Is this much movement normal for a connecting rod? YZ250

layenpipe25
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layenpipe25
Edited Date/Time 3/8/2021 1:28pm
Does this seem like too much horizontal movement for a connecting rod on a YZ250? I don't feel any vertical movement but the horizontal movement seems excessive.

I was getting a runaway throttle and burning oil. I figure it's likely the crank seal on the wet side. The bike is new to me so I tore into the motor a bit to see the condition. It has a Royal rods crank... I have never heard of them but I found them on ebay. Are they junk?

https://youtu.be/O-xK_0EnYwQ

https://youtu.be/pcrewQWzCTo

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JBoneMotorworks 12/20/2020 4:41am
12/20/2020 4:41am
I have not used Royals, only ever used Pro-X. If you do get the crank rebuilt, have the crank builder hog out a little of the plastic stuffers around the inside edges of the crank halves where the rod slides so more oil makes it's way in there.

Regarding the crank play, up down no good, side to side is usually ok, but the best way I have checked to see, (don't move the piston, hold the crank by pinching UNDER the piston, or remove piston), if you have "tilt" in the rod is to pull it up straight, and push on the top of the rod left and right but don't slide the lower big end so you may have to gently secure the bing end from sliding with your finger. You want to see how much play there is..again side to side it normal, but the tilt in the rod is really an indicator...image you are trying to turn your rod into one of those mechanical metronomes..if you have excessive play, time to get it redone.

Prox Rod Kit
Go to KOR for your crank rebuild

Ken did all of my cranks for years and never a failure..tell him I sent you. Good luck. J
layenpipe25
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layenpipe25 3/3/2021 4:58pm
3/3/2021 4:58pm Edited Date/Time 3/3/2021 4:58pm
I was able to fit a 0.9mm feeler gauge for the big end "D" measurement.
Falcon
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Falcon 3/4/2021 8:40am
3/4/2021 8:40am
layenpipe25 wrote:
I was able to fit a 0.9mm feeler gauge for the big end "D" measurement.
It looks to me in video 1 like you have much more than that. I can see the big end sliding back & forth on the crankshaft assy.
To reiterate what I saw above, a little side to side is OK. I'd be worried about that much, however.

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layenpipe25
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layenpipe25 3/8/2021 12:51pm
3/8/2021 12:51pm
It seems like one thing after as I dig into this bike. I am worried to open the cases and find more surprises. How do the transmissions hold up on these? If that has issues I don't know if it will be worth putting the money into it.
seth505
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seth505 3/8/2021 1:28pm
3/8/2021 1:28pm
layenpipe25 wrote:
It seems like one thing after as I dig into this bike. I am worried to open the cases and find more surprises. How do the...
It seems like one thing after as I dig into this bike. I am worried to open the cases and find more surprises. How do the transmissions hold up on these? If that has issues I don't know if it will be worth putting the money into it.
Go by measurements, not feel but I agree with above. That (visually) looks like a lot of play side to side. My experience with a yz 250 was shattered 3rd & 4th gear (not all that uncommon). While frustrating, it might be a good thing in the long run if you open up the entire motor and take a look.

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