Cam shaft By potwashman (Read 631 times)

[potwashman]

Hi, just upgraded my Superbyke Powermax 50 4T to 80cc (finished 2 hrs ago). Looked at countless videos on YouTube to get info on how to do. Put it back together exactly how it was and works fine but the only thing that's bugging me is the cam shaft. On all the vids I saw it showed the camshaft in the correct timing position as having 2 small holes aligned with top of the cylinder (say 12 o'clock & 6 o'clock) with another larger hole on the cam at 9 o'clock looking from the left hand side of the bike. The fly wheel was matched up with the T for timing. Well on my bike when the T was matched up and the small holes were aligned with the top of the cylinder the large hole was at the 3 o'clock position and not the 9 o'clock so my cam seemed to be 180 degrees out. I was tempted to spin it round so large hole at 9 o'clock but figured if bike worked before on current settings it would do so again so left it as it was and it did work when all re-assembled. Burning question is why is my cam 180 degrees out but still working. What would happen if I put the cam back as it should be. Gonna be on my mind so any replies appreciated. I set gap to 0.05mm on intake & exhaust, sounds a bit 'tinny' but I guess piston will need a little bit of bedding in. Cheers

[Alleyoop]

So are you saying the little holes are lined up with the top of the head but the big hole is not straight up?? There is only one big Hole on the CAM unless you put on a different, which some have a bunch of holes or the cam you have has the big hole off center.

Also .05mm is not much of a gap, at least go .08mm which is .003 inchs. Normally on a 150 we set the intake and .004 inchs and .005 inchs on the exhaust or both to .004 inchs which is .10mm
Alleyoop

[Moat]

Nov 9, 2013 19:27:27 GMT -6 potwashman said:

Burning question is why is my cam 180 degrees out but still working.

The camshaft turns at half of the crankshaft speed - IOW, it takes two revolutions of the crankshaft to rotate the camshaft once. So if you had just rotated your flywheel one more turn around to the T mark (360 degrees), you'd have found the cam had rotated 180 degrees, and the "big hole" at the proper 9 o'clock instead of 3 o'clock. That's normal - you just so happened to be looking at TDC (Top Dead Center) of the exhaust stroke instead of TDC of the compression stroke, by mistake.

Now... your cam timing might be spot-on, but if you set your valve clearances there (big hole at 3 o'clock instead of 9 o'clock) - then they are set wrong (very loose) and likely the reason for the "tinny" clatter you mention. Valve clearance must be set at TDC of the compression stroke only!

[potwashman]

The pic you posted is how I expected it to look like as that is the same as the ones on You tube I've been viewing. My Cam, like most, has 3 holes, 2 small and one large but whereas the hole on the pic is 'straight up' my cam was 'straight down', in the opposite direction. Can't understand why as Pulley was 'T'd up. I will adjust gap later today, thanks for advice. What about the Cam though, it would seem to be on the wrong way (how it was when I took off) but still works??
Thanks

[potwashman]

Hello, I'm an idiot. I must have been typing my post when Moat was typing his so have only just seen his post. Yes I just realised this morning that it takes 2 revolutions of the Pulley to make the Cam revolve once as when I put it in timing this morning it was in the TDC position. As you pointed out, when the Cam was in the correct TDC the valve clearance was very loose. I re-gapped the bike this morning and it is running much better. Last night when I took it out for a spin just after doing it I was pretty disappointed with the result as it didn't seem much better than before but after doing it correctly this morning it is like a new bike. Goes like a dream up hills and feels so much better. Thanks for help & advice.

[Bashan]

I don't mean to insult your mechanical skills but it's impossible for the engine to run if you have the cam/crank parameters set at the orientation you described. That would put the piston at the wrong position for compression, result in a collision of the valves and piston, and generally ruin your day. I admit anything is possible but the likelihood of the cam being stamped with the timing markers 180 off is infinitesimally small.

[Moat]

Nov 10, 2013 8:17:44 GMT -6 potwashman said:

... but after doing it correctly this morning it is like a new bike. Goes like a dream up hills and feels so much better.

Sweet! Just a simple mistake - easy to overlook, easy to fix.

[Moat]

Nov 10, 2013 8:43:51 GMT -6 Bashan said:

but it's impossible for the engine to run if you have the cam/crank parameters set at the orientation you described.

I think you may have misunderstood his post, Bashan - he basically had it timed right, but was just looking at it wrong - one turn of the crank away from lining things up correctly.

[shop242]

Those T marks can be off 3-5 degrees.. China BS