This may be an obvious question, but does every M20 experience a fair amount of handlebar vibration, and if so do you all just deal with it? Or are there known adjustments that can remedy the vibration? I get pretty numb fingers after about 30-min or more, and have noticed some lasting nerve damage unfortunately. Nothing serious, but obvoiously not ideal, and nothing I've experienced on other bikes.

My bars are steel, 23/32" ID 7/8" OD, and I recently fit a "vibranator" bar insert a friend uses on a newer bike. It may have helped, but hasn't solved the issue. I've heard filling the tubes with heavy foam or other dense mass can also help. Anything else others have tried? I didn't see any discussions on the forum. Thanks for the help-

Craig

email (option): cpdoberstein@gmail.com

If its becoming a serious issue it may be worth you considering the rubber mounted top yoke available for those girders, I'm assuming yours is the solid type, rubber type are very expensive but if its becoming a health issue its justified outlay.
I have girder BSA's with both types & its a big difference.

I would check the bike over carefully. Is the vibration rpm or road speed related ?

Points to check would include engine mountings (they may need reclaiming if bad) and presence / fit of the headsteady. Chain wear and tension and wheel balance could also be factors.

Unfortunately, crankshaft alignment has a significant effect on this type of engine. Do you know the history of your engine ?

It could also be caused by a misaligned crank, or a flat on the tyre or a badly seated tyre (just realised that I've been beaten to it by Rick on the misaligned crank!)

email (option): davmax@ntlworld.com

Yes Dave your right thats in 90% the reason for the vibration !!
Have lath it balance by several bike's and it a big difference.

regards,

Bram

email (option): bram@ockhuizen.com

Thanks for the input guys! Well, I guess the good news is you've probably solved my problem, the bad news is it sounds like I'm headed for a crankshaft rebuild.

The vibration is entirely RPM related. Just sitting still and revving I can get some pretty high frequency and very noticeable vibration. I assumed the big single would be pretty vibratory, but mine seems pretty bad. I don't know the history of the engine, just the number (XM206203). It's a '46 civvy, I've only owned it for a few years. Piston, barrel, and rings looked good a year ago, but I've never opened up the bottom end. Engine mounts seem good, but I've never pulled the big end. So it sounds like it's most likely the crankshaft, yes? Any other suggestions for things to check before I go down the rebuild path? At least Ian's tech info on the crank rebuild is top notch. Crap, I wish I tackled this in the winter, not early summer as it's getting nice out finally. Thanks for the input, very helpful!

Craig

email (option): cpdoberstein@gmail.com

Quote "it's getting nice out finally"

You obviously don't live in the UK

Ron

email (option): ronpier@talk21.com

Could a heavier (read pattern) piston be throwing the balance out? Don't immediately rip the crank down, before stripping it, take it to an engineer and get them to measure the run out on the shafts, The shafts are more important with regards to run out than the flywheel rim's run out and if it exceeds 0.002" then it is time to hit it with "the big copper hammer"

email (option): davmax@ntlworld.com

I am overhauling the engine; same crankshaft but new piston. Never had problems with vibration, but now I fear it will be different, since there is a difference in weight:
old piston: 565 gram = 19.93 ounce = 319 drams = 1.25 lbs
new piston: 534 gram = 18.84 ounce = 301 drams = 1.18 lbs.
Should I have the crankshaft statically balanced, or is the difference not that great

email (option): viaconsu # planet dot nl

its an old trick and works quite well, having end caps in the bars i left one in after a light greasing, set the handlebars on end in a bucket of sand and poured a couple of kilos of molten lead into them, it certainly reduces vibration. done this with a number of machines,the thing to remember if you have them is to leave room during the lead filling to put the other end cap in! if you dont have end caps, plug one end, plant it in the ground or a bucket of sand(firmly!) and away you go,

Hi Hans..You shouldn't have a problem..The accepted 'rule of thumb' is that if the difference exceeds 1 1/2oz. rebalancing is required.. Regarding Jons method of cutting down vibration I would think if you use any means to alter the 'sympathetic' vibration frequency of a part you may be successful. Basically you have to move this point to a part of the rev range where it is not so obtrusive..when you are 'flat out' for instance, which you don't do that often on an M20!..Ian

email (option): ian@wright52.plus.com

Thanks Ian, I'm happy again

email (option): viaconsu # planet dot nl

Thanks everyone. I'll check both the shaft and wheel runouts. Dave and Ian's tech tips seem to cover the whole big end repair really well - thanks for taking the time to write that up. I didn't check the piston weight last year, but I'll also confirm it's in-line with the 58%-60% balance factor.

And for the bars, I thought about filling it with lead shot, but I think I'll start with the balance first and then see how much vibration is left.

p.s., I'm in the US, in the pacific northwest. We;ve had terrible June weather, but summer is supposed to arrive literally tomorrow. Perfect time to break down the engine.

This forum continues to save me many hours and $$, thanks all-

Craig

email (option): cpdoberstein@gmail.com

Hi Craig..Glad you mentioned Daves tips..he has put more information on than I have on this one.
Look out for a pattern piston as previously mentioned..some of them are far too heavy..Perhaps you could weigh it when you strip the motor (unless it is obviously original) and post the result for comparison...
If you have an original piston the crank shouldn't need balancing but will still need to be checked to ensure it is running true..
Make sure you have a head steady fitted as well...this makes a lot of difference...
Also check the fit of the engine plate studs in the engine plates..if they are badly worn things can rattle about.
While the transmissions off also check the clutch and the sleeve gear bushes in the gearbox..the box can make a contribution to the vibes as well....Ian

email (option): ian@wright52.plus.com

quote: "Perhaps you could weigh it when you strip the motor (unless it is obviously original) and post the result for comparison"

Will do. Probably not for another month or so though. And the head steady is in place and tight. Studs also appear in good condition. Clutch was replaced last year, but I didn't open the gearbox at that time. Either way, the vibration is very apparent standing still in neutral, so I'm becoming ever more confident that it's the engine. Good to have it narrowed down, but now the fun begins...

email (option): cpdoberstein@gmail.com

Hi Craig..Let us know what you find...and while your in there don't forget to check the length of the drive side main bearing spacer...it should be 1.000"-1.005"..Ian

email (option): ian@wright52.plus.com

Going back to the piston, if it is a bit heavy you can remove some of the weight by tapering the inside edge of the piston or dremeling out a little bit under the crown of it, you should be able to lose some weight by using this method.
Before you do any of this, jack up the front end of the bike and spin the wheel, looking for any flat spots on the tyre where the tyre may have sat on in storage for years and also check that the wheel stops at any point, by marking the lowest point of the wheel with chalk, then spin it again to see if it lands in the same spot, if it lands somewhere else the balance is ok, but if it lands on the same spot you can (just for starters) wrap a bit of solder around the OPPOSITE spoke nipple, keep on adding a bit more and see how much it takes to get the wheel to stop in any place, when you've sorted it out, you can wrap a bit of lat lead around it (to the same weight) or get an appropriate wheel weight. Tyres do sometimes develop flat spots in them where they have been stood flat for a period of time and unfortunately the only way to sort it is a new tyre

email (option): davmax@ntlworld.com