I recently restored a 1971 Commando, ground up restoration. I took it out for the first run about two weeks ago and the vibration was bad enough that my hands were numb. The bike has the upgraded isolastic system and the clearance is correct for the front and rear units. Unfortunatly I have stripped the engine down due to a blown head gasket. Upon inspection and delivery to another shop the parts were found to be incorrectly machined. I would like to balance the crank shaft and it seems to be a good time to do so. Has anyone on the Commando forum had this done? If so how would the machine shop accomplish this? The volume in the sludge trap will have to be accounted for meaning the weight of the oil in the calculation. Any help would be apreciated. Thamk you, Craig
I would just take it to a…
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Craig, large torque conver…
Craig, large torque converters are filled with wax for balancing, to simulate the oil loading. Most people wouldn't worry for a bike engine. After all, the correct balance factor is a matter of opinion. Regards John.
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In the workshop manual (fo…
In the workshop manual (for a MK3) two balance factor % are given, one wet i.e crank full of oil, approx. 50%,and the other dry, approx 63% from memory, check these figures. I too would take the crankshaft plus reciprocating parts to a recognised balancing specialist, this is not necessarily the same as a shop keeper who sells parts! Also compare your isolastic rubbers with another set from a reputable source, they may be of the wrong grade of rubber, too stiff, which will transmit unacceptable amounts of vibration.
Simon.
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Thank you all for the very…
Thank you all for the very useful information. I am taking the lower end to a shop that specializes in balancing crankshafts. The reason I questioned the sludge trap was due to statements in the INOA tech digest page 1-17 which says, an oil filled sludge trap can change the balance factor by10-12%. I would take the meaning to be that somehow the weight of the oil that will fill the sludge trap must be accounted for when the crank is turning, but how? The volume of the oil must be known to obtain the correct weight to add to the parts attached to the crank, I would think. Do any of you know how I can calculate this weight for the people at the performance engine shop? The isolastics came from Andover, hopefully they are correct. I owned a 1971 Combat Commando in that year and had it for 8 years and I do not recall the level of vibration that I am experiencing now. Craig
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Craig, you don't have to…
Craig, you don't have to calculate the weight of the volume of oil, you use the 'dry' balance factor as provided in the workshop manual. I too fitted genuine Andover Norton isolastics several years ago and was informed by Norman White that there had been some manufactured with the incorrect rubbers. One thing I have learnt over the years is to never assume something is right, alwayscheck.
Simon.
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Thank you Simon for the in…
Thank you Simon for the information. How would I determine that the isolastic rubber units were in fact the correct rubbers? Craig
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I received my balanced par…
I received my balanced parts today. The shop did a good job at least visually. After tearing down my newly built engine to accomplish this balancing act I had the shop check the cam dimensions to make sure it was good. Alas, the cam was worn several thousands on the exhaust lobe for the right cylinder. Scrapped the cam and ordered one from Andover today. I also reread the haynes manual regarding the head stay and the proper set up and it looks like I adjusted it incorrectly, on the center stand, a definite no no,so that alone may have contributed to the excessive vibration. Hopefully I will be able to reassemble the engine and get everything up to snuff before the cold weather sets in. Best regards, Craig
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I would just take it to a company that specialises in crankshaft balancing, as they do this all the time. When I had my crank balanced, I was told that the whole moving system needs to be treated as one, i.e. they wanted the crankshaft, conrods, pistons and rings assembled as a single unit. I am not sure what you mean about the oil. Just strip and clean everything then have it all balanced.
Balancing does not mean the total elimination of all vibration. With two pistons going up and down and changing direction many times per second, that would be asking too much. I was asked what I was going to use the bike for and at what r.p.m. I would like the vibration damped to the maximum possible. I went for 4000 r.p.m. which moved the roughest spot to about 2750.