Post by KrisW on Jul 20, 2019 14:24:19 GMT -5
Before I get started on this a few words about myself...
I'm 61..5 time certified Master Mechanic, worked on just about every form of small-large sized engines for over 50 years, AS in electronic Engineering, 10 years repairing Avionics in the Marines, and I have over 30 years working in gthe Automotive industry, fixing everything from Scooters to Mack trucks..
I have a motto:
If I cant fix it..it ain't broke.....
\
And up until this week that motto applied. This is what happened:
I have a Tao Tao scooter, big-bored with a 47mm cylinder, 20mm carb, stock ignition and a canister muffler.
So far so good, right? A nice basic hopup kit. I've had electrical issues in the past that required replacing the battery and voltage regulator, and a month ago the pickup in the Stator died, was replaced and ran fine after that. Until last Sunday, the 14th.
I should mention that the engine has been down on power lately, due to a couple of apparently hot runs, but still ran and got along pretty well. I was on the verge of re-ringing the piston to get the power back, but otherwise it was doing pretty well.
Driving through Greensboro at 25 mph, no traffic, in the evening and it suddenly sags for power, catches itself and goes back to full song, then sags again. I turn around and head for home, just in case something major is going on, since I don't want to be stranded 1.5 miles from home. I get about a block and the power keeps dropping and then it just dies. No rattling, no banging, no strange noises, it just shuts down. I pull over and let it sit for a while and try a restart. It cranks 2-3 tries before I manage to get it started but it's super weak and then just fades and dies. So I hang my helmet on the handlebar and start the long push. Fortunately half the trip home has a long downhill and I get a coast, but it's a good workout.
Next morning I check things out. It has spark and gas, fires while cranking but won't rev and get running, just fires as it turns over. So, good spark, and probably good carburetion. It seems to have decent compression, with moderately strong exhaust and intake pulses while cranking. It get one start, for about 8-10 seconds, but it's struggling and just fades out. So, now I sit and think about it a bit. The plug is very sooty, like it's flooding, but that's probably due to my pumping the accelerator pump with the throttle to try to get it primed while cranking. I begin to think I've overheated the engine enough to where the rings have lost seal, and it's finally TIME. I order another cylinder kit with head and gasket set, toss in a new carb, just to make sure, and get the new intake snorkel and figure I'll replace the rubber lines with neoprene and do the fuel filter at the same time, just for the sake of it. While I'm waiting I go through everything, rechecking the Stator and ignition, even putting in my backup ignition module and coil just to double check, and nope, no change, still cranks/no starts the same, so I go to default ring damage mode.
I get the bore kit, and do a careful look at the old parts. yup..piston skirt is speckled and scored on both thrust and drag sides, minor scoring of the bore, rings don't appear to have as much tension as I'd prefer and the exhaust valve leaks slightly when the chamber is filled with fluid. Typical overheating damage. The Con rod roller bearing has a tiny amount of play, about what would be necessary in a roller setup, less than .005", and allows a slight rocking motion of less than 5 degrees, so I label it as good and press on. Crank bearing have about 1/32" of end play, just enough to be felt, and I figure as the engine warms up that will tighten up as things expand, so I give that a passing grade as well. No oil leaks noted except around the head gasket, where it might have been leaking combustion gasses after getting too hot. Everything goes together properly, I set the cam by the marks at TDC, double check it about 6 times to make sure, put everything together by the book using a torque wrench for the head studs and bolts.
I set the carburetor at 3 runs out on the idle mixture, 3 turns open on the idle speed screw. Fresh oil and a fully charged battery.
I try to crank it and it does the EXACT SAME THING!!!... Won't start..runs along as it cranks over but not enough to accelerate to even idle. I get it to start once using Ether and it runs for 5-8 seconds and shuts down, and that's IT. I just went through everything again, even installing a backup stator I had on the shelf, just in case, and no improvement. Hooked up to a car battery to get the best cranking, it still won't go.
SOOOooooo.... I finally ran into something I can't fix....Any suggestions would be appreciated.
One last thought, which may, or may not, be important. The flywheel seems to be advanced about 8 degrees from where it should be at TDC. I get TDC set by the position of the piston, and centering the crankshaft rocking across the dead spot at TDC, and the T mark is always well advanced. Probably as much as 8 degrees. This also advances the ignition timing, I think, causing 'chuggle' or difficulty spinning over as the piston almost stops as it fires on the compression stroke. It will spin, stop, continue, pause etc etc etc, unless I give it gas to keep it from firing early, at which point it will go into run-on while cranking but will not start. Wondering if the flywheel and ignition exciter block being advanced that much could be causing a lot of the problems I've been having. And if they are, then a new flywheel may solve the entire situation. Only problem is..if I get a new flywheel won't it locate off the woodruff key in the same exact orientation , and won't that just cause the problem to continue?? I've never seen any other scooter do this chuggling during startup..only mine, so it seems this flywheel being advanced the way it is could be a major influence for my problems.
I've been tempted to take a grinder to the woodruff key slot in the flywheel,so I can back the timing off a bit then tighten the nut to lock the flywheel in the new place. Since the crankshaft rotation would be toward the front of the wider slot, it would not change timing as it spun because the key would limit it from going forward under the power pulses of the crankshaft. Advice on this idea would be appreciated as well.
A second idea would be to grind down the exciter block a little to move the leading edge of it back. The pickup triggers as the blocks front edge passes, and it's not magnetic, simply a piece of steel sticking out to trip the magnetic field of the pickup coil. It might just be worth the effort to change it to alter the timing and get rid of the chuggle. Just an idea.
TIA
Kris
I'm 61..5 time certified Master Mechanic, worked on just about every form of small-large sized engines for over 50 years, AS in electronic Engineering, 10 years repairing Avionics in the Marines, and I have over 30 years working in gthe Automotive industry, fixing everything from Scooters to Mack trucks..
I have a motto:
If I cant fix it..it ain't broke.....
\
And up until this week that motto applied. This is what happened:
I have a Tao Tao scooter, big-bored with a 47mm cylinder, 20mm carb, stock ignition and a canister muffler.
So far so good, right? A nice basic hopup kit. I've had electrical issues in the past that required replacing the battery and voltage regulator, and a month ago the pickup in the Stator died, was replaced and ran fine after that. Until last Sunday, the 14th.
I should mention that the engine has been down on power lately, due to a couple of apparently hot runs, but still ran and got along pretty well. I was on the verge of re-ringing the piston to get the power back, but otherwise it was doing pretty well.
Driving through Greensboro at 25 mph, no traffic, in the evening and it suddenly sags for power, catches itself and goes back to full song, then sags again. I turn around and head for home, just in case something major is going on, since I don't want to be stranded 1.5 miles from home. I get about a block and the power keeps dropping and then it just dies. No rattling, no banging, no strange noises, it just shuts down. I pull over and let it sit for a while and try a restart. It cranks 2-3 tries before I manage to get it started but it's super weak and then just fades and dies. So I hang my helmet on the handlebar and start the long push. Fortunately half the trip home has a long downhill and I get a coast, but it's a good workout.
Next morning I check things out. It has spark and gas, fires while cranking but won't rev and get running, just fires as it turns over. So, good spark, and probably good carburetion. It seems to have decent compression, with moderately strong exhaust and intake pulses while cranking. It get one start, for about 8-10 seconds, but it's struggling and just fades out. So, now I sit and think about it a bit. The plug is very sooty, like it's flooding, but that's probably due to my pumping the accelerator pump with the throttle to try to get it primed while cranking. I begin to think I've overheated the engine enough to where the rings have lost seal, and it's finally TIME. I order another cylinder kit with head and gasket set, toss in a new carb, just to make sure, and get the new intake snorkel and figure I'll replace the rubber lines with neoprene and do the fuel filter at the same time, just for the sake of it. While I'm waiting I go through everything, rechecking the Stator and ignition, even putting in my backup ignition module and coil just to double check, and nope, no change, still cranks/no starts the same, so I go to default ring damage mode.
I get the bore kit, and do a careful look at the old parts. yup..piston skirt is speckled and scored on both thrust and drag sides, minor scoring of the bore, rings don't appear to have as much tension as I'd prefer and the exhaust valve leaks slightly when the chamber is filled with fluid. Typical overheating damage. The Con rod roller bearing has a tiny amount of play, about what would be necessary in a roller setup, less than .005", and allows a slight rocking motion of less than 5 degrees, so I label it as good and press on. Crank bearing have about 1/32" of end play, just enough to be felt, and I figure as the engine warms up that will tighten up as things expand, so I give that a passing grade as well. No oil leaks noted except around the head gasket, where it might have been leaking combustion gasses after getting too hot. Everything goes together properly, I set the cam by the marks at TDC, double check it about 6 times to make sure, put everything together by the book using a torque wrench for the head studs and bolts.
I set the carburetor at 3 runs out on the idle mixture, 3 turns open on the idle speed screw. Fresh oil and a fully charged battery.
I try to crank it and it does the EXACT SAME THING!!!... Won't start..runs along as it cranks over but not enough to accelerate to even idle. I get it to start once using Ether and it runs for 5-8 seconds and shuts down, and that's IT. I just went through everything again, even installing a backup stator I had on the shelf, just in case, and no improvement. Hooked up to a car battery to get the best cranking, it still won't go.
SOOOooooo.... I finally ran into something I can't fix....Any suggestions would be appreciated.
One last thought, which may, or may not, be important. The flywheel seems to be advanced about 8 degrees from where it should be at TDC. I get TDC set by the position of the piston, and centering the crankshaft rocking across the dead spot at TDC, and the T mark is always well advanced. Probably as much as 8 degrees. This also advances the ignition timing, I think, causing 'chuggle' or difficulty spinning over as the piston almost stops as it fires on the compression stroke. It will spin, stop, continue, pause etc etc etc, unless I give it gas to keep it from firing early, at which point it will go into run-on while cranking but will not start. Wondering if the flywheel and ignition exciter block being advanced that much could be causing a lot of the problems I've been having. And if they are, then a new flywheel may solve the entire situation. Only problem is..if I get a new flywheel won't it locate off the woodruff key in the same exact orientation , and won't that just cause the problem to continue?? I've never seen any other scooter do this chuggling during startup..only mine, so it seems this flywheel being advanced the way it is could be a major influence for my problems.
I've been tempted to take a grinder to the woodruff key slot in the flywheel,so I can back the timing off a bit then tighten the nut to lock the flywheel in the new place. Since the crankshaft rotation would be toward the front of the wider slot, it would not change timing as it spun because the key would limit it from going forward under the power pulses of the crankshaft. Advice on this idea would be appreciated as well.
A second idea would be to grind down the exciter block a little to move the leading edge of it back. The pickup triggers as the blocks front edge passes, and it's not magnetic, simply a piece of steel sticking out to trip the magnetic field of the pickup coil. It might just be worth the effort to change it to alter the timing and get rid of the chuggle. Just an idea.
TIA
Kris
They come with a warranty, no miles on it, and clean title, so it's a pretty good deal, IMHO. One vendor is in California, two are in Texas, and Amazon sells the same scooter for $880 so I have plenty of options available for me.
