Hi Forum,
When trying to adjust the valve clearence on my ยด53 B31 the manual says to measure 0.003 " between the tappet and the push rod.
As I see it the pushrod is located on the tappet with a pin not allowing to push a feeler gauge all the way in between the tappet and the push rod
Can this be right , and how do you measure the clearence?
BR
kim
You measure the gap to the side of the pin, it should be the same both sides and rotate the rod a little while you do it.
Push the pushrod up (with an old screwdriver or similar) as you measure the clearance, to take up the slack above. Otherwise the weight of the pushrod can give you a false reading; you can think you've got the clearance spot on but it's actually too big.
The trick is to have the feelers with the 3 and the 5 so you can be sure the 5 won't go in.
Quote from: limeyrob on 22 Aug, 2025, 10:33 The trick is to have the feelers with the 3 and the 5 so you can be sure the 5 won't go in.
Good tip. This might also help the OP.
Quote from: Rog1 on 21 Aug, 2025, 23:32 Push the pushrod up (with an old screwdriver or similar) as you measure the clearance, to take up the slack above. Otherwise the weight of the pushrod can give you a false reading; you can think you've got the clearance spot on but it's actually too big.
Im interested to know how much slack would you expect to find, i have adjusted mine several times and still have a tapping noise, so wondering if i should be looking for something else
These are 70 year old air cooled engines so they do rattle and tap quite a bit. Also the valve gear is just under the cover so you can hear it working. BSA did introduce ramp cams which run a bit quieter but I think these were standard by '53. Anyone know?
What condition are the cams and tappets in? These engines will run happily with some significant wear. My B31 had a spell of closing up the plug gap, then it went back to normal. This baffled me and after a few months I decided to pull the head. There was a 1/4" of the top land missing and no top ring. It seemed the top ring had snapped off a bit at a time, sometimes hit the plug, then gone out the exhaust valve. Point is engine ran fine.
Quote from: rustyboots on 22 Aug, 2025, 13:32 Quote from: Rog1 on 21 Aug, 2025, 23:32 Push the pushrod up (with an old screwdriver or similar) as you measure the clearance, to take up the slack above. Otherwise the weight of the pushrod can give you a false reading; you can think you've got the clearance spot on but it's actually too big.
Im interested to know how much slack would you expect to find, i have adjusted mine several times and still have a tapping noise, so wondering if i should be looking for something else
I had carefully adjusted the tappets several times previously but the tapping remained. After I'd taken up the slack (I hadn't before) while adjusting the clearance, the tapping went away.
I find setting the tappets on the B motors a right pain and fiddly with the feeler gauges in the pushrod tunnel. I wait until I'm doing other work and whip off the tank and rocker covers and measure the clearance direct at the valve stem. The rockers are symmetric about the spindle so it works well. Maybe not worth the effort if you only want to check the tappets though.
You can also get a tapping noise from the timing chest if there is some excess play between the crank and cam pinions. The valve springs and followers will sharply rotate the cam as it comes of the peak of the lobe resulting in clashing of the pinion teeth..
As you have an early engine it will not be fitted with cams that have quieting ramps. These are tappetly. Get yourself a set of later cams with the quieting ramps. They are a straight swap. Fitted to later M20. B31. B33s.
I know that the quietening ramps were fitted to the Gold Star cams from 1952 along with a change in part number but the B series engines used the same 65-2420 part number from at least 1946. I've got 6 spare 65-2420 cams if anyone wants a pair.
I had a look at the B series cams that I have 3 are marked with what looks like "2-V", two are marked with a "D" and one has no markings at all apart from a tiny, very faint "61". The ones with the 2-V marking look very slightly wider across the flanks but that's only eyeballing them I haven't measured them. So it's possible that the 2-V ones are possibly the later cams with quietening ramps.