My 1360 always vibrated a lot. There wasn't a smooth spot anywhere, the higher the revs the higher the vibration level.
The fellow who supplied the crank and a lot of other motor parts suggested it would smoothen out after break-in .
It didn't.
I messed with carb synch and valve timing to no avail.
Finally two weeks ago I disassembled the engine to have a dynamic crank balance done.
This meant pressing the flywheels apart here in my shop (12 tons!) , removing the rods and rod bearings, then reassembling and trueing without rods. I
He insisted that I true the crank to the same spec as it would get on final assembly, which makes sense, but what a job for a temporary thing! I was at least 5 hrs getting it to run to spec. You get close then get far away again, start all over. It doesn't help that this is a " Picador" type crank, considered unserviceable when Vincent built them. That was because of the 12 ton interference fit which makes the crank tend to hang together but very hard to adjust in tiny increments.
The balancer then makes up a temporary bobweight which fits on the crank pin for the dynamic balance.
The balancer couldn't drill the flywheels with his little Mill/drill as the flywheels are made out very hard steel.
I brought the crank home and drilled it to his specs in the K&T mill. It was a lot , approximately 330 grams or 3/4 of a pound to get the 60 percent BF we were after. There was also a 22 gram side to side difference , so we corrected that as well.
When it came back from the Balancer for the final time, I pressed it apart and refitted the conrods. After reassembly and trueing I checked the balance factor with the crank in the lathe on oiled centres.
With a made up weight hung on the connecting rods( made to 60% BF calculations) the crank was perfectly balanced. It would sit whever it was left.
I added one flat washer to the weight and it wouldn't balance, it would rotate so that the conrods hung straight down.
So his balance job was spot on at 60 %.
I finished reassembling the bike today and went for a ride.
What a difference. Its now as smooth as a 998 Vincent at 70 mph and that is pretty smooth. From 80 mph on up it is smoother than the 998 s, .
For the size of motor and the tune level, this is a good outcome.
After many hours of struggle, I managed to get the mainshafts running to a total indicated runout of .001", that probably helps a little. Runout was only .0015" before, so this is only a slight improvement.
I think the dynamic crank balance is the main factor in the improvement.
The only way to go!
Glen
The fellow who supplied the crank and a lot of other motor parts suggested it would smoothen out after break-in .
It didn't.
I messed with carb synch and valve timing to no avail.
Finally two weeks ago I disassembled the engine to have a dynamic crank balance done.
This meant pressing the flywheels apart here in my shop (12 tons!) , removing the rods and rod bearings, then reassembling and trueing without rods. I
He insisted that I true the crank to the same spec as it would get on final assembly, which makes sense, but what a job for a temporary thing! I was at least 5 hrs getting it to run to spec. You get close then get far away again, start all over. It doesn't help that this is a " Picador" type crank, considered unserviceable when Vincent built them. That was because of the 12 ton interference fit which makes the crank tend to hang together but very hard to adjust in tiny increments.
The balancer then makes up a temporary bobweight which fits on the crank pin for the dynamic balance.
The balancer couldn't drill the flywheels with his little Mill/drill as the flywheels are made out very hard steel.
I brought the crank home and drilled it to his specs in the K&T mill. It was a lot , approximately 330 grams or 3/4 of a pound to get the 60 percent BF we were after. There was also a 22 gram side to side difference , so we corrected that as well.
When it came back from the Balancer for the final time, I pressed it apart and refitted the conrods. After reassembly and trueing I checked the balance factor with the crank in the lathe on oiled centres.
With a made up weight hung on the connecting rods( made to 60% BF calculations) the crank was perfectly balanced. It would sit whever it was left.
I added one flat washer to the weight and it wouldn't balance, it would rotate so that the conrods hung straight down.
So his balance job was spot on at 60 %.
I finished reassembling the bike today and went for a ride.
What a difference. Its now as smooth as a 998 Vincent at 70 mph and that is pretty smooth. From 80 mph on up it is smoother than the 998 s, .
For the size of motor and the tune level, this is a good outcome.
After many hours of struggle, I managed to get the mainshafts running to a total indicated runout of .001", that probably helps a little. Runout was only .0015" before, so this is only a slight improvement.
I think the dynamic crank balance is the main factor in the improvement.
The only way to go!
Glen
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