Need help- Valve timing

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Jerry Doe

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Hi All,

I am getting my motor back together. It is on the bench. I have timing disk on primary side of crank, and am checking valve timing with a dial gauge on magnetic stand. The head is torqued down and valve clearances are set.

I cannot remember what cam is in my bike and I am getting some funny readings. Any advice on these readings is appreciated. I am considering getting another cam even though bike was running ok before. I am also considering advancing about 10 degrees by moving pinion.

I dont really want to take the motor to bits again.

The measurements were taken 3 times and are not perfect but as good as I can get them. I am sure about the lift but am probably off a few degrees on disk.

Left Hand:

Inlet opens: 72
Inlet closes: 95
Lift: 429

Ex opens: 72
Ex closes: 63
Lift: 453

Right Hand:

Inlet opens: 76
Inlet closes: 92
Lift: 425

Ex opens: 76
Ex closes: 62
Lift: 415

Any advice is appreciated. I noted the combat cam opens at about 59 degrees,

Thanks,

jerry
 
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valve timing

Hi Jerry,Best info. I have is :- Inlet opens BTDC -- 50 deg.,Inlet closes ABDC 74 deg., Exhaust opens BBDC -- 82 deg., Exhaust closes 42 deg. ATDC. these numbers apply to 750 and 850 motors and are measured at .013" cam lift. Good luck, ride safely. James.
 
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Jerry, I assume you are using a one inch travel dial on the valve collar. and that you have also set all the valves at .016. Have you included the rocker ratio into your figures? Without doing that math all the lifts will be off. Also when you don't know the grind of the cam your likelihood of picking the right clearance gap is slim.
When you say you could be off a few degrees this is a concern. Got to get this right many posts on using a dead stop tool described in many of my old posts. I pulled the .016 number because that's what i used for my 4S cam. The lift on each pair of intake and exhaust should be the same with in reason. With lifts like you list, if their right, it's cam time.
 

Jerry Doe

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Cam time

Yes it certainly looks like cam time. I have valves set at 10 thou.

Yes dial gauge is on valve collar.

How do I include the rocker ratio?

I think I am going to get a new cam from Fred maybe 560-00.

Oh well i will take the motor down again!

I find it weird the lift is so much. My observations are actually accurate. i took all readings again since the last post.

[and thanks for confirming what I thought]

regards
 
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If I remember right the rocker ratio is 1.13 to 1 or so. So the lift # are going to look high unless you do the math. The lift of the cam is different than the amount the valve travels.
 

Jerry Doe

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Correct Commando valve timing check method

Ok,

Due to brain spasm and conflicting info I need someone to tell me the correct way to check my valve timing and tell me rough parameters to be within. It is possible I have done something wrong.

I have motor on the bench with the head on and timing cover off, cam chain is adjusted and all pinions are in place. I have timing disc on primary side of the crank.

I have a dial gauge with magnetic stand.

Please dont tell me to align the dots etc.

Thanks for the help,

Jerry
 

L.A.B.

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Inlet rocker ratio is 1.13 inlet, 1.1 exhaust.

What figures do you get at 0.016" clearance?

Are the followers flat or radiused?
 

Jerry Doe

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Radiused?

The lifters are radiused. Here is a photo and some other photos of what i am doing:

Need help- Valve timing


Need help- Valve timing


Need help- Valve timing


Need help- Valve timing
 

L.A.B.

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Are you keeping the gauge plunger in line with the valve stems (it doesn't look like it in the photos)?
 

Jerry Doe

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Plunger

No it's off to the side a bit. I shall re-align. Why do I need a .016 gap?
 

L.A.B.

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Re: Plunger

Jerry Doe said:
Why do I need a .016 gap?

That's just it! There's no definite proof that you do, at the moment we appear to be dealing with an unknown quantity!!!! But generally these cams seem to need to be checked at either 0.010" or 0.016" (which allows for the ramp I believe?).

If the gauge isn't in line with the valve stem (at right angles to the face of the valve collar) then you will be adding an error to the readings, the further off the line of the stem the gauge is then the greater the error will be.
 
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Jerry here's an old post that could help. And L.A.B. is right about the stem of the indicator and the stem of the valve being inline.


Posted: Tue Jun 20, 2006 6:32 pm


First you need something to stop the piston near the TDC. You can tap a spark plug and put a socket head cap screw in it. Brake off the ceramic part of the spark plug and remove the hook on that end and drill it out #29 drill,then tap the hole #8-32. Use an 8/32 with 1 1/4 of unthreaded shoulder. run it in till it bottoms out. than cut off the head of the bolt and grind a bullet shape on the end. If you go biger than 8/32 your valves will hit the tool turning in a lathe to 3/16 is the best.

Get the bike up on the centre stand and put her in high gear.Using the rear wheel bump the motor around and get the pistons down. Put your dead stop tool in and gently bring the piston up against it.
Put the degree wheel on the end of the crank You will need to adapt it to fit. Not tight just yet. Now bump the motor very slow and gentle to the stop.
Wrap a wire around a couple of jug nuts and make a pointer out of it at around 12 oclock
Set the dial on the wheel to an arbitrary number like 30 BTDC . Now bump the motor around the other way until it stops using the same gentle feel. In a perfect world it would come out to 30 degrees but it won't. Lets say you get 40 Now you may want to slip the dial a bit to try 5 Bump the motor back and you should get 30 the other side of TDC
You want to end up with the same number on either side of TDC then snug the wheel and re-check the number is not important just be the same each side.
Now remove your tool and you can move the motor around to TDC zero degrees using the pointer and the degree wheel You can now find 31% BTDC.
Set it at 31 then put your chaicase on and see how close your gauge is to true 31 degrees.
 

Jerry Doe

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Moving forward

Hi all,

i spent all day yesterday reviewing valve timing settings and checking over and over different ways. I have decided it is good enough to move forward.

if the bike does not run right, i'll take the motor out and put in my other cam,

thanks for all the great advice!

i have gone to earlier posts in this thread and updated figures.

Jerry
 
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If you've got a cam ground for flat followers and using it on followers with a radius, that could be your problem? I reckon there'd be a loss of overlap an increase in dwell, and the timing might not be accurate due to the ramp pick up change.
Just a thought.
 
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Jerry,

Those lift readings would seem to indicate the right exhaust lobe is worn out. And I'm told that once they go, they continue to wear away rapidly. I'd look into that further - at least pull the top end and give the cam a visual inspection.

Sounds to me like it's new cam time.

sorry,
Debby
 

Jerry Doe

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Ex

hi debbi,

I checked the cam before putting it in and all was good,thats why its weird. I am putting it back together for now and will see about a new cam later!!
 
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I would have thought that when the cam lobe wears out there's a loss of lift, with the flanks hardly wearing at all, and it's the flank that initiates the timing. A flat follower will lift the valve earlier, close it later and pick up on a different part of the cam profile compared with a radiused follower. And perhaps pick up on the wrong part of the profile, why not try a larger gap.
It would be interesting to find out the cause.
Having said that if it were my motor I'd pull it apart.
 
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