Author Topic: huge vibration  (Read 2272 times)

Offline emilios

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huge vibration
« on: 08.10. 2011 16:31 »
Hi...its been a long since i wrote in this forum...the reason: no problem with my Plunger A10..
But a friend just bought one plunger A10 1953 and on the first ride he told me that the bike has huge vibration..
Also the compresion on the kickstart doesnt look like an A10..more like a B31..
I did the compression test with the one piston at 125psi and the other one at 100psi...both with close throttle position..
The different compresion can cause the vibration or i have to check something else before a crank balancing?
Thanks

Emilios
1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus

Online bsa-bill

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Re: huge vibration
« Reply #1 on: 08.10. 2011 17:18 »
Hi Emilos
I think compression test is done with the throttle wide open, so maybe that would give different result, don't think that is too bad though for a low compression ratio.
Others here will have more knowledge of vibration causes, maybe timingside bearing, worn primary chain ??
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline a10gf

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Re: huge vibration
« Reply #2 on: 08.10. 2011 17:39 »
Start with the basics, and from there eliminate possible causes. Are all the engine mount bolts tight?

A10 GF '53 My A10 website
"Success only gets you a ticket to a much more difficult task"

Offline emilios

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Re: huge vibration
« Reply #3 on: 08.10. 2011 18:03 »
Yes tonight im going to check the engine mount bolts and the ignition timing...
Ill let u know
1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus

Offline Beezageezauk

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Re: huge vibration
« Reply #4 on: 08.10. 2011 20:15 »
Don't forget the head steady bolts!!


Offline wilko

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Re: huge vibration
« Reply #5 on: 08.10. 2011 21:07 »
Broken crank, too tight primary chain,piston weight wrong!

Online orabanda

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Re: huge vibration
« Reply #6 on: 09.10. 2011 01:26 »
Check all engine bolts are tight. Double check the head steady bracket!

Also, check petrol tanks bolts are tight; especially the front bolt (below the handlebars).

Richard

Offline RichardL

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Re: huge vibration
« Reply #7 on: 09.10. 2011 19:09 »
Emilios,

The Cultural Centre project may yet come to life, so maybe we eventually get to meet.

Compression should not need the throttle open. Adequate air supply will get to the cylinders for the test. Otherwise, our engines couldn't idle.

100 psi does not indicate a broken piston, and firing with that compression imbalance would not lead to "huge" vibration. Running on one cylinder, in my opinion, also does not lead to "huge" vibration, but is easily checked by pulling one plug wire off while the engine is running and feeling the difference. Compression problem sounds like one of the following: gasket leak; valve leak; ring leak; test method error. To test for ring issues, shoot two or three squirts of oil into the cyclinder and test again. If the rings are at fault the compression should rise.

I am thinking you did not find engine or head-steady bolts to be the problem, or you would have told us.

If it's a broken crank, as far as I know, the engine isn't running.

Is there noise in the area of the crankcase? When I lost lubrication to one rod journal (in 2007), the bearing spun and the rod became very loose, but the engine kept running. Plenty of vibration. I think, you could get different degrees of the same problem that result in even more vibration. Here is the video I sent to SRM for help. They replied, "Don't start the engine again before a tear down." Lifting off the barrels exposed the loose rod right away. Anyway, eliminate the easier and more accessible possibilities before tearing down.
 
http://www.youtube.com/watch?v=T9grUuIEzM0

Richard L.






Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Offline emilios

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Re: huge vibration
« Reply #8 on: 11.10. 2011 17:37 »
Thanks to all of u..
Richard if u are coming to Cyprus let me know..it would be pleasure to meet u..
Well the engine mounting bolts were tight...the ignition timing was far wrong (full advance on 3 degrees BTDC)
I set the ignition to 30 degrees BTDC and run the bike for 20 miles...a very bad noice from the crankcase..bigger when  engine got hotter..
I believe is a conrod..but for sure i will see when i will strip down the engine..
So a lot of work to do..

1956 BSA A10 Plunger
1954 BSA B31 Goldstar Replica
1970 Honda cb750K0 project
Cyprus

Offline wardleybob

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Re: huge vibration
« Reply #9 on: 29.10. 2012 16:47 »
I would check your crank timeing side bush for excese play

Online Ted_Flash

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Re: huge vibration
« Reply #10 on: 29.10. 2012 20:23 »
Check that the bolt that fixes the tubes from the plunger units to the main top rail are tight.  The bolt is just at the back of the petrol tank, under the nose of the seat.  I once went down the BSA field day at Lutterworth and the vibration was almost unbearable, had to wrap strips of inner tube round the handlebar grips - eventually traced it to this bolt.
Ted Wilkinson, Ramsbottom, Lancashire
1950 Golden Flash

Offline wilko

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Re: huge vibration
« Reply #11 on: 29.10. 2012 21:54 »
Six months ago and you're replying now?