Degree a Cam and Check Valve to Piston ClearanceHuge thanks to everyone who helped me understand this. Especially Flatlander and Bwaller. A lot of this will be taken from Flatlander's post a few pages back. I'm just going to go into a bit more detail. Hopefully this post will help others.
First, you'll need a few special things:
• dial indicator with long spindle
• modified cylinder head cover to be able to access the bolts on the cam sprocket. Looks like this:
link (you can make one or if you have a 650 you can borrow mine, just pay shipping back and forth)
• degree wheel (you'll be dealing with fractions of a degree so the larger the better)
• 2 light springs – 1lb springs should do (to replace the valve springs so you can push them down by hand when checking clearance)
• piston stop (to find exact TDC)
I'm using a Megacycle 126-20 cam and my goal was to degree the cam and also verify that the valves clearance is within spec.
It's not required, but it was nice to have softer springs to be able to push the valves down by hand to check valve to piston clearance. The soft springs aren't required if you're only degreeing a cam.
Degree Cam1: attach your degree wheel. I put mine on the alternator side. Make sure it's secure so that the degree wheel won't spin accidentally. Find a bolt on the motor and attach a copper wire to use as a pointer. Get it as close to the wheel as you can without it touching.
2: install cam, sprocket and chain per the manual.
3: find true TDC on the #1 cylinder with your piston stop. Look on YouTube how to make one and how to use it. After you find true TDC
make sure to remove the piston stop! You don't want to crash your piston into your stop as you spin the motor.
4: install your modded cover with rubber bands holding back the tappets so you don't bend a valve.
5: adjust cam chain tension per the manual.
6: set #1 cylinder's tappets to running clearance. Many people say to set it to zero clearance, as does the cam manufacturer, but apparently it's better to use running clearance. MRieck says so, so do it! If you're using the soft springs it'll be difficult to use feeler gauges because the feeler gauge forces it's way in and pushes the valve down. So what I did was set my dial indicator squarely on top of the tappet screw and measure the clearance by wiggling the rocker up and down. Easy peasy.
7: setup your dial indicator on the intake valve spring retainer and zero it out. Make sure the rocker doesn't touch the spindle as it's moving or the spindle touch the rocker cover. You want the dial indicator to be positioned squarely over the valve retainer perfectly in line with the valve's line of travel. For the 650, the intake valves are angled at 64° so position your dial indicator to 64° also. See what I'm getting at? The exhaust valves are at 61°.
8: your cam card will have a valve lift value. Mine was .040" for intake and exhaust. But since we set the valves to running clearance that number will be smaller. My running clearance is .004" for intake and .005" for exhaust so my valve lift for intake becomes .036" (because .036 + .004 = .040). My exhaust valve lift becomes .035".
Assuming your #1 cylinder is now at perfect TDC of the compression stroke (where both valves are fully closed) and both your dial indicator and your degree wheel are indicating zero, you want to rotate the engine in direction of engine rotation. For us that's CCW (we're looking at the alternator side remember). Rotate until the dial indicator is indicating .036". Look at your degree wheel and note the degree. That number is your valve opening event BTDC. Once you write that down, continue to rotate the engine CCW until the dial indicator makes a few revolutions and then starts to go backwards. Stop at .036" again and look at your degree wheel. That number is your closing event ABDC. If you overshoot your mark on the dial indicator, back the motor up like 10° to reload the timing chain and try again.
9: now we can calculate the intake duration.
open BTDC + close ABDC + 180 = intake duration.
My duration never matched the card, but that's ok.
10: calculate intake lobe center.
(intake duration ÷ 2) - open BTDC = intake lobe center.
That's the critical number. You'd like it to match exactly to the cam card, but it's very unlikely. You want to get it as close as you can but more importantly, you want the intake lobe center to match the exhaust lobe center.
11: loosen the two cam sprocket bolts and rotate the engine independent of the cam (a little goes a long way).
I moved the cam independent of the cam sprocket by tapping on a cam ear but as stated below Bwaller and Cal advice against this because it's possible to break a cam ear if you're tapping on it!
Hint: To increase the intake lobe center, rotate the crank CCW. To increase the exhaust lobe center, rotate the crank CW. Again, as looking from the alternator side. Work on the intake until you get it as close as you can then continue to step 12
12: move the dial indicator to the exhaust valve and put the engine back to TDC of the compression stroke and have the dial indicator zeroed out.
13: again rotate the engine CCW but this time stop at .035". Note the degree wheel. That number is your exhaust valve opening event BBDC. Keep rotating until .035" is indicated again. Note the degree wheel. That number is your exhaust closing event ATDC.
14: now we can calculate the exhaust duration.
open BBDC + close ATDC + 180 = exhaust duration.
15: calculate exhaust lobe center.
(exhaust duration ÷ 2) - close ATDC = exhaust lobe center.
Hopefully you're very close. Make minor adjustments until you're as exact as you can. My final lobe centers were less than 1/8th° off of each other.
16: lastly, you need to verify that your true TDC didn't shift accidentally during the work you just did. Put your piston stop back in and check that you're still exact. If it shifted, do the degreeing over. Be aware that if your piston stop reaches too far down into the cylinder it can interfere with the valves opening. Might want to remove the rocker cover for this.
Valve to Piston ClearanceOur goal here is to measure the clearance the valves have to the piston. For my Kibblewhite springs the
minimum values are .040" intake and .060" exhaust. I've seen clearance numbers as large as .100". Read this post for more info
link, but to be sure, contact the cam or spring manufacturer.
We're going to be checking clearance with the dial indicator. Some people prefer the clay or solder method but this is much more accurate and we already have the dial indicator setup and soft valve springs in.
We need to check clearances at the following degrees:
5°, 8°, 10°, 12° & 15°.
1: rotate the engine to exact TDC of the exhaust stroke. This is done because during the top of this stroke the valves are opening and closing and are the closest they're going to be to the piston.
2: setup your dial indicator on the intake valve retainer
3: rotate the engine CCW to 5° and zero out your dial indicator.
For intake we check clearance ATDC because that's where that valve will be open the most.
4: without touching the dial indicator, push down the tappet screw until the valve hits the piston and write down the number on the dial indicator. That's your valve clearance at that given degree.
Repeat steps 3 & 4 for all the degree marks listed above. As you advance and measure the remain degrees the numbers will change. Your goal is to find the tightest clearance.
5: move the dial indicator to the exhaust valve and rotate the engine to 15° BTDC of the exhaust stroke. For exhaust valve clearance we measure at the same degrees as intake but before TDC.
Go through the same process working backwards from 15° - 5° remembering to zero your dial indicator after moving to the next degree and being careful not to touch the dial indicator when pushing down the valve.
That's it, you're done! Hopefully you're in spec. If not, you have options. Ranging from flycutting the piston, altering the cam degree one way or another to gain a few thousandths of valve clearance, or changing to a different head gasket. Changing to a thicker head gasket is an easy method but you don't want to go too thick or you'll alter the quench area. The area where the edges of the piston top meet the cylinder head and claps the air/fuel mixture into the center of the combustion chamber. Do research on this to see why it's important if you're interested.
Link to Flatlander's original post:
linkSome good YouTube videos:
If anyone sees misinformation let me know and I'll correct it post haste!
