stock cam vs a9 (139qmb gy6 50cc)

I don't know the specs but here is a visual representation of the difference between stock and a9 cam for 139qmb gy6 50cc

scooter modifications, big bore kits for gy6 139qmb 50cc
znen, chinese scooter, moped, taotao, ruckus, chickus, bbk for scooters

[davidg.]

Someone mentioned the base circle and that the lift shown in the video may not actually show the true increase in lift. But as you watch the base circle side of the cam come by the space to the straight edge, it's obvious that the A9 and stock cams are similar or at least close to the same. More than that is that obviously the profiles differ. The little stock cam has peaked domes, the A9 more radius, a longer curve, indicating more duration of open valve time.

As to the question on timing the cam on install, it's simple. The two little holes parallel the head surface with the base circle side of the cam lobes against the rocker arms. If the peaks of the cam are against the rockers, it's 180 degrees off. Never mind the big hole. You always adjust rocker arms to the base circle of a cam. I don't care if it's a scooter or 600hp race car. But some A9 cams had the gear pressed on 180 out, so you can't always go by that big hole being up. Go by the low rounded side of the cam ( base circle) against the rockers.

Now what I'd like to know is what brand A9 is this one, because all A9 cams are not created equal ?

[waynesteinmacher]

THANK YOU i finnally know the diffrence

[seanmayo]

What does the a9 go on
Engineering should say right?

[thelagmeister]

It definitely has more lift which will help low rpm. I had one in my 171cc and the thing would take off quick. Top speed was another story though.

[thundercatt]

I think I'm gonna try one on my big bore head it's got 23 mm /in.And 20 mm/ex. Valves and 64 instead of 69 Valve length on a 50 mm cylinder with a hybrid supercharger...it decel pops because of my stock intake and exhaust

[robertmason]

Actually the straight edge across there doesn’t prove it has more lift unless both cams are ground on the same base circles! I don’t know if your familiar with camshaft terminology or how they are made, but to compare them you need to measure the diameter of the lobe at the portion where there is no lift-(that’s called the base circle). Then measure the total height of the lobe going across the shaft. Then subtract the base circle from the total height of the lobe-this gives you the cam lift. Take that times the rocker ratio (usually anywhere from around 1.3-1.9 depending on the specific engine) and the result is your actual lift.
Think about it, those two cams could have been ground with different base circles and still had the exact same lift. Look it up it if your not familiar. Duration you need a special jig/fixture called a cam doctor to measure precisely, or install the cam in the engine with a degree wheel mounted on the crank and a dial indicator tracking the axis of the valve to measure linear valve motion precisely! From there you can figure out actual duration at any set point be it .040”1mm or .050” such as most aftermarket cam manufacturers in the US do. Total duration is hard to track as ramps are so fast and often less meaningful as flow below .040” is relatively small.
I’m trying to get an American company to grind me up some real performance scooter cams cause the Chinese cams are basically garage IMO.

[wes]

I am getting tapping sound with the a9 like the valves are to tight but they good

[zorroblings]

I want to get a performance camshaft with higher lobes but I’m afraid it will mess with my timing. My previous scooter caught on fire because of a backfire a few months ago so the last thing I need is the valves not fully closing during the power stroke and having a fire under my ass. What do you think?

[williamlawrence]

Hope you see this rn if I put the a9 cam do I have to change my valve adjustment from stock ?

[seanmayo]

Dude . On the bearing end of the shaft . I got 2 cam shafts. One hole in middle of bearing is bigger then other. Why

[GhettoWrench]

Do you know where the "NCY" cam falls in the mix? Is it big like an A9 or just a gimmick?

[mrcleanisin]

Why didn't you show the timing marks when it's in the neutral position where you can set the valves one has a different holes drilled

[ibroughtaturbo-chargerfrom]

Will the a9 fit on a Chinese 49cc 2 stroke engine that is sold on Amazon?