Author Topic: BSA B31 top end noise  (Read 5261 times)

Offline terryk

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BSA B31 top end noise
« on: 10.01. 2010 15:04 »
Hi All, I ride a 1949 BSA B31 daily to work etc and it has developed what seems to be a top end noise. It has heaps of compression and doesnt blow smoke so I dont think it could be piston slap. The tappets are set. I run 98 octane fuel and the timing is fine so its not pinking cause it also does it at slow revs. The bike seems to run ok but the noise is fairly loud. I thought it might be that its not getting oil to the rockers so I pulled the covers off and run the bike. It is fairly dry of oil around the rockers. I pulled the oil pipe off the rocker shafts to see if it was pumping oil and it is so the oil pipe is clear. I thought it might be blocked oil pipe bolts but they are clear so I put it on TDC on compression stroke and pulled out the rocker shafts and they are clear. There was a small amount of oil on the shafts. My question is should there be alot of oil to the rockers on a B31?
I put it back together and ran it for at least 15 mins reving it quite a bit.The top of the valves where the rockers push the valve doesnt seem to be getting oil. I also put my finger over the hole in the oil tank so more oil would go to the rockers but this didnt seem to do anything. My feeling are that there should be oil everywhere around the rockers. Whats your thoughts before I pull it to pieces.
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1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm

Offline MG

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Re: BSA B31 top end noise
« Reply #1 on: 10.01. 2010 15:56 »
terryk
A noise similar to piston slap can also be caused by worn small end bushes.
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Online muskrat

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Re: BSA B31 top end noise
« Reply #2 on: 10.01. 2010 20:31 »
I also put my finger over the hole in the oil tank so more oil would go to the rockers but this didnt seem to do anything.
g'day Terryk, if that be the case there must be a blockage or the scavenge side of the pump is running out of puff. The rockers don't need a lot of oil, a few drops per minute is ok, the tappets rely on mist/splash. Just a thought a broken valve spring will give a noisy tappet sound. Is the noise crank speed or valve speed. You can hook up a strobe as per ign timing. Faster than strobe = crank, same as strobe = valve/cam/ign. Good luck, noises can be hard to track.
Cheers
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Offline trevinoz

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Re: BSA B31 top end noise
« Reply #3 on: 10.01. 2010 21:41 »
Terry,
            Loose valve guides get a bit rattly.
  Trev.
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Offline Desburnett

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Re: BSA B31 top end noise
« Reply #4 on: 10.01. 2010 21:45 »
Try the old trick of placing a wood dowel / screwdriver to various points on the motor (whilst running) with the other end to your ear, you will hear a symphony of mettalica or rattle.

Des
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Offline terryk

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Re: BSA B31 top end noise
« Reply #5 on: 11.01. 2010 05:45 »
Thanks everyone for your comments I really appreciate it and I am very thankful for this forum. I think I will have to pull it apart and investigate to be sure as the irish say.
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1950-53 A10 rigid/plungers, 1958-61 A10 super rockets, 1947-50 A7 longstrokes, 1949 Star twin,
1951-54 A7 plungers, 1940s M21, WDM20s,
1948-50s B33s rigid/plunger/swingarm, 1948-50s b31s rigid/plunger/swingarm