Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Big Vibration around 45 MPH

Big Vibration around 45 MPH

Moderators: Curt!, Pa

Post Sun Apr 28, 2013 8:11 am

Posts: 20
Location: MA, USA
Just getting my 45 running and it runs great, but has a big oscillation/vibrations around 45mph.

Is it possible this has anything to do with adjusting the front end suspension, or is is simply most likely tire/wheels out of balance? The bike has aftermarket chrome spoke wheels and no apparent weights on them.

The vibration is really bad, but I am able to accelerate to 50 MPH or so and it gets a little bit better. It is pretty scary with the whole bike shaking. Can this simply be a balancing problem?

Post Sun Apr 28, 2013 11:11 am

Posts: 693
Location: somerset, oh usa
You should be able to check static balance of your wheels simply by elevating them independently and spinning them while observing the stopping points. Be certain that the tire beads are properly seated. At the same time you can check for excessive wheel hub end play and bearing wear. Also whether the tread runs consistantly without any wobble. Also check your steering head bearings and wheel alignment.
I gather that it effects handling and isn't just a loose engine, etc?

Post Sun Apr 28, 2013 8:06 pm

Posts: 35
do u have the correct front end, AND the correct triple trees?
i had a similar problem with a Servicar(at a lower speed range). in my case, after a wreck, the wrong trees were used and the front tire was too close to the frame. with the proper trees, the geometry was corrected and the issue went away.

Post Mon Apr 29, 2013 9:13 am

Posts: 20
Location: MA, USA
Excellent feedback/ideas. I was able to put 75 miles on the bike this weekend. Yesterday I pushed the ol girl up over 50 MPH and she smoothed out quite a bit so I think it may just be a tire/wheel balance issue.

I need to get a lift so I can put her up in the air and check the static balance and look for warpage.

I will post some pics of the front end and see if you guys think it is correct.

Post Mon Apr 29, 2013 12:07 pm

Posts: 693
Location: somerset, oh usa
Sounds like your havin' fun now! Agreed that it is likely a balance issue but with a new bike it's best to check all of the things mentioned considering handling issues.
Should you find the tires with no separations and well beaded and significantly out of balance as is indicated, it might also be a good idea to roughly indicate the rim in while elevated as if it's out of balance a bunch, then it's likely the rims are not running true.
Good luck, have fun and be careful out there!

Post Mon Apr 29, 2013 3:44 pm

Posts: 693
Location: somerset, oh usa
Just thought of something else that you could try and should check. Roll the valve stems to their lowest position and deflate the tires. Perhaps someone put a bandaid fix on a leaking tube with a leak stop fluid. If so i feel you would get some indication when deflating them.

Post Mon Apr 29, 2013 5:56 pm
Pa Site Admin

Posts: 5801
Location: Ohio USA

Spoke weights work rather well for balancing. I've seen tire beads not seated which caused the same symptoms to boot. Look for tire runnout as well as balance.

Post Wed May 01, 2013 8:59 am

Posts: 20
Location: MA, USA
All good tips I will use when checking the tires and rims. I plan on doing a static balance and visual check first. A local shop with a high speed balancer said they would give it a shot, but I am not sure if they will have the right adapter for these rims.

I did push in the clutch at the peak of the vibration to see if it was an imbalanced engine, and the vibration stayed the same.

What is a safe top cruising speed for these bikes??

How would I check to see if there is stop leak or "slime" in the tire tube?

thanks! :mrgreen:

Post Wed May 01, 2013 5:59 pm

Posts: 693
Location: somerset, oh usa
37ULH wrote:
Roll the valve stems to their lowest position and deflate the tires. Perhaps someone put a bandaid fix on a leaking tube with a leak stop fluid. If so i feel you would get some indication when deflating them.

Post Thu May 02, 2013 5:54 am

Posts: 20
Location: MA, USA
Sorry I guess I don't understand exactly, that is why I was looking for clarification:
"Roll the valve stems to their lowest position" Do you mean rotate the tires so that the valve stem is at 6:00?
What indication exactly would I expect to get when deflating the tires, are you suggesting that stop leak might come out of the stem?

Still wondering what is a safe top cruising speed for these bikes??

thanks

Post Thu May 02, 2013 10:07 am

Posts: 693
Location: somerset, oh usa
Exactly. If no evidense when deflating pull the valve core and if it's clean, proceed with checking static balance, etc.

Post Thu May 02, 2013 10:27 am

Posts: 693
Location: somerset, oh usa
If you are talking chassis, and everything is correct, it should remain stable enough to go 125+. The racers use the same chassis and run right around 100 to 105 top speed at Daytona. If you are talking a stock engine, short bursts of 70 shouldn't hurt it but there are alot of other factors as engine sprockets are available from 17 tooth to 34 tooth.
It will be happiest at speeds up to around 60, depending these other factors including state of tune, carb size, gearing etc.
For the technology available, they are an amazingly durable machine.
BTW, there is also a limit as to how many questions can be answered before you show us photos of your bike, hint, hint.
There is already a topic for it or you could add it here.

Post Thu May 02, 2013 2:21 pm

Posts: 20
Location: MA, USA
Harley 42WLA smaller.jpg



Oh OK, here is a pic or 2 before I cleaned er up...
You do not have the required permissions to view the files attached to this post.

Post Thu May 02, 2013 2:58 pm

Posts: 693
Location: somerset, oh usa
Wow! Very Nice. I hope you have an understanding wife as i see the beginnings of a lasting affair here.

Post Thu May 02, 2013 3:16 pm
Pa Site Admin

Posts: 5801
Location: Ohio USA

37ULH wrote:
Wow! Very Nice. I hope you have an understanding wife as i see the beginnings of a lasting affair here.


Ditto to that for sure !

Post Mon May 06, 2013 7:29 am

Posts: 20
Location: MA, USA
I have owned a few bikes over the years and I must say that riding this old girl is a completely different experience. Every gear change is different and a treat, and trying to master the foot clutch is challenging but coming along.....

I don't think I have actually ridden back roads like I do on this bike. The general slower pace and less forgiving brakes put me in a more relaxed, but also very alert state. I really like it. The next big thing is getting rid of the darn vibration so I can enjoy a slightly faster pace more comfortably.

I bought a 45 because my Dad bought one new when he got out of the service and rode it across the US. He always talked about how comfortable his "Buddy seat" was.

My wife is used to my mechanical exploits and addictions, thank goodness!

Post Mon May 06, 2013 7:21 pm

Posts: 693
Location: somerset, oh usa
Hopefully you find something easily resolved.
I really like the way the panels were laid out on the fenders. It's a good looking machine.
The connection to your father's experience makes it that much cooler. As reflected in their pricing over the last 10 years, more people that summarily dismissed the small twins are discovering what i've known since building my first one from a basket case at 17 some 40 years ago. My current count of 45's is 6 and it has been a lifetime affair.
Have you by chance tried to trace lineage for the specific bike your dad had?

Post Tue May 07, 2013 1:18 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Nice bike. It certainly seems that the problem would be somewhere in the wheels and tires, or wheel bearings. Is the transmission firmly bolted down?

My other question would be, has the bike always done this? Did you build/purchase the bike and it did this the first time you rode it? Or did it kind of "grow and develope"?


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