Question about adjustable cam gears

Kray-Z wrote:
3. With 46 teeth, 10 or 12 degree slots (5 or 6 degrees each way from center) are easy to remember when reading/ setting the dial on the rotary table, and won’t be greatly oversized.



Kray-Z this is the sentence that exactly answers the question that I couldn't think of how to phrase properly. It perfectly sums up exactly what I need to convey to Nebr_Rex.
Thank you so much for explaining this and answering all of my questions!!

Camshafts are measured in crankshaft degrees.
So there are 720 crank degrees on a cam sprocket.
On the KZ440 and KZ750/4 cam sprocket there are 15.65 crankshaft degrees per every tooth.


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Nebr_Rex wrote: Camshafts are measured in crankshaft degrees.
So there are 720 crank degrees on a cam sprocket.
On the KZ440 and KZ750/4 cam sprocket there are 15.65 crankshaft degrees per every tooth.


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That math makes perfect sense now. I was initially getting confused by the mixup between the math of the 42 tooth gear and my 46 tooth gear.
Check your PM

I'm really sorry I didn't elaborate more on why I said "if your sprocket is 42 teeth". I realize the math confusion that can create. Glad you got it figured out.

And yes, the slot need only be 1/2 tooth in each direction plus a tad more to be sure to get overlap between when the chain is in one position or walked by one tooth.

I find the easiest way to walk the chain is to simply remove the bolts and slide the sprocket off of the shoulder. By moving to the smaller diameter part of the shaft, there is more slack on the chain. The tensioner will want to take up that slack, so I usually have the cross-wedge out at that point. The main tension spring (not the cross-wedge spring) will still take up slack, but will also give it back. Again this is 550 talk, so this is in case the 750 is the same. I'm not sure how the hyvo tensioner is constructed on the 650-750 motors.

No worries! It was entirely my fault as I had been searching for days for someone who might make a 46 tooth gear but all I saw was “42 tooth” so that number was already stuck in my head. It didn’t dawn on me until this morning that I had made a stupid mistake.

That is a GREAT suggestion on how to re-index the chain without taking the cams out. I hate to constantly tourqe down cam bolts only to take them right out again. I always fear that sickening feeling of the threads coming out with the bolt.
I only use manual chain tensioners so releasing and reapplying tension takes seconds and I also have a zr-7 upper chain tensioner I can bolt to the head as well as one made from an old valve cover. So I will have to see if those will need to be removed when moving the chain.

I really appreciate the tips and information!

My method is convenient because I don't use locktite. With locktited bolts it would be a problem with locktite crumbs going into the motor. So that re-time method should be before locktite is applied, but only after the cams have been removed and locktite thoroughly wire-wheeled off of the bolts. I'm not racing and have gotten away without locktite on the sprocket bolts for over 25 years. In a race situation I think I would be using locktite blue.

As the world continues to move toward "instant information", and a lot of people just wanting the answer, it is great to read and see posts like this where time is taken to help others understand the answers to their questions. Good information here.


Digging through my Megacycle Cam 615cc Race Engine, when I was degreeing the cams. Notice the long slots in the gears? These gears came that way on a parts bike, and from the info posted above, they are way overkill in the slotting department, to get the desired 105* intake and 108* exhaust.







This one shows how much slotting was done to the intake cam gear. Once again, these gears came this way on a parts bike. They work just fine.

Nebr_Rex wrote: Camshafts are measured in crankshaft degrees.
So there are 720 crank degrees on a cam sprocket.
On the KZ440 and KZ750/4 cam sprocket there are 15.65 crankshaft degrees per every tooth.


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Yep-Four stroke cam sprockets or gears must always be twice as" big" as the crank sprockets, as they always turn half -speed (or angle) of the crank rotation. The idea of the cam sprocket slots being one cam sprocket tooth (plus 0.040" total) long is that you can place the cam timing anywhere you want - infinitely adjustable, in other words. So no matter how the cams are indexed and ground, you can set the timing wherever you like....
And yes, there are plenty of 2 stroke engines that use camshafts and poppet valves....

CoreyClough wrote: As the world continues to move toward "instant information", and a lot of people just wanting the answer, it is great to read and see posts like this where time is taken to help others understand the answers to their questions. Good information here.


Digging through my Megacycle Cam 615cc Race Engine, when I was degreeing the cams. Notice the long slots in the gears? These gears came that way on a parts bike, and from the info posted above, they are way overkill in the slotting department, to get the desired 105* intake and 108* exhaust.

This one shows how much slotting was done to the intake cam gear. Once again, these gears came this way on a parts bike. They work just fine.

Your timing of 105 In and 108 Ex. is interesting. I've found that most any engine with "mild performance" cams and compression ratios around 10:1 the best all around street performance is achieved with 105-106 / 108-110....very interesting....

Your timing of 105 In and 108 Ex. is interesting. I've found that most any engine with "mild performance" cams and compression ratios around 10:1 the best all around street performance is achieved with 105-106 / 108-110....very interesting....

Megacycle specifications for their 478-60 Grind Cams.

CoreyClough wrote:

Your timing of 105 In and 108 Ex. is interesting. I've found that most any engine with "mild performance" cams and compression ratios around 10:1 the best all around street performance is achieved with 105-106 / 108-110....very interesting....

Megacycle specifications for their 478-60 Grind Cams.

Last one is a Honda XL350 bored to 410 cc, 10.5:1 CR, re-branded Megacycle cam from an XL specialty shop. There was no timing card supplied with the cam, and the Mega Cycle website numbers didn't really make sense to me, and it seemed like the cam was ground out of index and the lobe centers weren't exactly right from each other according to the website specifications. Regardless, it made good power with the IN @ 105.5 ATDC and EX @ 109 BTDC. Since it is SOHC, we had to split the difference from our target, setting the intake and exhaust close to 106 and 108. The engine pulled well at every RPM. Then the cam gear had to come off for other service work, and the timing gear was replaced "close", maybe a couple of degrees out (wasn't checked, just "eyeballed" to where it had been set before....). Mid-range and top end dropped noticeably (indicating the cam timing is now more than IN @ 105.5 ATDC ), and now running rich on the same jetting....so, yes, precise cam timing does matter....

Will these work for ya?


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