P11 Taming Vibration

elefantrider · Feb 18, 2015

Rode for a while without foot peg rubbers but they are going back on. Without them, the vibes are not nice in 4th gear. Actually will be looking at getting new ones, with newer, softer rubber to dampen the vibes.

What handlebar grips are you using? I am thinking going to foam or softer rubber. The original plastic grips do not do a good job of taming the vibes at speed.

BillT · Feb 18, 2015

I use the Gran Turismo grips, as found on the Commando. These are also the same grips that were on my G15 when I got it. The original Doherty grips offer no cushioning.

I've had no issues with footpeg vibes, but rarely rev the bike over 4G. I also had it balanced when I rebuilt the motor, either 82 or 84%, can't remember at the moment.

elefantrider · Feb 20, 2015

Not sure what grips mine has on, but they are hard as a rock.
Looks like there are several makers of the Gran Turismo Commando style.
Italian and Japanese made.

Might try the Andover Gran Turismo versions, which are rated highly and are flat black.

Would really like something like foam, or very soft gel rubber but these will probably look too modern on my bike.

elefantrider · Feb 20, 2015

Saw these which have a similar shape as Gran Turismo's but seem softer. They are made for Harley paint shakers but come in 7/8 size also.

frankdamp · Feb 20, 2015

Sorry, guys, you can't "tame" the vibrations. You might be able to ut systems in place that minimlse the effects. During my test riding of an early P11, I lost the tail light when the bots holdong it vibrated loose!

Incidentally, N-V had no idea what the hell a Norton P11 was. We got a message from some lawyers in Claifornia that they were suing Norton because one of their policy-holders had been killed in a desert race when the steering went into an "uncontrollable oscillation" that reulted in his being pitched off to his death.

As I remember, the P-11 was a cobbled up bike created by the California importer, who stuffed the 750 Nort0n engine into a G50) Matchless frame. Not testing, no analysis. As a result of the lawsuit we got one to test. What a scary SOB it was. I got to do the inital break-in miles. It was fine at lower speeds, but once I got into the 70-80 mph bracket, it really got squirelly. Runing up the motorway, it started to weave side to side at about 55 mph. By the time it got to 75 or so, it was weaving the full width of a freeway lane and couldn't be controlled.

Another test rider, braver than me, said it straightened out above 80 mph and was quite a pleasant ride. We tried all kinds of kludges to try an fix the problem, but were stymied by the lack of decent test instrumentaion. I left N-V while the controversy was still raging, so I don't know what the final solution was. My personal opinion was that the frame wasn't up to the torque the engine put out and there was a bending oscillation that nobody understood.

elefantrider · Feb 21, 2015

I do not want to open a can of worms here. These bikes are classics, almost 50 years old and judging from prices they bring, they have quite a popular following..... especially in the UK. Based on this, it seems the cobbled up bike created by a California importer hit their mark and the UK factory was pleased to make them as fast as they sold. N-V caught on and later offered their own high pipe scrambler S and SS versions, to questionable success. I am not sure of your weight but I am 200lbs and I find the bike to be stable (although quicker turning than a commando)....... but I am not taking it above 60 mph often. Vibration is not unbearable, many other bikes of the same era are just as bad.

Would be interesting to hear what types of testing/analysis N-V actually performed. My sense of N-V testing /analysis back in the day is no different than a couple of guys jumping on a bike for a spin down the road.......dare I say to the pub.........far different than what today's manufacturers do.

CanukNortonNut · Feb 22, 2015

elefantrider said:
I do not want to open a can of worms here. These bikes are classics, almost 50 years old and judging from prices they bring, they have quite a popular following..... especially in the UK. Based on this, it seems the cobbled up bike created by a California importer hit their mark and the UK factory was pleased to make them as fast as they sold. N-V caught on and later offered their own high pipe scrambler S and SS versions, to questionable success. I am not sure of your weight but I am 200lbs and I find the bike to be stable (although quicker turning than a commando)....... but I am not taking it above 60 mph often. Vibration is not unbearable, many other bikes of the same era are just as bad.

Would be interesting to hear what types of testing/analysis N-V actually performed. My sense of N-V testing /analysis back in the day is no different than a couple of guys jumping on a bike for a spin down the road.......dare I say to the pub.........far different than what today's manufacturers do.

Elefantrider
Regarding the weave.
I believe there was a service report on two types of front-end shocks/springs setup: one for street use and one for dirt /off road. I can’t find the source for that article but the recommendation was to not use the off road setup for street use.
To tame the vibes for the P11 I chose the expensive route when I had to go to +0.020 pistons. I bit the bullet and got the JS Motorsport lightweight piston/carrillo rods. I am still going to get the crank balanced so it’s not in the engine. I can’t comment just yet on its effects to improve the buzz / tingle. I bought my P11 as a basket case so I never had the privilege of before/after effect results with the Norton twin in a solid frame.
Cheers,
Tom
CNN

BillT · Feb 22, 2015

The reference to off-road forks is in the owners manual for the G80/G85/P11A

I originally posted it on page 2 of 'The P11 Thread', and will repost it here:

" IMPORTANT MODEL P11A

The P11A machine is fitted with front fork suspension units for use on the road. They do not prohibit use on normal desert terrain but are not recommended for the roughest ground. The relevant part numbers for these suspension units are as follows:-
Part No. Description Quantity
022369 Main Springs 2
022890 Fork damper tubes 2
022079 Buffer springs 2
022021 Buffer-spring collars 2

Machines with the following engine numbers are fitted with these road front fork suspension units when they left the factory:-

Engine numbers following 124370 and also 122572: 122792: 122938: 122939: 122940: 122950: 122988 to 123012.

A 3.25 X 19 ribbed-type tyre for the front wheel is recommended for high-speed road use.

If, however the machine is to be used for competitive desert scrambling or over the roughest ground, scrambles front fork suspension units designed for the purpose should be used. The relevant part numbers of these suspension units are as follows:-
Part No. Description Quantity
016782 Main Springs 2
028048 Fork damper tubes 2
Note: Buffer springs and buffer-spring collars are not required

Machines fitted with scrambles front fork suspension units are NOT suitable for high-speed road use.
Machines with the following engine numbers are fitted with scrambles suspension units when they left the factory:-

Engine numbers up to 124370 but excluding 122572: 122792: 122938: 122939: 122940: 122950: 122988 to 123012.

It is essential to ensure that units are fitted appropriate to the intended use of the machine.

Fitting instructions are given on page 47."

Bikes built up to 124370 were all 1967 models, though the last P11 was 123012.

The first P11A was 124372, the last 126123, with about 1300 built (or about half of non-Commando production for 1968)

CanukNortonNut · Feb 22, 2015

BillT said:
The reference to off-road forks is in the owners manual for the G80/G85/P11A

I originally posted it on page 2 of 'The P11 Thread', and will repost it here:quote]

Thats where I saw it. :roll:
Thanks BillT
Cheers,
Tom
CNN

Bernhard · Mar 2, 2015

You want to tame the vibration :?: :shock:
Ride slower

Now you know why I had to get rid of my Atlas……or buy a Commando.

frankdamp · Mar 2, 2015

elefantrider:

You're pretty much correct about N-V's testing. I was hired to build a test instrumentation lab, having worked in a similar lab in the machine tools industry and served an apprenticeship in aviation, which included a lot of flight test stuff.

It quickly became apparent, after I moved to N-V, that funding, that had been promised in the interview for my suggested instrumentation system, had been pissed away on the PR consultant's idiotic "Green Ball' logo promotion. I ended up being a test rider on the Commando and subsequently on the AJS Stormer programs. I did a lot of miles on the Commando prototypes and on the "Roadster/Trials" version of the Stormer. I wouldn't mind getting one of those, but riding motorcycles in this area is close to a death wish.

It was evident, as I approached two years with the company, that it was unlikely to get better. With a very good offer from Boeing, I emigrated, with DW and two children, to Seattle. Best move I ever made. Now retired after close to 30 years with the "Lazy B" and living in Anacortes, one of the nicest small towns in Washington State. My sister, who still lives in Leyland (Lancs. UK) says this is "where God goes on vacation".

elefantrider · Feb 6, 2019

Currently, I have these grips which, due to age, are more hard plastic than rubber.
They might be stock, but do nothing to absorb the higher RPM vibration.

Instead of replacing with newer versions of the same, or pattern Doherty/AMAL, I have found some dual density gel grips which may provide more comfort, if I you can live with their appearance.
https://www.progrip.com/shop-en/motorcycle/road/grips/custom/842-grip.html

Hardness: SH 58 INSIDE – GEL SH 15

Unfortunate, they all look to have open ends.

Personally, I have always preferred the feel of foam grips which I have run on Commando and Ducati bikes. I don't know if I can bring myself to use foam on P11, although arthritis may make that decision for me!

Junglebiker · Feb 6, 2019

I put a set of these on a big single that I ride every day ('85 XR600R): http://www.ourygrips.com/oury-road-grip-with-flange/ and have noticed a definite improvement in terms of how long I can ride before my hands get numb. Admittedly I was using hard compound Renthals before... Anyway, I was so impressed with the Oury grips that I had pretty much made up my mind to use them on the P11 as well.

Closed ends and available in a variety of colors, including (among others) tan, muddy brown, grey, and black.

Junglebiker · Feb 6, 2019

I've toyed with the idea of re-engineeing my P11 to include Commando style Isolastic engine mounting. (Yes, I'm aware of how difficult this would be to do, and am aware of the fact that Commando's have different crank balancing, etc., etc.) Right now I'm not interested in hearing how impossible it would be to do, as I've pretty much decided not to do it. Has anybody ever tried it?

mdt-son · Feb 6, 2019

frankdamp said:
Sorry, guys, you can't "tame" the vibrations. You might be able to put systems in place that minimise the effects. During my test riding of an early P11, I lost the tail light when the bolts holding it vibrated loose!

The laws of physics explains why vibration is amplified in a light and stiff frame. This has to do with very low structural dampening and eigenfrequencies higher up in the frequency band compared to a heavy frame like tHe G15 or the slimline Featherbed. To avoid vibrations, you need to avoid the excitation, i.e., fit an engine which doesn't excitate or at least whose excitation is a minimum. The 360 parallel twin vibrates up and down only due to reciprocating masses. This is true for all the harmonics. Reducing vibration for a given design can be accomplished by ensuring

* Static balance
* Dynamic balance

If altering the design premises is an option, reduced vibration is obtained by
* Reducing reciprocating masses (i.e., lighter conrod and pistons) and possibly fitting a stiffer crankshaft
* Change the firing order from 360 degrees to 270 degrees.
* Fit some kind of counterbalance device.

frankdamp said:
Incidentally, N-V had no idea what the hell a Norton P11 was. We got a message from some lawyers in California that they were suing Norton because one of their policy-holders had been killed in a desert race when the steering went into an "uncontrollable oscillation" that resulted in his being pitched off to his death.

Excuse me Frank, but that can't be the case. N-V management wasn't that daft. The P11 program generated a lot of work and expenses, and of course the top brass had approved it. Maybe you guys on the shop floor, remote to Plumstead, were not aware of what was going on. That I can believe, but in Wolverhampton I am quite sure middle and top management were well informed.

-Knut

mdt-son · Feb 6, 2019

Junglebiker said:
I've toyed with the idea of re-engineeing my P11 to include Commando style Isolastic engine mounting.

Do something about the source of vibrations rather than trying to camuflage them. Fit a 270 degree crankshaft. Perform a meticulous balancing. Fit a balancer as designed by Doug Hele. These measures would be successful if applied to the P11 motor.

-Knut

Junglebiker · Feb 6, 2019

Yeah, I've decided that maybe I don't care. All my life I've ridden thumpers, many of which were famous for their ability to vibrate, (Yam XT500 and the aforementioned Hon XR600R, for example). Maybe the P11 won't seem that bad to me. I'll let you all know in a few years when I get a chance to put it together.

I do very much like the idea of a 270 degree crank, but that was an expensive mod to do on my XS650 engine, where rephasing the crank is a relatively simple matter of pressing the crank apart, rotating one half of it and pressing it back together (the shaft between the halves of the crank is splined). I can't imagine how much more expensive it would likely be on a Norton, where the best way to rephase seems to be to get a complete new crank. And then there's potential problems with the cam loading, too.

Perhaps an even better idea would be to reduce the displacement (gasp!). Go back down to a 650 or even a 500. You go first. I'm keeping mine a 750...

CanukNortonNut · Feb 6, 2019

You could go to the Js motorsport lightweight pistons and con rods then use thick copper base gasket and thick copper head gasket to De-tune the flat-top pistons, as the original pistons were dished. But that is an engine rebuild and if that is not an option or money doesn't equate then put up with the vibration. I would do that before a 270 degree crank as a Norton needs to sound like a Norton. IMHO.

Cheers,
Thomas

Junglebiker · Feb 6, 2019

Well, being a Norton Newbie, I've pretty much decided to focus on getting mine ridable first, then deciding what needs to be changed. Though if I discover that I need to bore the cylinders, I am planning on a set of JS or MAP pistons, possibly rods as well. Of course, that drives the compression back up again, but isn't it really the weight of the pistons and not the actual compression ratio that contributes to the vibration? For example, if I install 10:1 pistons that weigh half as much as 8:1 pistons (these are all hypothetical numbers which I came up with just for the sake of discussion), then the vibration will still be less than the 8:1 pistons, right? (For now let's set aside the possibility of a piston being too light and, for purposes of discussion, assume that the lighter a piston is, the better.)

mdt-son · Feb 7, 2019

Junglebiker said:
For example, if I install 10:1 pistons that weigh half as much as 8:1 pistons (these are all hypothetical numbers which I came up with just for the sake of discussion), then the vibration will still be less than the 8:1 pistons, right?

Correct. Vibration is chiefly a result of acceleration of masses, in this case pistons and rods. However, the crankshaft flexes under load and will contribute to vibration as well.

CanukNortonNut said:
I would do that before a 270 degree crank as a Norton needs to sound like a Norton. IMHO.

A 270 degree crankshafts is state of the art engineering, but should be complemented by other measures, such as lighter pistons. I'd really like to try out the balancer devised by Doug Hele. Too bad AMC didn't have the time and money to develop the bike fully.

Agreed, the Norton has a lovely sound, but if I can buy myself an enjoyable ride, I am prepared to give away the sound experience. A badly balanced (err, stock) P11 is not an enjoyable ride, IMHO. Maybe they were better when new.

-Knut

P11 Taming Vibration

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