Serious vibration issue. Need advise! Video explanation.


12 replies to this topic
  • coop63

Posted November 14, 2012 - 10:19 AM

#1

I recently rebuilt the bottom end of my 2004 yz450 due to a hole punched in the crankcase (another story all together). Replaced all the bearings with dry ice and a heated case. They just dropped in, no pressing. All torque settings were accurate and re-checked. The frequency of the vibration is very high and felt throughout the bike. A lot higher frequency than i would expect from the bottom. I really did not notice how bad it was until i rode my son's yz250. It was causing severe numbness in the hands, creating a dangerous situation. I took the balancer out and check the runout and it was fine. i took off the valve cover to inspect things and noticed that the intake cam has a serious issue. It does not freely rotate in the journals, as does the exhaust cam. This leads me to believe that there is obviously some major distortion present. The camshaft satisfies all specifications, except the cap to camshaft clearance, which i did not measure(no plastigauge), but after seeing the videos its obvious that this parameter is not within normal limits.

But the source of the vibration could be from this forced eccentricity when the caps are tightened down to the head. It certainly needs correcting, but how is the best way to accomplish this? Camshaft replacement, cam cover replacement, head replacement,... I have an Ebay bid for a used head as backup. I can't get a part number for the cam covers. I guess they are machined as a unit and not sold separately. Used, or a completely new head may be the only answer. Please see the following videos which will help explain the situation. Thanks in advance for any advise! I hope these video links work.

http://www.youtube.c...e&v=cYXEVlxY3io

http://www.youtube.c...e&v=q8REOie6QQ8

http://www.youtube.com/watch?v=taMi0MjbPVg&feature=player_detailpage

  • grayracer513

Posted November 14, 2012 - 11:01 AM

#2

The cam caps are not sold separately; they're bolted onto the head while the cam bores are machined ("line boring"). In the event they become damaged, a competent small engine machinist can restore them. Also, I recommend reducing the torque specified to 75 in/lb (6.25 ft/lb) from the listed 86 in/lb when using oiled threads as called for by the manual.

Secondly, there is no way for you to accurately measure cam runout by clamping the ball bearing in a vise. To understand why that's true, set the dial up again as you have it in your embedded video and instead of rotating the cam, rock it back and forth in the bearing toward the dial. You can probably get as much as .004" even if the bearing was new. The cam has to be gauged for this either turning between centers, as shown in the manual, or in a pair of V blocks, or on a roller stand to eliminate the motion you see in the ball bearing.

It is not uncommon at all for the intake to exhibit this behavior. Cam clearance is listed as 0.020 ~ 0.054 mm (0.0008 ~ 0.0021 in), which, at the lower limit is extremely small. Clearance increases as the engine warms, too. Check it with Plasti-Gage as shown. If you want it a little looser, you can polish a little off the cam journals by winding a narrow strip of 320-400 grit emery cloth once around the shaft and working it down slightly.

The cams could not generate the sort of vibration you report. First place I would look at is the timing of your counter balancer gears.

Download a manual if you don't have one:

http://www.yamaha-mo...uals/index.aspx

http://www.yamahaown...ook.com.au/?r=0

  • KJ790

Posted November 14, 2012 - 11:09 AM

#3

What kind of a crankshaft did you put in? If you reused your old crank, how did you remove the crank when you split the cases? If the crankshaft has been hit with a hammer at all or miss handled (accidently dropped or something similar) then you can end up with a bad vibration.

  • grayracer513

Posted November 14, 2012 - 12:25 PM

#4

Good point. Hot Rods cranks aren't bad, but I've seen some of the cheaper replacement cranks that were not really very true brand new out of the box.

  • coop63

Posted November 14, 2012 - 04:10 PM

#5

What kind of a crankshaft did you put in? If you reused your old crank, how did you remove the crank when you split the cases? If the crankshaft has been hit with a hammer at all or miss handled (accidently dropped or something similar) then you can end up with a bad vibration.


I installed a new Hot Rods crank and connecting rod combo. I also am using a Vertex 13.5:1 piston. New bearings were " placed" not pressed. NEVER was a hammer or any tools used to seat the crank. I used the Tusk crank installer and pulled the crank into both halves of the crankcase after the bearings were placed.

I also placed the primary drive and balancer driven pulley in alignment as per the manual. Dots lined up, and the pulleys are oriented
properly. I changed the oil after a moderately aggressive break in period, and found no metal shavings to speak of. Engine mounts are all tightened to spec.

Even if the camshaft is not the source of the vibration, then the binding would eventually cause problems, or would it?

I will attempt to find a good motorcycle machine shop to line bore the cam journal true again.

I am still at a loss as to why the vibration is occurring.

  • KJ790

Posted November 14, 2012 - 04:14 PM

#6

Hmm, I wonder if the crank was damaged during shipping or something. You didn't happen to measure the runout on the new crank before you installed it did you? This is one of those things that you tend not to think about until you are trying to track down a problem like this.

I have found that hotrods cranks do tend to vibrate a little more than stock, but nothing that should be making your hands go numb. Seems like there has to be something major there somewhere.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • coop63

Posted November 14, 2012 - 04:45 PM

#7

Hmm, I wonder if the crank was damaged during shipping or something. You didn't happen to measure the runout on the new crank before you installed it did you? This is one of those things that you tend not to think about until you are trying to track down a problem like this.

I have found that hotrods cranks do tend to vibrate a little more than stock, but nothing that should be making your hands go numb. Seems like there has to be something major there somewhere.


No, didn't check the runout on the crank. Assumed quality control would check that at Hot Rods. But I shouldn't assume even that. Damn, I don't want to take it apart again. I need to look at the warranty terms. This so sucks.

  • coop63

Posted November 14, 2012 - 06:05 PM

#8

Good point. Hot Rods cranks aren't bad, but I've seen some of the cheaper replacement cranks that were not really very true brand new out of the box.


If it is the crank, then would reinstalling the stock crank assembly be the next step in determining the vibration source?
Also, how is the crank, rod and piston assembly balanced.? Statically or dynamically?

  • marv02

Posted November 14, 2012 - 06:22 PM

#9

I had the local Honda dealer rebuild one of my Cranks out my Old CR 250 after they touched it never the same I end buy a complete NEW OEM crank in the box.

A bad crank can cause you headachs feel for you I hope you get ths worked out.

I always buy a Complete new OEM crank from that point on But My CR500 you could not get a Complete crank for factory any more So I went with a MSI rod it worked fine But I took that crank to a place that specalized In crank rebuilds leason learned the hard way.

  • grayracer513

Posted November 14, 2012 - 08:11 PM

#10

If it is the crank, then would reinstalling the stock crank assembly be the next step in determining the vibration source?
Also, how is the crank, rod and piston assembly balanced.? Statically or dynamically?


Yes, that would be a troubleshooting step you could take, but it's a lot of work, don't you think? Better to take the crank somewhere and have it looked at.

Engine balancing is an inexact art, and is in some ways a bit like voodoo. The crank can be balanced either statically or dynamically, but cranks are balanced with the understanding that it can't be done. Not completely, anyway. The force exerted by the reversal of the piston is stronger at the top than the bottom, so you can't ever totally offset the vibration caused by reciprocating weight in a single. Static balancing is obviously inferior to a good dynamic set up, but they're not all that great and the operator still comes into it.

But the reality is that a lot of shops that rebuild cranks, even ones the do a good job of it, don't check the balance, nor should they have a reason too if they use good components. Vendors who make rods, crank pins, bearings and such work with specifications as to the weight as well as size of these parts. This even goes to the extent that the weight of each end of the rod has to fall within a specific weight range. You'll usually see evidence of grinding at each end of a typical connecting rod, often on raised lugs put there just so they could be ground down to the right weight after machining everything else.

The point is that if the crank was built with proper parts, it will run as smooth as OEM IF it's trued up correctly. And that might be exactly what the problem ends up being, the crank out of true.

But check the gear timing before you pull it out of the bike. Might save some work.

  • camman

Posted November 15, 2012 - 09:47 AM

#11

I know that Hotrods uses a laser scanner for QC to verify the forging a are identical to stock. This is what lead to the updating of their YZ crank forging a couple years ago. If you have a newer Hotrods crankshaft (last couple of years) there should be no difference in vibration from stock. If somehow you received a much older HR crank there could be slightly more vibration. However very few of those cranks are still floating around. I haven't seen one for a long time. I personally have never seen a Hotrods crank out of alignment however that doesn't mean yours wasn't damaged in shipping or rolled off a table when your motor was being built. I would measure the crank. Also verify your balancer is timed properly. Good luck.

  • coop63

Posted November 19, 2012 - 08:11 AM

#12

After the vibrations began, i stopped running the engine and disassembled it to check all components. This is what i found. rather than post every pic and video, the link to my photobucket album is http://s1354.photobu...681/drjclark63/. There are also some pics of the cylinder wall after the break in period. Very noticeable scratches
are present relating to the intake and exhaust positions of the cylinder wall.
Posted ImagePosted Image



I rehoned the cylinder and all aspects of the cylinder and piston (new vertex 94.94mm 13:0) are in spec.

First cylinder hone when vertex first installed
Posted Image




Second hone, not yet installed. Most all scratches eliminated
Posted Image




Also notice the oil present on top of the piston, and pooled in the exhaust valve recesses
Posted Image




I also tried to unscientifically determine if the crankshaft should be sent to a professional to be balanced and trued. There does seem to some eccentricity in the shaft. But i really don't know how i should interpret it.http://s1354.photobu...=rendrunout.mp4

Also, who would be the best at possibly balancing and truing the crankshaft.

One more thing! I just got the stage I Hot Cams intake cam and in their instructions they mention " Check for coil bind. We recommend that at maximum valve lift there should still be at least .050" movement left in the spring before complete coil bind. Check your valve retainer/keeper to valve seal clearance. We recommend at least .030" clearance between the seal and the retainer. Any clearance less than .030" will pump oil into the cylinder through the valve guide."

My question is, how do you measure such a clearance?

  • coop63

Posted November 19, 2012 - 08:19 AM

#13

Damn, i didn't think pics would be that large, sorry!





Related Content

Forums
Photo

05 yz450f not fast enough by RedeyeYZ


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies
Forums
Photo

Should I buy this bike? help....... by Numsa Hul


Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies
Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017
Forums
Photo

The "going back to the other darkside" adventure... by Monk


Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies
Forums
Photo

James Stewart back on a YZ450F by YamaLink


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.