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Post by florida on Feb 2, 2016 1:04:58 GMT -5
scooter is a 2011 139qmb longcase Gorilla motorworks 50cc with 8000 miles. Modified to 100cc bbk, a9 cam. orange cdi box, cone filter etc. I did all the work myself and have a tidy workspace so it was rather easy for me.
The other day I mistakenly used the .128mm/.004in. feeler gauge to adjust my valves rather than the .038mm. on both the intake and exhaust.
The result was my bike ran rather badly and at about mile 10 the timing chain came off.
After inspecting the bike and verifying that the timing chain came off I am prepared to fix it.
Can someone familiar with this repair please give me a rundown of what I need to do?
thx, I have all the tools including a beam style torque wrench.
The timing chain tensioner and guides ( the two long black plastic pieces ) were inspected when I installed the bbk 1800 miles ago and they are in good shape. Since the scooter was only driven for 10 miles with the valves misadjusted I don't think that they could have been damaged.
I plan on:
-removing the engine from frame and taking the head and maybe jug off. I would like to inspect whatever the cog is that turns the timing chain and in turn the cam. I want to make sure that the chain didn't damage anything down in the engine. What could have been damaged?
-inspecting the timing chain for wear and damage.
-taking out the timing chain adjuster and inspecting it for wear and indication of malfunction causing the chain to fall off.
-inspecting the chain guides for malfunction and wear.
-Should I space the piston rings again?
-inspecting the cam for damage.
-reinstalling chain and installing the chain adjuster.
Is there anything I missed or something I should address?
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Post by steve on Feb 2, 2016 11:03:29 GMT -5
Don't take the jug off. You will have to hone the cylinder if you separate the piston from the cylinder.
Honestly, the chain probably just slipped off the sprocket, and you can work it back on there by just removing the cam. You can see if the sprocket is damaged by flashlight.
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Post by steve on Feb 2, 2016 11:10:49 GMT -5
You just need to make sure the flywheel is aligned at the "T" mark.
Remove valve cover
Remove chain tensioner
Remove rocker arm assembly.
Remove the cam.
Work the chain back on the sprocket. You can use a long screw driver, or a coat hanger.
Then, put the cam, and rocker arms back on. Make sure the cam is aligned at TDC position.
Put the chain tensioner back on, and the valve cover. And you are done.
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Post by steve on Feb 2, 2016 12:48:38 GMT -5
I forgot to tell you, the chain is driven by a sprocket on the crankshaft, then goes to the cam. If the sprocket on the crankshaft is messed up, you will be able to see down there with a flashlight, if it's damaged, you will have to replace the crankshaft. It probably just came off the sprocket. Your rocker arm assembly may have broken. Or your cam bearings may have gone. You will just have to look when you open her up.
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Post by florida on Feb 2, 2016 13:47:55 GMT -5
OK steve, thank you. Ill get back after I'm done. Is Columbia the capitol of SC? I used to live on Hilton Head in the mid  's. My little sis and I used to walk with my father as he pushed his ducati from our new house and past the main gate of the plantation we lived in. |
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Post by rcq92130 on Feb 2, 2016 14:45:03 GMT -5
A 150 may be designed completely different, but had the same problem.
After a lot of wasted time with a long screw driver and a coat hanger, finally gave up and removed the jug. It was then pretty easy. If doing this, make sure you do as follows so you don't have to deglaze the jug:
take off all the top end stuff
wiggle the jug till it's just free from the crankcase gasket (you will need both a new paper gasket there, and a new head gasket)
rotate the flywheel 'till the connecting rod is all the way up (should be TDC)
GENTLY press the piston down in the jug JUST SO YOU CAN GET TO THE GUDGEON PIN.
remove the circlip and slide out the gudgeon pin.
the piston is now no longer fixed to the rod, and the piston & jug will just lift away together. If you don't jostle the thing, so the piston remains more or less in the same position, you can then - when done - just put it together in reverse order. Since the piston isn't disturbed, no honing needed. Just put it all back together.
But maybe you will have better luck then I getting the chain back on w/o removing all that.
Seems very, very odd the chain was on and then came off. Something had to have caused this ... as Steve said, maybe the sprocket teeth, maybe something else. But it shouldn't just "come off". Incorrect valve clearance will not cause this. Is the tensioner working?
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Post by steve on Feb 2, 2016 15:08:35 GMT -5
Cola is the capital.
I'm curious as to what happened.
I had the chain come off the sprocket while installing a BBK. I was able to get it back on without taking the cylinder off. It will save you a lot of time to not take the cylinder off.
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Post by urbanmadness on Feb 2, 2016 21:31:53 GMT -5
The only problem with all of that is...... Was it running? I think these motors are interference and if they loose valve timing, pistons hit valves and cause all sorts of nice things to happen. I would think about pulling the head and make sure the valves are ok and not bent.
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Post by florida on Feb 3, 2016 11:31:42 GMT -5
IDK yet if the tensioner had failed.
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Post by florida on Feb 3, 2016 11:44:52 GMT -5
The only problem with all of that is...... Was it running? I think these motors are interference and if they loose valve timing, pistons hit valves and cause all sorts of nice things to happen. I would think about pulling the head and make sure the valves are ok and not bent. OK, piston could hit valves if valves have lost timing. Heres something you may be able to help me with: If you read my entire first post, -My valves were mistakenly adjusted to .128in rather than .004 by me. Both intake and exhaust. If they were adjusted to a bigger clearance than manufacturers recommendation, would the valves be going further "down" than normal, enough to hit the piston and get bent? I'm new to small engines so this is exciting to me. How much room is there in between the top of the piston and the valves? 10cm, 1 inch? Would I have heard any terrible noise coming from my engine with the misadjusted valves? What would it sound like? |
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Post by florida on Feb 3, 2016 11:51:16 GMT -5
Urbanmadness, I read your bikes stats that appears at the bottom of your posts, did you happen to get "upgraded valves" after they were damaged by the piston?
What does the manufacturer say about performance gains?
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Post by steve on Feb 3, 2016 14:04:30 GMT -5
If you put a larger gap, the valves would not be opening enough.
If the chain came off while it was running, the valves would have stopped opening at all, so I don't think anything would have gotten bent.
You will find out when you get it started again, but I doubt it.
Set the valves again while you are in there.
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Post by rcq92130 on Feb 3, 2016 17:56:22 GMT -5
Not true, Steve.
If the chain came off or failed, the cam would stop rotating. The valves would then stop IN THE POSITION THEY WERE WHEN THE CHAIN FAILED.
Open valves would remain open until the piston came back up. Then, when the piston smacked the valve, either a hole would be punched in the piston or, more likely, the valve would be bent back out of contact.
In any case, the chain "coming off" is a very odd condition (other than, as you said, during a time, like doing a BBK, when you are messing with the thing). Falling off while simply riding indicates, to me, somehting else causing this. Maybe the cog teeth. Maybe the tensioner. But something!
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Post by onewheeldrive on Feb 3, 2016 19:04:24 GMT -5
The other day I mistakenly used the .128mm/.004in. feeler gauge to adjust my valves rather than the .038mm. on both the intake and exhaust. My valves were mistakenly adjusted to .128in rather than .004 by me. Both intake and exhaust. Which one is the typo? |
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Post by steve on Feb 4, 2016 6:35:30 GMT -5
The other day I mistakenly used the .128mm/.004in. feeler gauge to adjust my valves rather than the .038mm. on both the intake and exhaust. My valves were mistakenly adjusted to .128in rather than .004 by me. Both intake and exhaust. Which one is the typo? With how those lobes are rounded, I would think the valves would close. With no chain on the cam, the pressure from the valves would turn it, I would think. Maybe you are right, and they could get stuck open. He will find out when he gets it back together. I wouldn't take the piston out of the cylinder, unless he absolutely has to. I am curious as to what made the chain come off. Please report back as to exactly what happened. |
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