Carbide wood cutter 42mm opens out cam tunnel for Combat cam

Bought a 42mm carbide wood boring tool and used it on an M head Bridgeport to bore out the cam tunnel on pre 72 cases for fitting of Combat cam. Neater than getting out the dremel.

I always thought the clearance was required for the bottom of the barrel lifter bores?
I just offered my twin chain Norvil 2S (not SS 22729) into the atlas cases and there was no problem at all.
I then put a 7S and it just not quite cleared the center oil shield ring. Very minor relief work for that one...

Cam lobes were fouling in the tunnel, cases in the 13100 range. Measured 42mm on a set of 72 combat cases.

Do I need to do that to fit the 2S combat cam into my 850 ?

Al I run a 2S cam in my 850 and it fits the tunnel on mine ok without opening it up its been in there since the early 80s but of course you got to check it out to make sure.

Ashley

kommando said:

Cam lobes were fouling in the tunnel, cases in the 11300 range. Measured 42mm on a set of 72 combat cases.

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11300 is 1947?

If commando is 20M3 than drive side case is same casting as atlas, and both are twin chain engines.
If your engine is 20M3S ? then its a later single chain engine. New 06- castings on both DS and TS. If so..
I will grab my 20M3S research case and try 2S and 4S in that one.
Will be interesting since rumor/literature that "combat tune" was offered prior to 200000 combat breather cases.

11300 Edited?

kommando said:

cases in the 13100 range.

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13100'0' (1969)?

IAW INOA tech digest:
131257 first "S", first 20M3S single chain engine
I own 12725x, 12827x and skip all the way to 20M3S 15159x

20M3/131198



Double chain as the studs for the distributor were there.



Case has 69 stamped on the timing side in the oil pump chamber just below the barrel face.

4th Mar 69 build date according to NOC, exported to US but I got them from Northern Ireland.

Who's supplying the 2S grind on a twin chain core or are you doing a single chain conversion?

Single chain conversion. The breather through the camshaft breather holes are present in the SS cam and have kept the oil shield ring for the camshaft breather holes so can remove the timed slots undr the cam bush and breath using a reed valve out the cam end hole back to 72 oil tank, if it's not enough the large sump plug is available for additional breathing.

ashman said:

Al I run a 2S cam in my 850 and it fits the tunnel on mine ok without opening it up its been in there since the early 80s but of course you got to check it out to make sure.

Ashley

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Thanks for that. I was going to kill two birds with the one stone by fixing my engine oil leak while fitting the 2S cam. However the engine oil leak has been there for years and is very slow. The leak in the gearbox worries me more. So I will fix that and probably not change the cam in the engine. The engine is fast enough for it's purpose already and I feel uncertain about that the 2S cam might do to reliability.
I don't know what your weather is like in Brisbane, but down here it is rare that I can get a day which is cool enough to work in my shed. I am getting really sick of this heat. My main problem is I don't want to start work on the bike then have to leave it partly disassembled due to the heat. I need about three days straight with no interruptions.

FWIW bit of trivia...
The 69 is not the year but it is the id # for the timing cover sn. The case and timing cover are sanded and buffed as a set and were then both stamped as a mate. The two I have here are 29 and 46 stamped inside the timing chest, same as yours, and on the flat over the OPRV in the cover.
This is quite in keeping with the bottom of the engine cases which were both stamped to show left and right mating as a set.

On these cases the matching numbers are not on the bottom but stamped on the insides of the cases, the timing cover is long gone.

Al the 2S cam is very reliable in my 850 motor its been in it since the early 80s I run 40thu flat top pistons but my head has a lot of port work done to it but still running my stock valves, it has never let me down in all those years of running it and I ride my Norton pretty hard, but its great when the cam kicks in and will keep reviring freely way past 8,000 rpms if you let it but I wouldn't if you don't want the rest of the motor to go bang.
As for heat I built a open carport off the front of my shed, my bike lift table is kept under it and I do all my bike work under the carport as inside my shed dueing the day is way to hot, but I have good lighting inside my shed for working at night if I need to do any machining, best part about the open carport we get a good sea breeze as I am only 1 mile from Moreten Bay and up on the highest part of Brighton, once the SE breeze starts to blow things cool down, my shed is set up for bikes only can't get a car up the back of my yard and was built for bikes only, its a well set up shed, music, beer fridge and bikes, what else can a man ask for and my girls need permission to enter, except for my female cattle dogs lol.

Ashley

I will get VIP status just so i can post pictures directly.....
Recently using a 3/8 parallel tungsten bit i manually milled out with my Bosch router the centre recessed sections of the Z plates, took a fair while but I'm well happy with the result

I'd be careful using a router. They are made to cut wood and plastics, and as such their working RPM range is a higher speed as is the their feed rate than machines used for milling metal objects. The shapes of a wood bit's cutting angles reflect these differences too. A better "bodge" would be to chuck the wood bit in a drill press or milling machine where you can control the cutter speed better and the feed rate. Using a router on metal is crazy... I've also used a waxy lubricant on the teeth of a negatively raked carbide circular saw blade to cut aluminum angle. the waxy lube is to keep the chips from sticking to the carbide

M head Bridgeport is a vertical milling machine.

The alloy of the Z plates is surprisingly soft... it took me around a hour on each & there is no "dulling" or damage to the bit
I did try light lubricant, but cant say it made any real difference