dommie.

Paul

I wrote on January 9th 2011:

>â?the boss in the 20M3S-onward Commando covers would need milling down about 3/8" to fit a Dommie.<

Well, Iâve had a look at my 20M3S Commando timing covers and should hold my hands up to having underestimated the alterations which must be done to them in order to create a cutaway cover for use on earlier twins with their ignitions driven from the magneto, or distributor positions.

The later covers will need the spindle boss milled down ?â.

Also, because the earlier intermediate spindles extend ?â further out than the 20M3S ones, the later boss bores will need deepening by ?â as well. Not a job that can be done with a hand drill, without spoiling the fit of the spindle.

It looks as though the earlier covers are the best choice for making this tool.

There was a discussion on the accessnorton site, where a chap worked all this out while attempting to create a cutaway cover for his early Commando, using a later cover.

He got there in the end; but, looking at the photo he posted of his finished (cutaway) cover, it looks as though he cut off the parts of the cover which have the dowels! So there is nothing, other than the remaining loose-fitting screws to hold the spindle in position. The Dunstall tool he used as inspiration is modified in a similar way; but retains both dowels.

http://www.accessnorton.com/lesson-making-intermediate-shaft-support-tool-t4672.html

It is worth mentioning that these timing covers were specific to each individual engine and were stamped accordingly, to match the timing side crankcase they were machined for.

The parts books point out, that should a replacement timing side crankcase be required, the drive side case and timing cover should also be returned to the works, in order that they may be matched accurately (and presumably re-stamped).

I was thinking of posting this update a few days after my original post, and then I thought it might be interesting to see who else picks up on it, and how they would express themselves. No takers thoughâ?.oh well.

Paul