Knocking noise in Linhai 250cc. By jburd (Read 2,854 times)

[jburd]

Hey guys, I'm hoping I can get some help with this. I have a linhai 250cc scooter and I was riding awhile back and the engine started running really hot. The fan wouldn't come on. I was quite a distance from the house. I checked the coolant and it was low so I added. I got it home after several hours of riding and stopping to let it cool and riding a little more, stopping etc. At one point I lost power for a short period of time. It came back but now my scooter has a slight knocking noise in the engine. It's almost exactly like in this youtube video even though that's a different bike.

I'm hoping I didn't destroy my bike. I did figure out that I had a pinhole in one of the heater hoses. I have replaced that. I haven't yet been able to get the fan to kick on after purping it several times. I'm not sure why yet but the knocking noise has me concerned even more. I have no lost power at all when I take it around the block. It just knocks. Does anyone have any ideas? Any help is really appreciated.

[JR]

First thing is you need to work out the cooling issues and make sure all is well since you got it hot. Burping is a PITA but if it's got the smallest amount of air in the system it'll act stupid especially the fan. We have how to in the tech section on burping.

On the noise one thing comes to mind quickly is the valves, need to pop the covers off and check them and adjust them if needed.

The other thing the person in this video mentioned was listening to the engine with a stethascope and they do really help on hearing a engine internal problem. Still runs good then lets hope it's not a main bearing but again just needs the valves adjusted.

JR

[richardthescooter3]

JR, about 2 years ago I had loose power and knocking, my buddy and I adjusted the valves and discovered the top intake nut came off and luckily we found the nut in the bottom of the exhaust valve area

[wheezy]

I agree that it sounds like the valvetrain. Could be an adjustment, or a spring could have broken since it overheated.

If you can't find a stethoscope, any solid object will do in a pinch. I've even used a stick. You're listening more for the volume than tone. The noise is loudest in the section with the bad part.

[bobf]

True about long solid objects. I often have used a long screw driver. Put the end on the engine where you want to listen and then put your ear over the end of the handle. Seemed to work well for me.

[jburd]

I am in the middle of adjusting the valves and noticed on the exhaust valve the rocker (the part that you adjust - see attached pic) rocks in and out towards and away from the spring. The top valve didn't seem to do that. Is that normal? Is there a spring on the other end of it?

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[JR]

No jburd if it moved back and forth it's way too looses and there's the noise. The bottom valve is the exhaust valve and most of the time it's way too tight and has no play at all.

Let us know how she sounds now.

JR

[jburd]

The interesting thing is that when I check the clearance and tighten the adjuster bolt down, the whole thing still rocks back and forth. What is on the other end up in the valve that holds the whole rocker arm firm? Is there a spring?

[jburd]

Alright so I'm not feeling too good about this right now. Kind of have a knot in my stomach. (The only good thing so far is I'm learning a lot about my scooter.) I adjusted and tightened the valves and turned it on. It was running smoother but still had the knocking. When I was listening with my stethoscope for where the knocking was, it didn't seem to be coming from the valve train area. It seemed to be strongest from the back on the case that you check the oil in. I changed my oil today and had something come out of the bottom of the engine with the screen and spring. I've attached a couple of pictures of it. Does anyone have any idea what it is and could it be the reason for the knocking noise - like something really is broken up in the engine? Does anyone have any thoughts?

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[jburd]

OK guys, I think I might have found the knock. I took the outside cover off the magneto coil (where the oil stick is) to see if I could figure out what that piece was to. When I opened it up I found the small gear at the top above the magneto rotor just sitting in there loose. It was connected to the gears but wasn't fastened to anything. (see the attached pic) I turned the engine over by hand and I'm pretty sure that's what the knocking is. That gear was jumping all over the place. I tried that little piece I posted earlier that fell out the bottom in the center of that gear to see if maybe it went there. Doesn't fit. Anyways I thought I would at least post this and see what you guys think. I'm really hoping someone can help me here. I'm desperate to get this thing back on the road.

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[wheezy]

jburd, the other end of the rocker arm is the lifter. I haven't had the pleasure of dismantling my scooter engine, but I have on cars. And that first pic has got the appearance of a lifter. It wouldn't be logical that it would just fall out though, unless the cam lobe has failed somehow, so I'm not guaranteeing that it is a lifter, only that it looks like one.

[JR]

That piece is the oil screen insert and it just pops back in with the big end pointed up. It keeps the oil screen in place:



Now when you say rocks back and forth can you explain that a little more? What are you setting the valve clearance at?

JR

[wheezy]

yeah, jr, I didn't think these had lifters, so thanks for clarifying what the part was.

Could it be that the crank is not at the correct position for setting the clearance? That would lead to free play.

[JR]

Adjusting the valves on this scooter can be a challenge to say the least sometimes, clearance needs to be no more than .006 on the exhaust valve but I like .005.

JR

[JR]

Sept 16, 2012 19:02:24 GMT -6 jburd said:

OK guys, I think I might have found the knock. I took the outside cover off the magneto coil (where the oil stick is) to see if I could figure out what that piece was to. When I opened it up I found the small gear at the top above the magneto rotor just sitting in there loose. It was connected to the gears but wasn't fastened to anything. (see the attached pic) I turned the engine over by hand and I'm pretty sure that's what the knocking is. That gear was jumping all over the place. I tried that little piece I posted earlier that fell out the bottom in the center of that gear to see if maybe it went there. Doesn't fit. Anyways I thought I would at least post this and see what you guys think. I'm really hoping someone can help me here. I'm desperate to get this thing back on the road.

thescooterprofessor.proboards.com/index.cgi?board=ncmanuals&action=display&thread=265

Jburd take a look at the YP250 Majesty service manual on page 134 and you'll see your gear is the starter clutch gear. I'm not sure but I believe the shaft it goes on has a snap ring on the end to hold it in place?

Don't sign that in blood though but do take a look at it because it should not make noise except maybe when you're starting the engine?

Here is another view:

.oemmotorparts.com/oem5.asp?M=Yamaha&T=YP" rel="nofollow" target="_blank">.oemmotorparts.com/oem5.asp?M=Yamaha&T=YP MAJESTY 250&Y=1996&L=YA-YP-MAJESTY-250-5&O=STARTER&F=YA-YP-MAJESTY-250-5_am&L2=YA-YP-MAJESTY-250-5_am

JR