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.

franque · 12-13-2022, 10:52 AM

I'd give these guys a call: https://tboltusa.com/

For 1-3, I'm not sure, but for 4, if everything else is the same, I doubt that it would matter, but I would just call tbolt.

dirtbkr188 · 12-13-2022, 03:23 PM

1. Click HERE for the head

2. Click HERE for a 32T sprocket

3. No, if you need a 32T cam sprocket, that means the crank sprocket is 16T, you have to keep the 2:1 tooth ratio between the two sprockets.

4. That would depend on the location and depth of the flycuts on the piston dome. Chances are, if your engine has the typical low-compression flat-top or dished piston, the 1mm shouldn't make a difference.

novicewrencher · 12-13-2022, 06:02 PM

Here is some good information from the Tbolt USA website that relates to my issue. Thanks franque for directing me to their webpage.

4 Stroke engine crankshaft/camshaft gear ratio is always 2:1, which means that for every two revolutions of the crankshaft the camshaft will rotate through one revolution.
This is a 2:1 ratio and must always remain
The top cam sprocket will have twice as many teeth as the crankshaft cam-chain sprocket.
Typically, Honda 50 and 50-110cc Chinese engines and Lifan 140, have 28 tooth cam sprockets.
Jailing and GPX and YX 140 engines have a 32 Tooth cam sprocket.
When installing a performance camshaft you may replace the cam sprocket but only due to the bolt pattern.
The new cam sprocket must have the same tooth count as the original sprocket.

novicewrencher · 12-16-2022, 11:16 AM

Quote:

Originally Posted by dirtbkr188

1. Click HERE for the head

2. Click HERE for a 32T sprocket

3. No, if you need a 32T cam sprocket, that means the crank sprocket is 16T, you have to keep the 2:1 tooth ratio between the two sprockets.

4. That would depend on the location and depth of the flycuts on the piston dome. Chances are, if your engine has the typical low-compression flat-top or dished piston, the 1mm shouldn't make a difference.

dirtbkr188,

I appreciate your feedback. Remember, I am just a novice at this. Before I order some parts, I have one more question. The head in the link you gave me shows a 28 tooth sprocket included with it. Then you sent a link to a 32 tooth sprocket. Am I going to have trouble with timing of the cam lobes lifting and opening the valves if I just swap out the 28 tooth that comes with it for a 32 tooth? The 32 will be in sync with my existing crankshaft, but will the 32 tooth sprocket rotate the cam in the right timing? Thanks,

dirtbkr188 · 12-16-2022, 02:22 PM

As long as you're maintaining the 2:1 ratio of the cam sprockets, it should work just fine. One thing to advise you of, is the size of the center hole of the 32T sprocket you have, the one I posted may not work for you, hole size-wise. You may need THIS ONE, depending on what the center hole size is on the DRATV head.
You can reach out to Vince at TBolt and ask him if the above 32T sprocket will work with THIS HEAD that he sells on his site.
I do know that some heads have a "cam chain guide", but I'm not sure if it would interfere with the bigger 32T sprocket or not.

dirtbkr188 · 01-01-2023, 07:34 PM

Did you ever resolve this? Is the 32T sprocket you have now one with the 17mm center hole, like the one I linked to in post #6? Also, can you post a pic of the cam end where the sprocket bolts into place?

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.
	0

12-13-2022, 10:52 AM	#2
franque Join Date: Nov 2017 Location: Marseille, France -> Conakry, Guinea Posts: 1,481	I'd give these guys a call: https://tboltusa.com/ For 1-3, I'm not sure, but for 4, if everything else is the same, I doubt that it would matter, but I would just call tbolt.
	1

12-13-2022, 03:23 PM	#3
dirtbkr188 Join Date: Aug 2009 Posts: 502	1. Click HERE for the head 2. Click HERE for a 32T sprocket 3. No, if you need a 32T cam sprocket, that means the crank sprocket is 16T, you have to keep the 2:1 tooth ratio between the two sprockets. 4. That would depend on the location and depth of the flycuts on the piston dome. Chances are, if your engine has the typical low-compression flat-top or dished piston, the 1mm shouldn't make a difference.
	1

12-13-2022, 06:02 PM	#4
novicewrencher Join Date: Dec 2022 Posts: 4	Here is some good information from the Tbolt USA website that relates to my issue. Thanks franque for directing me to their webpage. 4 Stroke engine crankshaft/camshaft gear ratio is always 2:1, which means that for every two revolutions of the crankshaft the camshaft will rotate through one revolution. This is a 2:1 ratio and must always remain The top cam sprocket will have twice as many teeth as the crankshaft cam-chain sprocket. Typically, Honda 50 and 50-110cc Chinese engines and Lifan 140, have 28 tooth cam sprockets. Jailing and GPX and YX 140 engines have a 32 Tooth cam sprocket. When installing a performance camshaft you may replace the cam sprocket but only due to the bolt pattern. The new cam sprocket must have the same tooth count as the original sprocket.
	0

12-16-2022, 02:22 PM	#6
dirtbkr188 Join Date: Aug 2009 Posts: 502	As long as you're maintaining the 2:1 ratio of the cam sprockets, it should work just fine. One thing to advise you of, is the size of the center hole of the 32T sprocket you have, the one I posted may not work for you, hole size-wise. You may need THIS ONE, depending on what the center hole size is on the DRATV head. You can reach out to Vince at TBolt and ask him if the above 32T sprocket will work with THIS HEAD that he sells on his site. I do know that some heads have a "cam chain guide", but I'm not sure if it would interfere with the bigger 32T sprocket or not.
	1

01-01-2023, 07:34 PM	#7
dirtbkr188 Join Date: Aug 2009 Posts: 502	Did you ever resolve this? Is the 32T sprocket you have now one with the 17mm center hole, like the one I linked to in post #6? Also, can you post a pic of the cam end where the sprocket bolts into place?
	0