ChinaRiders Forums - View Single Post - ISO Cylinder Head with 32 teeth timing sprocket

novicewrencher · 12-13-2022, 10:28 AM

Just joined the group and hoping to find some feedback. These Chinese machines can be a challenge. My son has a Raytech Chinese 125cc ATV and the exhaust valve blew. I ordered him a new machine, but I hope to fix this one and sell it. I have already tried just repairing the valves but after lapping the valves I am still getting blow by. I have done the flashlight test in a dark room and I see zero light coming through the valves but when installed and cranked I cannot get over 90psi. When I pressurize the head, I get blow by on the intake valve. So, I have given up on just repairing the valves. I am looking for a 52.4mm cylinder head that has a 23mm intake valve and a 20mm exhaust valve BUT with a 32 teeth timing sprocket.

All I can find are the 110cc heads with 28 timing sprocket. Which has all the same specs but for the timing sprocket. From what I can tell, my 125cc is basically a 110cc cylinder head, a 110cc piston and 52.4mm cylinder block (common to the 110cc) but with a 32 teeth timing sprocket and a slightly longer stroke. The bigger timing sprocket and the longer stroke contribute to make the engine a 125 rather than a 110. I have asked VMC Chinese parts for any in their inventory. They have one cylinder head with a 32 teeth timing sprocket but it’s out of stock and they don’t know when they will get more. The tricky thing is, even if it is in stock, the valves on that head are 23 and 19. At least that is what the website says.

My questions:

1. Does anyone know a supplier that can provide a 52.4mm cylinder head with 23mm and 20mm valves that has the larger 32 teeth timing sprocket?

2. Can I just use a cylinder head with a 28 teeth sprocket and swap in my 32 teeth sprocket? I have seen others post on some sites they have done it. They say it fit tight but it works. However, would that not throw the timing off with the valve cam?

3. Can I just use a cylinder head with a 28 teeth sprocket instead of one with a 32 teeth sprocket? Is that swap even possible without changing the timing change and flywheel?

4. Does valve size matter? If I find a cylinder head with a 32 teeth timing sprocket but it has a 23mm intake and a 19mm exhaust, will that 1mm less on the exhaust side make any difference?

Thanks for any feedback.

12-13-2022, 10:28 AM	#1
novicewrencher Join Date: Dec 2022 Posts: 4	ISO Cylinder Head with 32 teeth timing sprocket Just joined the group and hoping to find some feedback. These Chinese machines can be a challenge. My son has a Raytech Chinese 125cc ATV and the exhaust valve blew. I ordered him a new machine, but I hope to fix this one and sell it. I have already tried just repairing the valves but after lapping the valves I am still getting blow by. I have done the flashlight test in a dark room and I see zero light coming through the valves but when installed and cranked I cannot get over 90psi. When I pressurize the head, I get blow by on the intake valve. So, I have given up on just repairing the valves. I am looking for a 52.4mm cylinder head that has a 23mm intake valve and a 20mm exhaust valve BUT with a 32 teeth timing sprocket. All I can find are the 110cc heads with 28 timing sprocket. Which has all the same specs but for the timing sprocket. From what I can tell, my 125cc is basically a 110cc cylinder head, a 110cc piston and 52.4mm cylinder block (common to the 110cc) but with a 32 teeth timing sprocket and a slightly longer stroke. The bigger timing sprocket and the longer stroke contribute to make the engine a 125 rather than a 110. I have asked VMC Chinese parts for any in their inventory. They have one cylinder head with a 32 teeth timing sprocket but it’s out of stock and they don’t know when they will get more. The tricky thing is, even if it is in stock, the valves on that head are 23 and 19. At least that is what the website says. My questions: 1. Does anyone know a supplier that can provide a 52.4mm cylinder head with 23mm and 20mm valves that has the larger 32 teeth timing sprocket? 2. Can I just use a cylinder head with a 28 teeth sprocket and swap in my 32 teeth sprocket? I have seen others post on some sites they have done it. They say it fit tight but it works. However, would that not throw the timing off with the valve cam? 3. Can I just use a cylinder head with a 28 teeth sprocket instead of one with a 32 teeth sprocket? Is that swap even possible without changing the timing change and flywheel? 4. Does valve size matter? If I find a cylinder head with a 32 teeth timing sprocket but it has a 23mm intake and a 19mm exhaust, will that 1mm less on the exhaust side make any difference? Thanks for any feedback.
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