Joined: May 2007 Gender: Male Posts: 457 Location: SW Oklahoma
GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Thread Started on Aug 30, 2007, 3:25pm »
I've seen several cams named but haven't seen much in the way of specs. They all seem to be named "A" something. Is there only one manufacture of GY6 cams or do they copy the names too?
It's not like you can go to Crane Cams or Crower Cams and find scooter specs. Is there any good information out there that I haven't found?
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #1 on Aug 30, 2007, 8:36pm »
there are OEM manufacturers and aftermarket ones .. I just put a new cam in my scoot today. an A-12 intake 27.2mm exhaust 26.8 mm.. the old cam"the stock one" didn't have any "A" on it It has a "J". Don't quote me on this but I am assuming that the Letter represents the Grade of metal,steel etc.. my stock cam is all a dark brown color and the new A-12 is shiny like polished steel...I must say after i've put this cam in it has made a good differance on performance as well...im a happy camper...but still need to re-jet to meet peak performance
Joined: Jan 2007 Gender: Male Posts: 8,657 Location: Grapevine Texas
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #2 on Aug 30, 2007, 9:06pm »
This is all I got on Camshafts so far, if someone has some more info I'll add it to my collection here:
GY6 Camshafts:
PFS GY6 POWER CAMSHAFT For GY6 125 or 150, 26.14mm lobes 6.45mm lift.
MRP (Martin Racing Performance):
CAM SHAFT FOR GY6 A9 26.94 INTAKE 26.77 EXHAUST #26535
CAM SHAFT FOR GY6 A11 27.22 INTAKE 27.10 EXHAUST #26533
N-MP-09448-4 CAM SHAFT GY6 A12 #27000 27.2MM EXHAUST , 26.8MM INTAKE N-MP-09448-4 Racing Cam shaft for GY6 ATV, GO KART, SCOOTERS, AND SMALL MOTORCYCLES. CAM SHAFT GY6 A12
N-MP-09448-5 CAM SHAFT GY6 26.2MM, 26.4MM #26999 26.2MM EXHAUST , 26.4MM INTAKE Racing Cam shaft for GY6 ATV, GO KART, SCOOTERS, AND SMALL MOTORCYCLES.
N-MP-09448-6 UPGRADED CAM SHAFT GY6 25.8MM, 25.7MM #26998 N-MP-09448-6 CAM SHAFT GY6 25.8MM, 25.7MM Racing Cam shaft for GY6 ATV, GO KART, SCOOTERS, AND SMALL MOTORCYCLES
Type 9 HP camshaft for all 150cc Go-karts/ Scooters and ATV. This fits your Sunl/Explorer/Carter/Twister/Xterro/Kinroad/Roketa/Gk01 Sahara150/Boxer150/Raptor150Yerf-dog Howhit/ or any other Chinese150cc Go-kart and Scooter. Best acceleration/top speed. Intake lobe height: 26.92mm Exhaust lobe height: 26.82mm. Increases horsepower by changing valve timing which allows more fuel & air to get into cylinder. Works great for scooters, too! For best results use with pipe kit and 135 main jet.
A A8 offers higher top end for scooters. Slightly less lift than the A9 cam. A A9 has best acceleration and top speed. Someone used this cam and got a hig performance boost on a 155cc GY6 with 30mm carb and MRP exhaust. A A10 was for climbing and not for top speed, more torque.
Type 10 HP camshaft for all 150cc Go-karts/ Scooters and ATV's. This fits your Sunl/Explorer/Carter/Twister/Xterro/Kinroad/Roketa/Gk01 Sahara150/Boxer150/Raptor150 Yerf-dog Howhit or any other Chinese150cc Go-kart and Scooter. Better low-end torque for better climbing power. Intake lobe height: 27.08mm Exhaust lobe height: 27.13mm. This cam is GREAT if you are building a low end, mild hill, and trail climbing machine for use in the Eastern US. Also good for dunes as well. Works great for scooters, too, if you feel like your scooter won't pull well up hills. For best results use with pipe kit and 135 main jet.
Type 11 HP camshaft for all 150cc Go-karts/ Scooter and ATV's. This fits your Sunl/Explorer/Carter/Twister/Xterro/Kinroad/Roketa Gk01/Sahara150Boxer150/Raptor150 Yerf-dog Howhit/ or any other Chinese150cc Go-kart. Best low-end torque for climbing & rock crawling. Intake lobe height: 27.18mm Exhaust lobe height: 27.08mm. This cam is what you want if you are building a low end, slow going, rock climbing, and trail jumping machine for use in the Eastern US. Also for the desert and the Rockies. Too low for dunes. Not recommended for scooters. For best results use with pipe kit and 135 main jet.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
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Always bet on black.
Joined: Mar 2006 Gender: Male Posts: 2,940 Location: Preston, MD
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #3 on Aug 30, 2007, 9:30pm »
You can clearly see that MRP puts some spin on what they use for descriptions. They often ask me what works where, and in all honesty, they don't listen very well. A 135 main jet is way too much for a 150 with a stock carb. Stan
Quote:
This is all I got on Camshafts so far, if someone has some more info I'll add it to my collection here:
GY6 Camshafts:
PFS GY6 POWER CAMSHAFT For GY6 125 or 150, 26.14mm lobes 6.45mm lift.
MRP (Martin Racing Performance):
CAM SHAFT FOR GY6 A9 26.94 INTAKE 26.77 EXHAUST #26535
CAM SHAFT FOR GY6 A11 27.22 INTAKE 27.10 EXHAUST #26533
N-MP-09448-4 CAM SHAFT GY6 A12 #27000 27.2MM EXHAUST , 26.8MM INTAKE N-MP-09448-4 Racing Cam shaft for GY6 ATV, GO KART, SCOOTERS, AND SMALL MOTORCYCLES. CAM SHAFT GY6 A12
N-MP-09448-5 CAM SHAFT GY6 26.2MM, 26.4MM #26999 26.2MM EXHAUST , 26.4MM INTAKE Racing Cam shaft for GY6 ATV, GO KART, SCOOTERS, AND SMALL MOTORCYCLES.
N-MP-09448-6 UPGRADED CAM SHAFT GY6 25.8MM, 25.7MM #26998 N-MP-09448-6 CAM SHAFT GY6 25.8MM, 25.7MM Racing Cam shaft for GY6 ATV, GO KART, SCOOTERS, AND SMALL MOTORCYCLES
Type 9 HP camshaft for all 150cc Go-karts/ Scooters and ATV. This fits your Sunl/Explorer/Carter/Twister/Xterro/Kinroad/Roketa/Gk01 Sahara150/Boxer150/Raptor150Yerf-dog Howhit/ or any other Chinese150cc Go-kart and Scooter. Best acceleration/top speed. Intake lobe height: 26.92mm Exhaust lobe height: 26.82mm. Increases horsepower by changing valve timing which allows more fuel & air to get into cylinder. Works great for scooters, too! For best results use with pipe kit and 135 main jet.
A A8 offers higher top end for scooters. Slightly less lift than the A9 cam. A A9 has best acceleration and top speed. Someone used this cam and got a hig performance boost on a 155cc GY6 with 30mm carb and MRP exhaust. A A10 was for climbing and not for top speed, more torque.
Type 10 HP camshaft for all 150cc Go-karts/ Scooters and ATV's. This fits your Sunl/Explorer/Carter/Twister/Xterro/Kinroad/Roketa/Gk01 Sahara150/Boxer150/Raptor150 Yerf-dog Howhit or any other Chinese150cc Go-kart and Scooter. Better low-end torque for better climbing power. Intake lobe height: 27.08mm Exhaust lobe height: 27.13mm. This cam is GREAT if you are building a low end, mild hill, and trail climbing machine for use in the Eastern US. Also good for dunes as well. Works great for scooters, too, if you feel like your scooter won't pull well up hills. For best results use with pipe kit and 135 main jet.
Type 11 HP camshaft for all 150cc Go-karts/ Scooter and ATV's. This fits your Sunl/Explorer/Carter/Twister/Xterro/Kinroad/Roketa Gk01/Sahara150Boxer150/Raptor150 Yerf-dog Howhit/ or any other Chinese150cc Go-kart. Best low-end torque for climbing & rock crawling. Intake lobe height: 27.18mm Exhaust lobe height: 27.08mm. This cam is what you want if you are building a low end, slow going, rock climbing, and trail jumping machine for use in the Eastern US. Also for the desert and the Rockies. Too low for dunes. Not recommended for scooters. For best results use with pipe kit and 135 main jet.
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #4 on Aug 30, 2007, 9:49pm »
it seems that the higher the A# is the bigger the lift on the valve..My question is how a lower lift transfers into a better top end...I would think the higher the lift, the more fuel/air it could move in at higher rpm thus better top end...Anyone have some thoughts on this????
Joined: Jan 2007 Gender: Male Posts: 8,657 Location: Grapevine Texas
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #5 on Aug 30, 2007, 9:56pm »
High lift makes it easier for valves to float, so you lose power at higher RPMs. So a low lift cam would help keep the valves from floating. You have a limit on how stiff you can make the springs without causing the valves to stretch or the cams and rocker arms to start wearing faster.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
Joined: Jan 2007 Gender: Male Posts: 8,657 Location: Grapevine Texas
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #9 on Aug 31, 2007, 9:39am »
thelawnmoreman, The real trick is actually being able to find better valve springs to fit a GY6 150 engine. But to increase the RPM you need stiffer springs, usually you have to resoirt to dual springs, on inside the other to increase the spring strength. But eventually you hit the wall so to speak and the valves will start floating anyway at high RPMs. Ducati and some others solved the problem by going to a desmodromic valvetrain system where the cams and rocker arms both open and close the valves. Thus they only need a weak spring to keep the valves closed so you can start the engine. One reason everyone has been going towards double overhead cams is to reduce weight and inertial forces on the valve train at high RPMs. The cams operate the valves directly without the use of a rocker arm. But in that case they still hit the wall on RPM limits as you can only make the springs so stiff.
With a high lift cam, at higher RPM's the valve is literally slammed open roughly. it takes a moment in time before the spring overcomes that opening effect and forces the valve closed. So as the speed increases more and more eventually you hit a point where the spring can't overcome the opening fast enough and the valve stays open longer than it should. So like MLN stated, a high speed came has other things in the cam shape to help make the opening and closing of the valves better.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #10 on Aug 31, 2007, 9:55am »
thanx for the info earl, I knew it was more complicated then i made it seem. But how hard do you think it would be to raise the max HP to like 8000 or 8500 or even 9000. I dont really want to go past 10000 rpm max. I think the engine can physically handle these #s. Also I assume that the gy6 is a non-interference motor. Do you know of any those cams would change that with their different configurations and all
Joined: Jul 2007 Gender: Male Posts: 1,098 Location: NC
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #11 on Aug 31, 2007, 10:30am »
So If you went with say an a-10 or 11 low end boost cam, would that work better with say a more stock cvt setup far as weights n spring rates go, since the stock config tends to shift early in the powerband? I live in the foothills of NC and its a rather 'hilly' area...
« Last Edit: Aug 31, 2007, 10:34am by YellowScooter »
Joined: Jan 2007 Gender: Male Posts: 8,657 Location: Grapevine Texas
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #12 on Aug 31, 2007, 10:49am »
yellowscooter, The A10 or A11 cams are designed for ATV's so they can have more low end power for climbing hills and such. You lose some off the high end speedwise. But you normally don't go fast on a ATV anyway.
Most stock GY6 engines benefit from changing the variator weights to change the shift point. You normally don't need to mess with putting in a different cam. For example my scooter came with 13g weights stock. it had some trouble getting up the hills and tended to shift too soon when you take off from a stoplight. So i put in 12g weights and that made a lot of difference for me. it now accellerates a lot better and goes up the hills acceptably for me. Someone else might find 11g weights better still.
Another thing that can affect people without knowing it is the CVT drive belt. The OEM belts tend to wear and stretch fairly fast. Putting on a kevlar belt can make the scooter feel like you have a new high gear as it lowers your RPMs at higher speeds.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
Joined: Jan 2007 Gender: Male Posts: 8,657 Location: Grapevine Texas
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #13 on Aug 31, 2007, 10:53am »
thelawnmowerman, Well the OEM GY6 engines are already capable of 9,000 to 10,000 rpm. 9000 rpm stock is normal. Going 10,000 rpm and over usually only requires putting on a uni-filter and racing exhaust along with a racing coil and CDI, and rejetting the carb. now getting higher speeds like say 12000 rpm plus is where it can get messy.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
Joined: May 2007 Gender: Male Posts: 35 Location: Sweden
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #14 on Aug 31, 2007, 2:34pm »
Hi
This evening (fri 8.30 PM Swedish time) I just installed a A9 camshaft. Unfortunatelly I hadn't got time to try the gain vs. stock camshaft but I hope that I have the time to do it on suturday. (I'll get back to you on this).
My first feeling though was that I got more "noice" frome the valve mechanism, and YES I have adjusted the valves properly. Any one else that have that feeling?!?
I know that when I friend of mine got a Suzuki DR650RS cam re-grounded his opinion was the same. He got a more clappering sound from the valves... but it didn't seem to make any troubble...
One thing that I'm getting really annoyed about is that it is common to use the max. lobe dimension when talking about camshafts here. The first time that I have seen this is on these scooter camshafts. On no other camshaft (car or motorcycle) is this messuremen mentioned. The numbers we really need to make the correct choise is lift, duration and overlap... and of course lobe profile. I haven't seen any of these figures on the scooter camshafts.
When installing the A9 camshaft I took the opertunity to messure the lift. I also have a A10 at home and also got the number for this one + the stock one.
Joined: Jan 2007 Gender: Male Posts: 8,657 Location: Grapevine Texas
Re: GY6 Cams- A8, A9, A10, A11, A12 Oh My! « Reply #15 on Aug 31, 2007, 6:32pm »
Let us know, sound sgood so far.
I think what we need is for someone with a set of cams to run the different cams on a engine in a scooter with a dynanometer so they can graph the performance effect for several cams out. That would give us an excellent idea of what the cams do. Having the scooter setup with performance stuff ahead of time would be neat, except for a run as a stock scooter with OEm stuff to serve as the baseline.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
yellowscooter, The A10 or A11 cams are designed for ATV's so they can have more low end power for climbing hills and such. You lose some off the high end speedwise. But you normally don't go fast on a ATV anyway.
Most stock GY6 engines benefit from changing the variator weights to change the shift point. You normally don't need to mess with putting in a different cam. For example my scooter came with 13g weights stock. it had some trouble getting up the hills and tended to shift too soon when you take off from a stoplight. So i put in 12g weights and that made a lot of difference for me. it now accellerates a lot better and goes up the hills acceptably for me. Someone else might find 11g weights better still.
Another thing that can affect people without knowing it is the CVT drive belt. The OEM belts tend to wear and stretch fairly fast. Putting on a kevlar belt can make the scooter feel like you have a new high gear as it lowers your RPMs at higher speeds.
Okie then... I happen to have some 12g sliders and new belt on the way Along with my carb and ignition kit, should take care of all thats ailing it right now. (upshift issues, and unexplained power cut after warmup) before winter hits. I ride yr. round so it's getting an extensive tuneup. along with a new back tire.
there was just another thread posted where the guy got a big top end increase going with a A12 cam...This seems to go against the grain with what is being said in this tread...Here its said that the A9 cam is for top end and the A12 is for low end torque.. Even Stan says the A12 is a "racing cam" and it increases the over all RPM which is what I initially speculated mainly because of the higher lift it has which would allow the valves to let in and out more air. Of course we dont have all the info concerning duration and such but I was just "assuming" (i know its a dangerous word around here) that its probable that the duration of the lift is also increased or the same...Unless the higher lift cams are square I would like to hear everyones take on this new info
My information doesn't say anything much about the A12 except it is a racing cam. So I don't really know much about it. But apparently it does provide high RPM power. The Type 10 and 11 are low end high torque types of cams.
Unless you are using a CNC xrayed and magnafluxed (and maybe shot peened too) connecting rod, I'd probably avoid the racing cams. Unless you can afford the rebuilds. The crankshaft is pressed together, so it is tricky to install a racing rod.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
90GTVert Global Moderator Global Moderator member is offline
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Joined: Mar 2006 Gender: Male Posts: 2,940 Location: Preston, MD
Stick to the cams with the lower end of the lift increase and you will be better off all the way around. If you want to use the MRP numbers as a scale (which mean nothing really), the A8 or A9 are your best choice if you aren't building a race engine that is disposable or rebuild regularly. I will warn again, that the connecting rod cannot take the high RPM stress the racing cams need and want. I'm done with the warnings now. Run what you like, but find a source for new engines before you do. Stan
Quote:
there was just another thread posted where the guy got a big top end increase going with a A12 cam...This seems to go against the grain with what is being said in this tread...Here its said that the A9 cam is for top end and the A12 is for low end torque.. Even Stan says the A12 is a "racing cam" and it increases the over all RPM which is what I initially speculated mainly because of the higher lift it has which would allow the valves to let in and out more air. Of course we dont have all the info concerning duration and such but I was just "assuming" (i know its a dangerous word around here) that its probable that the duration of the lift is also increased or the same...Unless the higher lift cams are square I would like to hear everyones take on this new info
Also high lift cams wear out faster too. The wearing surfaces on the cams and rocker arms will wear out faster than normal because of the higher stresses.
I also remember, not on scooters so far, is guys putting in high lift cams on a hi-perf engine they built and not checking for valve to piston clearances carefully. Just because the valves aren't touching the piston when you turn the engine over slowly with a wrench doesn't hack it. You need to use clay and carefully measure the valve to piston gap and allow for the slamming open effect causing the valves to go farther into the combustion chamber.
This is a inertial momentum effect. If you force open a valve at say 9,000 rpm it is literally slammed open very fast. Inertial momentum will have it go farther open than the cam pushes it open. if the clearances are tight the valve literally hits the piston even if you thought it didn't touch the piston. What happens is the va;lver continues on into the combustion chamber farther after opening before for the springs can overcome the effect and smal them shut again. On racing cams I have seen wear patterns where the tips of the cam aren't wearing on the backside as the valve isn't really touching the cam at that point.
So far no one has ever mentioned anywhere how much valve to piston gap or clearances is needed for the GY6 engines. I remember putting in raceing cams on engines before and they had specs like this on the data sheets that came with the camshafts. Of course maybe it isn't very important yet as maybe the pistons have a lot of excess clearance or gap that keeps it safe so far. I don't know. But the guys putting on stroker cranks should be very careful in measuring all these clearances for sure.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
Those lift numbers you gave are over 40% higher than the stock lift numbers. Did you change valve springs too? Did you check for coil bind? It seems like a big change for a drop in cam to me.
Stan or anyone with experience,
Have you had good success with these cams and where did you get the most improvement for the cam you chose. Also, which cam was it?
Because I believe the only safe and useful power increase on a GY6 is in the low and midrange RPM's, I have not (and won't) use anything higher than what MRP terms as their A9 profile. Actually, I don't use their cams at all, but if you want more performance and still want to maintain the engine durability, I would not go beyond the A9 profile. Also, if you don't have a tachometer, add one before you do anything else so you can tell what is going on. Even with a stock engine I consider this an essential tool to have. Stan
Quote:
Messiah
Those lift numbers you gave are over 40% higher than the stock lift numbers. Did you change valve springs too? Did you check for coil bind? It seems like a big change for a drop in cam to me.
Stan or anyone with experience,
Have you had good success with these cams and where did you get the most improvement for the cam you chose. Also, which cam was it?
Those lift numbers you gave are over 40% higher than the stock lift numbers. Did you change valve springs too? Did you check for coil bind? It seems like a big change for a drop in cam to me.
Stan or anyone with experience,
Have you had good success with these cams and where did you get the most improvement for the cam you chose. Also, which cam was it?
MLN
So far I have not changed the valve springs when switching to the A9 camshaft, but I will... As you say, the lift is increased quite alot and my feeling is that the rocker is not completelly following the cam lobe when the valve is closing. (Maby the reason why I hear more ticking from the valves although they are correct adjusted). A stronger spring will make the rocker follow the lobe better (which also, of couse, is the intention...) but at the same time also increase the pressure and then also the wear. I have though no problem if the wear goes up a little. Really cheap stuff for these Chinese bikes!
To be honest I did not check for coil bind since I saw that other people on this forum also had fitted the A9... and it seams to work . But I agree with you that this is something that should have been checked since the lift is so high compaired to stock.
So far I have only used a re-jetted stock carburator together with an V8 exhaust and my top speed went up from 59 to 64MPH (GPS) on a flat road (using 10gr SR weights). Feels though like the stock carburator is limiting the performance (rpm) and I will therefore put on my PWK28 which I have in the garage. I have seen that alot of you do not like the PWK... but we'll see how it works for me.
Does any one know where to purchase stiffer valve springs?!?
The added "ticking" is the valve slamming shut since you are now opening it a lot more than you were before. This is one of the dangers of the high lift cams in that the valves can literally drive the seats into the head. I don't have a great deal of faith in the quality of the heat treating (if any) of the aluminum castings used in the Chinese head and cylinders. Keep a close watch on the tappet clearance and if it starts to decrease, the seat is being recessed into the head. Stronger springs will only make this worse. Stan
Quote:
So far I have not changed the valve springs when switching to the A9 camshaft, but I will... As you say, the lift is increased quite alot and my feeling is that the rocker is not completelly following the cam lobe when the valve is closing. (Maby the reason why I hear more ticking from the valves although they are correct adjusted). A stronger spring will make the rocker follow the lobe better (which also, of couse, is the intention...) but at the same time also increase the pressure and then also the wear. I have though no problem if the wear goes up a little. Really cheap stuff for these Chinese bikes!
To be honest I did not check for coil bind since I saw that other people on this forum also had fitted the A9... and it seams to work . But I agree with you that this is something that should have been checked since the lift is so high compaired to stock.
So far I have only used a re-jetted stock carburator together with an V8 exhaust and my top speed went up from 59 to 64MPH (GPS) on a flat road (using 10gr SR weights). Feels though like the stock carburator is limiting the performance (rpm) and I will therefore put on my PWK28 which I have in the garage. I have seen that alot of you do not like the PWK... but we'll see how it works for me.
Does any one know where to purchase stiffer valve springs?!?
This is the rare occasion that I don't totally agree with you. If the clearance starts to go away it could also be the valves tuliping (stretching). The head of the valve starting to stretch and thus clearance goes away.
If the valves are making noise since the cam change I wonder if it's because the valve springs can no longer keep the rocker arm in contact with the valve at all times like it's supposed to? The profile of the lobe may be too hard to follow for stock valve springs. If that is the case stiffer springs are needed. Mark
Quote:
The added "ticking" is the valve slamming shut since you are now opening it a lot more than you were before. This is one of the dangers of the high lift cams in that the valves can literally drive the seats into the head. I don't have a great deal of faith in the quality of the heat treating (if any) of the aluminum castings used in the Chinese head and cylinders. Keep a close watch on the tappet clearance and if it starts to decrease, the seat is being recessed into the head. Stronger springs will only make this worse. Stan
Also, if you don't have a tachometer, add one before you do anything else so you can tell what is going on. Even with a stock engine I consider this an essential tool to have. Stan
I have a Tiny Tach on the way. The cheapest I could find was from this company on Ebay.
You have some good points and I don't disagree. I still don't trust the metalurgy of the Chinese castings, and keeping track of the tappets is the main point regardless of the cause. Good post and good points. Stan
Quote:
Stan
This is the rare occasion that I don't totally agree with you. If the clearance starts to go away it could also be the valves tuliping (stretching). The head of the valve starting to stretch and thus clearance goes away.
If the valves are making noise since the cam change I wonder if it's because the valve springs can no longer keep the rocker arm in contact with the valve at all times like it's supposed to? The profile of the lobe may be too hard to follow for stock valve springs. If that is the case stiffer springs are needed. Mark
Quote:
The added "ticking" is the valve slamming shut since you are now opening it a lot more than you were before. This is one of the dangers of the high lift cams in that the valves can literally drive the seats into the head. I don't have a great deal of faith in the quality of the heat treating (if any) of the aluminum castings used in the Chinese head and cylinders. Keep a close watch on the tappet clearance and if it starts to decrease, the seat is being recessed into the head. Stronger springs will only make this worse. Stan
messiah, it looks like no one really sells valve springs specifically for a Gy6 engine. So you'll need to get creative. Think about what multicylinder motorcycles use 150cc size cylinders. Maybe something like: A 750cc four cylinder engine has 4 187cc cylinders. A 350cc two cylinder engine has two 150cc cylinders. A engine with a 4 valve head would work too, especially if it is a DOHC model, probably something with cylinders around 250cc to 300cc would be worth checking out as the individual valves would be about the same size. So since the cylinders are similar the valve springs become good candidates to use. Just make some measurements to ensure they'll work. it is possible one might have to make custom valve clip retainers though.
The other old trick was to shim the valve springs to make them stiffer.
2007 Roketa Fiji 150 2007 Roketa MC54-250B 1992 Harley Sportster 1200 ----------------------------------- "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming -- WOW--What a ride!!!"
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Along with my carb and ignition kit, should take care of all thats ailing it right now. (upshift issues, and unexplained power cut after warmup) before winter hits. I ride yr. round so it's getting an extensive tuneup. along with a new back tire. 
. But I agree with you that this is something that should have been checked since the lift is so high compaired to stock.![[Home]](http://images.proboards.com/new/menu/home.png "[Home]")
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