107cc chinese cam upgrade impressions

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Artsi_L

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Just did cam upgrade on our family's kids 107cc bike.

I had previously modded cam sprocket bolt holes to oval shape to get advance/retard adjustability. I had tweaked stock cam back and forth for good bottom end grunt (it's easier to learn to ride a bike that is reluctant to bog and shut down as revs drop down).

Just recently I got around installing 3 year old tuning cam that came with the second hand bike. I sourced HONDA CT110 stock valve springs to go with it.
Initially I swung the intake cam lobe timing to 105º ATDC, which is a good starting point for hot cams in automotive and motorcycle engines. I changed the dial gauge then to the exhaust side, just to verify that all is well there. Not all good. Not at all. Exhaust lobe timing was bucket loads too late.

After some calculations I conducted that the lobe separation angle is as generous as 95º.

Without proper cam timing card (provided by the cam manufacturer), I chose to time the thing "straight up", and hence left the intake at 95º ATDC, and the exhaust at 95º BTDC.

Our kid reported the bottom rpm pull to be somewhat like it was with stock cam (when stock cam timing was set at good all around performance), but did have more oomphh at mid- and high revs. Not tremendeous increase in power delivery, but top speed has increased. Verified top speed with a tie wrapped Garmin navigator to be 85km/h. Apparently the bike took to the top speed effortlessly and just refused to accelerate from thereon. I guess it hit the rev limiter.

What I am baffled with is the lobe separation angle of 95º, and also the lobe durations do not seem aggressive at all.
My measurements at 0,040" (i.e. 1,0mm) lift on the cam follower - NOT on the valve :
- intake duration 216º
- exhaust duration 234º

I could not get the dial gauge on the valve (engine is on the bike frame). Only room available was to measure valve lift through cam housing lid. That is not 100% accurate, even 'tho I did get the dial gauge fixture to lock on perfectly, so no wobble there at all.
I did perform these measurements three times over, back and forth, so the numbers can not be far off.

Generally speaking high comp. piston ought to be used, but we do indeed have some cranking pressure there when kicking it into life, like with the stock cam. Low cam duration numbers seem to let us get away with low compression stock piston.

I guess wider lobe separation angle would offer a wider powerband, than what present 95º lobe separation does.
I have not ventured into what is the max lobe separation this hemi 2-valve head can take before the valves start making a contact between each other. I am told this can happen with this type of 2-valve head.

For the time being, I'm gonna leave this bike like it is.

Happy cam timing to all.
 

sean01

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sounds like the cam your using is a bit of a lemon..

i have used a akunar A1 cam designed for lifan 125 in a 110 before.. i just had to shorten the cam in a lathe.. it made a good improvement..

these engines do like a wider lobe sep, split duration isnt always good either...

id try raising your comp a little as it will def help with bottom end torque, also you might need to make a tuned pipe so you can raise the main jet and get more top-end power..

i guess another thing is some people expect a lot out of these little engines..

for further comments can you post up what bike and specs of the engine you are using... some pictures of the bike would help too...
 

The_GDFP

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I've had good all-around performance with the stock 5.25/5.5mm lift e22 short cams in 72/88/107 builds. I do some port cleanup and replace the inner springs, but otherwise not much fussing. 52.4mm high-squeeze piston, or bore for 54mm, or swap TB 54mm jug & slug will wake up the soggy bottom. I like using the YX outer rotor ignitions on the small-blocks, too. Light weight and the extra advance doesn't kill parts like on 160+ builds. 20mm carb, matched manifold, smallish pipe should make it real snappy.
 

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