Weird clanking noise during rides

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userix

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Jan 29, 2011
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Before riding today, I checked the crank bearings, no play, move freely and smoothly. Just to play it safe, I replaced the piston, piston rings, and needle pin bearing for the piston.

Took it out for a test ride and after 15-20min, the engine seized completely. Before it seized, it still had that loudness at higher RPMs, even with new gaskets and a new exhaust. I took off the cylinder head and found the piston completely stuck in the cylinder. I couldn't move it with my hands. I tried looking through the exhaust port to see if anything was stuck, but it looks fine. I am guessing the new ring got caught on something. The cylinder walls were perfect (no gouges, no scratches) and smooth right before today's test ride. Ever since I started having problems with this engine, I couldn't get it back to normal working condition. :(

I decided to try out my previously rebuilt RAW engine, while it runs fine, it's top speed is no where near close to what it was able to do brand new and it is weaker as well. I don't understand why it can't go as fast as it preivously could. I have new piston, new piston rings, new cylinder head and jug, new spark plugs, new gaskets, new exhaust, new crankseal, and new carb. The engine idles fine and there are no air leaks anywhere. I can't figure out why it won't run as powerful or fast as it did brand new.
 
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biknut

biknut

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Sep 28, 2010
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It seems like it's kind of hard to seize a piston in these engines, especially in the winter.

What oil ratio were you running? Are you using the stock jet? A B6HS shouldn't cause any problems.

How was your idle before it stuck?
 
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userix

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maintenancenazi said:
Did you say you were running 32-1? I wonder if maybe you just got a bad batch of 2 stroke oil??
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alienboy366 said:
someone tell me what this sound means..... Broken - YouTube
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biknut said:
It seems like it's kind of hard to seize a piston in these engines, especially in the winter.

What oil ratio were you running? Are you using the stock jet? A B6HS shouldn't cause any problems.

How was your idle before it stuck?
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Running 32:1. Stock jet. Idle is fine, around 2000 rpm, doesn't dip. But I do noticed that it would sometimes die randomly after a few seconds of idling normally. This happened before I replaced any parts (piston rings, piston, etc) and still happened after replacing the parts previously mentioned. When I opened up the cylinder, there was normal amount of oil in the chamber and on the piston top, so it is getting lubrication. Whenever I WOT before it seized, the engine would run fast like it should (except for it being extremely loud at higher rpm), but then after 10 sec or so, it loses speed and power fast, like it doesn't want to pull anymore. It still runs somewhat after losing power, but doesn't die completely. Then after a few more minutes, when I was trying to accelerate, then the engine seized completely.

How do I get the piston unstuck? It's stuck pretty much in the center of the cylinder. I am guessing a ring go stuck on the intake or side ports. I looked in the exhaust port and don't see the rings through it. I tried pushing it with my hands, but it's stuck pretty well in there.:-||

And I still can't figure why my old RAW engine doesn't run as strong as when it was new. I practically replaced all the parts.
 
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vachon644

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It sounds like the engine is/was running lean. Check for the gas tank venting, if the fuel has troubles going down into the float bowl because the gas tank has low pressure you lean the engine. Try to check for air leaks, on the engine, on the intake, exhaust, carburetor (are you missing screws?), etc.
 
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userix

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maniac57 said:
That would be the carbon thingies stiking out all around your sparkplug hole in the head. Those can start glowing as you run and cause pre-ignition or "pinging"
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Thanks. So is this because of lean or rich condition?
 
bairdco

bairdco

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Aug 18, 2009
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did you replace the piston correctly? if you put it in backwards, the ring gaps line up with the port. it could expand and catch on it, break the ring, and jam the piston.

there's a bunch of different things that could have happened. the circlip on the piston pin could have popper out ( or left out accidentally) causing the pin to slide out, jamming it into a transfer port.

could be a lean condition, but doubtful if there's oily fuel around it. lean would make it heat up, the metal expands, and the piston seizes.

whatever the cause, it ain't good. a seized piston usually means game over for the engine.

you could try using a piece of wood for a punch and knocking it loose by carefully hammering on it. once you get it out, you'll probably be able to tell what happened.

as for your raw motor not running like it used to, a few things might be happening. it might need to break in again with the new rings and stuff, or
it might have lost compression as the cylinder bore wore out. on real engines, the cylinders are bored out and larger pistons replace the older ones due to wear. it might be getting excessive blow-by due to the wear.

it could be something simple like a warped head causing a small leak, intake leak, old gas, weak spark, weak mag, low fuel flow, to name a few. just stupid little things that happen as an engine ages.
 
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userix

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Here's an update from the previously seized grubee engine. An errant piece of metal, from where I do not know, got in the chamber and messed up the piston big time, as shown in the pictures. Surprisingly, the cylinder wall is in pristine shape! No a single gouge or even a scratch. I had to hammer the piston out using a large deep socket. I thought since so much force was required to drive it out, I thought the cylinder was toast for sure. The crank needle bearings both on the piston and crankshaft side are perfect as well. Thought hammering would have destroyed them in the process as well.

The first picture is the previous piston that was replaced by the damaged one shown. Is this an abnormal amount of blowby? Would something like this cause loss in power? It's also localized to the area shown in the picture. The other side of the piston is no where near as bad in terms of blowby.
 

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userix

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Now with the new engine, I have this weird idling issue. Brand new speed carb and new CDI as well. It's fluttering during idle and not consistent, constant idle. Also, when I am acutally moving at moderate speeds (~25mph), the speed would flutter as well randomly. Not sure what is causing it.

http://www.youtube.com/watch?v=ViM4zK6V0SM
 
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userix

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Jan 29, 2011
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biknut said:
That sounds like a intake leak.
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I sprayed carb cleaner around all the gaskets and didn't find any leaks. Also, if I move at a slow speed for a few seconds and then stop, the idling would go back to normal. It does this weird idling after riding near WOT or higher speeds/RPMs.
 
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nightcruiser

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Mar 25, 2011
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When you put the piston back on the motor make sure the arrow on the top is pointing in the direction of the air/fuel flow.
Take a look at the wrist (piston) pin on your Grubee. I had heard someone talk about piston slap at high rpms on a Grubee, it was hypothesized that the wrist pin might be flexing and allowing the piston to tap the plug a bit at high rpm, a thin/weak pin might have explained that problem. When I rebuilt my Grubee I noticed the wrist pin was considerably thinner (and lighter) than the pin on my other motor and the pin I replaced it with. Newer and older Grubee's have a thicker pin, but some kits that went out in 2011 had an inferior wrist pin installed. (I have pics where you can see the hole in the pin is larger on one, and I measured the wall with a caliper to confirm. The pin with the bearing around it definitely has a thinner wall) I am not saying this is your problem, but since you have them ripped apart you should take a look, and use the thicker pin if you have one.
On your strange idle issue, have you checked out the carb thoroughly and done any experimentation with the float setting? Perhaps your fuel delivery (mix) is fluctuating at different points in your ride due to a bad float setting, or due to slowed fuel delivery because of a clogged filter or petcock, or bad gas cap venting isn't allowing enough fuel to flow at top demand? Going up and down hill makes the fuel pool toward the front or back of the carb bowl, if the float is not set to a nice moderate position sometimes a little bit of riding at an angle (on a hill) can make the motor run lean or rich for a while, possibly load the motor up a bit with fuel by the time your off the hill, or running abnormally hot depending on the condition it is causing. Just a thought....
Also, when you installed the new magneto did you sand the varnish off the bottom side so it makes a solid connection to the motor housing? Perhaps the old magneto was flaky and the new magneto not grounding well? This Grubee web page gives lots of info on the magneto and says you need to sand away that layer of varnish before installing a new magneto.... http://www.grubeeinc.com/USA/Magneto Mystery.html
 

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