Chinese 125cc ATV not starting

[Gwbarm]

You are right, not really much to that piece, if it is what you say I have never seen one before , but don't work on pit bike engines much.

[EugenM]

I've never seen anything like this before either, but I don't see that mechanism having any other role than to prevent the camshaft from rotating in the opposite direction...this is to prevent the timing from shifting...

[Mech]

It's not going to be to prevent the engine turning backwards.. The mounting bracket isn't tough enough for that, and it would damage the cam chain.

It will be for a de-compressor. I see that the cam has a flat machined onto it right next to that thing. I'd suspect that has something to do with it, and I'd suspect there is a part missing..

[EugenM]

Mech I thought the same thing, but if you search on the internet you find countless pictures of this type of cylinder head and  doesn't seem to be anything missing from there 

https://www.motorkit.com/en/spare-parts-yx125-140cc-/23933-cylinder-head-for-yx-and-lifan-engines-125cc-with-27-and-23mm-valve.html

[Mech]

Yeah I couldn't find any pictures of it.. I still think it's to decompress somehow.

Could that plate get turned over or around ? I have a feeling the flat bit on the cam shaft is going to be there for some reason.

I found parts manuals for the motor, but there were none of the lifter or the lever shown.

[Notallthere]

12 hours ago, EugenM said:

Mech I thought the same thing, but if you search on the internet you find countless pictures of this type of cylinder head and  doesn't seem to be anything missing from there 

https://www.motorkit.com/en/spare-parts-yx125-140cc-/23933-cylinder-head-for-yx-and-lifan-engines-125cc-with-27-and-23mm-valve.html

Yep that's the same head spot on. 

 

I also see that there's a manual decompressor for it. I wonder if it could be fitted to mine. https://www.motorkit.com/en/spare-parts-skyteam-125cc-engine/23195-lifan-yx-125cc-engine-manual-decompressor.html 

[Mech]

I saw overhaul kits for them. They had kits for models with and without the auto de-compressor. The de-compressor kits had that bracket and the plain kits didn't.

[Mech]

One of those rockers looks like it's better made than the other. I wonder if it's not genuine and causing the problem. It looks like the other rougher rocker has a bit of over-hang to the side. I wonder if that's meant to get held up by that bump on the sprag clutch thing.

[Notallthere]

That's a good eye. I will have a look in the morning cheers Mech.

[Notallthere]

On 4/3/2023 at 9:14 PM, Mech said:

One of those rockers looks like it's better made than the other. I wonder if it's not genuine and causing the problem. It looks like the other rougher rocker has a bit of over-hang to the side. I wonder if that's meant to get held up by that bump on the sprag clutch thing.

Mech there isn't any problems with anything catching or interfering with each other.

[Mech]

Well I think if I was there I'd have a magnifying lens out and I'd be inspecting things minutely(including the rockers) for signs of where they mate up or rub on one other, trying to figure what is meant to hold the rocker up.

I'm pretty sure that mechanism won't force the valve open by force, it will just prop it up after the cam has lifted it, and, it's likely to get the prop trapped under there till the next valve lift when the prop flicks out of the way again..  that big spring I think does that flicking out of the way. It's likely/possible that the propping up of the rocker happens when the engine bounces backwards as it stops.

Not sure at all about how exactly because I haven't seen one of those before, but those are fairly common operating principles for auto de-compressors.

Edited April 5, 2023 by Mech

[Gwbarm]

The rockers do seem different, one is more polished than the other, maybe a replacement, when it was together and you rolled the engine over did it appear to do anything.

[Notallthere]

Right sorted the two rings on the left are the directional bearing and when it rotates the lobe gets stopped at the top by that silly thin piece that goes between the two shafts. So the cam rotates and the decompressor stays put, so the side of rocker is lifted and released by the flat on the left. So now have to work out why it's missing the decompressor when the two rocker arms are the same apart from the rough casting on the one, but they do have the same casting number on them. Thank you all for your help and input.

Cheers

  

[Mech]

Sounds right.. I think it only happens as the engine bounces backwards as it stops.

So I wonder whether there is meant to be some different rocker that hangs over the edge of the cam face enough to get held up by that flat.