a new rattle....

GoldenMotor.com

Dougan

New Member
Apr 5, 2010
78
0
0
wisconsin
66cc skyhawk gt5 slant head, 2009 manufacture, 4 gallons of gas through it so probably 400-600 miles on it. 25:1 lucas semi-synthetic is what I run.

I've recently got a new rattle in the engine assembly. My bike maxes at about 30mph even and I usually ride at probably 28mph. The normal vibrations (the ones that shake the bike because I didn't put rubber in my mounts) get noticeable around 25mph or so. Usually I don't hear any noises besides some chain rattling (haven't upgraded the chain yet) even wide open. However, in the past couple days, the motor has started to make a pronounced rattling noise at about 25mph or more. I don't have a tachometer, so I can't speak on that, but the rpms where the rattling starts is right around the point where the "normal" vibrations start to get noticeable.

It's hard to describe the rattling, except that it's very noticeable and goes from nonexistant to very noticeable in a very short rpm variation. It sounds like something needs to be tightened down. Like something that turns isn't tightened down and is rattling around on the inside. It's hard to say if it's coming from the engine or something inside the engine compartment.

I originally thought it was one of the many noises that come from the driveshaft/engine sprocket area. But, I discovered that if I pop the clutch and rev high, the rattle will happen when not in gear. When revving in "neutral", the rpm level at which the rattling occurs is right at that "borderline area" where you don't want to rev it any higher in neutral.

Also, I noticed a lot of oil on the bottom of the motor today. I noticed because my exhaust pipe was smoking due to oil on the outside and took a look. This thing has always leaked a certain amount of oil and I could easily see this being a coincidence, even though it is more oil than I've seen on it before.

I recently oiled the gears inside the clutch area in accordance to some tutorial on this forum, so I don't think it's that.

Any ideas? I can probably take it apart to look at stuff sometime next week, but haven't even taken the casing off the clutch to look yet.
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Strange sounds are not uncommon with the 2 stroke engines. Some of the noise comes from the clutch, some from the gears and some from loose tolerances of the crankshaft/connecting rod/piston/etc. Some of us have several bikes and I will assure you that those of us who do will tell you that every bike has unique noises.
You said you had "oiled the gears". Oil is not the proper lubrication for the primary (right side) gears. A small dab of good quality bearing grease will be sufficient for lube. As for the oil leak you've discovered, check for the source. It could be the exhaust manifold gasket if you see oil down the front of your engine. What oil/fuel mix are you currently using? The often recommended 16:1 mix is too much oil. If you are using that much oil you'd benefit from dropping the mix to 32 to 40:1. Let us know what you find and my recommendation is don't wory too much about strange noises. They're to be expected.
Tom
 

Dougan

New Member
Apr 5, 2010
78
0
0
wisconsin
Strange sounds are not uncommon with the 2 stroke engines. Some of the noise comes from the clutch, some from the gears and some from loose tolerances of the crankshaft/connecting rod/piston/etc. Some of us have several bikes and I will assure you that those of us who do will tell you that every bike has unique noises.
You said you had "oiled the gears". Oil is not the proper lubrication for the primary (right side) gears. A small dab of good quality bearing grease will be sufficient for lube. As for the oil leak you've discovered, check for the source. It could be the exhaust manifold gasket if you see oil down the front of your engine. What oil/fuel mix are you currently using? The often recommended 16:1 mix is too much oil. If you are using that much oil you'd benefit from dropping the mix to 32 to 40:1. Let us know what you find and my recommendation is don't wory too much about strange noises. They're to be expected.
Tom
I didn't have any of the recommended greases on hand, but I used outboard lower unit lube for the gears. I figured if it's used for the same purpose on an outboard, it'd be the best thing I had on hand. I only used a slight amount. I was limited on time today but i opened up that casing and poked at stuff and didn't notice anything (I was hoping one of those two cogs was the problem). So I don't think it's the lubrication in here.

As far as the oil leak, I am quite stumped. That's why I think it's a coincidence. My motor is one of those that I hear about often here in that it leaks a certain amount of oil from basically every connection. There has always been a slight amount of oil all over the engine. I have suspected it's a very slight leak in the exhaust manifold. I reattached my exhaust with more care and a new gasket and it never solved the "problem". It always ran well so I didn't experiment beyond that.

It's hard to tell where the oil is coming from. It's difficult for me to understand how the oil got on the exhaust in teh spot that it did (right before the elbow going into the biggest part-- in front of the motor!). I think what I am going to do when I have time (might not be in the next two weeks) is wash the exterior down good with some brake cleaner and then pay good attention to see if I can identify where the oil is coming from. If it's not coming from the bottom of the motor, I don't think there's a mechanical problem. If there hadn't been such a sudden quantity on the muffler, I wouldn't have even noticed or mentioned it.

Like I said, I run 25:1. Which is a bit rich, I know. Another reason surface oil hasn't really concerned me too much. From other peoples' reports, my engine runs relatively hot, and I ride WOT a lot so I figure I'd err on the richer side. Since this is richer I could see it causing problems but not rattling.

If I do find anything, I will post here, even if it's weeks from now (which is probably how it will go). I always finish out my threads if I figure out the problem-- I hate digging for threads, only to find one with someone describing my problem, and never explaining their solution.

Thanks so far, any more advice is appreciated. I know "my engine rattles" is probably something over 50% of us here can legitimately say.
 
Last edited:

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
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up north now
Like I said, I run 25:1. Which is a bit rich, I know. Another reason surface oil hasn't really concerned me too much. From other peoples' reports, my engine runs relatively hot, and I ride WOT a lot so I figure I'd err on the richer side. Since this is richer I could see it causing problems but not rattling.
You may be running hot because 25:1 can make your engine run lean (fuel to air).
Your rattle may be from a loose motor mount.
 

Dougan

New Member
Apr 5, 2010
78
0
0
wisconsin
So, did you figure it out?
I had a wedding this weekend and haven't had a chance to take it apart. I might spend this week out of town as well so I may not have a chance to break it down until this coming weekend. Hopefully I get a chance to get this figured out sooner than later... :)
 

Dougan

New Member
Apr 5, 2010
78
0
0
wisconsin
Okay, finally got a few hours of free time, and got around to all of the maintenance I've been waiting to do. The problem is now gone.

-Spark plug replaced
-Opened clutch cover and cleaned any oil that happened to be inside
-wiped down engine to clean oil off
-remounted engine to frame using rubber in-between frame and engine
-carb cleaning
-oil and tighten chain

The engine runs much better all around. I attribute this mainly to the spark plug change. I think it's possible that the engine was just running bad because the spark plug sucked. It's also possible that the rubber is helping to dampen vibrations and made it go away.

I also noticed that the rattle would not ever happen while accelerating but would happen while the rpms accelerated if I was revving in neutral. I believe that the chain itself, when tight, might help to dampen vibrations as well. The chain had gotten a bit loose so I tightened the tensioner position. Might have had an effect.

Whatever the solution, I didn't address any specific problem and didn't have to open up teh crankcase. So I'm chalking this down to just a standard china motor noise. We'll see if it comes back.
 

GearNut

Active Member
Aug 19, 2009
5,104
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38
San Diego, Kaliforgnia
Thank you for the up-date!
Isn't is amazing what a new spark plug can to for engine performance, especially when you are replacing the lousy stock one?
A loose chain can rattle when the engine is revved at a stop, and will surge when at speed.
I bet that is what you were hearing.
 

jburr36

Member
Jul 17, 2008
285
0
16
Idaho
Check the head bolts. That 'rattle' may actually be a leak from the head gasket during combustion. Oil can ooze from that too. That happened to me. Tightened them up and eliminated my noise. It could be an exhaust leak from the exhaust gasket as well.