Hi guys, i just installed a 72cc BBK into my Tao Tao scooter, i followed all of the steps and made sure to align the flywheel to the T mark when i took it all apart. Now here is the problem - When i started to put the put the scooter back together after installing the new piston, i got to where the Cam shaft gets installed and i noticed that the T on the flywheel was moved way out of place, so i spun it to the right until the T was lined up again. Then i put the camshaft in and made sure the big circle was facing up just as the guide said, did the valves to .004 clearance.
I started the bike up and it sounded great, but when i took it for a spin i only made it about 600 feet before i heard panging noises in the engine, and then it cut off on me. I could start the bike up again but it immediately made noise so i shut it down and walked it home ...I took the valve cover off and with the T lined up on the flywheel, my exhaust valve is very loose and i cant get it to .004 anymore.
Im not sure but is it possible that i installed the cam 180 out and was not really in TDC??? If the T is lined up on the flywheel does that always = TDC, or do you have to spin it twice to get there?
The kit i bought is just the 72cc piston, cylinder and assorted gaskets and rings that came with it. It said it should be compatible with the stock 50cc head/cam so i used the stock for that. I have the valve cover off of it and i can tighten the top intake valve to .004 but the bottom exhaust i cant do that, its still loose even all the way in....I will take pictures in a bit and upload them. Im really not sure what the problem is, other than perhaps when i put the cam in @tdc, it was TDC but not on the compression stroke, i think that is possible.
Well i tore her down today and i found where the noise was coming from, the exhaust port on the head had the stem literally pushed out of its socket so thats why the rocker arm never was tight enough there. So im going to buy a new head for it, also the cam had some nicks on it so im going to buy a new cam as well. I looked at the piston and it had no cracks or damage to it really other than light scuffs. I think the carbon buildup will cover that up in no time.
So at this point in time, i think i did what i suspected and i had the bike in TDC but it was set to the exhaust TDC and not to the compression stroke TDC...So when i set the valves to .004 at the exhaust setting, it made it wayy to tight @compression and caused the head damage. This is a duh moment to me because i was meticulous with the BBK but that totally slipped my mind.
Anyways i did take a few pictures. I do have a question about the current head and its valve size. It looks to me that mine is a 69mm Valve head [thanks for the vid you linked btw it was helpful] but im not completely sure so i do have a side view pic of the head for reference.
Just a update, i received a new kit a few days ago that had a new head/piston and cylinder, i installed it and the scooter runs great. I have 20 miles on it so far with the new install and still breaking it in. I think the issue with the other install was most likely that the valves were done in the wrong stroke since i rotated the flywheel a few times before doing the valves, or the stock head was not fully compatible with the kit. The replacement head is a big bore kit head so it is possible.
Something to keep in mind is that at any particular valve position half the cam is the lobe and the other half is the flat. The valve gap will be the same anytime the valve is off the lobe.
The rocker arm should be loose when the valve is anywhere on the flat.
While I think it is good practice to use the flywheel marks and inspect everything possible, I think it helps to understand the works if you look at things from different perspectives. You should actually be able to set the lash simply by looking at the cam / valves. That's how its done on multiple cylinder engines.
Next time your in there take some time and play around. Turn over the engine and watch the cam / valves. As the lobe goes on the valve, you will see the gap disappear, then the valve moves away, then the valve moves toward, then the gap reappears. If you turn the cam maybe 30 degrees more just to be sure of being away from the lobe, you will find that gap to be the same anywhere along the flat.
Moral of the story is to learn the workings and use methods to double check when possible.