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6ril

did I just break that engine ?

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Hi all,

I'm desperately in need of your help! I think I just made a BIG mistake !

I bought this bike, Sherpa 125cc, last week, it was in very good shape! It even started after a few kick start.

I didn't use it, just tested it, and then it suddenly stoped while I was riding it, after less then a minute. After that impossible to start it again. So I checked many things, changed all oils, and cleaned the carburetor.

That where I made a huge mistake ! When I fixed back the carburetor, I inserted the "bushel" in the wrong position, 180deg offset from the right position. I thought it was ok because I saw some guides inside the carburetor and thought it must be like this.

Unfortunately, it fitted in, but the carburetor was always FULL OPENED ! And I didn't know and that time !

Then I finally found the culprit, it was a bad spark plug, giving sparks but somehow it was wrong. Bought a new one, and then tried to start the bike ... with a FULLY OPEN Carb !!!!

The engine went up in revs ! really HIGH ! for maybe 8 or 10 seconds, the time for me to stop it by unplugging the fuel line. I had installed a kill-swith, but it was unplugged then.

So I fixed the carburetor, placing the bushel in the right position, and tried to kick start the bike. Result : almost no compression, and a very unpleasant noise coming from the engine.

Now, I don't know what to do... I unmounted the piston and cylinder but they seems fine (to my novice eyes at least).

 

Here are a few short videos of what I did :

 

 

All feed back would be much appreciated !!

thanks,

cyril.

Edited by 6ril

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The bore has scrape/seize marks, the piston is scored and the piston ring looks to be stuck in the groove, Also the cylinder head has small impact marks from debris collision.I would strip it entirely, check and the big and small end, check the crank bearings, then get a rebore and a new piston and ring set.

Edited by misscrabstick

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Yep that piston is done and sadly some metal was shaved away at least a new piston with next overbore and a matching rebore with honing to the cylinder.

 

I would also replace upper piston pin and bearing cage. 

Then please check the lower bearing of the con-rod too, if it feels a bit rough replace the con-rod and the lower bearing and pin also.

As you thrn have to split the engine fresh crank bearings and crank seals are also to replace. 

You might then examine the complete engine bearings and clutch. 

That was a very unfortunate happening.

That is a very nice bike you have there, at least it is worth effort. 

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Hey Misscrabstick, pschrauber,

thank you both for the feedback !

Wahoo I was really not aware that the piston was done. I'm going to have a proper look at it again, with your comments in mind. Got to learn a lot !

Now I know I can't do almost any of it myself, I'll have to seek (paid) help from a proper mechanic.

Dam what an idot ! I did f#$% that beauty straight from the get go ! Congrats Cyril : /

 

thanks again !

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In video three, think it may be the camera angle, but your forks look bent!

anybody else notice it?

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Jonboy - 

Probably nothing more than "barrel" distortion (camera lens).

Did notice that the conrod. looks to have been replaced already.........and why two cyl. base gaskets, I wonder ?

Edited by lorenzo
  • Like 1

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hey Jonboy, Lorenzo,

it's definitely the lens distortion (gopro).

For the multiple gaskets, there's actually 3 of them ! One went up stuck to the cylinder.

There should one be 1, right ? One good one.

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here, a few close ups of the piston and cylinder. It's probably hard to judge with photos but...

 

dsc_0018.jpg

dsc_0019.jpg

dsc_0020.jpg

 

dsc_0021.jpg

dsc_0022.jpg

dsc_0023.jpg

 

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On 7/14/2020 at 10:29 AM, lorenzo said:

Jonboy - 

Probably nothing more than "barrel" distortion (camera lens).

Did notice that the conrod. looks to have been replaced already.........and why two cyl. base gaskets, I wonder ?

Altering the gasket thicknesses or number changes the port timing by moving the barrel upwards in relation to the piston, it also lowers the compression, people do this to change the power characteristics of their two stroke.

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thanks for that info Misscrabstick !

So adding gaskets would add or remove power ? the thicker the joint, the bigger the exploding chamber, right ? But for the same amount of fuel, so ...  help me there :)

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Found the culprit of the nasty noise in the engine.

 

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You will also find the kickstart lever is much easier to get off and on if you remove the bolt completely before you try to put it on or take it off.

Edited by bullylover
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OH ok, thanks for the tip Bullylover !

  • Like 1

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Nice bike you've got there!  Sorry she seized up on you so early in your ownership... but, on the upside, you are becoming quickly familiar with all you'll need to keep her running happily for many good times in the years to come.

Not knowing how far you're planning to tear down your motor, definitely pull that flywheel if you haven't already.  I suspect that your incident may have possibly sheared (shorn?)... buggered your woodruff key.  All those rpms with a sudden stop at the end might've caused the flywheel to spin over the key on the shaft if the key was not in good condition to begin with or missing entirely.  All the more likely given the retaining nut had spun entirely off the shaft.  At the very least, the timing will be off if the key was intentionally removed (...for timing purposes?  Who knows!) by the previous owner.  

Also, it may be possible to remove shavings that have fallen into your case by entirely filling the crank area with some pre-mix and carefully working the crank to dislodge any debris from beneath the crank and bearings. Most of that stuff will come loose and can be drained off and blown out with compressed air after a few treatments. Learned that from an old article Rick Sieman (superhunky.com) wrote for Dirt Bike Magazine many years ago.

Good luck with your work.  I'm sure she'll be even better than before once you get things all back together!

PS  I loved your videos.  Nicely done!

Christian

 

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cyril - 

Don't want to be too hard on you.........I'm sure we all made stupid mistakes as raw novices - I know I did......

However, "culprit of the nasty noise in the engine" is unlikely to be just a nut that's come undone - that's more likely to be merely a symptom of other damage. As vintagenut has suggested, the woodruff key is probably also sheared, with attendant damage to the tapers of flywheel and shaft. Also, depending on the revs. reached (and for how long) when  the bike started w.f.o. you may have damaged the conrod bearings. As misscrabstick and pschrauber have said, engine now needs a total strip and rebuild.

On 7/11/2020 at 7:03 PM, 6ril said:

Now I know I can't do almost any of it myself, I'll have to seek (paid) help from a proper mechanic.

 

Best thing you can do is follow your own admission, and entrust the work to someone who actually knows what he's doing. Be prepared for a sizeable bill...sorry !

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