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Need help, 2016 YZ250 23 hours from new, top end

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Hi guys doing first top end on this bike. So bikes done about 23 hours. I say "about" because i bought the bike almost brand new, barely a scratch on it and i put an hour meter on it before i used it which has recorded 17.1 hours and iv guessed it had about 6 hours use by first owner. Been running it at 32:1 with belray semi synthetic. Jetting is 180/52 2nd clip. 

Always done air filter after every ride. Oiled and bit of grease on the surfacing/joining edge. 

 

I use the bike in the trails here in Western Australia. Alot of wide open high speed and also alot of technical slower single track type riding. Probably about 50/50. 

 

Now the crank appears to have had some surface rust form at some point. Im guessing its from the bike being washed or maybe being in storage by previous owner as iv never ridden in the rain or puddles yet as its been dry here. Definitely never a river a crossing. 

 

The piston appears to have alot of blow by and is evenly coated on the top with a good layer of carbon. It also shows a hot spot on the underside. When i removed the gudgeon pin a bit of, what i thought was very watery oil, dribbled out with the bearing. I also thought the bearing had alot of play when still mounted on con rod however im no expert. 

 

The bore has what looks like stop marks running around the bore circumference which iv never seen or heard about before. 

The top of bore where piston is at TDC had a thick coating carbon buildup.

 

Any thoughts please guys? I thought it was running rich but it appears to have run hot at some point from looking at the underside of the piston.

 

FYI i have ProX piston kit ready go in.

 

Any thoughts be much appreciated!

 

Mike

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Edited by Michael N
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3 hours ago, Michael N said:

Hi guys doing first top end on this bike. So bikes done about 23 hours. I say "about" because i bought the bike almost brand new, barely a scratch on it and i put an hour meter on it before i used it which has recorded 17.1 hours and iv guessed it had about 6 hours use by first owner. Been running it at 32:1 with belray semi synthetic. Jetting is 180/52 2nd clip. 

It looks like more than 23hrs to me or it has had a tough life. You really need to fix the jetting and consider a oil with a lower flash point. Since you do both low speed and high speed, jetting really needs to be right. The amount of carbon build up is ridiculous and unnecessary. 

Always done air filter after every ride. Oiled and bit of grease on the surfacing/joining edge. 

👍

 

Now the crank appears to have had some surface rust form at some point. Im guessing its from the bike being washed or maybe being in storage by previous owner as iv never ridden in the rain or puddles yet as its been dry here. Definitely never a river a crossing. 

Some oils don't protect against rust well. This could've been from simple condensation during storage. I swear storage is worse for a bike than riding it.

 

The piston appears to have alot of blow by and is evenly coated on the top with a good layer of carbon. It also shows a hot spot on the underside. When i removed the gudgeon pin a bit of, what i thought was very watery oil, dribbled out with the bearing. I also thought the bearing had alot of play when still mounted on con rod however im no expert. 

Too much carbon, fix your jetting. The hot spot underneath could be from the carbon, it retain so much heat... Always use new wrist pin and wrist pin bearing.

 

The bore has what looks like stop marks running around the bore circumference which iv never seen or heard about before. 

You have a carbon ridge. Soak cylinder in gas and clean entire bore with a scotch brite. If you leave this you could break a new ring. Soak the head to clean it while you're at it. Fix your jetting.

 

 

 

 

 

 

Edited by zeke383
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Zeke pretty much hit it all on the head. When bikes are stored and piston is in correct position, condensation will get in and rust will start to appear. Plug the exhaust helps. Most of the heat marks on the crank are normal from rod installation. If the rod bearing is starting to go, you will have greater heat marks. Best check that one for spec.

I'm with Zeke, although you put an hour meter on it, it very well could have already had over 20 hours on it. Wear on frame can be an indicator, but not exact. If a bike was ridden around an area where it didn't bounce a lot, then boot wear will be minimal, and hours hi. So, I don't go with appearance.

Correct jetting, check float level, and try a better oil. The carbon build up can retain heat and give a false sense that the underside of piston was like that in the beginning  

Scoring on cylinder can be from all the carbon build up, dirt and  material. As said, clean it up, check grooves for depth with fingernail, measure bore and piston, put a new one in. 

When I bought my boys used YZ's years ago, I just test road them and handed them over. Let them get as much as they could out of what was left. Once they broke, it was rebuild completely, install hour meter and now we know where we are. 

So, measure crank, rod, make sure the bearings are tight, replace all the seals with top end if bottom end is within spec. and if not, do a complete rebuild and mark the hour on meter in your notes. But yah, I would definately set float, correct jetting, try a new oil. 

Peace, 

let us know what you find. 

Edited by Gary YZDOC
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The pics are not very clear but it appears you have some detonation going on and the head is pitted in the squish band on the exhaust side. If that is the case you need to run higher octane fuel, retard the timing, or get the squish clearance reduced to about .045". Any of those or a combination of the three will get rid of the detonation. 

 

Also if that piston has 23 hours on it I don't want to run whatever oil and ratio you are using. That piston has a lot of skirt wear and blow by. See below pics of a 20 hour YZ125 piston. These were 20 really hard hours on a deeply tilled MX track. Premix was Maxima 927 mixed at 32-1 with Avgas 100LL. As you can see a 20 hour piston should have very little to no wear visible. 

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I agree with others on the hrs... This is my 16' 250X piston and rings  with over 100hrs...   So same piston and I ran the piss out of it many times.

 

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Edited by Nevada Al
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Thanks for all the replys guys. Appreciate it. 

 

Ok so i cleaned up the bore and head. The bore came up really good with scotchbrite and wd40, nice even cross hatching and the score marks are less visible and still have crosshatching over them. Definitely cant feel them.

 

The head ive cleaned and cant see any detonation it all looks nice. The powervalve was dripping wet with oil. Have cleaned that out. Will post some photos in about an hour. 

 

Sill a bit upset how worn it is. But yeah i guess its all down to bad jetting and carbon build up retaining the heat. Iv never jetted a bike before. Always been a little scared ill lean it out destroy engines. But guess ill start learning 

 

I would maybe round the hours up to 30ish... but honestly the bike was like new when i picked it up. But who knows  

 

I measure the ring end gap. Old ring was 0.65mm (0.26) new is 0.58mm (0.23) just for some useless information. 

 

Thanks for the help. Il start learning a bit about jetting and setting float level correctly

 

Also bought some Motul 800. Never heard a bad thing about it so im gonna stick with that til next tear down. 

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Edited by Michael N
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If you don't mind post up some pics of the head now that you have it all cleaned up. And also pull the plug after you put a few hours on it to see how it's running. Should look similar to this if your jetting is close. IMG_4181.thumb.PNG.7f2981586ec57dc359906f357965373e.PNG

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50 minutes ago, Michael N said:

Iv never jetted a bike before. Always been a little scared ill lean it out destroy engines. But guess ill start learning

Honestly, it wouldn't happen. It could, but it would be extremely obvious you are running too lean. The bike would start pinging and you would "feel" it's getting hot.

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I don't agree with that /\ /\

You can run lean, and the bike will have sweet power until you burn a hole in the top of the piston. (At least that is what the guy told me) I bought a bike off a guy that said bike was running excellent, had gobs of power, and all of a sudden, no compression. The piston had a hole purned right through it on exhaust side, and the plug was melted BR8EG. I'll see if I can dig up the piston and plug, I usually save stuff like that for conversation pieces. I like things a little on the fat side.

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1 hour ago, Rocket416 said:

If you don't mind post up some pics of the head now that you have it all cleaned up. And also pull the plug after you put a few hours on it to see how it's running. Should look similar to this if your jetting is close. IMG_4181.thumb.PNG.7f2981586ec57dc359906f357965373e.PNG

This is about as clean as i could get it with wd40 and a rag

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Edited by Michael N

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Question... how can you check the crank bearings other than feeling for up and down play on the con rod and feeling for play on the fly wheel? I hear people talkong about measuring something somehow. All i have is Very near calipers and feel gauges though. Wish i had a bore dial gauge too. Might get one before next rebuild and keep learning haha 

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Dial indicator in the spark plug hole. At TDC you can check the bearing, if the dial pauses at the top then that can indicate bearing ware.

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21 minutes ago, Kinger317 said:

Dial indicator in the spark plug hole. At TDC you can check the bearing, if the dial pauses at the top then that can indicate bearing ware.

Thanks for the info ill add that to my list of tools

 

Anyone still reading this thread.. if you know of a link to a good thread about jetting and float setting etc that would be really helpfull as im struggling to find good ones while searching. Cheers

Edited by Michael N

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I would run it at 32:1 with the new oil first check ur plug and go from there. That oil u were using it crap. If nothing else u have a little extra oil for ur brake in,then start rejeting after break in. Just my 2 cents

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10 hours ago, Michael N said:

Thanks for the info ill add that to my list of tools

 

Anyone still reading this thread.. if you know of a link to a good thread about jetting and float setting etc that would be really helpfull as im struggling to find good ones while searching. Cheers

Read the Spanky's jetting guide in the tech sticky...   Float should be between 6-7mm I think.  6.5 is what I set my X too..

Edited by Nevada Al
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Thanks all for you help. Bike is back together and tomorrow i will drain the fuel tank and put new mix of Motul 800 in check the float height and go for a ride. Then see how it runs and check plug color. Will update for anyone interested. Thanks

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Here is a link to Spanky's jetting guide. It is the simplest guide I've ever seen.

http://users.conwaycorp.net/virtus/page2/speed/jetting.htm

Jetting a 2stroke is pretty simple because the bike gives you great feedback. I think it just overwhelms beginners.

 Here is a link that shows how to set float height by blowing air into your carb. I like this way because it's very accurate. Just don't eyeball it like this guy though, use your measurements from the manual. I make a gauge out of stiff paper that has a cutout with the dimension I need.

 

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Yep, Spankys is the go to thread for jetting. 

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Thanks for the info ill add that to my list of tools

It's the same tool you will use for checking/setting timing, so it won't go to waste.
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Update: 

 

Did just under two hours on the YZ yesturday. Wasnt sure how to run it in. Ended up starting it and warming up to temperature at stationary idle (about 5-10minutes) then shutting off. Then the next day rode it for about 20minutes upto about 80percent power then let it cool down for half an hour then after that rode it like normal. 

 

Bike went pretty good but had spooge coming out after the first ride (just replaced muffler packing and checked float height). So next time im out will be purley to re jet the carb.

 

Forgot to do a plug chop while i was out. Oops. Thanks for the help and ill definitely be referreing to Spankys jetting guide ?

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