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Top Dead Center on the Compression Stroke

Hi everyone. Not long ago I did my first valve adjustment on my Zuma 125, and wow, it really improved the response and speed by doing this. I removed just about everything to do this to make sure that I was at top dead center on the compression stroke like the maintenance manual says. I’m putting it out there to you experts, to see if there’s an easier way of doing this.

I have some fancy-schmancy cooling fins on the valve covers and the breather cover and (especially that breather cover) is a little bit more difficult to remove for this procedure, but the breather/chain timer area has that cool little etched-in line that tells you exactly where the TDC on the compression stroke is.

I’ve also taken off the plastic air shroud for AC Magneto Rotor/Fan cover and it has that stationary arrow and TDC marks on the crankcase. However, it alternates between the compression stroke and the exhaust strokes. I’ve heard that some people will just remove this part and put in a chopstick or a screw driver inside the spark plug hole to see when the cylinder moves up to the compression stroke.

So, how do you do this? Is there an easier way of doing this that you recommend? Thanks ahead of time for any of your suggestions.

— Rick
 

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Top Dead Center on the Compression Stroke

Hi everyone. Not long ago I did my first valve adjustment on my Zuma 125, and wow, it really improved the response and speed by doing this. I removed just about everything to do this to make sure that I was at top dead center on the compression stroke like the maintenance manual says. I’m putting it out there to you experts, to see if there’s an easier way of doing this.

I have some fancy-schmancy cooling fins on the valve covers and the breather cover and (especially that breather cover) is a little bit more difficult to remove for this procedure, but the breather/chain timer area has that cool little etched-in line that tells you exactly where the TDC on the compression stroke is.

I’ve also taken off the plastic air shroud for AC Magneto Rotor/Fan cover and it has that stationary arrow and TDC marks on the crankcase. However, it alternates between the compression stroke and the exhaust strokes. I’ve heard that some people will just remove this part and put in a chopstick or a screw driver inside the spark plug hole to see when the cylinder moves up to the compression stroke.

So, how do you do this? Is there an easier way of doing this that you recommend? Thanks ahead of time for any of your suggestions.

— Rick
The piston will be all the way up when it shows TDC on the crank marks, what you need to do to make sure it is on the compression stroke in make sure both valves are closed when it is at TDC
 

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Recently, I’ve gone ahead and checked my valve clearances on my Zuma. I have kept the plastic scoop off of the AC Magneto Rotor, where you can see the fan blade behind its plastic circular cage.

There is a gap in the middle where you can fit a 17 millimeter socket to easily rotate the crankcase. Naturally, you need to remove the spark plug to make this easier. I didn’t even bother putting a pencil or chopstick in to see the location of the cylinder.

Then it’s just a matter of removing the valve covers and breather cover. Despite me having those cooling fins, I was still able to unscrew the 8 millimeter bolts with a little bit of effort. It’s kind of tight in there. I’m sure that it would be much easier with the smaller, stock covers.

There’s a nice line that you can match up to the little arrow on the breather/chain area to rotate right to top dead center in the compression stroke. There’s no guessing. You’re right where you need to be to start sticking the feeler gauges to check the clearances.

This seems to have worked very well for me and a valve job's time would be cut in half. 🛵💨
 

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Not familiar with the product so say I had to get a whole lot of whatever to get to the crank to turn it to set the valves? My loop hole is place it in 1st gear. look in the spark plug hole, watch my carb or intake side's intake valve open and keep slowly pushing the vehicle forward to see the valve move back up into the head.

I am on my TDC-C stroke. I now use a wooden item like chopstick, move the stick down to the top of the piston. I want to just push the bike ever so short of movement and stick goes back in... where am I coming up?

Eventually, the piston comes up and stops. Move the vehicle back if the piston drops down past TDC. The flyweight helps it go down some, so once you find the teeter totter either way, you are way close enough to set the valves and who needs the mark at the crank.
 

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Hi TripleT,

I’m sorry for not responding very quickly. The Zuma has a Continuous Variable Transmission. No first gear to put it in. I’m not sure what bike you have. Pushing the bike on the Zuma won’t move the flywheel on this particular bike. I can’t advise you on your procedure, but it sounds like you have an interesting work-around. 🛵💨

— Rick
 
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