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#881837 05/30/22 1:50 pm
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raf940 Online Content OP
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took the A65 bitsa out yesterday for 50 mile run first time i had ridden it in quite a while ran great i had tightened all the engine mount nuts/bolts and found vibes were reduced greatly from previous outing ...but still got lots o vibes around 45mph but smoothed out around 50 what rpm/mph are you guys getting most vibes at? oh single carb and Pazon on the bike also lead fishing weights in bars and squishy beston type grips
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Last edited by raf940; 05/30/22 1:51 pm.

1972 Triumph T120
1968 BSA A65
1968 MGB Roadster
1979 Chevrolet Camaro Berlinetta
1969 Honda Mini Trail
2004 Honda Shadow Aero
1949 Ferguson TE20 tractor
1975 yamaha xs650b
1971 SL 175 Honda project
2 olive drab WWII military bicycle replicas
British motorcycles on eBay
raf940 #881852 05/30/22 3:14 pm
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Not ready yet to check mine, will be done in a few days:

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raf940 #881920 05/31/22 5:51 am
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My OIF t'bolt vibes at 68-70 then smooths out that
equates to around the 4k mark in top. At 4.5k it's fine
then starts buzzing at around 6.4k up to 7k. The rev limit
cuts in then so i change up.

raf940 #881921 05/31/22 5:57 am
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Every bike will have a "sweet spot" where most of the vibrations cancell them out & the bike seems to run really well.
The trick of happy BSA owning is to adjust the gearing so the "Sweet spot" is smack in the middle of the speeds you mostly ride at.

No use asking every one because every bike will be a little different so mine will not necessarily be in the same rev range as yours and of course if I do nothing but green lane riding & you do mainly international touring we will be doing different speeds .


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raf940 #881981 06/01/22 12:13 am
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MIne is buzzy at about 2.5k-3k and smooths out nicely by 3.5k. In top this is about 55 mph. Starts to feel like its working again around 75 mph. NickL has more balls than me. I rarely rev above 5.5k. smile

Commuting is crap, but cruising is great.

Retarding the timing a bit helps reduce vibes for me, but it not as zingy though.

For mine it depends a little on the warm up cycle. Traffic vs no traffic when commuting makes a difference. I put this down the rate of heat transfer between cases and crank etc.

All the some one warmed up though.

Last edited by BrizzoBrit; 06/01/22 12:16 am.

BSA 1969 A65F
BSA 1966 A65H
Triumph 1968 T120
Kawasaki A1R
& too many projects!
raf940 #881996 06/01/22 8:53 am
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My 1971 OIF thunderbolt only really got bad for vibration at an indicated 70 in top at about 4000-4500 revs, and vibration wasn't really an issue bellow that, I am currently rebuilding it and have had the crank dynamically balanced so i'm hoping for some improvement.


1971 BSA A65T
1968 BSA B44
raf940 #881998 06/01/22 9:41 am
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Things that make a difference. Apart from the motor.
Bottom engine mount shim, can go either side, without it the frame is sprung when the bolt is tightened, that makes it sing.
Wheel balance, both wheels.
Badly fitted tyres.
Chain wear/ tension, sprocket condition.
OIF handlebar P bolts fitted incorrectly.
Loose components.

In the motor, matched rod and piston weights, carb synch, equal ignition timing, crank dynamic balance. Its a vertical twin even when evrything is optimal it will still have ruff and smooth bands, my motor is smooth from 3.5 K to 5.5 K, stock balance factor with dynamic balance and matched fettlings.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
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BrizzoBrit #882048 06/02/22 12:26 am
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Originally Posted by BrizzoBrit
MIne is buzzy at about 2.5k-3k and smooths out nicely by 3.5k. In top this is about 55 mph. Starts to feel like its working again around 75 mph. NickL has more balls than me. I rarely rev above 5.5k. smile

Commuting is crap, but cruising is great.

Retarding the timing a bit helps reduce vibes for me, but it not as zingy though.

For mine it depends a little on the warm up cycle. Traffic vs no traffic when commuting makes a difference. I put this down the rate of heat transfer between cases and crank etc.

All the some one warmed up though.

Ray
I don't rev it like that all the time but only when the 'mood grabs me'
My license has taken too much of a pounding over the years...........
As long as the bottom end is good on these they are happy to rev a little.
The crank is very strong and they are a short stroke etc.
When i rebuild this one i'll try getting the crank dynamically balanced, i've
only done it on edges myself. It'll be due shortly as it's on 28.6k miles now,
i may fit new bearings too, if it needs 'em.

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