Resonance between 65 and 75 MPH

[julianop]

I've put 14,200 miles on my Connie in the 10 1/2 months we've been together (yup, accounting for the winter that'll be getting on for 18,000 by the end of my first year), so needless to say I am in tune to every pop, clunk, whine and rumble that she shares with me. On my long, weekly commute between Minnesota and Illinois, the one thing that bothers me most is a mechanical resonance that peaks between 65 and 75 MPH. I feel it in the handlebars and also, but to a lesser degree, in the footrests. At 80, it's smooth, but coming down out of 80 (as I have to do at highway cross-overs every mile in the motorist-friendly state of Wisconsin, just in case there is one of the State's finest lurking in the dark), that throbbing picks up noticeably.

Is this normal for the bike, or does it suggest there's something amiss or out of adjustment. If it's normal, will SISF's 7th gear mod improve things, given that 70-80 is my "economic" (i.e. avoiding speeding tickets) speed range?

[JDM]

Check your top motor mount, the bolt may have sheared or it might need to be shimmed.  Better still check all the mounts.  HTH JD

[Summit670]

Check for loose fasteners/mounts.
Have the carbs been syncronized.
Has the balance shaft been adjusted, not sure if that would cause it anyhow.
How many miles - are wheel bearings good.
Tire pressure/treadwear/balance.

[T Cro ®]

All of the mechanical advise given is good but yeah what your finding out is the down fall of putting a high spirited Ninja sport-bike motor in a touring bike built in the 55 MPH area and then asking it to hold todays highway speeds of 70 + MPH for long distance.... Yup it is going to drone in this slightly elevated RPM range..... So yes SISF's 7th gear mod is going to help the highway bound bike a lot by lowering the RPM of the motor while still holding the same steady 70 + speed. Another thing that really helps the bike that does a lot of slabbing is to install a taller rear tire as it too will lower your RPM slightly for the same given speed; in other words install a 160/80-16 tire in place of the stock 150/80-16 tire.

[julianop]

Thanks for the checklist, guys, I'll get to it. I balanced the carbs last fall, and will do it again as soon as I've check the valve clearances. I remember at the time that the balancing made such a difference it brought happy tears to my eyes, but that's because I had awful low RPM problems at that time, a broken #1 plug lead and dirty carbs, as some may remember ;-)

Yes, T Cro, I'll bet you're right. It is smooth below that resonant range and smooth above it, so short of an expensive, custom engine balancing project, the 7th gear mod sure seems like the answer. As I said, I'm doing over 800 miles a week while the weather is good, 85% of it on the slab, so I really would like to smooth it down - my hands are numb for two days after each trip, and I don't want to sustain nerve damage. SISF's cam job will have some effect too, right? Although as I understand it that mod is most noticeable at lower RPMs.

Which segues into another happy comment: I am long past the obsession with low RPM I was suffering from last fall. This machine is happy as a lark above 3000, and positively sings at 4000 and above (though short of the occasional spirited getaway I have little opportunity to do much more than that) and I've learned to love it. I have really gained a lot of confidence with the bike over the past 14,000 miles, and while it is still tall and top heavy, and unforgiving in the parking lot, I've learned not to let my guard down.

I'll also look at the tire idea at the next change; I'm still on my original tires with enough tread to last me to the end of the season at this rate. I must be one sissy rider, I guess ;-)
 

[jim-d]

With everything bolted to everything else, its amazing the Concours doesn't rattle more.

Aside from motormounts as suggested I would look under the fairing, loose bracket or even a loose horn.  Fairing and windscreen should be snugged down.  I tried a strip of inner tube where possible but most times the clearance is too tight to do it.

After looking at the easy stuff, nothing will change the personality of the bike more than a valve adjustment.  Mine has vibrated so bad I wanted to burn it and purred like a kitty kat, all from the valves.  As the eperts here say, on the loose side and all as perfectly uniform as possible is the best setting.

[George R. Young]

There should be 3 bolts inside each fairing pocket, holding it to front, side and bottom.

The fork lock may be rattling.

With the Concour, the vibration is not really a problem, it's the rattling that drives you nuts.

[julianop]

Thanks for these suggestions, guys.

Jut to be clear, though, I did say resonance - not vibration or rattling. It's a noticeable increase in the magnitude of that ever-present vibration between 65MPH and 75MPH, particularly noticeable when I come down out of 80 MPH. The vibration as I'm accelerating up through that range is a function of torque, and is to be expected.

It might be as T Cro says - just what one should expect from such a spirited engine.

On your point, jim-d, most of my money is also going on the valve adjustment,  and that is where I am now in trouble, so... I'll post on that separately...

[julianop]

While I was fighting to remove the cylinder head cover, I noticed this bolt was loose (see attachment)

I take it this is a problem? Why is it spring loaded, though?

[T Cro ®]

While I was fighting to remove the cylinder head cover, I noticed this bolt was loose (see attachment)

I take it this is a problem? Why is it spring loaded, though?

What are you talking about spring loaded? If there is a gap in between the motor and the frame it is because it needs to be filled with a small shim or washer and then tightened up. This will cause the bike to handle poorly and yes cause it to resonate.

[Mettler1]

  Looks like that's where the motor mount bolt is supposed to go but never saw a bolt like that. Never saw a spring either. Should be a solid bolt and nut on the backside with shims on the bolt between the engine and the frame.

 Tony types faster than me!!

[julianop]

T-Cro, Mettler,

On further investigation, the nut on the back side is missing completely, and the springiness I felt was the bolt pushing against a plastic molded part that is behind the top of the water radiator that is loose and which spans the gap between the two nuts. I would think that it should be retained somehow, but it isn't - at least not at the top.

Sorry to be slightly vague on occasion, but I'm fresh to this, and there's a lot to take in. I'm reporting as completely and as quickly so I can to make th best use of your guidance.

I'll have to replace the nut, obviously, but yes, I'm sure this is a major contributor to the resonance.

This also seems to be a good time to tell you about the valve clearances - they're quite awful:

Inlets, cylinders 1 to 4, values in mm:
0.16/0.16; 0.23/0.23; 0.16/0.40; 0.15/0.67.
Yes, that's 0.40mm on right hand inlet valve of cylinder 3, and 0.67mm on right hand inlet valve of cylinder 4.

Exhaust cylinders, 1 to 4, values in mm:
0.23/0.23; 0.28/0.28; 0.33/0.33; 0.33/0.33.

Comments welcome on those values.

I've seem a recommendation for aiming them at 0.15 for inlet and 0.20 for exhaust. Would that be good?

[julianop]

While I wait for some input on this. I've run through the valves, set all inlets to 0.15mm, and all exhausts to 0.20mm.

I'll wait for words of wisdom before I close it all up.

On the engine bolt: there is a gap of 3.22mm - just over 126 thou - between the left side of the engine and the frame bracket. I cannot see any shim on the right side.

I had found a nut and two washers luring at the bottom of the fairings during disassembly: I guess I now know where they came from ;-)

Should I use any lubricant on the engine mounting bolts during reassembly?

I noticed that ensuring the front edge of the rubber seal is correctly located between the cover and the head is  little challenging. I guess I'll know if I get it right if I don't see oil spewing all over the place.

Finally, what is that plastic part on front of the cylinder head?

[George R. Young]

The plastic part to the front of the cylinder head is an air dam to force hot air to go elsewhere than to heat the rider.

You can sort of push the bottom part forward to assist getting the valve cover and its gasket in place on the front. Then pull the bottom part back and force the top part forward and down. It's supposed to have little square nubbins to latch onto, but the whole process isn't very elegant.

[billhook]

The valves were loose?  Some of them were right on, but the rest were loose and, real loose at that.  The clearances tighten up with wear.  They must have been making quite a racket. Instead of .15 and .20, you might want to go to the loose end of the range, .18 and .23.

[julianop]

Thanks for the info on the plastic air dam, George.

Billhook, when you say tighten with wear I assume you mean wear on the cam and cam-follower surface, right? That would make sense to me. I hate to think what the clearances would have been when it was actually adjusted.

I would suspect that the large variation on the inlets would have caused fairly significant imbalance in the fuel/air input to cylinders 3 & 4, which would correspond to a reduction in output from those two cylinders and an overall imbalance in the engine's operation, especially with the firing order 1-2-4-3.

Coupling that with the loose top engine mounting bolt, and it's no wonder I have numb hands after driving my 360 weekly commute.

[Mettler1]

While I wait for some input on this. I've run through the valves, set all inlets to 0.15mm, and all exhausts to 0.20mm.

I'll wait for words of wisdom before I close it all up.

On the engine bolt: there is a gap of 3.22mm - just over 126 thou - between the left side of the engine and the frame bracket. I cannot see any shim on the right side.

I had found a nut and two washers luring at the bottom of the fairings during disassembly: I guess I now know where they came from ;-)

Should I use any lubricant on the engine mounting bolts during reassembly?

No shims needed on the right side. I tightened the right side bolt and then add shims on the left side to fill the gap between the frame and motor mount. I used washers that I cut a slot in each one to slip over the bolt.I didn't use any lube on the bolts as I never had them out. I also set my valves a little on the loose side. As we say, "A tappy engine is a happy engine. "

[julianop]

Tappy = happy ... I like that :-)

Well I ran through them all last night using a loose .15 and .20 for inlet and exhaust, and allowing for maybe a couple hundredths of a mm on the nip-up of the lock nuts I think I'm good to go - at least until I bite the bullet and get SISF's cam kit.

As I think about it, I probably dropped the washers (oh, sorry, "shims"!) myself as I was investigating the loose bolt. I'll pop that lot back together, cross my fingers that I properly captured the front edge of the rocker cover gasket, and move on to an oil change and balancing the carbs.

I'm hoping to be amazed and impressed by an engine with a smoother sound and feel than I've ever experienced after this...

[billhook]

By wear, I mean that as the valves and seat "settle" in, the clearances become smaller.  So, yes, it is kind of scary thinking what the valves were set at the last time they were adjusted.  With the larger clearances, the valves were "slamming" into the seats, instead of "tapping".  Also, the valves would not have been opened as long, so you'd have less intake mixture brought in and exhaust pushed out.  Conversely, too tight of clearance, and the valves don't contact the seats and are open longer, so heat isn't dissipated (burnt valves) and cylinder pressure is lessened.

[julianop]

Yes indeed, Bill, comparing the sound now to the sound before, I realize it was a bit clattery.

Well it's all back together again now, and I warmed it up till the cooling fan came on then balanced the carbs and took it for a brief spin.

It is sssmooth, mmm - mmm !

I'll take my weekly run from Minneapolis down to Rockford Illinois now, and see how she behaves on the open road.

Good point about the head dissipation. Of all the impacts that came to my mind, loss of heat dissipation through the valve seats with a valve that is open too long was not one of them (not that that was my problem in this case, of course, but I do like to think through things so I have a complete understanding). Thanks for that jewel.

Thanks, all, for the help on this thread. I'll report back on the resonance.