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Hi All

This a very subjective question I know but just how much vibration is too much. I'm running a 71 TR6 (single carb), timing strobes perfect, tappets spot on, compression at exactly 160 psi per pot (hot) and running a Boyer with matching dual coil. Easy starter, good tickover, plugs good colour and general performance seems excellent.

Seems a bit vibey around 45-55 mph, (this is approx as speedo is out of cal), not to bad lower down and seems to smooth out after about 55-60.

Problem is Ive been mostly brought up on a diet of Jap fours and modern Harleys so Ive not really got a good frame of reference.

Almost impossible question I know but are there any steps I can take to reduce the vibes, or am I worrying about nothing?



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You don't have a vibration problem, from what you write there.

Welcome to Brit Twinland!


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Rob -
These bikes DO vibrate more than your usual Jap bike. No doubt. Vibration does flatten out at specific RPM ranges. If you can find that range and ride in it you'll be much better off.

But there are some areas you can work on or check...
• Try a 20T countershaft sprocket
• Make sure you have no gap between the bottom engine mounting bolt and the frame. There are 2 washers there that often get left out during engine rebuilds.
• Make sure all the engine mounting bolts are tight.
• Renew your handle bar isolastic mounts in the fork crown.

Hope this helps!


Don't hide 'em, Ride 'em !!

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Originally Posted by Rob_Heap


just how much vibration is too much.


When your eyeballs are shaking so much you can't see. That is just before the gas tank breaks apart and a piston comes up between your legs. laughing

Originally Posted by Rob_Heap
Seems a bit vibey around 45-55 mph, (this is approx as speedo is out of cal), not to bad lower down and seems to smooth out after about 55-60.


Sounds purrfect. smile

Originally Posted by Rob_Heap
am I worrying about nothing?


Worrying about nothing. See thread on balancing. wink


Bob, Lifetime bike: '71 T120R, bought in '71 at Ken Heanes, England.
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Originally Posted by RF Whatley
Rob -

• Try a 20T countershaft sprocket


Don't do it Rob, unless you:

1) Are in your 20's, or on a second adolesence
2) And Know all the cops in the area. Excuse me, bobbies for you.

Else you will be lugging that engine. wink


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I think I agree with Bob...

I added a tooth to my BSA A65 (21). I did the calculations in another thread and it was only a couple hundred RPM for the most part.
( https://www.britbike.com/forums/ubbt...;Main=32131&Number=296046#Post296046 )

Seemed like a good idea, but I don't have the huevos to run her out. Might as well not even have 4th gear, I'm amazed at the difference. I'll go back down someday, acceleration is more fun!!!

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Originally Posted by btour




Don't do it Rob, unless you:

1) Are in your 20's, or on a second adolesence
2) And Know all the cops in the area. Excuse me, bobbies for you.

Else you will be lugging that engine. wink


You will only be lugging the engine if you don't know how to use a gearbox.I get away with sprocket combinations like 21/47 and 20/44 on a T120.Not the most ideal in city traffic,but neither is top gear with standard sprockets.Its fine for highway use,and I've still over-revved in top gear.

That's not likely to help Rob Heap,though.What Rob says is true;they run smooth at 4000-4500 rpm.If its rough below that,just check what RFW mentions and also check all sprocket runout and chain-wear/adjustment.

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Sources of vibrations:

Out of sinc carbs

timing off from one side to the next

loose mountings

any worn components such as primary chain, drive chain clutch bearings engine bearins.

out of balance clutch

broken or cracked frame

out of balance wheels. (not likely in your case)

port biasing

compression not equal from left to right

Or perhaps you particular sensitivity to vibration

I think it is unusual to have vibration at this speed range. Usually this speed in top gear is very smooth on a Triumph.

I would be looking at something other than the engine itself such as mountings and alignments.

Bill



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I read an old road test for a brand new 66 Trophy and it said there was some "unpleasant vibration at around 4400rpm" It was above and below. I would say my 67 vibrates most at about this figure or slightly lower. The oil in frame bikes are different, of course.
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My 51 T´bird ( hard tail, pre unit)vibrates all the time, if it gets so bad that the petrol starts to foam, your feet wont stay on the foot rests, and your vision becomes blurred, just tighten the loose engine mounting bolts up again( this happens about every 1000 miles if you dont give them a tweek every week). Or if you are doing over 70mph, slow down!(this can take a while with 7 inch front drum brake)so plan ahead!

Last edited by Badmechanic; 05/20/10 8:49 am.

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I agree with Bill. At 45, it should be pretty comfortable. Motor mounts, chain adjustments and wheel balance would be at the top of my list.

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Now for a story that should get the sceptic's riled! I was riding the Blue Ridge double up on my '70 T-120 when the vib's got so bad that I thought the frame had cracked. I even removed the center stand thinking that loose bolts could cause the bulb shattering vibrations. When I got home I removed the engine and checked the frame carefully and all was OK here. I had an extra engine ready to go so I installed it and the situation didn't change a bit. Now here comes the interesting part. I notice the swingarm bushings were pretty badly worn.A change in W/A bushings corrected the vibration problem and I put the original engine back in. Now I'm ready for it. I've got the old fireproof suit on!! Ha Dick

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I believe you, Dick. Twas a secondary resonant vibration. Nice catch that was, to find it. smile


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Dick,
That's a flameproof posting if I ever saw one. I think we often overlook power pulses as sources of vibration. Add to the list rubber clutch buffers and rear wheel buffers for bikes that have them.
Bill


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In the factory the cranks are only balanced statically. That means that there can be a difference in weight between the left and right hand side of the crank. I had mine dynamically balanced by an old expert in England. The engine still vibrates a bit, but in a more butt-saving way grin

The crank on the picture is partly re-balanced because of heavier pistons but you can clearly see that all the weight is removed from the drive (left hand) side of the crank. The expert says that the construction of the sludge trap makes the crank a lot heavier on the drive side

[Linked Image]

Last edited by hein weijers; 05/25/10 9:55 am.

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Hi,

vibrations is what you want on these bikes. I have a 20T sprocket on mine, but it has the 5 speed gearbox. On a 4 speed gearbox I would prefer the 19T sprocket.

Ralf


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Originally Posted by rstar45
I think I agree with Bob...

I added a tooth to my BSA A65 (21). I did the calculations in another thread and it was only a couple hundred RPM for the most part.



I agree with you here on this point, there is only a couple of hundred rpms in it.

Depending on the prime function of the bike, the longer legs and lower RPM can be good.

I have to disagree with Bob about the matter of the engine being lugged in 5th with the higher gearing (that's what 4th gear is for Bob)

My T120 runs the 20T front sprocket on mainly highway conditions. A very comfortable bike at 60mph (approx3800rpm). it Pulls strongly and quickly to 70/80mph without gear changing.

For a touring bike, the higher gearing is almost a must. RR


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Originally Posted by RetroRod

My T120 runs the 20T front sprocket on mainly highway conditions. A very comfortable bike at 60mph (approx3800rpm). it Pulls strongly and quickly to 70/80mph without gear changing.

For a touring bike, the higher gearing is almost a must. RR


Hi,

I use my bike not for touring, but for riding around on the country roads in my area. I enjoy the good acceleration even in the lower gears. For someone who rides mainly in the highest gear it is no difference between 4 or 5 speed gearbox.

Ralf


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Vibration is not a problem , its character. And it keeps you alert!!, Well thats what my Dad used to tell me!


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Guys,

I was being a bit cheeky, about the 20T. I have one. I like it. It makes 2nd gear much more usuable, than before. But one must take care not to lug it. And slipping the clutch must be done more under certain conditions, or you are subject to pinging with the gas today.

I was being cheeky, because Rob is probably older, and his description with the speed instead RPM, suggested to me, that he was already lugging the bike a bit. With the extra tooth, his focus on MPH, instead of RPM, may lead to a problem.

Of course, this is all based on the experience of the rider. I think Triumph did the orginial gearing of that sprocket based upon the fact that some riders, would indeed lug the engine, and lots may not have skill base with using the clutch, and to avoid clutch problems. So....

I was just being flippant. Anyway, if he were to do that, he should be aware of the issue. smile



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As we used to say,
"What vibration?"
Entirely too much is made of balance factors when the real solution to the problem lies is other areas. As stated above dynamic balancing nets way more in the way of benefits than static balancing. Just think for a minute about it. The rocking couple that is cured with a dynamic balance job occurs in the horizontal plane perpindiculat to the line of the frame. This translates into vibration felt in the ends of the handlebars and footpegs. Having handlebars that grow in diatmeter with engine rpm is a real downer in my opinion. Any out of balance in the static axis is in line with the frame so vibrations will be felt in the seat of the pants and the fuel tank mostly. This will vary with rpm range and power loading of the drive train. My '62 is smooth in the extreme with full throttle and pretty smooth everywhere else. It has a BF of 85% and was dynamically balanced.
In my opinion static balancing is the key with only secondary attention paid to the BF. Then use gearing to move the vibrations out of the comfort zone.
Bill


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Right on Tiger!! I was saying about the same thing on the "Balance Factor" title in this board,but you said it so much better. Dick

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If you think your Triumph vibrates, try a ride on a Norton Atlas or P-11. They'll numb your hands and shake your teeth loose.

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Im not sure what Nourish used to bal with but took mine to a shop with a state of the art machine and said the factore was right on but it was out cheek to cheek.Here i have this 1700 crank and the guy pulls out his grinder to take some weight off a spot, almost sh-t.


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Took the advice and went over everything, single carb so not much to do there, strobed the Boyer spot on and both pots almost exactly 160 psi hot. Rechecked tappets and adjusted rear chain. Went over engine mounts, tank and side panel fixings etc.

Since strobing the Boyer (PO had set way way advanced),its smooothed out noticably as confirmed by the missus on the last run into town. Still reckon I could improve though...

Could a slightly loose primary chain add to the vibes? Im seeing about 20mm slack as opposed to the 9.75mm in the workshop Manual, tried to adjust but its a real pig to get to due to the frame rails. Is there some sort of trick method to this or do I neeed to pull the casing off?


1971 TR6R Rolling restoration
07 Harley FXSTC 96ci
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