Big boy scooter - at wits' end

[Walterp79]

Please help I am desperate. I blew my gy6 engine, I think the timing was out. The piston burnt and the chain adjuster broke. So I replaced the piston, barrel, head, chain adjuster, chain guides,oil pump. It cranked without starting. Then I cleaned the carburettor. It cranked without starting. I checked the fuel flow. It spurts when I turn the petrol. The carb bowl has fuel. I checked the spark. I also did the valve clearance properly. But it has a weird plunging sound when it cranks. Any ideas?
Oh, I also opened the starter motor and cleaned it. I thought that the plunging sound could have been oil inside the starter. There was some black stuff at the bottom. Not sure if it was oil.
I have 5 bar of compression. The guys here says that's the best I can hope for it should start.

[Jack 807]

Is there fuel on the spark plug after you try to start it? Have you tried spraying a little starter fluid in the air cleaner to start? How old is the fuel?

[Walterp79]

Thanks for the response 😁 I did try other fuel but this came from a canister so now I went and got fresh fuel again. That didn't work. I tried spraying carb cleaner into the air cleaner because I did not have starter fluid. I saw this in a video. I don't know if I should get starter fluid specially? The spark plug is also dry. The spark looks tiny but regular. Is that something that can happen? That the spark is too small? (scraping the bottom of the barrel I guess) I understand why you suggested the spark plug though. That plunging sound does sound wet, but maybe that's the new piston that has to work in🤷 also, I've been doing these things with the air cleaner completely off till now. I thought the engine should start without the air cleaner attached. I did put it back in now before I did these things. And the exhaust is off but I can't see how that could be a problem?

[Jack 807]

The dry spark plug suggests there is no fuel getting to it. You can pull the plug and drop a little fuel into the head replace the plug and see if it pops. What kind of carburetor is on it?
What are your valves set for? Mine are .004 for intake and .005 for the exhaust. Were the timing marks in the correct position to set the valves? What type of scooter is it? 5 bar equals about 72 PSI My scooter has about 145 PSI which is about 9 Bar. You replaced the piston did you put the rings on it, so the ring gaps are staggered?

[Walterp79]

So I removed the spark plug and sprayed 5ml of petrol into the hole where the spark plug goes with a little syringe. When I replaced the spark plug and cranked it over, the petrol sprayed out of the hole where the exhaust goes and there was no pop sound. I have my original gy6 carburettor. It is on a Chinese big boy scooter. I will check a few videos on how to fix a dry spark plug. I never knew that there should be petrol on the spark plug. Even though it does make sense to me now 😂🙈 I am pretty sure the ring gaps are staggered. I am in South Africa, and the mechanics I talked to here says the petrol is not that good which contributes to the (lower) compression I can expect. When I put the cam on, I put the flywheel on the T and made sure the gear is in the correct position, with the big hole centre top, so that should sort the timing issue? I set both valves at 0.005.🤷Thank you so much again. 👍👍👍

[Jack 807]

Are you sure the valves are fully seating and you don't have a bent valve stem? Or a small crack somewhere creating a vacuum leak? Here are some links to help you out.

https://gotscoots.com/gy6-engine-101/

https://www.buggydepot.com/tech-cent...ad-center-tdc/

https://www.buggydepot.com/tech-cent...ross%20pattern.

[Walterp79]

The head is also new and I got it with the valves already installed.(everything is new 🤷&#128584. I didn't check the valves though. I just installed the head. I also got new gaskets, but the valve cover didn't have a gasket. I put some silicone where the valve cover seals for a gasket. From the timing links you sent I think the timing must be fine because I also did this job a million times trying to get more compression. What I can say is that when I put the camshaft in, it did feel to me like the chain might be a bit too tight because the shaft lifted up a millimeter or so on the other side I thought. Obviously before I bolted down the rocker arms etc. 🤷 The only move I have left for the engine is to get a professional to put it together for me again.

[Jack 807]

With the head off rotate the crank until you are at tdc and take a look at the valves then slowly rotate and see what the valves are doing in relation to the piston position. What valve is open what valve is closed and where the piston is. I think this will turn out to be one of those "how did I miss that?" Please don't overlook the carb as well since you said the plug is dry. Maybe give the carb a good cleaning just to rule it out? The one document explains it very well the GY6 101

[Walterp79]

So the first thing I noticed when I took off the valve cover is that there's oil running out. My limited knowledge tells me that this should not be happening? There is no valve clearance on the exhaust valve anymore either. So I think I should start by opening up and making sure that the rings are staggered and then put everything back together nicely? And then start it with the valve cover off and see what it's doing?

[Jack 807]

Yes, Take it all apart inspect everything make sure everything is clean no metal shavings etc... you may have to unfortunately replace all the gaskets again. Make sure the cam sits flush I think you mentioned something about the chain seeming tight.. I think this time you will be successful.

[Walterp79]

Do you think I should just get new gaskets, or do you think that I might see damage to them and then I will have to replace them?

[Jack 807]

If they are cheap enough, and available locally I would just buy new, I typically don't reuse gaskets. Here's a good video on ring gap placement so you can see how yours line up

https://gy6-info.page.tl/Piston-rings-install.htm

[Walterp79]

So I checked a very similar video and I clocked the piston properly. Or so I thaught. The oil is still gushing out of the valves. So, I am going to take it apart again. First get gaskets and then try again. It can only be the piston rings in my mind?

[Jack 807]

or head gasket.