Tappet adjustment on AJS 37/8

Information relating to Matchless and AJS Models built prior to 1939
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Tappet adjustment on AJS 37/8

Postby Diana3899 » Wed Jul 26, 2017 8:42 pm

According to instructions the correct clearance between the rocker ends and valve ends when valves are closed on a cold engine should be the nearest approach to nil clearance. My motorcycle has high lift cams fitted and my question is should this make any difference to this recommended clearance?

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Re: Tappet adjustment on AJS 37/8

Postby Rob Harknett » Wed Jul 26, 2017 10:01 pm

I do not see why high lift cams could make any difference to tappet adjustment. As the tappets are adjusted with the valve closed. If tighter than nil, when hot the valve may not fully close. Too loose and the high lift cams would not come into effect until clearance is taken up. I do wonder why you have fitted high lift cams. Are you racing the bike? The bike is already running on fuel about 20 octane higher than 1937 76 octane unleaded fuel.

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Re: Tappet adjustment on AJS 37/8

Postby Diana3899 » Thu Jul 27, 2017 8:51 am

Thanks for response Rob, I did not fit the high lift cams, they had already been installed when I bought it. The reason for my question was that when setting up the mag spark timing I noticed that with the piston on TDC there was a little up and down play in the exhaust push rod which I have now adjusted to zero clearance so that the push rod will turn but with no up and down play. As I had found slight play I just wondered if a previous owner had intentionally introduced some play because high cams had been fitted. You have now put my mind at rest and I will continue to put things back together. Having had the Mag checked, emptied the petrol tank and cleaned the carb I am hoping that I have solved why she is cutting out when riding. I will of course put in a new spark plug before I take her on the road.

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Re: Tappet adjustment on AJS 37/8

Postby Rob Harknett » Thu Jul 27, 2017 10:08 am

Could be muck in the carb. The old bikes do like to get warmed up a bit before you fully advance the A / R lever.

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