Wrong top dead center


8 replies to this topic
  • Ronnie.sensiba

Posted March 11, 2016 - 04:24 PM

#1

Alright don't laugh at me all this stuff is new to me. I adjusted my valves. Before I put the motor back together I turned it over a couple times to make sure everything was smooth. When I looked at all the timing marks everything looked completely backwards so I swapped it all around. Did this a couple times before my brain realized there are two top dead centers.

Called my dad who told me it doesn't matter because the valves determine which tdc your at. When I put the bike back together and started it up I noticed a new whining sound coming from the top of the engine. Bike seemed to be running fine and I didn't hear any knocking sounds. No metal in the oil or anything.

So here is my question. Does it matter if you set the valves on the compression stroke? Could not doing this cause damage to my engine or cause a whining noise from my valves?

I'm on a 2005 wr450f. Any input is greatly appreciated as I would love to get back on the trail.

Edited by Ronnie.sensiba, March 11, 2016 - 04:27 PM.


  • stevethe

Posted March 11, 2016 - 04:34 PM

#2

Valve clearence must be set on the compression stroke. When the piston is on the top.

  • Thefischerman

Posted March 11, 2016 - 04:40 PM

#3

Correct me if I'm wrong, but:

For every 360 degrees of rotation, your piston is at TDC twice (180 degrees, and 360 degrees). Until you put your cams on, it doesn't matter if you're at 180 or 360 degrees; with the cams off, your piston simply moves up and down. It's not until you put the cams on until the actual "timing" matters. You're timing your valves, not your piston. When putting the cams on, make sure the piston is at TDC, then align the cams to the compression stroke. This is the logic I used on my CRF450 and it's worked for me.



  • Ronnie.sensiba

Posted March 11, 2016 - 04:42 PM

#4

Correct me if I'm wrong, but:

For every 360 degrees of rotation, your piston is at TDC twice (180 degrees, and 360 degrees). Until you put your cams on, it doesn't matter if you're at 180 or 360 degrees; with the cams off, your piston simply moves up and down. It's not until you put the cams on until the actual "timing" matters. You're timing your valves, not your piston. When putting the cams on, make sure the piston is at TDC, then align the cams to the compression stroke. This is the logic I used on my CRF450 and it's worked for me.


That's how I understand it. I was abled to find in the manual where it states the check it on the compression stroke.

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  • mlatour

Posted March 11, 2016 - 05:10 PM

#5

Correct me if I'm wrong, but:

For every 360 degrees of rotation, your piston is at TDC twice (180 degrees, and 360 degrees). Until you put your cams on, it doesn't matter if you're at 180 or 360 degrees; with the cams off, your piston simply moves up and down. It's not until you put the cams on until the actual "timing" matters. You're timing your valves, not your piston. When putting the cams on, make sure the piston is at TDC, then align the cams to the compression stroke. This is the logic I used on my CRF450 and it's worked for me.

 

 

The piston can only be at TDC once per 360° revolution,

if you start at TDC at 0°, it will be at BDC (bottom dead center) at 180°, and back up to TDC at 360°

 

You may be confusing that in a 4-stroke engine, it requires 2 crank revolutions to complete the cycle.

(piston is at TDC twice in the cycle, on intake stroke and on the power stroke)


Edited by mlatour, March 11, 2016 - 05:13 PM.


  • Thefischerman

Posted March 11, 2016 - 05:17 PM

#6

The piston can only be at TDC once per 360° revolution,

if you start at TDC at 0°, it will be at BDC (bottom dead center) at 180°, and back up to TDC at 360°

 

You may be confusing that in a 4-stroke engine, it requires 2 crank revolutions to complete the cycle.

(piston is at TDC twice in the cycle, on intake stroke and on the power stroke)

Oh duh... never-mind, ignore what I sad about rotation. However it is still correct to say that if the cams are off, TDC is TDC and there is no "wrong" TDC until you put the cams on no? There is no "cycle" until you put the cams on; the piston just moves up and down.



  • mlatour

Posted March 11, 2016 - 07:32 PM

#7

Well, say first we take an assembled engine,

the service manual will indicate which of the 2 possible TDC the crank has to be positioned to adjust the valves or line up timing marks.

 

Normaly the TDC in the top of the compression stroke is used (I called it the power stroke in my previous post)

 

Say by mistake you set the crank on TDC of the intake stroke instead, the cam timing indicators are going to be off,

requiring you to spin the crank another 360° to line things up, you could refer to that as the wrong TDC.

 

As you said, until the crank/rod/piston assy. is connected to a chain/valvetrain,

TDC is TDC no matter how many times you spin the crank, it doesn't know which cycle it's in yet.


Edited by mlatour, March 11, 2016 - 07:35 PM.


  • Ronnie.sensiba

Posted March 12, 2016 - 12:39 AM

#8

Thanks guys. I pulled everything apart again, added more assembly lube, triple checked the timing and was super careful torquing it. I think the 3/8 torque I was using was a bit in accurate and I was tightening in too big of chunks.

I tightened it very slowly in the star pattern and the motor seems to turn a lot smoother. I also suspect it could have been the chain tensioner so I cleaned lubed and very carefully installed it.

It's too late to fire it up but we will see in the morning if the whining went away.

  • grayracer513

Posted March 14, 2016 - 01:19 PM

#9

One potential cause of such a noise after valve clearance resetting is misplacing the half circle locating ring that is supposed to locate the camshafts in the correct side-to-side orientation.  Shifting the cam one way or other will cause the chain to run onto and/or off of the the sprockets at a lateral angle.  Far enough off and it will sing.

 

Regarding torquing cam caps, the following is extremely important:

 

  • NEVER pull the cam caps down into place by tightening the bolts down.  You must be able to seat the cap in place over the dowels, etc., BY HAND, using no assistance other than a few light taps from a screwdriver handle or similar.
  • Torque the caps in 3-4 progressively tighter stages, not all at once.
  • Limit the torque.  I find that I do not like the feedback I get from running the full specified torque on these (87 in/lb or 7.2 ft/lb), so I use 75 in/lb (6.5 ft/lb) instead.





 
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