GY6 valve head replacement

[Larry33]

I have been working on this yerf dog scout cuv for over a month and still only have 1/2 throttle.

Not sure if it is a bad valve or what. It just runs rich and has no leaks around carb.

I have a new valve head and want to know if there is anything I should watch for or whatever when taking out the old one and putting in the new one. Also how tight does the head have to be?

Thanks

[kliff]

If you are referring to the cylinder head assy, the torque specs are"
head bolt main 180 inch lbs
small 84 inch lbs

I also like to spray both sides of the head gasket with CopperCoat. Use the aerosol, NOT the brush on. Available at most auto parts stores.

[chuckorlando]

You sure the timings right on the one you got and valves adjusted

[Larry33]

I decided to give up on this peice of junk. It looks great but like everything else from china they dont last. I tried to get the head off and one of the small bolts on the side refuses to come out and the head started to strip. So I just retimed it again.

After 1 month of working on it everyday I give up. I have set the timing atleast 10 times. I feel the piston come to the top and check the flywheel and it is on the T mark, set the valves at .002 in and .003 out and still is real hard to start. Have to play with air/mix screw and idle screw to get it to start and will not restart.

When idleing it is great...give it gas and it bogs at 1/3 peddle....I dropped it off at a friends to see if he could do something but it sounds like he has no idea with this type of set up.

Today I noticed a small amount of white smoke coming out of tail pipe but wonder if that is because I sprayed wd40 in the head and let it sit. Had lots of smoke when I first started it after the wd40 yesterday. Today very very little smoke

Sprayed all around carb and nothing so no leaks. He is going to take carb off again..20th time and see if he can find anything.

[chuckorlando]

First off bro, dont give up man. I just refuse to let a china motor beat me.
http://www.youtube.com/watch?v=TJkNsxlA6v8&feature=plcp

Thats the only engine that almost beat me. Nothing but problems. But the worst, was no parts supply for it. So I beat it and done a motor swap.

That being said, I would never ever ever pay attention to timing marks on a gy6. They are off way to often. Stick a straw or what ever in the spark plug hole, roll the piston till it's all the way up. Now make sure the big hole on the cam is pointing up and both valve are loose. It's timed. Remember, if the valves aint loose, your 180 out.

Va;ves should be .005 and .006. I run both at 5. You have them super tight bro.

Again, just step back and relax, then head back in. Dont get beat by a slant eyed fool. He got it running, you can get it running

[chuckorlando]

If you know where ride royal blue is at, we will have a whole group up there next month. If you cant fix it, bring it down and I'll see what I can do for ya

[Larry33]

Loved the video.....It is getting close to that point.

Thanks for the insite. Everywhere I read says to set the valves at 002 and .003. Only the high performance stuff was 005 006. I noticed when the gap is larger it starts better. I take a small flathead screw driver and insert in the spark plug hole to feel the piston come to the tdc and then adjust the valves. The flywheel mark is in the right spot so etched a line in it to also see where it is at and they seem to line up well.

What advances the spark on these things? The stator is a 6pole. Ordered and 8 from bmi but they sent a 6. 6 pole is what was originally on it to begin with so that is all new.

I just ordered a 49cc scooter...also a chinese probably junk vespa clone to run around the camp ground. Hopefully I will be able to keep it running and will adjust it often rather than waiting this long.

I know it is something with the timing. No back fires but just have a feeling. Though about putting an electric fuel pump on it but refuse to pay 80.00 for one. The filter never seems to fill much. Just a small bit in the bottom. It is new also. Waiting for another vacuum fuel pump to arrive in the mail. Everything on it now is new but the piston and rings and is still running rich and black carbon on the back end of the dump box when it is in the up postion while working on it. Does the air filter being off while adjusting make any difference. I got a new free flow filter for it.

I wont let it beat me. I have rebuilt so many things but this one has been a challenge

[Larry33]

I have a question on timing. I did not read it anywhere but is there a starting point?

I have everything lined up and piston tdc and someone asked*** do you time it on the intake stroke or the exhaust stroke?***

The compression is only 60 using the compression gauge that scres into the plug hole and also 60 with the rubber tip type........any ideas???

[chuckorlando]

Theres no such thing as intake or exhaust till the cam is in. The cam sets the timing.

Piston up, cam hole up, it should be in time or with in a tooth either way. If you pay attention to the flywheel marks, then line them up before you set the cam so they are usable next time.

[Larry33]

We can not figure why compression is only 60psi using 2 diffferent types of gauges and wonder if the timing is all messed up. It was running after you could get it to start, idles and still only 1/3 peddle before bogging, so redid the valves at 006 as recommended and and re-timed it again and still have only 60psi and will not start. I have 2 other people working on it now. One is a lawn mower guy and they both say that the timing is off.

Could the yerfdog scout gy6 howhit whatever it is be different timing than the regular gy6?

[Larry33]

The one guy noticed when at tdc and you start to rotate the fan that it takes a while before the intake valve starts to open.

[chuckorlando]

It only times one way. Piston up cam up. But like I've said, I have seen more than one gear pressed on a cam wrong which can make it very hard to time. Any single cyl 2 valve head only has one way to time it.There is no physical diffrance piston or crank wise on compression stroke or exhaust. The piston and crank dont care it's all in the head.

It's gonna take just as long as it takes to complete the rotation. No matter how you set it, it will take just as long to get from point a back to point a

[chuckorlando]

Others can feel free to chime in here. Seems I post in a thread and it ends up just me posting in a thread. I aint sure what thats about

[Larry33]

maybe I will put the original cam back in and try it all again. I got it from bmi on ebay.

[metalstudman1]

Originally Posted by chuckorlando

Others can feel free to chime in here. Seems I post in a thread and it ends up just me posting in a thread. I aint sure what thats about

CHIME-CHIME!!!! Nothing else to add that you haven't covered.-It does sound like the cam sprocket is pressed on incorrectly or something wrong there(never had that issue though). I doubt the timing has the compression screwed up so bdad that it's dropped the psi that low, unless you have a bad seat or bent valve- 60 psi is pretty low, but with good spark and fuel that will still run.
I guess pulling the head & jug is out of the question? Would be nice to pin point why it's only 60 psi.

[Larry33]

I got the new rings and piston for the cuv...now I am finding it is a real pain trying to get the jug back on. This engine is in the cuv so real hard to work around.

I noticed one valve was somewhat burnt and coved in carbon etc. so I am replacing the head with a new one and new valves.

Which is the bigger valve, intake or exhaust? When looking at the original piston that is still in the engine, the IN is on the bottom which is the exhaust side. If I turn the piston over the in would be on the top but would be printed NI so am a bit confused on this.

Tried for 3hrs to get the jug on and no go. Any suggestions. I read the article about it and it sounds so easy. Seems the bottom rings just are the hardest to get the 3 all in.

Thanks

[GX150]

Intake is up top and exhaust is on the bottom.

[Larry33]

I replaced the jug and piston and rings. The old piston had a small groove worn in the exhaust slot on the piston. It appeared to be upside down because the slot on the piston has a larger slot for intake and smaller slot for exhaust. I turned the new piston to match the size of the valves in the head. I tried the valve lash at 006 as one post said and it would not start. Tried them at 004 and I can get it to idle but that is about it.

[Larry33]

Finally got it running real good, just hard to start and have to back off the idle stop screw all the way and slowly turn it down and get it going. Revs good and moves good but still will not climb a hill.

If I tighten up the valves more, should that give it more power?

Where can I find a carb that will work on this cuv?

thanks again for all the help

[Larry33]

I got it running much better and it is climbing the hill if only it would start easy. It has a real hard time getting past TDC and is rather hard to turn it past TDC by hand.

I bought another new carb with electric choke. Bought a resistor and hooked it up with resistor on ground wire. Valve lash is .005 on both...good gas flow, and good spark. This carb seems to be more sensitive with the air/mix screw. I turned it out about 2-2 1/2 turns but still have to screw idle screw out and apply throtle by hand till it starts.

The timing marks all lined up when the piston just gets to TDC. The piston stays top for a moment and then moves down. Could the cam be off a tooth and retarding it?

I noticed when running wide open it still seems to bog some at WOT but much better than it was. Any suggestions?

Thanks again