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Post by jloi on Mar 3, 2019 17:46:40 GMT -5
I have a new 150cc gy6 -I'm doing a valve clearance check and my holes on the cam gear aren't where they should be when my flywheel is on the "T" mark. Anybody seen this before? Can anyone offer any suggestions. I'm being real careful with this new motor and don't want to drive it like this . I don't know enough to know if I should just line the holes up and adjust the valves there; or line the mark on the flywheel up and adjust the valves there . I rotated 360 and it was even further off which makes me think I was on the compression stroke the 1st time. I have the plug out and I'm pretty sure I felt the compression with my thumb on the spark plug hole ; lined up the mark on the flywheel and the holes in the cam gear aren't lined up completely- they're only close. I could use some input ; this is my only transpo.
Here are 4 pics . 1st 2 are with flywheel at the T mark an you can see the holes in the 2nd pic aren't lined up on the cam gear.
the next 2 pics are with the holes very close to where they should be and you can see the flywheel isn't where it should be. I taped a piece of cardboard to the metal piece on the case where the flywheel mark is supposed to be next to. You can see the mark on the flywheel is the mark that is at the bottom of the directional arrow stamped on the flywheel , which is way left of the T mark ; yet the holes in the cam gear are where they should be.
thank you
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larryhobman
Scoot Enthusiast
Posts: 117
Location: Delaware beaches
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Post by larryhobman on Mar 3, 2019 17:50:44 GMT -5
The flywheel is often stamped wrong. I have one motor where I checked 4 different flywheels and 2 of them were off. I always pull the head and put the piston at top dead and mark the flywheel with a sharpie where top dead is. Then put the head on and set the cam.
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Post by jloi on Mar 4, 2019 7:37:09 GMT -5
Larry, thanks a lot.
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Post by tortoise2 on Mar 4, 2019 11:27:38 GMT -5
I always pull the head and put the piston at top dead and mark the flywheel with a sharpie where top dead is. Or . . just insert a probe into the sparkplug hole to feel for piston TDC. If flywheel "T" mark does not align with case indicator, crankshaft-flywheel woodruff key may have sheared. |
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larryhobman
Scoot Enthusiast
Posts: 117
Location: Delaware beaches
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Post by larryhobman on Mar 4, 2019 16:15:32 GMT -5
Usually if the key is sheared off, the flywheel is not even close. I like pulling the head because you can really see the position if the piston and flywheel and adjust it where ever you want it and if you are putting in the cam the is loose anyway. You can take the flywheel nut off and see the key too.
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Post by GrumpyUnk on Mar 5, 2019 15:25:42 GMT -5
I think I would use a plastic straw down the spark plug hole, and bring the piston to TDC slowly, watching the straw get pushed out of the hole. It should stop moving out when at TDC. Ignore the mark on the flywheel until you have found the actual TCD point. Once the straw starts to draw back, you are past TDC. You can rock the flywheel back and forth, noting the straw move, halt, and move in the reverse. If you want, you can sharpy mark the 'move' points in both directions, and what is the middle point between the marks will be actual TDC.
If confused, rotate the crankshaft back and forth 'around' TDC, watching a straw or pencil move back and forth. The center between the 'move' points is TDC as the piston passes from rising to falling in the cylinder. There is a small area of rotation where the apparent movement of the piston stops as the big end of the connecting rod passes from rising to falling.
tom
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larryhobman
Scoot Enthusiast
Posts: 117
Location: Delaware beaches
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Post by larryhobman on Mar 5, 2019 22:23:48 GMT -5
Check the valve clearance With either method.
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Post by 90GTVert on Mar 6, 2019 10:58:00 GMT -5
I'd put a degree wheel on it and find true TDC and mark that on the flywheel so it aligns with the timing pointer in the case. That is after I verified that the woodruff key was present and in good condition. I'd make sure the cam was installed to align with actual TDC. Then I'd probably check the ignition timing with a timing light to see if it seems correct because otherwise I'd be paranoid about something being off. I'm weird like that though. Plus, I had one where the flywheel was not just stamped wrong but actually clocked wrong because of the position of the key relative to both the T mark and the reluctor. IIRC something like 21 degrees off when checking the mark vs true TDC. The scooter actually ran alright, but it was slower than it should have been.
In reality, making sure you know where TDC is within a few degrees and making sure the cam is set there should be OK as long as the engine is running well and you have the expected performance.
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Post by jloi on Mar 7, 2019 10:42:46 GMT -5
If it walks,talks,looks,smells and runs like a duck . Well, when enough people think something is a certain way and I hear what are basically horror stories then I don't want anymore horror stories of my own to tell. .I'm gonna start tearing this top end down today.
I was hoping not to have to do all this , especially with a brand new motor. Unlike some of you I'm not able to enjoy a scooter from a hobbyist point of view or from a professionals business perspective ; It's simply my only mode of transpo. In about 3 years I've probably got just over 2 thou in this scooter including 800 purchase.Everything from shocks to crank bearings to speedo lens. You name it I've changed it . Now a motor . I'm ready now though to stop feeding it and look around for a car.
I downloaded the template a couple of days ago so I'll go get 1 printed out and put it on a disc.
While I'm at it I'll head over to H Freight and get the small torque wrench again .
thanks everybody
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Post by GrumpyUnk on Mar 9, 2019 13:33:00 GMT -5
Why are you fiddling with the cam timing? Is there a problem?
If the cam was as 'behind' as shown with the piston at TDC, the engine would likely very low on power. Do you have a low power situation?
If it is running well, leave it alone, no point in fixing things that are not broken.
tom
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Post by jloi on Mar 9, 2019 14:39:41 GMT -5
I checked valve clearance only because it was recommended in Brents' new motor early maintenance suggestions in a "FAQ" I read or I wouldn't have known to do it . So when I checked I found that the timing mark doesn't sync with holes in cam gear.
I wasn't 100% satisfied with idle / carb adjustment either before I checked the timing ; couldn't put my finger on it , but also power wasn't quite right. Wasnt extremely off I just wasn't satisfied it was right.
Anyway with all the examples of bad flywheels etc. and how critical valve clearance is I want to make damn sure I don't ruin a new motor straight out of the factory. So I'm gonna be tearing head off today I hope. I got parts to make a piston stop etc., made a degree wheel . I'm tryin to do things smart and not take chances. I haven't worked on vehicles in about 30 yrs till I got this scooter about 3 yrs ago. So I'm way out of the loop. PLus , small pension , no money to waste.
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Post by GrumpyUnk on Mar 11, 2019 10:45:35 GMT -5
Y9ou are {IMO) going way too far. You can get a pretty darn close TDC using a straw/coat hanger down the spark plug hole. You'd rock the flywheel back and forth, noting the 'end' where the piston starts to move(mark A), rock the other direction until the piston starts to move(mark B). TDC will be halfway between mark A and mark B. The accuracy gotten by that method will be so close a degree wheel, etc, are a waste of money & time, as would be removing the cylinder head to obtain the same mark.
You should be able to get a repeatable TDC using the above method, used in car & truck engines for years. Used by hot rod mechanics, and back yard mechanics along with red neck mechanics from days of the Model T. It works. It uses readily available equipment. A degree wheel is more useful for observing & recording cam timing. I have yet to use one since 1964 when I started muddling with engines.
There are few examples of bad flywheels, or erroneously marked flywheels. Just a few that I have heard of. The valve clearance will be fine if you set it properly no matter how the cam is timed to the crankshaft. Unless your chain/cam is so far off from TDC that you have valve:piston interference, it should not matter, and if you do have the valves meet the piston, the engine won't run before that anyway. When you assemble the cam chain to time the cam, it is good practice(after releasing the cam chain tensioner) to rotate the engine two complete turns. That will take it through all 4 cycles, and operate the valves the way they should work when the engine is running. If you cannot rotate a full 720 without problems, then NOW is the time to find out before trying to crank & fire the engine. The 720 also checks that the cam is truly timed properly as it should align with the cylinder head top when the flywheel is at TDC. Again, then is the time to re-set and investigate any discrepancies.
tom
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