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Thank you for this Bashan. Well I didn't know if the gear should pass over the washer and nut, I felt that such an arrangement would be unstable and "loose".
Good that we cleared that one up and thank you very much for taking the time to have a look at this

Do you agree with this?

Thanks guys. Am in contact with the guys at motopartscenter where I'll be ordering parts.

Bashan: I'm probably mixing up terms here, english not my native language  

Will keep you guys posted on the progress.

Geir, Reykjavik, Iceland

Yes I definitely have the same problem as rob63 in the link above. I.e. "With the washer and nut in place and tightened, I can move the gear towards me, so that it slides over the washer.
"

You can see this in this video that I just recorded:



There is no damage in the crankshaft or the threads on the crankshaft, the nut even though the nut had come totally loose.

Any ideas what is going on here? Incorrect assembly? As I understand it, this bike had been used very little.

Crankshaft in-and-out play: 

Hi all.  

I'm wondering if a total rebuild would be recommended after finding metallic particles in the lubricating oil, after the starter clutch being wrecked.

Starting problems - never got it to run.
I had problems with getting my son's ATV to start properly (it started for like 2 seconds, but never got it to run) so I took out the starter which had very worn teeths (did this after going over spark, fuel and air related items). Once I removed the starter, I noticed that the dual gear had broken teeths.  I ordered this from www.motorpartscenter.com (http://www.motopartscenter.com/images/parts/21070059/500.jpg).

Starter clutch assy - wrecked.
After I later opened up the side cover of the motor to remove the dual gear, it turned out that the over running clutch assy (starter clutch assy) was toasted (see here:  www.motopartscenter.com/images/parts/21072025/500.jpg).  This assy basically came out in pieces, so I'm not fully aware of how this is supposed to be. The needle bearing was also completely toasted.

This is a 1P57QMJ-2 engine.  I got from the dealer part 2 part catalogs for the 150 cc ATV, since there are two versions of this 150 cc ATV.  Comparing the catalogs gives 2 different versions of the starter clutch (can't upload it here, why???).  After searching on ebay, this engine that I'm dealing with, seems to have a "regular" GY6 starter clutch, see e.g. motopartscenter link or ebay link here: 

www.ebay.com/itm/SCOOTER-125CC-150CC-GY6-OEM-HIGH-QUALITY-Starter-Motor-Clutch-/171406064132?pt=Motorcycles_Parts_Accessories&hash=item27e898fa04&vxp=mtr

This seems to compare nicely with the one from the motorpartscenter link above, but I'm not fully sure.  As I understand it the motopartscenter item includes the needle bearing.

Draining the lubricating oil - metallic particles.
I had earlierly drained the lubricating oil from the engine, but did not find any "rough" metallic particles in it, none at all. I did, however, see some very very very small metallic particles or metallic color which were only visible in the oil but could not feel it with my fingers.  After I opened up the side cover, to remove the dual gear, I did find some "rough" metallic particles in the bottom of the engine, but not much at all. Since it was the starter clutch assy that was completely toasted, I'm hoping that this has not effected the rest of the bottom end, hmmm.

Earlier test on compression.
When I was dealing with the starting problem in the beginning (spark, fuel, air) I did some compression tests, but only to a limited extent since the engine would only start for maximum 2 seconds. I got from 100 - 120 psi.  I did manage to get it to start like three time for about 5 seconds, getting a compression 140 - 160 psi. So I've assumed that compression was not a problem and that the top end has not been effected by the metallic particles.

Cranckshaft play.
I can't find any play up-and-down or side-to-side, when I grab the end of the crankshaft. When I try to move the crankshaft in-and-out, there is some play.  Of course I have removed the nut that holds the flywheel etc.  I have video of this, but can't find how to upload it here, should it be possible?

Questions:
What I would like to ask you guys is:

1. How much in-and-out free play of the crankshaft is permissible?  I assume, once the engine is running, it gets hot and the oil is being pumped, that this will reduce.
2. Those of  you, who have good mechanical skills and understanding, would you recommend a total rebuild due to the metallic particles, despite the fact that I was getting good compression when I did get the engine to start for a few seconds?
3.  When I took out the starting clutch assy, it basically came in three parts.
Part no. 1: First was the gear (see item to the left here: 
www.motopartscenter.com/images/parts/21072025/500.jpg)
Part no. 2: then came the item to the right in this photo.
Part no. 3: The third part is a flange (most likely the back of part no. 2), which seems to have threads in the center and screwed (pardon my french!!) onto the crankshaft (again, can't upload a photo of this).  Parts no. 2 and 3 were fixed together with 3 litle bolts, that had come loose.  
My understanding is that parts no. 2 and 3, are supposed to be bolted together with 3 bolts. Is this correct?  Do you have any good links that show the composition of the starter clutch or information on this?

I would like to avoid having to rebuild the whole motor if possible. I admit that I'm not experienced in rebuilding motors, but I feel that the compression tests that I did indicate that the top end is ok.

4. At last is it possible to upload photos/videos here, I can only find a way to insert links to photos/videos.

Hopefully you guys can assist me on this

Kind regards, Geir, Reykjavik, Iceland

Thanks for this    Just for curiosity, do you know how many degrees before TDC the ignition (spark) takes place?