TY150 Cam VS CRF230F Cam

[jamrock876]

Hi all;

Trying to find the function of the third lobe on a TY150 Camshaft.



I am on the verge of attempting to change the bearing from the undriven side of a CRF cam to a 6203 to fit into my bike but I am concerned about the missing third lobe.

From what I can see it seems to be a slightly modified CRF230F Cam, it has the third lobe which I presume has some oiling function, and sports 6203 bearings on both ends. The third lobe acts on a spring-loaded pin accessible by removing a bolt on the tappets-cover, I have removed this bolt with a running engine and did not see any oil coming out the top. Due to the design of the engine, I am unable to run the engine without the tappets-cover to see what is actually happening below.

Do you guys have any idea if this will work?

[franque]

My guess is that the third lobe is for a decompressor on the intake valve, they're quite common in single cylinder engines, though this one is small enough that it *shouldn't* need a decompressor (though it might be there to spare the kicker gears, etc.).

As for the CRF 230 cam, again, there are a lot of critical measurements that need to line up for it to work with your motor, even the cam base circle, for example, and potentially where the lobes are placed on the cam, in relation to the rocker arms.

I would very carefully turn the engine over by hand several rotations (looking for hangups or binding, after very carefully measuring everything) before even attempting to run the motor, as there's still a good chance, even if you managed to get it installed and bolted together, of your install ending in a crunch.

Another thing to think about is how the cam gear is installed, and how everything is clocked in relation to one another... This is a very sensitive thing, as even with the correct camshaft, getting it off by a couple of degrees can lead to a crunch and needing new parts. The gear that comes with the cam (if it comes with one) might also have a different number of teeth or a different chain pitch.

With the potential expense and complexity of making everything fit, not to mention the distinct probability of things being broken, unless you're a good machinist, I would not attempt to make the camshaft work. It would be much easier to talk to Webcams in the US, send them a stock camshaft, and have them reprofile that cam, going for a modest increase in lift and duration so that you don't overstress the valvesprings or have the piston make contact with the valves. There are ways of measuring that clearance, which I can explain if you're interested, but you'll also need to know your rocker arm ratio so you don't make valve to piston contact.

Edit... The list of measurements and things to check is not comprehensive, I thought of another measurement offhand that would also be necessary. Take your time and don't force anything.

[jamrock876]

Originally Posted by franque

My guess is that the third lobe is for a decompressor on the intake valve, they're quite common in single cylinder engines, though this one is small enough that it *shouldn't* need a decompressor (though it might be there to spare the kicker gears, etc.).

As for the CRF 230 cam, again, there are a lot of critical measurements that need to line up for it to work with your motor, even the cam base circle, for example, and potentially where the lobes are placed on the cam, in relation to the rocker arms.

I would very carefully turn the engine over by hand several rotations (looking for hangups or binding, after very carefully measuring everything) before even attempting to run the motor, as there's still a good chance, even if you managed to get it installed and bolted together, of your install ending in a crunch.

Another thing to think about is how the cam gear is installed, and how everything is clocked in relation to one another... This is a very sensitive thing, as even with the correct camshaft, getting it off by a couple of degrees can lead to a crunch and needing new parts. The gear that comes with the cam (if it comes with one) might also have a different number of teeth or a different chain pitch.

With the potential expense and complexity of making everything fit, not to mention the distinct probability of things being broken, unless you're a good machinist, I would not attempt to make the camshaft work. It would be much easier to talk to Webcams in the US, send them a stock camshaft, and have them reprofile that cam, going for a modest increase in lift and duration so that you don't overstress the valvesprings or have the piston make contact with the valves. There are ways of measuring that clearance, which I can explain if you're interested, but you'll also need to know your rocker arm ratio so you don't make valve to piston contact.

Edit... The list of measurements and things to check is not comprehensive, I thought of another measurement offhand that would also be necessary. Take your time and don't force anything.

Thanks for the detailed response, I do know there are a lot of things that will need to be measured and checked before I go ahead with an installation. After which I fully intend to turn the engine over by hand with the plug removed.

The biggest issue for me up to this point though was not knowing what that lobe did. It is closest to the exhaust lobe but too far out of phase in my opinion to be a compression release. I was convinced so far that it had something to do with oiling as the pin it acts on is inside what appears to be the oil gallery for the head. My test with removing the bolt however has me doubting the accuracy of that, although it could be that at such low revs there is not much oil pressure.

[franque]

Post a picture of the top half of the cylinder head (the top part that helps to hold the cam in place)... I'm curious what it looks like, including the rocker arms, etc.

[jamrock876]

Originally Posted by franque

Post a picture of the top half of the cylinder head (the top part that helps to hold the cam in place)... I'm curious what it looks like, including the rocker arms, etc.

This is the only picture I have currently sadly. It was taken at an odd angle but the pin I was referencing can be seen just above the exhaust rocker.



I will try to get a better picture when I have it apart again. Still waiting on some angled feeler gauges to properly adjust the valve lash.