Using a 150cc GY6 Cam In A 139QMB 50cc
Sept 27, 2013 1:11:15 GMT -5
wolfbat3, oldsman, and 1 more like this
Post by oldsman on Sept 27, 2013 1:11:15 GMT -5
This is how I did my 150 to 50cc cam swap. It took a few day for me to do it but in total time I spent about 4 hours.
The first thing to do is find a good donor 150 cam with good bearings. You will need to mic the 50 cam in the following places and write them down. You will need to have this in order to make sure the 150 cam is exactly the same in all places in order to work.
1. Back of cam gear to outer bearing inner.
2. Back of cam gear to outer side of the outer bearing.
3. Between outer side of cam bearings(between both bearings).
Now that you have that comes the fun part. On the 150 cam mic the back of cam gear to the closest bearing inner. If it is within .25mm that side will be OK. If it is any more than that the cam gear will have to be removed. Mine needed to be removed so I heated the cam gear with a torch and used a short pipe that the cam fit and placed the cam in it. I used a 3/8 drive extension and a small sledge hammer to drive the cam out of the gear. Make sure you mark with a scribe or something so the cam and gear can be installed in the exact same spot.
Mill down the cam gear bearing side till you get the difference you measured. It should be the same as the distance the the 50 cam gear is (as measured from the back of cam gear to outer bearing side). Reinstall the cam gear and check the measurements are the same. You will need to have the gear side done in order to go any further.
Now you will have to remove the outer bearing and that anti reverse clip. Trash that clip. There will be a step where the bearing is and the anti reverse clip (ARC) was. You will need to mill down that step but not the whole step. With the measurement you have from the cam gear from the back of the cam gear to the outer bearing of the 50 cam you will need to mark that on the 150 cam. Mill up to that mark the same as what the bearing sits on. It must be exact or the bearing will fit too lose or too tight. (It will result in bearing failure if is not done correctly.) The bearing will go on further that what is originally was and that is what we are going for.
Now you can reinstall the bearing and mic the distance from the cam gear to the outer side of the bearing and from the outer of the cam bearings. They should be the same. If they are a tad smaller that will be OK as long as they fit into the rocker arm assy.
Now test fit the cam into your engine but do not tighten it down. You will need to rotate the cam and look for anyplace the cam lobes are close to hitting the head and the rocker arm assy. Grind down anyplace it is close on the head or rocker assy. I had to grind very little on the rocker assy for clearance.
Clean everything up and add some oil to the bearings and make sure the move freely and install. Adjust the valves like you normally would and rotate the engine by hand to make sure the valves don't hit the piston. Enjoy your mod and increased power and throttle response. Oldsman
The first thing to do is find a good donor 150 cam with good bearings. You will need to mic the 50 cam in the following places and write them down. You will need to have this in order to make sure the 150 cam is exactly the same in all places in order to work.
1. Back of cam gear to outer bearing inner.
2. Back of cam gear to outer side of the outer bearing.
3. Between outer side of cam bearings(between both bearings).
Now that you have that comes the fun part. On the 150 cam mic the back of cam gear to the closest bearing inner. If it is within .25mm that side will be OK. If it is any more than that the cam gear will have to be removed. Mine needed to be removed so I heated the cam gear with a torch and used a short pipe that the cam fit and placed the cam in it. I used a 3/8 drive extension and a small sledge hammer to drive the cam out of the gear. Make sure you mark with a scribe or something so the cam and gear can be installed in the exact same spot.
Mill down the cam gear bearing side till you get the difference you measured. It should be the same as the distance the the 50 cam gear is (as measured from the back of cam gear to outer bearing side). Reinstall the cam gear and check the measurements are the same. You will need to have the gear side done in order to go any further.
Now you will have to remove the outer bearing and that anti reverse clip. Trash that clip. There will be a step where the bearing is and the anti reverse clip (ARC) was. You will need to mill down that step but not the whole step. With the measurement you have from the cam gear from the back of the cam gear to the outer bearing of the 50 cam you will need to mark that on the 150 cam. Mill up to that mark the same as what the bearing sits on. It must be exact or the bearing will fit too lose or too tight. (It will result in bearing failure if is not done correctly.) The bearing will go on further that what is originally was and that is what we are going for.
Now you can reinstall the bearing and mic the distance from the cam gear to the outer side of the bearing and from the outer of the cam bearings. They should be the same. If they are a tad smaller that will be OK as long as they fit into the rocker arm assy.
Now test fit the cam into your engine but do not tighten it down. You will need to rotate the cam and look for anyplace the cam lobes are close to hitting the head and the rocker arm assy. Grind down anyplace it is close on the head or rocker assy. I had to grind very little on the rocker assy for clearance.
Clean everything up and add some oil to the bearings and make sure the move freely and install. Adjust the valves like you normally would and rotate the engine by hand to make sure the valves don't hit the piston. Enjoy your mod and increased power and throttle response. Oldsman
