Valve timing problem

[pablohoney]

I just rebuilt my engine and now I am trying to time my valves and I have the camshaft set up like the picture in my manual and with the alignment mark facing up and the punch mark facing back and flush with the head and the intake valve doesn't open until 241 degrees, when it is supposed to open at 47, that is way more than a link or two off. I have no idea what is going on. Should I just say screw the alignment marks and make it so the valve opens at 47? But why have the alignment marks where they are, if they are so far off? Thanks.

 

[xsjohn]

Is the cam in backwards.......xsjohn

 

[pablohoney]

Nope, I am sure that it is in the right way, if it was in backwards the punch mark would be facing forwards. I have made that mistake before.

Anyone else had this problem?

 

[xsjohn]

Well maybe look here to double check everything...........

http://www.650motorcycles.com/CamTiming.html

 

[pablohoney]

I double checked it with that link and no change.

 

[inxs]

- interesting problem...some things to check

is the threaded end of the camshaft to the right-advance side?​

when installing the chain where the lhs cam lobes in the compression stance?​

has the cam chain tensioner been adjusted?​

when doing the adjusting did you set the crank by turning it only counterclockwise?-if you go over never rotate back clockwise as this takes the tension off the chain​

did you have the cam chain sprocket off the cam at any stage?​

 

[grizld1]

I can't see how timing could be that far out without locking up the valves. Could there be setup error somewhere? How are you reading your degree wheel? Is your dial indicator mounted rigidly, zeroed correctly to the base circle, and set up on the valve collar, parallel to the valve stem? Is the cam chain tensioner installed and adjusted? How have you located TDC? Have you verified that the degree wheel hasn't moved on you? Have you set the valves to the inspection valve lash?


241* BTDC=61* BBDC which is in the ballpark for the exhaust valve opening.

 

[pablohoney]

Before I answer all of those questions and suggestions, which I thank you for, I want to ask one more thing. I don't think I am doing it right for some reason, so let me know if this makes sense. How can there be much compression and power if the valves open when the crankshaft is only 1/8 of a revolution past top dead center and just on its way down.
If that doesn't make sense to you, here is how I do it.

Set degree wheel up to read 0 at tdc. Put the camshaft mark facing straight up and punch mark facing back. Put the head on and tighten it down a bit. adjust the camchain Set the dial indicator up over the intake valve adjuster with the lobes facing down. Turn the crankshaft 1/8 to 47 degrees and see it hasn't moved. Something in here isn't right. Know what it is?

 

[grizld1]

1. Don't use OEM timing marks for TDC location unless you've calibrated them.

2. The intake valves open BTDC, not ATDC; the intakes open when the piston's on the way up.

3. Don't set up your dial indicator on the valve adjustor; the rocker arm doesn't stay in line with the valve stem and the indicator won't stay in contact due to the arc of the rocker. Set the indicator up on the valve collar with the plunger in line with the valve stem.

4. Re. no movement, be sure the shaft of your indicator is moving freely and there's no flex in your mount. If you're set up on the adjustor you'll be putting some side load on the indicator shaft; it may be binding, and a flexing mount could be moving the whole indicator.

Hang in there--it'll all make sense after awhile!

 

[pablohoney]

The manual told me to set it up over the intake valves, but they should open ATDC so it will suck fuel in on the way down. If they opened at BDC it would spit all the exhaust into the carburetor. The exhaust valves are open at BDC so it pushes the exhaust out of the exhaust port.

Thanks for the tip on dial indicator placement.

 

[pablohoney]

It set the valve timing so the valves would open just after tdc at 47 degrees and there was no compression, the valves are unharmed and everything is sealing well, there is just something wrong with my procedure that I mentioned before.

 

[grizld1]

Don't second guess this. Intakes open BTDC. Your opening event on the stock cam is measured with .012" valve lash when the valve begins to lift. The valve must be well open by TDC to charge the cylinder. I've done a few of these, both OEM and aftermarket. Misunderstanding of where the intake opening event takes place is part of the difficulty you're experiencing.

 

[yamaman]

Don't forget pablo, the 4 stroke cycle is over 2 crankshaft revolutions (one camshaft revolution).
As grizld said the Otto cycle is intake, compression, ignition, exhaust!

 

[pablohoney]

Ok,So do I have the dial indicator over the intake or exhaust valve and on which side? Lobes facing down or up?

 

[yamaman]

 

[grizld1]

Pablo, if you're measuring the intake events, set up on an intake. If you're measuring exhaust events, set up on the exhaust. I take readings from all four valves and if there are discrepancies in grind (a more frequent occurrence than it should be) I figure the lobe centers and time to that. If that sounds complicated, just time by intake opening. A Valve begins to open when the lobe starts to rise against the rocker.

 

[pablohoney]

Ok, so the intake should open when it isn't on the combustion stroke. At 47 degrees past tdc.

 

[grizld1]

No, Pablo. The intakes open 47 BTDC, as was just explained. BTW, a thumbs-up to ya for taking on this job for the first time! It's great that you're taking nothing for granted, and you'll have some new skills and insights as a result. Keep this in mind. The camshaft turns at 1/2 crank speed. For one whole rotation, the lobe stays on the base circle. The valve opens when it opens. Don't overthink it!

 

[pablohoney]

Thanks grizld1.

 

[pablohoney]

Damnit, the valve needs to open before tdc! I know you guys said that, but it just didn't click. I though it needed to open at 47 not at 313, which is 47 before tdc. Thank you all for the help, please forget this ever happened.