Which cam timing dot to use on 1950 model 18

[Invicta]

OK I know there are a lot of threads on this subject and I have probably read most of them but still managed to get things wrong. Using Ken De Grooms joining the dots and the number 2 dots for AJS, (the number 1 dots being for matchless or so I had read. When following Kens instructions and pointing the inlet cam lobe at two O'clock there was no dot anywhere near the one on the valve timing gear, which was set to the centre of the inlet cam bush. It was nearer to 4 o'clock before the number 2 dot lined up.
With this setting the exhaust vale seems OK but the inlet was way out , fully opening at 80 degrees after TDC and closing at 70 degrees after BDC. I swapped over and lined the number 1 dot up on the inlet cam and the results were much closer to where they should be . Inlet fully open 30 degrees BTDC and closing about 60 degrees after TDC. I had read somewhere that for a 1950 AJS the number 1 dot should be used on the inlet cam and the number 2 dot on the exhaust cam. I can not now find where it was I read that. Can anyone please confirm that that is the case. I used a timing disc and a pointer fixed to an engine stud, with the rocker box off and just watching the movement of the push rods. Not very precice I know but good enough to see if the cam gears are roughly where they should be.

[Invicta]

To confound my brain even more , the Pitman Book of the AJS states that on 1950 to 51 engines the 1945 -49 proceedure applies but it is important to note that each cam wheel has two timing marks 1 & 2 . Always use the number 1 mark & disregard the number 2. (That goes in the face of number 2 for AJS and number 1 for Matchless)

In the technical archives Heavy Weight Cam Information states use the No 1 mark for the exhaust cam for all touring modles and use No 2 on the inlet cam for 500cc touring and competition models.

[Duncan]

You may have cams marked for a rear facing (Matchless) magneto hence none of the marks lining up, its easy to transfer the marks by counting the teeth and marking with paint

[56G80S]

Duncan's point is sound. I think the cam wheel dot arrangement changed depending on years as well; I thought Ken's article referred to that. Certainly the broad, non dot related, approach worked for me. Having said that I'm using the 350 timing on my 500.

Johnny B

[Invicta]

Hi I tried Ken's method again and bought a DTI to check the movement of the pushrods properly . Using this in conjuction with a timing disc printed off from the Matchless clueless site I checked the timing again, with the following results. The inlet starts to open at 65 degrees BTDC and is fully open 60 degrees BBDC and is fully closed at 32 degrees BTDC. The exhaust starts to open 65 degrees ATDC is fully open at 80 degrees BTDC and is fully closed at 55 degrees BBDC. The timing disc was set at TDC with both valves closed using a a rod in the plug hole to find TDC. These readings do not seem to bare any resemblance to what the manual states they should be. I will take off the nut on the timing pinion to make certain that I did mark it where the dot is, as when the nut is on it can' be seen. Either that or whoever keeps hiding my parts has altered the cam positions since I put them in.

[Invicta]

I just tried the cams again following Pitmans intructions to the letter. For a 1950 engine with cam gears marked 1 & 2 , which is what I have. The result was both valves opened at the same time more or less, which is obviously wrong. The engine is 1950 but maybe the cams are later. Pitman says that for 1952 and 1953 use the number 2 dot, which is how I had them set up before. Argggggh

[Ralph]

Around TDC on the exhaust stroke the exhaust valve should be closing and the inlet opening so the valves should be rocking
around TDC, not an exact thing but a ball park to see if you are close.

[Invicta]

Thanks for that Ralph. Yes this is what they do towards the end of the exhaust stroke as the piston approaches TDC the inlet opens before the exhaust has closed. There is a bit more of an overlap than I would have thought. The rest of the valve timing is still no where near what it should be. I am not talking about a few degrees, but masses. So something is still not right . David