Tight Timing Chain

[GrouchyOle'Man]

Hello, On my 150cc GY6 after installing new chain guides (but not the tensioner) I find that my chain once installed on the CAM sprocket is SO tight, that the cam cannot even rest on its bearing journal on the end opposite the sprocket. I have had the cylinder off and the head off numerous times. Videos I have seen show substantial SLACK in the timing chain allowing one to easily correctly time the engine. I tried it with the cylinder and head dowels placed correctly and the 2 long head bolts in place and snugged up. There is some slack, but not enough. Has anyone else experienced this?

[crawford]

Did you check old parts with new? There really shouldn't be a big difference between old and new it really sounds like there is a wrong part to me to be that tight.

[GrouchyOle'Man]

Hi Crawford, I suspected a timing issue with this engine as it was not drawing fuel out of the carburetor; so it had a no-start condition. I have installed a few new parts, but no new engine parts. Today I found a blue link on the timing chain that would not rotate as easily as all the other links and was kinked. I straightened it out. I do not know if the chain was ever tampered with. Everything is as I found it except the cylinder base gasket and head gasket which I replaced since I had the top end of the motor off. They were identical to the ones they replaced. Even after straightening out the blue link, the same situation exists. The inside cam bearing is above the journal it rides on about 1/2". Also, I cannot properly set the cam in correct timing position. It is always off by one tooth. Either side of the sprocket, I get the same result. Off one tooth and camshaft not seating. So, the only parts to compare OLD to NEW are the 2 gaskets and chain guides. I may opt for counting the links in the chain to see if one was previously removed to facilitate tightening up the chain. I do not know yet if a new chain will fix this. The gear on the crank the chain rides on is suspect also. I fear it is quite worn. This scoot has over 11K miles on it according to the odometer.
Again, this is with the automatic chain tensioner NOT installed. The old timing chain guides had some damage to them and I replaced them. I initially thought a piece of plastic off the bottom of the lower guide was stuck in the timing chain gear on the crankshaft, then I found the kink in the blue link. At any rate, the chain seems to be too short to properly reinstall.
So after trying to assemble the top of this engine numerous times without success; I guess my next step is to count the number of chain links in my timing chain and compare it to a new one. I just counted 45 links and the chain is about 11" long. I have seen new ones for sale that are exactly that size.

[crawford]

My question before you has any body been in it before did you get it this way ?

[Roscoe]

Something isn't right. Is the chain seated on the crankshaft gear?

[GrouchyOle'Man]

Hello crawford, Yes, the scooter had a previous owner. It just quit running in the rain one day this summer. My Grandson was riding it.

Hi Roscoe, Yes, absolutely something was not right. The chain had a slight kink in it. Keeping the chain on the crank gear has proved to be quite a challenge. The kink in the chain could have been from when it possibly jumped time a couple months ago. I sprayed lube on it and let it soak overnight and today it was less stiff and I was finally able to assemble the top end of the engine. I also timed it and adjusted the valves again. There is a very slight gap where the timing chain rides on the teeth of the cam gear. Hopefully she will not jump time, but we will see. If it does, it is going to need a new crank gear and/or timing chain. I am going to install the fuel system and let you guys know what happens.

[crawford]

It really sounds like you need to count the links on old one and see if you could get another. I believe you will be doing it again maybe stuck and will be walking it back no fun. Do it right the first time you chain is bad and it will fail just trying to save you extra time redoing the job again.

[GrouchyOle'Man]

Crawford Lubing the chain helped. I was able to install it with the cam and rockers, etc. Now though...and this is odd...the exhaust valve KEEPS coming out of adjustment; not the Intake but the exhaust. It stays open a small amount sometimes when the Intake valve is opening. Also, after assembled engine does not start. Just to let you know the adjuster and lock nut are in good condition and are not stripped. I do not overtighten the locknut when I set it.

[crawford]

Try squirting some spray lube on valve stem while you open and keep closing valve even if you need to tape valve closed keep doing it you most likely find valve start moving freely again you may have built up carbon inside of valve guide.

[jerome_merritt]

Originally Posted by crawford

Try squirting some spray lube on valve stem while you open and keep closing valve even if you need to tape valve closed keep doing it you most likely find valve start moving freely again you may have built up carbon inside of valve guide.

Hello Crawford what type of tube?? I am having the same problem

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[GrouchyOle'Man]

Hi Jerome If your exhaust valve guide seems ROUGH as the exhaust valve travels up and down in it, use some strong solvent on it to break up the carbon and clean it. The stronger, the better. If the valve is removed, of course the job will be much easier. There are a variety of solvents out there you can use to break up and clear away carbon on the guide and on the valve stem itself. It may take a few rounds of using it, but after a time, it can be cleaned.

[jerome_merritt]

Originally Posted by GrouchyOle'Man

Hi Jerome If your exhaust valve guide seems ROUGH as the exhaust valve travels up and down in it, use some strong solvent on it to break up the carbon and clean it. The stronger, the better. If the valve is removed, of course the job will be much easier. There are a variety of solvents out there you can use to break up and clear away carbon on the guide and on the valve stem itself. It may take a few rounds of using it, but after a time, it can be cleaned.

Thanks

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[jerome_merritt]

Originally Posted by jerome_merritt

Thanks.....But if they're stuck I should hear some restriction noise right??

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[GrouchyOle'Man]

Hi Crawford The valve moved freely through the guide when I reassembled it and seemed like it was not sticking when I put it back in the HEAD as I had removed the cylinder head and cleaned the carbon out. You may be right about carbon in the guide though. I did not pay that a lot of attention. We had run some fuel additive in the gas and there was not much carbon on the head or piston. Trying to start the engine with Gunk Carb/Choke Cleaner aerosol spray had broken up even more carbon. It has all been removed. I have adjusted the exhaust valve when the Intake valve is open on the Intake stroke, and adjusted it when the Piston is at TDC. Once I try to start the engine with the electric start, the clearance closes up and the lock nut and set screw for the exhaust valve become very, very tight...even tighter than I had tightened it. That results in the valve being partially open. I do NOT overtighten it when I set it. I know better.
The engine STILL does not fire up or start. I may check the flywheel key today, even though I had set the timing initially with the head off the engine so I could see the piston, not just gauge it. I pulled the head to inspect the condition of the valves and springs and to clean the carbon.

[crawford]

could valve be a site bent just enough to hang up? when apart did you try moving valve up and down with no sticking?