Vibrations and how to cure them

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51Hog
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Joined: Fri May 20, 2005 7:29 pm
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Location: Wasilla, Alaska

Vibrations and how to cure them

#1

Post by 51Hog » Tue Feb 24, 2009 6:20 pm

I am in the process of removing the major components from the frame of my 51 hydra.
My plan is to check over the frame for cracks that may be amplifying vibrations,
re-install the engine to be sure that it is shimmed properly.
I know I do not need to remove the engine for this, but I will be installing new intake nipples, new pan gaskets, and trying to find out why I am leaking oil from the top of the case behind the rear lifter block. I may as well do this on the bench.

I need to hear from everyone on vibration.
We all know that our engines are not mounted on rubber so any and all vibrations are transmitted directly to the frame.
We also know that since the engine is a 'v', It cannot be balanced for all rpms.
What causes it?
What amplifies it?
What cures it or masks it?
Dale



john HD
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Re: Vibrations and how to cure them

#2

Post by john HD » Wed Feb 25, 2009 12:40 am

dale,

i know firsthand that a bad or cheap repop rear sprocket will make you think your motor is about to come apart.

do the simple or obvious stuff first.

john

mbskeam
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Re: Vibrations and how to cure them

#3

Post by mbskeam » Wed Feb 25, 2009 12:46 am

worn out primary chain will do it also

108
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Re: Vibrations and how to cure them

#4

Post by 108 » Wed Feb 25, 2009 2:00 am

I had a rear sprocket with excessive run-out causing a tight spot in the rear chain. I was able to correct it by just rotating the brake drum on the hub. The lower springs on my springer fork used to vibrate to a blur at about 70 mph with a 25T trans sprocket but I fixed that by sliding rubber shock absorber bushings from a car half way down the rod where they just touched the inside the spring.

VT

Re: Vibrations and how to cure them

#5

Post by VT » Wed Feb 25, 2009 3:18 am

Also a worn (matching clamshell halves) in a compensator sprocket will make the motor shake and shimmy....heavy duty. That's when I exchanged mine for an n.o.s. standard 24-T spline-sprocket.
Shakes went away immediately in 1988.

51Hog
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Re: Vibrations and how to cure them

#6

Post by 51Hog » Wed Feb 25, 2009 6:05 am

Great info--Keep it coming.

Mine is almost certainly engine related--or a lot of it is.
While riding, i have missed 2nd gear a few times :oops: When the engine revs to a questionable rpm, there are some vibrations that are pretty strong. Yea---I know----Don't miss second gear....

Seems like most of my vibration shows up at about 2800 rpm.

I have new rear and tranny sprocket and a new rear chain that I will be installing.
I run an 11mm Belt inside the tin primary. (Worked awesome last summer)
Dale

62pan
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Re: Vibrations and how to cure them

#7

Post by 62pan » Wed Feb 25, 2009 2:33 pm

Another thing to check out is to make sure that the engine is line up properly with the transmission (although if you are running a belt it should already be straight). Also make sure that the top motor mount is installed and shimmed correctly. When I worked on bikes for a living I saw many owner installed motors that had the top mount installed wrong.

51Hog
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Re: Vibrations and how to cure them

#8

Post by 51Hog » Thu Mar 05, 2009 6:42 pm

Yesterday I pulled the Clutch, Primary case outer and inner, Seat, Forks, and the Tank.
The upper motor mount looked good and was tight.
I removed the upper mount to frame bolt and it was shimmed properly.
I removed the two nuts at the heads----Studs are great.
Mount is intact.
The mount appears to be too short. The rear end of the mount has a hole, the front end has a slot.
The slotted end looks to me like it should be longer. The end of the mount only reaches to the far side of the front stud. Any Thoughts?
Took the front engine mount bolts out.
The front mounts seem to be great with no shims.
I need to get the left front mount welded up.
Can it be safely done without disassembling the engine? Maybe using heat sink clay and a tig?
left mount small.JPG
The belt drive was not aligned properly. the belt was slightly polishing the rear of the clutch basket. It did not wear much on the edge because of the "Lubrication" from the leaking output shaft. There is some wear on the crown of the belt teeth. Vibration??? hmmm....
There are about 3000 miles on the belt and pulleys.
damaged belt small.JPG
front pulley small.JPG
oil rubber primary small.JPG
You do not have the required permissions to view the files attached to this post.

VT

Re: Vibrations and how to cure them

#9

Post by VT » Thu Mar 05, 2009 8:03 pm

Gnarly wear Dale. Thanks for the live-action pics of the belt wear pattern and descriptions.
Did you assemble the belt drive and align the pulleys exactly as described in Vol. 2 using intersecting flat-rulers? The center illustration in Fig. D.4 shows both shafts pointed towards each other which would cause wear on the outside edge of the belt like your pic above.
Is that an 1-1/2 x 11mm. belt?
Note: The procedures are from Stett and were reviewed by Riverva Primo® before publication. If anythings lacking we'd like to know about it.

Sure, that missing front left mount would be the source of the vibration. You might email Accurate and get their opinion on welding that mount tab. http://www.accurate-engineering.com/

What gauge shim was under the front left mount? If the motor didn't have one and there was more than a 0.002 - .003" gap, it can cause either one of the front mounts to break (depending on which side has the un-shimmed gap).
The only way to establish a shim thickness is to remove the top mount and front mount bolts and then tighten the rear motor mounts tightly. The motor has to be a complete long-block (a short-block would give you an inaccurate reading). - Vol. 1

51Hog
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Re: Vibrations and how to cure them

#10

Post by 51Hog » Thu Mar 05, 2009 11:23 pm

VT wrote:Gnarly wear Dale. Thanks for the live-action pics of the belt wear pattern and descriptions.
You are welcome.

Did you assemble the belt drive and align the pulleys exactly as described in Vol. 2 using intersecting flat-rulers?
Probably not----I did not have the book at the time. I sold the book so I can't tell you if I used the exact same proceedure or not.
I did use straight edges front to rear. I did use an angle finder for vertical, as the pulleys need to be alligned in all directions. Not only were the pulleys parralell in all directions, but they were also on the same centerline.


The center illustration in Fig. D.4 shows both shafts pointed towards each other which would cause wear on the outside edge of the belt like your pic above.

The shafts were not aligned properly--Must have slipped a hair when adjusting the tension. I checked the belt after running about 300 miles. It was just off center on the clutch pulley towards the outside but not rubbing on the basket. It was the same on the engine pulley. At that time I did not check parallel on the pulleys as the belt appeared to be running true.

Is that an 1-1/2 x 11mm. belt?
It Is a BDL 11mm x 1 1/2

Note: The procedures are from Stett and were reviewed by Riverva Primo® before publication. If anythings lacking we'd like to know about it.

Sure, that missing front left mount would be the source of the vibration. You might email Accurate and get their opinion on welding that mount tab. http://www.accurate-engineering.com/

The mount has been broken for 30 years that I know of.
It still bolts tight to the frame and holds torque.
A spacer placed under the washer to hold it square to the broken mount has worked for years.
It is time to repair it. I hope that it is the cause of the vibrations.
There is no gap under the front tabs with the top mount off and the rear mounts tight


What gauge shim was under the front left mount? If the motor didn't have one and there was more than a 0.002 - .003" gap, it can cause either one of the front mounts to break (depending on which side has the un-shimmed gap).
The only way to establish a shim thickness is to remove the top mount and front mount bolts and then tighten the rear motor mounts tightly. The motor has to be a complete long-block (a short-block would give you an inaccurate reading). - Vol. 1

fourthgear
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Re: Vibrations and how to cure them

#11

Post by fourthgear » Fri Mar 06, 2009 4:38 am

Upon inspecting my new belt drive once, I also found some belt material in the primary and traced it to a loose tranny plate( powder coat was not removed from all mating surfaces ,I missed two & thats all it took ) , been fine since. Ya that oil is not good for your BDL.

That motor mount will take some work for sure . I would also check your upper motor mount on the frame ,for hair line cracks , I found a couple on the 65 & had them repaired .

VT

Re: Vibrations and how to cure them

#12

Post by VT » Fri Mar 06, 2009 4:54 am

I've been thinking about how your transmission might have been aligned to begin with and then drifted crooked by the belt pulling on the clutch hub pulley non-stop when it's running. Wondering if one of those Even-Pull® transmission rear support brackets that fit on the trans studs would help keep it in place. They'll work on '36-64 (and late style transmission assemblies when they're installed in a rigid frame. (VT 17-6655). I've also heard that they won;t work in a swing-arm frame because the two back studs in the transmission aren't long enough to still be able to poke through the stacked trans base and bracket too - that you'd need to find extra long studs that are rolled (trans end) by pitch (plate end) thread.

Panacea
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Re: Vibrations and how to cure them

#13

Post by Panacea » Fri Mar 06, 2009 5:06 am

Both of my front mounts were busted off like yours when I got the bike, A very dissapointing discovery for sure. Yes I completely dissasembled the motor for a complete re-build...

mbskeam
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Re: Vibrations and how to cure them

#14

Post by mbskeam » Fri Mar 06, 2009 6:47 am

since the area that needs welded is small, you can do this with the engine together.
this is not a major issue for a good welder, build it up a bit on the bottom, grind most of the new weld away then file till flat. you have most of the pad left, you can use this to guide the file , so as to get it flat, and a good straight edge from the other side can help verify the repair ....

check that your engine and tranny shafts are parallel and square to each other.....

51Hog
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Re: Vibrations and how to cure them

#15

Post by 51Hog » Sat Mar 07, 2009 5:09 am

Thanks for all the good info.
I am going to check the crank for run-out.
Hope it is straight........

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