Loose flywheel


9 replies to this topic
  • Erik Marquez

Posted December 04, 2010 - 11:41 AM

#1

So, went to time the cams in the boys 2007 YZ450F, he had adjusted the valves and timed the cams.. After the test ride he heard a "noise" and the bike stopped running.

I got home, we re-timed the cams..... and at just before TDC Compression stroke, found the valves to be hitting the piston.... :blah::banghead:

Figured he had bent a valve with mis timed cams..

Checked valve clearance.. No new open gaps :worthy: Looked at valve cotters,, none popped up or out :worthy: Both signs of crashed / bent valves.

Re timed cams, triple check cam, crank timing.. Something still wrong,, intake valves hitting piston....:ride:

Checked nut on flywheel,, it was a bit loose, not hand tight, but not much more.. woodruff key was still present.

Checked timing set up one more time.. all was well.. So off came the head...... NO BENT VALVES :worthy::banana:;):lol:
But ..what then... only thing left was crank to flywheel index.

Pulled the cover, pulled the GYTR light weight flywheel...... and yup.. it was spun on the crank 10deg or so. Key was not sheared.
Posted Image
best guess is..... My son did not tq the flywheel nut sufficiently when he installed the flywheel,, nut backed off... flywheel broke taper.. spun... effectively making the crank / cam timing off even with the marks properly aligned.

In hind sight.. I could have diagnosed this by installing a timing wheel and piston stop.. verifying the flywheel timing marks.
or
I could have used a spark plug dial indicator set up I have to verify flywheel timing marks.

I was just more focused on my son telling me he had mistimed the intake cam 1 tooth... and now we had the valve inference issue.... In hindsight.. I now know the cam was mistimed due to the crank issue... he likely installed the cams perfectly :thumbsup:

It will still need valves soon (tightened twice in 19 hours):bonk: at $344 parts cost alone.. Not super happy about that... though Yamaha's did not wear though valves this quick (I'm the third owner.. no way to know what kind of airfilter maint was done by PO's, RPM use, etc etc)

The better news is.... Cody did it right when he adjusted the valves and set timing.. He missed on the flywheel nut tq some weeks back,,, but, well we all learned from our successes and mistakes,, he is no different.

Attached Thumbnails

  • flywheel.jpg


  • Erik Marquez

Posted December 04, 2010 - 12:13 PM

#2

Well I spoke too soon.... to confirm we had this figured out...
I had cody put the head back on, OEM flywheel installed...cams put back in.. crank/ cam timing double checked.. hand rotation over.....intake valves still hitting the piston :thumbsup::banghead:

I'm stumped.

The cam lobes are at the right position, when cam gear marks are aligned.. so I don't think the cam gears slipped on the cams.

The flywheel is indexed right on the crank.

Piston at TDC, flywheel marks centered, cam marks in position, cam lobes confirming right cam timing.. Just before TDC in intake stroke.. intake valves are hitting the piston.

So what am I missing?

This one is as baffeling as the timing issue I had with the KX due to the wrong crank...:blah:

Any ideas?

  • Erik Marquez

Posted December 04, 2010 - 12:55 PM

#3

Dial indicator proves the piston is at TDC when the flywheel marks are aligned with the cover index mark.

No cams installed, engine rotation confirms it is not the counter balancer that is making hard contact.

Marks in the carbon on piston at the intake valve pockets confirm it is the three intake valves that are contacting the piston.

  • KJ790

Posted December 04, 2010 - 01:14 PM

#4

Well if you have proven that the piston is at TDC when the flywheel mark says it is, and the intake valves are hitting the piston, then it has to be your intake cam timing. From your posts I can tell that you know the bike well, so obviously you know how to set the cam timing according to the timing marks on the cam sprocket. That leaves the cam sprocket spinning on the cam. Are the cam journals scored at all? It's possible the intake cam seized momentarily and spun the sprocket on the cam. You don't happen to have another intake cam to compare yours to do you?

  • Erik Marquez

Posted December 04, 2010 - 01:26 PM

#5

Well if you have proven that the piston is at TDC when the flywheel mark says it is, and the intake valves are hitting the piston, then it has to be your intake cam timing. From your posts I can tell that you know the bike well, so obviously you know how to set the cam timing according to the timing marks on the cam sprocket. That leaves the cam sprocket spinning on the cam. Are the cam journals scored at all? It's possible the intake cam seized momentarily and spun the sprocket on the cam. You don't happen to have another intake cam to compare yours to do you?


I dont have another cam.. But I do have the cam degree tools needed to confirm the sprocket is still indexed correctly... Thats what we are working on now.

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  • Erik Marquez

Posted December 04, 2010 - 01:46 PM

#6

Ok, much better... no more valve to piston interference.

We still have to deal with the sheared flywheel key, and valves that are wearing quickly. But the rest was just two things that went wrong at the same time,, with over lapping symptoms that were attributed to the work being done today and not from a flywheel install done two months ago.

  • brentn

Posted December 05, 2010 - 07:33 PM

#7

So what was it? Did the cam gear spin as well or something else?

  • Birdy426

Posted December 05, 2010 - 11:37 PM

#8

The better news is.... Cody did it right when he adjusted the valves and set timing.. He missed on the flywheel nut tq some weeks back,,, but, well we all learned from our successes and mistakes,, he is no different.


Man, I love your attitude! I assume Cody is your son...He's one lucky young man to have you for a dad!

  • Erik Marquez

Posted December 06, 2010 - 04:28 AM

#9

So what was it? Did the cam gear spin as well or something else?


Three things simultaneously..

1: Valves tightened, Cody (my son) adjusted them, as we have done together in the past.

Rotated engine by hand, no problems found.. Went for a test ride.. back at the garage,while idling.. bike just turned off....

2: What we did not know at this point was unrelated to the valve adjustment, the flywheel nut had loosened at some point. The woodruff key sheared and the crank timing was now off about 10 deg.

3: Rechecking of the cam timing showed they were out (thought to be because it was mis timed... not known it was flywheel key sheared) so cams were timed, and then piston interferance...... cams re timed, procedures checked.. still intake to to piston interference.

Was thinking we had a bent IN valve, so pulled the head.

When I found no bent valves I knew it was a timing issue, but not cam timing procedures..
Checked piston TDC with a Dial Indicator and we found the issue with the flywheel key.

.. after installing the GYTR spare flywheel I had Cody reinstall the head and cams, re time to confirm our find... valves hit.... still.. kind of..
In haste.. after doing the job right a dozen times that day.... He missed IN cam timing by one tooth.. When he went to hand rotate the motor it hit,,again,,,:blah:.. It was easy to spot once the engine was turned back... as we knew everything else was good to go.

So two issues unrelated but had overlapping symptoms and one issue rider induced that caused confusion , with symptoms related to an actual issue we were having, made for a long few hours in the garage.

Mistakes were made.. (flywheel install, 11th or so timing the cams for the day...

ENDSTATE
Intake valves tighten every few rides.. Needs new valves.. Head is going to SSW next month.

OEM flywheel ruined, will use GYTR flywheel till we can get another OEM.

New head gasket, flywheel key on the way.. bike will be running again in a few days :thumbsup:

  • brentn

Posted December 06, 2010 - 11:38 AM

#10

He missed IN cam timing by one tooth..

Doh!

I see now :thumbsup: Good to hear you got it all sorted out!





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