[imslow]

I've decided that I should degree in my Megacycle cam, no. 25162. But I want to make sure that I understand the process. I have ordered the vernier adjustable cam gear and an aluminum degree wheel. Bike is Yam XT500 engine

The specifications from Mega are as follows:
Timing at .040 lift at valve
Timing checked with zero clearance
TDC Lift is .233 intake .225 exhaust
intake opens at 48 BTC and closes at 72 ABC
Exhaust opens at 70 BBC and closes 46 ATC
Lobe center is 102 degrees on both
Duration intake is 300 degrees duration exhaust is 296 degrees
valve lash set to zero

Here are the questions.
1. Can I presume that the "TDC lift" is how open the valves are at TDC?
2. When I check for the intake opening at 48 BTC, does this mean that the intake valve should be open .040 inches? (in other words, I rotate engine till valve is open .04 [as indicated on dial gauge attached to engine] , then the degree mark should be at 48 BTC; If it is not at 48 BTC, then I have to move the cam gear in the right direction so it does?
3. If I check either the exhaust OR the intake, I should be good to go, and there is no need to check the other?
4. Does any of this affect actual ignition timing? I believe it is set to something like 27 btc.

While claying is a good thing, I just read something about a faster way (not safer) to do it, install everything, put pistone at TDC, then open valve with a pry bar and see how far it moves till it hits piston.

 

[jbranson]

Scott,

1. Yes
2. Yes
3. You can check both...but if one is good and the other is not...there is not a lot you can do about it since it would require a cam regrind. So...if intake is off 4 degrees and exhaust is spot on...you gotta decide if you want to adjust to make intake right, or exhaust right...or split the difference. I sure there are guidelines for this somewhere...I don't know them. It would also tell you how "bad" the cam is...which again sates curiousity but there is not much you can do about it except order a new cam....or try to convince Megacycle that it's bad enough to replace for free. Checking both...tells you something about the camshaft...checking one..tells you what you need to know about the position of the camshaft.

4. Depends...if your ignition is cam driven it effects the ignition timing. If your ignition is crank driven (sensor on the crankshaft) then it does not.

Very cool idea on the claying. Might be troublesome to get a dial indicator on the retainer and a pry bar in there on JUST the valve tip (or rocker) at the same time. But yeah, easier and probably a better indicator of true clearance. You could check it a TDC, and at 5 degrees forward and backward and get a real good picture of true clearance.
You know what...I think I'll build this:
Take an old Honda valve cover...drill and tap a hole in the center so you can screw in a bolt to press against the top of the rocker, drill another hole off to the side so you can stick a dial indicator probe in there to rest against the retainer. Zero in the indicator...then thread the bolt in until it feels like the valve hits the piston and just read the clearance off the indicator.
Cool idea...I'd be much more confident of this method than claying.

Of course another quick and dirty method is to slip a piece of soft solder into the plug hole so it is between the valve and piston...rotate the engine around once...pull out the solder and measure how thin it got squished to. Harder to do in practice that it sounds...and it doesn't account for high or low spots, or off angle valve pockets found on a lot of pistons.
Thanks bro,
JohnnyB

 

[aaron]

you'd rather use soft solder over clay?

aaron

 

[jbranson]

Aaron,
No, I'd trust clay over solder. The solder just doesn't cover enough area for me. And it's hard to get the solder down in the deepest part of the valve pocket close to the cylinder walls where the valve is most likely to have a problem.

Solder is good for a ball park check...but I wouldn't trust it past about .010" of accuracy. Just imagine a pocket cut in a piston at an angle that is one degree off....it may look fine at the middle of the valve...say it's .065...but at the top or bottom edge of the valve it could be .045 and you'd never know it. Plus...I don't like the way solder torques on the valve head if you do try to get it at the edge of the valve...that little "hump" you have to get over at TDC to compress the solder is applying a lot more pressure on the valve head than you might think.....and right on the edge of the valve.

Clay is good....but..I'd say Scott's method is the best overall...gives you a real mechanical measurement to take. Plus allows you to check at like 5 degrees before and after TDC to see if there are any clearance anomolies...due to maybe a cam out of time or something. I'm going to try it soon cause I'll have the heads off both bikes doing valve work.
JohnnyB

 

[imslow]

possibly also best to try it hot and cold . . . I found that "tip" on the Webcam Inc. website when searching for how to degree in cams.
JB, I like that idea . . . much easier than claying, cause you have to build the engine and then tear it apart to look at the clay. BUT it still may not tell you certain things about the angle of the valve in relation to the cut pocket in the piston etc. A lot of variables you can't see unless using clay.

 

[jbranson]

Yeah...probably right, a combination would be best. Clay the first time you put in a new piston design or combination of parts...and then the pry bar method for checking the assembled engine and subsequent assemblies using the same parts.

It's also something that could be done easily at the track to diagnose a possible bent valve, munged up piston or streched rod.

I get really tired of claying over and over. This will let me check things easily when I'm already pretty sure things are fitting the way they should.
The Clever Dog has learned a new trick baby!
JohnnyB

 

[bfd]

Evil
That spring/prybar method works great but would probably be a pain in the butt on a motor with a cam chain. I've used it on a pushrod motor and had some really light pressure springs so you could push the valve down carefully with fingers. That allows a nice measurement and is quick to do.
BFD

 

[imslow]

the other thing i realizeed in my dreams the other night was that you'd either have to construct a head cover with holes, or find some way to bolt on the head leaving the valve train exposed in order to realize an accurate view of celarance, ie the head has to be bolted down.

Anotherr thing I thought of would be to graph the cam on an x y axis, x being degrees on the timing wheel versus y the valve opening as shown on the gage. You'd get a real idea of what is happening in the engine, and the graph would also have the piston movement incorporated. Something that cam manufacturers probably have locked in vaults.

 

[jbranson]

Hmmm...wonder why I haven't seen a graph like that...seems like a good way to visualize the info. The open and close slope would give you a good idea how hard a cam would be on the valve train.

I guess a person could always plot a few data points and whoop out a graph.
JohnnyB