Resonance patch

Simon.gk
Posts: 12
Joined: Tue Feb 16, 2021 4:42 pm
Location: Nova Scotia, Canada

Resonance patch

Post by Simon.gk » Mon Aug 30, 2021 1:53 pm

Hi, We took the Triking out for a good run yesterday as the weather has now cooled down enough to make it bearable.
When I bought the car I was told about a resonance patch at about 3750-4000 rpm, especially in 5th. It was obvious but not annoying during our test run and my various trips. On the run yesterday it became really loud with us 2 up but still occasional. I tried pushing on the central tunnel side during one of these episodes and it seems to be on the right side of the tunnel just behind the gear shift.
The previous owner said that it had started after he had the rear wheel modified to take a car tire and that he had spent time checking wheel and tire balance as well as the wheel itself. None of this changed the buzz. It, of course occurs at about our normal highway speed/limit of 100km/hr but only on acceleration.
In looking underneath the tunnel is covered in and has what look like hatchways so it is going to be 'interesting to get in there to look at the drive shaft. I am sort of assuming that it might be that?
I would appreciate any advice or suggestions as I am very much a novice at all of this.
regards

westendguzzi
Posts: 490
Joined: Tue Sep 25, 2018 7:30 pm
Location: Huntingdonshire

Re: Resonance patch

Post by westendguzzi » Mon Aug 30, 2021 3:03 pm

I believe you have a reverse gearbox, Right?
The right hand side of the box may be very close to the tunnel, resonance in the steel may be causing contact.
Try easing a piece of thick rubber, say 3mm, up there and see what happens.
Tony

EricStarmer
Posts: 258
Joined: Fri Sep 28, 2018 3:51 pm
Location: USA

Re: Resonance patch

Post by EricStarmer » Mon Aug 30, 2021 3:13 pm

Hi, Simon - do you have a reverse gearbox ? I have a similar, but different problem in that when making right hand turns, without a passenger, I get a loud thrumming noise from the tunnel. It turns out that on my car, at least, there is only about 3 or 4mm clearance between the right hand side of the reverse gearbox and the tunnel sheet metal, and I think that a combination of the torque on the gearbox and/or some flexure of the frame causes the gearbox to touch the sheet metal, causing the thrumming sound. The more throttle I give it, the louder the sound, In my case it doesn't seem to happen with a passenger, presumably because the extra weight on the RHS ( I have a LHD Triking) reduces any frame torsion.
I'm guessing you have a similar problem. I haven't completely eliminated the thrumming, but I've reduced it considerably by forcing a piece of 4 or 5mm hard sponge rubber between the gearbox and the tunnel. You can do this by taking out the tunnel upholstery (you have to remove the seatbacks , the gearshift knobs/linkages and maybe the seats themselves to do this), and then you have access to the reverse gearbox. It may be easier in your case to do this from below, by taking off any sheet metal covering the bottom of the tunnel.

Hope this helps

Eric

EricStarmer
Posts: 258
Joined: Fri Sep 28, 2018 3:51 pm
Location: USA

Re: Resonance patch

Post by EricStarmer » Mon Aug 30, 2021 3:15 pm

Guess Tony beat me to it - I'm too long-winded :)

Simon.gk
Posts: 12
Joined: Tue Feb 16, 2021 4:42 pm
Location: Nova Scotia, Canada

Re: Resonance patch

Post by Simon.gk » Mon Aug 30, 2021 7:23 pm

Hi Guys
My Triking is a pretty original 1984 series 1. I do not have a reverse gearbox, a topic I am wondering about as a potential mod so just the normal guzzi motor, gearbox and rear drive.
The front shocks have been updated and the gearbox was shimmed. It has about 16500miles on it with recent tires.
It is pretty noisy in general, even after my caterham with lots of rumbles and chatter in the lower gears but settles into a happy 65-70mph, once through the resonance patch.
It is probably due a good service to re-balance the carbs, check the valves etc.
Back on topic, I am wondering if it is the centre bearing or somewhere along the drive train.
cheers

steveO
Posts: 47
Joined: Mon Oct 01, 2018 2:08 pm
Location: Calgary

Re: Resonance patch

Post by steveO » Tue Aug 31, 2021 2:12 pm

Hi,
I have a 1985 without reverse here in Calgary and have the thrumming After trying to find the cause unsuccessfully I put it down to part of Triking ownership.
May try some heavy bitumen type sound deadening. I have checked and lubed the drive shaft bearings, but makes no difference. There is no contact between any driveline components and the body other than the bearings. The tunnel split between the handbrake and gear lever slots so there is a vibration issue. The car has less than 10,000 miles so all items are old in years, but not use.
Interested if you find a cause. I know a couple of other owners have a similar issue.
I did wonder if UJ phasing could be an issue, but they are double carden type so probably not,
Steve.

Simon.gk
Posts: 12
Joined: Tue Feb 16, 2021 4:42 pm
Location: Nova Scotia, Canada

Re: Resonance patch

Post by Simon.gk » Tue Aug 31, 2021 4:31 pm

Hi Steve
Thanks for your comments, it is actually most encouraging to know that it is not a unique to me problem.
Having grown up fixing various, mostly british and mostly elderly (cheap) cars, I gave it up when I came to Canada in 1979, apart from minor stuff like oil changes. The only relevant experience was a 10 year affair with a Moto Guzzi Lemans 3. Very italian and somewhat of a a love/hate relationship, it was mostly straight forward to look after and had a wonderful sweet spot at 5000rpm equalling 100mph that was part of the pleasure of runs from Calgary to Radium Hot Springs and other similar destinations.
The Triking is so very much a hand built car, lovingly rebuilt and cared for by Neil that I worry about every little noise, rattle and shudder. I would love to have an actual manual but read a comment from Tony Divey suggesting that anyone needing a manual should not be driving a Triking so I am working hard to better understand the whole care and feeding process.
I am enjoying the forum and do appreciate all the sage advice.
regards, Simon

Doverhay
Posts: 234
Joined: Thu Sep 27, 2018 6:43 pm
Location: TA66NN

Re: Resonance patch

Post by Doverhay » Tue Aug 31, 2021 6:51 pm

I’ve not had the problem you’ve described; however, it didn’t stop me from sound deadening the chassis, well had to do something during lockdown 🥴😉
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DSU475
Posts: 42
Joined: Wed Sep 26, 2018 4:23 pm
Location: Worthington, Leicestershire.

Re: Resonance patch

Post by DSU475 » Tue Aug 31, 2021 7:58 pm

Hi,
My car is a series 1 of 1982 vintage, no reverse. I have bored many a Triking owner with tales of transmission / drive train vibration. After replacing the gearbox output bearing, both UJ's, both bulkhead bearings, the centre propshaft bearing, had the final drive rebuilt with new crown wheel bearing and output splines, new swinging arm bearings, new rear wheel bearings ...... it didn't make a blind bit of difference :oops:
I noticed that when I rocked the top of the rear wheel from side to side, I could clearly see the transmission tunnel flexing where the holes are cut out for the gear change and handbrake. On closer examination, cracks had formed between these 'cut outs' and from the 'cut outs' to the side walls. I had these cracks welded ...... it still flexed, but made a slight difference.
I then welded a 2mm plate onto the top of the tunnel from bulkhead to bulkhead and tacked it down both sides, making cut outs for the gear change and handbrake. This cured the flexing completely and reduced the vibration/harshness still further.
With rigidity restored, I then loosened the engine, gearbox, propshaft carrier bearings, moved the car forwards and backwards. I then tightened everything up, adjusted the swing arm position and bearings ..... The result is a significant reduction in vibration, there is still an increase of vibration at around 50mph in top, but this reduces and smoothes out at around 60.
I hope that some or all of this torturous tale will be of some use to you.

Andy.

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Throwley
Posts: 56
Joined: Wed Aug 07, 2019 9:19 am
Location: Olney, Bucks

Re: Resonance patch

Post by Throwley » Wed Sep 01, 2021 8:36 am

DSU475 wrote:
Tue Aug 31, 2021 7:58 pm
... I then loosened the engine, gearbox, propshaft carrier bearings, moved the car forwards and backwards. I then tightened everything up, adjusted the swing arm position and bearings ..... The result is a significant reduction in vibration, there is still an increase of vibration at around 50mph in top, but this reduces and smoothes out at around 60.
My T1 vibrates awfully at 70-75 MPH. It started out as a vibration throughout the range but doing the above brought it down to a narrow band, which is above cruise for me and therefore mostly manageable. The biggest difference came with loosening and retightening the engine mount bolts.

A significant improvement was also gained by balancing the carbs and a careful ignition retiming.

As a long-time Guzzi owner I'm a bit paranoid about the UJs, but they appear to be OK on mine and I'm putting the horrible UJ growl down to the fact that they're so much closer to your ear than on a bike!

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