Has anyone ever didi this before? I have to lower my cylinder by 1mm, and I might get the cam sprocket back to spec, and was just wondering how you would go about slotting the bolt holes, if lets say my cam is 2 degrees retarded. If anyone has any opinions regarding if I should leave the cam on my 140cc OGM retarded to gain a little more top end, at the cost of a little low end power. The engine has an AHP cam, 28/24 head, akunar hc piston with 8.5mm dome (im thinking the added compression will help the low end) there will be a total of 1.5mm added slack to the cam chain if I go with a thin head gasket as well as dropping the cylinder 1mm. Thanks a lot
slotting cam sprocket
damann33
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Has anyone ever didi this before? I have to lower my cylinder by 1mm, and I might get the cam sprocket back to spec, and was just wondering how you would go about slotting the bolt holes, if lets say my cam is 2 degrees retarded. If anyone has any opinions regarding if I should leave the cam on my 140cc OGM retarded to gain a little more top end, at the cost of a little low end power. The engine has an AHP cam, 28/24 head, akunar hc piston with 8.5mm dome (im thinking the added compression will help the low end) there will be a total of 1.5mm added slack to the cam chain if I go with a thin head gasket as well as dropping the cylinder 1mm. Thanks a lot
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I might be stupid but if you slot the holes on the cam sprocket, its gonna wobble really badly. The only way to lower the cam sprocket would be to lower the entire cam in the head. You can just lower the cam sprocket my moving the holes, the holes align it in center.
I think I understand what your asking, but maybe not.
I think I understand what your asking, but maybe not.
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3,757 Posts
The sprocket needs to be machined because it is a harden gear. I highly doubt that a drill press will work but you never know.
Make sure that when you do slot the sprocket, make sure you follow the curvature of the bolt pattern other wise you'll have a wobbly sprocket.
Because it is a SOHC design remember that when you change the intake, it WILL change the exhaust. You will have to check both numbers and figure out lobe separation so you can figure which way or how much you can go.
Make sure that when you do slot the sprocket, make sure you follow the curvature of the bolt pattern other wise you'll have a wobbly sprocket.
Because it is a SOHC design remember that when you change the intake, it WILL change the exhaust. You will have to check both numbers and figure out lobe separation so you can figure which way or how much you can go.
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62 Posts
I dont understand how its possible to lower the sprocket by slotting the holes...
Im not saying your wrong Im just curious, it doesnt seem possible, if you slot the holes, the sprocket may sit lower in one position but as the cam turns the sprocket is just gonna make a larger circumference...
Im not saying your wrong Im just curious, it doesnt seem possible, if you slot the holes, the sprocket may sit lower in one position but as the cam turns the sprocket is just gonna make a larger circumference...
well when I say slot the cam sprocket holes, im talking about filing them a bit so I can turn it to position the timing since the cam timing will be retarded from lowering the cylinder. Point taken though, it could wobble if I go to high or low, but there are 3 bolt holes, so maybe a little bit of filing wont hurt. I know I wont have problems with the engine leaving it retarded, its just a matter of how much low end power ill loose leaving it as is, but on the other hand ill have higher compression to help the low end out, and ill gain top end with the cam being retarded. The cam will be 1 degree retarded going 1mm down on the cylinder, if you think about it 1 degree isnt that bad as when people measure cam specs out or valve lift or w.e they may end up being 1 degree off... I will probably leave everything as is, after dropping the cylinder, and I might go and buy a thin head gasket, lowering the head around .4mm. Thats why if I can find an easy way to get the cam sprocket slotted a little, then its all good.
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slotting the sprocket doesn't lower the cam in the head.
Since he has changed the overall height of the engine with milling and gaskets, it's going to bring the cam closer to the head. Because there is a cam chain involved that is under tension, it will change cam timing because the two points ( cam to crank center ) are closer together.
You slot the sprocket to change cam timing back to the original spot or to optimize power. I do it all the time.
Filling the sprocket is a bad idea because I doubt you will follow the line of curvature with the bolts.
Since he has changed the overall height of the engine with milling and gaskets, it's going to bring the cam closer to the head. Because there is a cam chain involved that is under tension, it will change cam timing because the two points ( cam to crank center ) are closer together.
You slot the sprocket to change cam timing back to the original spot or to optimize power. I do it all the time.
Filling the sprocket is a bad idea because I doubt you will follow the line of curvature with the bolts.
so should i take it to a machine shop? once I find out how retarded the cam timing is, say 2 degrees, would that be like 2mm i need to add to the cam sprocket bolts? I will use two sprocket clamped together probably, and use one as a template
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3,757 Posts
damann33 said:
2mm each way will give you enough movement in the sprocket to get the cam timing the way you want.
Thing is you should have measured everything before you started milling and thinner gaskets because that's the only way you'll know how much you really moved.
i havnt done anything yet, and I plan on measuring today. The only thing is I am trying to get the cam specs for the AHP cam for the 140cc off Mark, he has to get back to me as he doesnt have any info on hand. I will probably measure when the valve open/close myself with a degree wheel, and hopefully someone can give me the specs just to be more accurate. If I cant get the specs, ill just play it safe and get the cylinder milled 1mm and leave it at that, as I might benifit from the cam being retarded a bit.
yeup, im not to worried though, I probably wont even notice the top end gain, probably not the low end gain either so... just saves me time slotting the cam sprocket, but if it comes down to it, I will since its not to hard of a job, and a 1 degree retard is not much. If I were going maybe 2mm on the cylinder and going .5mm down on the head gasket it probably will cause problems. There has got to be someone who has went 1mm down on something and ran their bikes, I wonder what the outcome was??? I would have gone .5mm on the cylinder gasket and .5mm on the cylinder, but ill gain more by going 1mm on the cylinder. the valve clearances are all fine, I have 5mm of clearance with everything stock, as I cut out the valve reliefs to suite a tb 300 cam and clear 28/24 valves.
Instead of taking all this time and money to drill holes in the sprocket why don't you just mark the timing chain and sprocket so that you know where it is and move the chain the two teeth or however many teeth you want. this will save you money and it takes about 5 minuted if you stop and drink a beer in the middle.
G
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·One tooth is too many degrees. Don't worry, slotting the sprocket isn't difficult.
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16,707 Posts
Run it.
dont get me wronge I wouldnt know what to do if I didnt get help from people like you, iv been on mini riders lately and there are some people there that know their ****, and im learning. Did you want to see pictures of slotting the cam?. If you do im not to sure if i will need to just yet, and would like to avoid having to. If I do I want to use one sprocket clamped to another but with the one underneth positioned to where I want it, then I can use the top sprocket as a template. If I do slot my cam gear, ill just use the one cam gear as a template to remove a little each time. Oh yea Cycle, is 2 degress one tooth? I just pulled 2 degrees off the top of my head, I am going to measure everything today once I pick up my valves, piston, and cam from the coating place, but I suspect that 1mm will be 1 degree of cam retard. When I measure the valve opening and closing, do I write down when the valve just starts to open, then after it is fully closed? Just want to make sure I take these degrees down right. This OGM engine is a treat to modify since its my first 4 stroke motor I have bought and mod. Its just a little harder to modify. I was wondering if maybe 700'sdad would know the cam specs off the AHP cam.
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