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Post by aimjewels on Sept 11, 2020 9:05:53 GMT -5
I had my Dongfang 50cc to upgraded to. 72cc. I let someone else install it. Now I have a piston slapping sound, and my bike won't go over 20mph. I was thinking maybe a vaccum hose wasnt connect back properly. Anyone know what could be the problem? I had a Naraku 72cc put in, as we as an aftermarket cam. Maybe the timing is off? Unsure but that knocking sound doesn't sound good. And the 20mph top speed is hair pulling frustration ... Any feedback or suggestions?
Dongfang df50sst
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Post by aimjewels on Sept 11, 2020 9:07:48 GMT -5
I meant to type new cam install. Got it from partsforscooters.com
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Post by aimjewels on Sept 14, 2020 9:05:10 GMT -5
Anyone have an idea of the problem?
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Post by FrankenMech on Sept 14, 2020 14:23:32 GMT -5
Take it back to the 'mechanic' who installed it. Or take it apart and try again yourself.
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Post by GrumpyUnk on Sept 14, 2020 15:01:10 GMT -5
It ain't spozta sound like that. Slappeta-bang-bang is not good.
There are three rules for engine assembly, but I forget what they are.
Cleanliness is next to Godliness.
Keep it clean.
Use lots of motor oil on things that move, rotates, and scrape/slide.
Keep it clean.
Do not force things.
If it doesn't feel right, take it apart and see what went wrong.
Keep it clean.
After you get it together, rotate the crankshaft 2 complete turns at a minimum.
Check cam sprocket timing.
Keep it clean.
Use lots of rags/towels to keep your hands clean.
Use a torque wrench, especially on the cylinder/head nuts/studs.
Keep it clean.
Do not rev the sh_T out of the engine after startup.
If it makes nasty noises at startup SHUT IT DOWN NOW!!!
Check your work.
If you can't do the above, find someone who can, and WILL.
If you watch some youtube, you can see it is not difficult, but can be
tedious because you have to keep it clean, and remove all the old gaskets
and clean up the sealing surfaces.
I have actually had engines start, after a BBK, when I was just turning
the crankshaft. No exhaust connected. Kinda popped like a small Honda.
tom
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Post by GrumpyUnk on Sept 14, 2020 15:06:18 GMT -5
Too tired to edit.
Piston slap is kind of knocking, not REAL low, but not a rap sound, not a loud TICK like
rocker arms/valve clearance, not a tap, closer to a ner ner ner. Slap occurs when the piston skirt does not make contact with the cylinder wall, is loose, and can flip-flop as the side force(connecting rod is not pushing/pulling directly up or down, but at an angle as the throw rotates. If there is clearance until the piston gets heated, but goes away when the piston is hot, expanded to fill the cylinder, that is piston slap. If there's enough clearance, it will still slap when hot.
The parts listed are supposed to be good quality. If noisy, you will have to take it apart and inspect, or
find someone to do so. If inspection shows damaged piston, figure why, work from there. If piston is not damaged, and cylinder not damaged, and it is NOISY, then check piston-cylinder clearance for being in/out of spec. Naraku & crew can make mistakes also, or their suppliers. I doubt Naraku has their own foundry, but I could be wrong, so they use suppliers, who can/will make mistakes. If it is bad from the box, they will likely stand behind it. mabye. but you have to figure out what's wrong.
tom
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Post by aimjewels on Sept 14, 2020 15:10:19 GMT -5
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Post by mikehailwood on Sept 14, 2020 17:39:27 GMT -5
Sounds better than my junker.
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claydoh
Scoot Enthusiast
Posts: 172
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Post by claydoh on Sept 14, 2020 19:57:22 GMT -5
Check the valve lash. If too loose, you get that sound (or at least I have), and speed will be slow. When looking at that, check that the cam is set correctly, via the timing mark under than fan cover. You need to be at TDC before adjusting the clearances so making sure the cam marks are lined up when the flywheel is lined up with the mark on the case will verify. It is not hard to be one tooth off.
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Post by GrumpyUnk on Sept 16, 2020 10:48:35 GMT -5
I think these machines are subsidized, keeping people employed in the cities. If not, they sure are a bargain for transportation. IF you know how to twiddle a wrench & screwdriver and are not afraid to get your pinkies a little oily and dirty. If not, the low cost of purchase and operation may be overshadowed by the cost of maintenance procedures.
They are finicky, especially if not used on a daily basis. The fuel orifices in the carburetor will get plugged if left to their ownself for any length of time, and then it's $$$ to get them going again.
If you live in a city/suburb, they are decent to ride if you avoid the more crowded 'commute' streets.
My home is a trap for them, as the only way to 'back streets' is by using a two lane with a 45mph speed limit, which is also a popular 'cut across' byway. Early Sunday morning, it is possible to 'get out' without too much worry about being tailgated or run over...
tom
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PDub
Scoot Enthusiast
Ann Arbor MEEEEEchigan
Posts: 139
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Post by PDub on Sept 27, 2020 18:30:38 GMT -5
I had my Dongfang 50cc to upgraded to. 72cc. I let someone else install it. Now I have a piston slapping sound, and my bike won't go over 20mph. I was thinking maybe a vaccum hose wasnt connect back properly. Anyone know what could be the problem? I had a Naraku 72cc put in, as we as an aftermarket cam. Maybe the timing is off? Unsure but that knocking sound doesn't sound good. And the 20mph top speed is hair pulling frustration ... Any feedback or suggestions? Dongfang df50sst Why didn't you take it back to whoever installed it?? |
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Post by aimjewels on Sept 27, 2020 18:33:38 GMT -5
They won't answer, and have moved.
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PDub
Scoot Enthusiast
Ann Arbor MEEEEEchigan
Posts: 139
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Post by PDub on Sept 27, 2020 19:26:07 GMT -5
Major bummer!
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Post by GrumpyUnk on Sept 28, 2020 9:44:28 GMT -5
I finally watched/listened. I think you need to adjust your valve clearance. Sounds a bit too tappy. While you have the cam/rocker cover off to do the adjustment, I would also remove the blower housing shroud and the spark plug. Rotate the blower until you see the T mark align with the mark on the block. Stick a pencil or straw into the spark plug hole, and check that the piston is at TDC by rocking the blower back and forth for maximum or topmost piston position. Should align with the "T" mark.
That done, leave it there, and check that the cam sprocket has the large-ish hole at 12:00 Noon.(not midnight, that would be dark), and the two small holes align with the surface the cover seals to. If they align, your cam is timed properly, given that the crankshaft and piston are still at TDC. You may find the large hole off a bit, either fore or aft of 12:00. If so, you should remove the chain, and re-set the sprocket so it is at 12. Need to remove the chain tensioner, and the head stud nute to remove the cam followers & rocker arm assembly to re-set the cam timing.
It is easy to get one tooth off when installing the cam. Checking after installing requires doing two full turns of the crankshaft, to get one turn of the cam sprocket/ shaft. The holes should align almost perfectly after doing 2 complete turns.
Cam timing being off will affect power developed. I don't have at my fingertips what it does, but generally you will find that you lose high or low end performance depending on which way the cam is 'off'.
Nice looking machine. Too bad it doesn't move as well as it looks. You can fix that.
I don't remember my prior comments, but it does not sound like piston slap to me, but loose valve clearance causing loud tappy-tappy sounds.
Clearance from SVc Manual: Cold Intake 0.06mm Exhaust 0.08mm{0.00236" & 0.0031"}
You can go to .003" and .004" with a bit more noise, the closer tolerance is common in the FE as the engines are not run as hard(high rpm) there, and a 'sewing machine' noise is preferred.
I figure I can run them a bit closer for two reasons. I will check adjustment more than suggested, I don't run them hard, and the tip of the rocker arm will not wear as much(cupping) with a closer setting. Plus I like the way it sounds. Other manuals indicate clearance of .004(.005) for both I and E. I figure that is mm of clearance, closer than the other manual. Perhaps that is the FE recommended.
Either way, I'd check clearance. It will give better performance if the valves start to open sooner and close later, which happens with the smallest allowed clearance. If not, the valve will have to wait until the clearance has been taken up by rotation of the cam... less time open... less power.
tom
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Post by aimjewels on Sept 28, 2020 11:37:23 GMT -5
That makes perfect sense. Thanks for taking the time to type that out. Much appreciation! +1 to you!
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