Excuse me sir, you have some puke on your shirt

BobPA
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BobPA 8/26/2015 6:35pm
8/26/2015 6:35pm
cwtoyota wrote:
You guys are really screwing with my mind right now! Are those all 250cc engines? I just bought my first four stroke... It's a YZ450F. This...
You guys are really screwing with my mind right now! Are those all 250cc engines?

I just bought my first four stroke... It's a YZ450F.

This new four stroke has about 22 hours on it. I'm changing the oil every ride (about 2 hours) with Rotella T6 and have been replacing the oil filter every other oil change with OEM Yamaha filters.

I was expecting this 450F to last me about 100 hours on a piston. What kind of life should a typical intermediate motocross guy expect from a 450F? Piston life? Valves? Crank?


I have had exactly zero issues with my 2008 and 2011 YZ125s. I basically ride them on the throttle stop.
I swap in a new piston & pin at 13 to 15 hours. Every other piston gets a small end bearing. The cranks are good for 80 - 100 hours. I check for bearing play every time I do the top end. I run 32:1 premix with a 50/50 mix of Trick 114 Leaded and Ethanol Free 92 octane pump.

125 clutches last a year of racing/riding (about 55 - 65 hours on the meter per year).
You should be fine. Think air filters and oil changes. I change the piston every 60 hours in my 350 KTM (3 so far). And they all looked mint, rings were still well within spec. Never had to adjust valves in 130+ hours. I put a fresh set of valves in this year for safety reasons. And I am not the nicest person to the rev limiter....
njracer46
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njracer46 8/26/2015 6:52pm
8/26/2015 6:52pm
Shit happens on two strokes as well..

2013 250sx with over 200 hours. 2 pistons done but original crank and clutch. Both are still good, thought that's what went! Bike seized racing 2 Saturdays ago, bought a new 15 on wed. Didn't want to miss one week! Cylinder is at power seal now getting fixed. Then selling it, thinking either bad gas or pulled a lot of dirt through.









harescrambled
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harescrambled 8/26/2015 7:13pm
8/26/2015 7:13pm
pete24 wrote:
heres one its a 14 crf 250 had a piston at 40 hrs, this is 58 hrs i think the rod broke, if someone has a...
heres one its a 14 crf 250 had a piston at 40 hrs, this is 58 hrs i think the rod broke, if someone has a different theroy lets here it





Yep...pretty sure the rod broke Blink . Judging by the discoloration by the conrod pin I'd say the bearing let go, causing the rod breakage

The Shop

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4stroke4DWIN
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4stroke4DWIN 8/26/2015 7:38pm
8/26/2015 7:38pm
jeffro503 wrote:
Damn brother! That sucker blew right out the bottom on that thing. I'm a 2 stroke advocate , but that stuff can happen to those too...
Damn brother! That sucker blew right out the bottom on that thing. I'm a 2 stroke advocate , but that stuff can happen to those too! I consider myself lucky ( knock on wood ) that I haven't had a bottom end go out on me as of yet. I have had to replace a few cylinders and top ends though. Gawd these pics give me a stomach ache.
It's the only 4stroke I have now. Got rid of my 125 and got me a RM 250. That 250f will sit till it rots away......
cwtoyota
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cwtoyota 8/26/2015 7:42pm
8/26/2015 7:42pm
BobPA wrote:
You should be fine. Think air filters and oil changes. I change the piston every 60 hours in my 350 KTM (3 so far). And they...
You should be fine. Think air filters and oil changes. I change the piston every 60 hours in my 350 KTM (3 so far). And they all looked mint, rings were still well within spec. Never had to adjust valves in 130+ hours. I put a fresh set of valves in this year for safety reasons. And I am not the nicest person to the rev limiter....
I'm always good on filters, oil, etc. I'd rather spend a few bucks extra today and ride a fresh bike than run them into the ground and repair catastrophic damage. It happens to just about everyone at some point if you play in this sport long enough.

I thought about picking up that KTM 350, it's one of the best bikes I've ridden. The other bike I considered was the current YZ250F with a 270 or 290 Kit. I decided on the 450 because I should be able to ride it at a lower RPM on average and should be able to get more reliable hours out of it than most other bikes.


MotoKiwi,
It looks like your ring snagged a port. I've seen bad fuel cause detonation that resulted in the ring groove tapering out. Eventually the groove gets so wide that the ring can twist, get bound up and hang on the edge of the port.

There are plenty of other causes for snagging a ring too. Power Seal does good work, I've had several cylinders re-plated by them.



cwtoyota
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cwtoyota 8/26/2015 7:47pm
8/26/2015 7:47pm
4stroke4DWIN wrote:
It's the only 4stroke I have now. Got rid of my 125 and got me a RM 250. That 250f will sit till it rots away......
The only positive to draw from these blown up 250F's are all the modern chassis that can be had for two-stroke engine swaps.
mmcmx
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mmcmx 8/27/2015 12:12am
8/27/2015 12:12am
My experience with four strokes has been pretty simple (two 250 and one 450) Change oil and oil filter every 10 hours. At 100 hours sell the bike.
Motofinne
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Motofinne 8/27/2015 12:59am
8/27/2015 12:59am Edited Date/Time 8/27/2015 12:59am
I have always changed the oil and the oil filter every 4-5 hours on my 4 strokes. Never ever had any issues.
HenryA
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HenryA 8/27/2015 2:55am
8/27/2015 2:55am
This thread gave me nightmares
Fresh
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Fresh 8/27/2015 3:09am
8/27/2015 3:09am
I was thinking about getting a second hand 250f.....
Twist1
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Twist1 8/27/2015 5:28am
8/27/2015 5:28am
TXDirt wrote:
you can buff that out.
Bingo. And some JB Weld.
NATEP231
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NATEP231 8/27/2015 5:43am
8/27/2015 5:43am
Sad thing is my 450 was just running like it always did. Great. I'm just chalking this one up to a shitty, very expensive, unlucky deal. I honestly thought about wedging a 2t motor in BUT haven't heard very many people using the 450 chassis
K-dubbb
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K-dubbb 8/27/2015 6:53am
8/27/2015 6:53am
4stroke4DWIN wrote:
It's the only 4stroke I have now. Got rid of my 125 and got me a RM 250. That 250f will sit till it rots away......
cwtoyota wrote:
The only positive to draw from these blown up 250F's are all the modern chassis that can be had for two-stroke engine swaps.
Agreed! I was going to say the same, save the chassis and drop a zinger in it!
jeffro503
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jeffro503 8/27/2015 8:15am
8/27/2015 8:15am
4stroke4DWIN wrote:
It's the only 4stroke I have now. Got rid of my 125 and got me a RM 250. That 250f will sit till it rots away......
Did you? What year of RM 250 did you get? I'm still madly in love with kine and have that dang 450 up for sale actually. I'm not dead set from getting a 250F , but for right now that old RM 250 is giving me more fun than anything else.
Tracktor
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Tracktor 8/27/2015 10:52am
8/27/2015 10:52am
Huh, we have blown 2 motors in the CR125 this season - Random shit. the RMZ250 is still running strong........SHit happens on all bikes. I will say I do a ton less major work on our thumpers...............
Ing
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Ing 8/27/2015 1:27pm
8/27/2015 1:27pm
Sure, it can and will happen to any machine. 2 or 4 stroke. The difference- the cost of repair when it does.

Pit Row

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davistld01
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davistld01 8/27/2015 2:19pm
8/27/2015 2:19pm
DA498 wrote:
This is the time Im glad to be old, slow and short shift!
Laughing I must agree!
big_g
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big_g 8/27/2015 2:34pm
8/27/2015 2:34pm
NATEP231 wrote:
[img]https://p.vitalmx.com/photos/forums/2015/08/26/102988/s1200_image.jpg[/img] I was bitten by the four stroke big once again.


I was bitten by the four stroke big once again.
Uhhh, ugly. Which bike is this?
NATEP231
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NATEP231 8/27/2015 5:02pm
8/27/2015 5:02pm
NATEP231 wrote:
[img]https://p.vitalmx.com/photos/forums/2015/08/26/102988/s1200_image.jpg[/img] I was bitten by the four stroke big once again.


I was bitten by the four stroke big once again.
big_g wrote:
Uhhh, ugly. Which bike is this?


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