Weirdest mechanical failure or problem

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5/10/2020 9:04 PM

Hey guys! So just a simple one to help pass some time,.
Tell me a story of your weirdest problem that led to a failure or stoppage..

I’ll kick things off.
I was competing in a desert race. About 3 days in a stick flew up and perfectly bumped the fuel tap to the off position.
The bike ran long enough for me to forget the stick hitting my leg and the bike stopped:.

Frantically tracing spark, fuel and electrical possibilities
The tap wasn’t marked so wasn’t clear which was off / on so it took me a good 2/3 minutes to figure it out while bikes were flying past me! lol

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5/10/2020 9:33 PM
Edited Date/Time: 5/10/2020 9:35 PM

That's a one in a million shot for sure!

I was riding at a club track Saturday that has a big step-down jump landing on a steep downhill straight.
Just as I was grabbing gears to hit that jump I saw another guy waving his arms to slow down.
Someone must have crashed on the downhill, hope they're ok.

I rolled slow over the jump, across the flat and over the edge of the downhill. There were three or four people spread out all over the hill looking intently for something on the ground. A lost contact lens?

I gave them a wide berth while watching out for any track junk that might snag my tires.
Near the bottom of the hill I noticed one of the people was a close friend holding a front sprocket with an OH-SHIT look on his face.

His front sprocket popped off without binding up the chain down a very hard, rocky 4th to 5th gear hill after a 50 foot step-down and he didn't crash. That's a lucky day!

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5/10/2020 9:47 PM

In 1983 I had a spark plug blow out of the cylinder only one mile from the end of the Desert 100 race in Washington. Called Mattawa 100 back them.

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5/10/2020 9:51 PM

at a local track on yz125 the spark pluc tip broke off, rattle in the cylinder then out the exhaust pipe. Lost a ton of power and bike wanted to shut off like losing fuel. was able to ride back to truck where it died

later pulled the head off and it only had minor damage. replaced the piston, sanded the head a little and raced the rest of the season

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"If you feel in control, you're not going fast enough" ~Mario Andretti

5/10/2020 10:16 PM

While leading a race a Mammoth, on the next to last lap, I came to a sudden stop in a slower turn. The countershaft bolt backed out of my Honda and locked up the chain. Just prior to the turn was the fast freeway part of the track. I was happy to not have it any worse than a turn tip over.

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5/10/2020 10:16 PM

Weirdest thing was actually 2 weeks ago. Neighbor brought his kids 93 kx80 down for me to look at. It was running 100% so I went through the carb and made an adjustment to the needle. Ran a little better down low, but didn’t want to rev out at all. Couldn’t figure out what it was. Finally got a wild hair after pulling my hair out for 3 hours, ripped off the spark arrestor and the thing ran like a brand new kx80! Told the guy to throw the stock silencer back on.

He put it on later and called me up later and could not believe how good it was running. He put the spark arrestor back on and said it ran like shit, then he put the stock silencer back on again and it ran perfect. Only the second time I’ve ever heard of the silencer being a problem like that.

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2017 RMZ450
2005 YZ250-sold :,(
1998 YZ250
2005 KX250F

80% of the time it works every time
IG @hamdaddyof2 & @2HRacing
Thanks to : Factory Effex, N2Dirt, Acerbis, DT1, Fasthouse, Matix, FMF, ASV, 100% & Mika Metals

5/10/2020 10:25 PM

I finished a long race and noticed this after. I can’t think of a single possible way that the spring disappeared without the pin coming out/peg falling off. PhotoAny thoughts? Obviously the cotter pin somehow came out too

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5/10/2020 10:27 PM

2005 I bought a brand new yz250. First ride the bike pops. The power valve was clipping the rings and caused the bike to fail. Thank god yamaha has the 30 day warranty and they covered it.

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5/10/2020 10:46 PM

blaze 57 wrote:

In 1983 I had a spark plug blow out of the cylinder only one mile from the end of the Desert 100 race in Washington. Called Mattawa 100 back them.

That happened to me today! I was riding a Vet track and all of a sudden I hear a big bang, engine gurgles and dies. I thought I had blown the thing up and pushed it back to the truck. Once I get home the plug is sitting out of the cylinder, hanging by the wire. D'oh!

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5/10/2020 11:32 PM

Nothing to add, just want to keep this up top because I am really enjoying these stories.

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5/11/2020 12:29 AM

My 06 kx125 had a tiny casting flaw on the side of the cylinder which caused a drop of coolant to come out when the bike was ridden. You couldn't see the hole it was that small.

I was friends with the Kawasaki dealer and the bike still had it's 6month warranty so I easily got a new cylinder (and piston I think). They said they'd never seen anything like that before.

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5/11/2020 12:53 AM

GoggleFiend904 wrote:

I finished a long race and noticed this after. I can’t think of a single possible way that the spring disappeared without the pin coming out/peg falling off. PhotoAny thoughts? Obviously the cotter pin somehow came out too

Someone boicotted you.
You've been soooooooo lucky.

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5/11/2020 1:40 AM

Bought a used rm85 from someone that became an elite level pro, I farted around on it for six months, it always seemed to run a little funny. One day it locks up and we take it apart, the piston was in backwards...pinch

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5/11/2020 5:29 AM


Bout 6 months ago was riding at one of my local tracks and put a new plug in my Cr250r after I leaned it out. Rode the entire day and on my last moto the spark plug rattled its way out. Thought I blew a hole in my piston.

On my trusty Cr125r I had quite the amount of rear brake problems. Blew a few seals then got the bore cleaned up. Got a ride or 2 on it where the brake was completely fine. I was riding my backyard track when I lost my rear brake for probably the 3rd or 4th time on this bike. Assuming it was still the bore I threw the bike in the back of the truck pretty frustrated. Once I got home I looked at it for a further inspection and there was brake fluid everywhere, come to fine out my sight glass fell out.

I’ve had a few more smaller ones. Definitely had a few front sprockets fall off from my Honda 2 strokes. And this year at wild boar gncc I completely tacoed one of my foot pegs and didn’t notice it till I was washing the bike.
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5/11/2020 5:46 AM

Non moto, but it's my go to mechanical story. Working in a dealer shop about 8 years ago, another tech had a Honda Rincon 680 a customer brought in, that wouldn't shift when in automatic mode (automotive style shifting), and wanted a service done only after we fixed the shifting problem. Tech checked everything electrical he could, eventually called in a Honda rep, who in turn just told him to keep checking connections/etc. Tech got frustrated with no progress and decided to just do the service anyway, and found out that the valve clearance was so loose that it wouldn't rev high enough to hit the RPM required to shift.

Moral of the story, always do a compression/leak down test first, no matter if you think it's an electrical or fuel issue.

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5/11/2020 5:53 AM

Many years ago, I some how found a way to close the spark plug gap, while the engine was running. Of course, engine wouldn't run that way. Can't even remember the bike. Bike acted like it had no spark, but I was surprised to find out why, when I pulled the plug out. Put a new plug in, & never another issue like that.

If you've ever ridden down old railroad tracks (after they've been removed) , you probably remember seeing lots of railroad debris - spikes, pieces of metal, etc. I always figured the odds of getting a spike positioned just right to go into a dirt bike tire were slim to nil.

I Can confirm that when you do find just the right spike at just the right angle, it does make a big hole in the tube/tire and you realize pretty quickly that you have a flat!

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2016 YZ250X

5/11/2020 6:03 AM

I had a 78 YZ 400 that I raced in vintage a few years back. I guess I screwed up when I torqued the nut on the end of the crankshaft, I was at a race, finished my moto and as I came off the track the bike just stopped in it's tracks. The nut had backed off and cut a perfectly cylindrical hole in the case. I took that as a sign that my relationship with that particular bike needed to come to an end!

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5/11/2020 6:03 AM

Couple years back i was riding my 2007 YZ250 and suddenly the engine grenaded while the throttle was full open. After the rebuild witch included a whole new crankshaft, piston and cilinder it did not start. After hours and hours trying to fix the error i still not could bring it alive. Tried several sparkplugs and a CDI, altough there was a spark. Also was there enough compression. Then i did the whole rebuild again.... Even tried to bumpstart it behind a car. But no way the engine wanted to come alive. I became nuts. Then someone told me to swap the flywheel.... i did and one kick and it started. So it seemed that while i grenaded the motor with blocked rear wheel the magnets on the flywheel where placed in a different spot because of centrifugal power when the engine suddenly stopped while running high RPM's....

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5/11/2020 6:11 AM

2005 I was riding a practice track at my buddies, and started hearing some clicking in the rear end. I stop to check out the bike, turns out i broke the rear spring. The next day i call my dealer and tell him what i did, he says no you didnt. Im like dude, i broke a spring. He said bring it in and we will check it out. Brought it in an he was shocked. They didnt charge me for a new one which was cool.

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Kevin Windham, The man, the myth, the legend! Gonna miss seeing this man on the line.

-----Do or Do not, There is no try-----

5/11/2020 6:21 AM

Not really weird, but I was doing runs for a desert race to work out gearing and top speed. Got up to about 180kph and I heard a momentary crunch and the rear wheel locked up.
Luckily I was on loose soil and it was actually confusing for a moment as It suddenly was quiet and there was a floaty feel as the bike drifted to a stop.

Nearly every single part of the engine was destroyed including cases. Was unable to find what actually went wrong due to the complete destruction of the engine.
Suddenly became shy about high revving expensive 4 strokes 😝

Awesome stories! Keep them coming!

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5/11/2020 6:27 AM
Edited Date/Time: 5/11/2020 6:30 AM

1 - carb stuck wide open on the fastest section of the track, noticed it just before the 180°
2 - the silencer grid broke, blocking 30% of the power
3 - the rubber mount of the carb cracked (on a 6 months old bike)
4 - a dick sabotaged my new bike in SX, putting a bit of sand in the gearbox when not watching
5 - clamp broke and snap my brand new road bike in half, noticed it just after stoping the bike
6 - rear master cylinder broke (on 2 years old bike)
7 - plug popping out cylinder on a car
8 - red 4 in 1 cracked on a car
9 - broke ABS on a hard emergency braking on a car
10 - exaust fell off and exploded rear tire and wheel on a car on crowded, wet highway
11 - broke alternator on a hydraulic controled car (steering, brakes, suspensions)

As none of the above resulted in a crash, i decided to take it easy from that point, i guess it is not bad ass but that is enough warning candles.

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5/11/2020 6:29 AM

2002 Yamaha Grizzly 660. I rebuilt the top end with a Wiseco hi-comp piston. Put everything back together and tested the starter just to make sure it was connected. ATV started on the first _whisper_ of the starter!!! YAY!!!!! Filled it up with gas, rolled it out and hit the starter again. CLICK... GRIND... bad noises. Hmmmm.... tried pull starting and it wouldn't BUDGE. Something is obviously locked up. I eventually got to the valve caps and much to my horror discovered that two of the tappet adjusters were GONE. WTH???? Oh, there's one of them!!! I rescued it from the top of the head but #2 was no where to be seen.

For some reason or another, I had the idea to lay the bike on it's side. I did that. Then I flopped it down on its wheels, and removed the flywheel inspection port. It was evening, the sun was setting, and I kid you not, a ray of light from the last vestiges of sun shot across the prairie and shone directly on the valve tappet adjuster screw sitting in the bottom of the case, visible from the port. It was like Indiana Jones in the map room when the light shines down the pendant to reveal the location of the Ark!!!

I put both of those back on with a new nut, and the bike ran for another 10 years.

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2015 Kawasaki KX 250F
2015 GasGas TXT Racing 125
2015 Husqvarna TC 125
2018 KTM 150 XC-W

5/11/2020 6:30 AM

I had a 2001 CR250 that for some reason I had the hardest time getting the carb boots/clamps back on after having the subframe off. At the farthest possible place on the track from the pits, I landed hard and it popped off, and instantly stalled. Pushed that thing uphill through mud to get it back to the van. Took awhile to finally figure out what happened too!

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5/11/2020 6:41 AM

Was adjusting the throttle free play on my 2003 Honda CR250. Got it adjusted to just about where I wanted and thought I should test ride to make sure.

Kicked it over and it cranked right up (engine ice cold). BUT, throttle stuck wide ass open. Tried a few things to get the engine killed but nothing worked. After about 20 seconds, there was a “clunk” and it stopped running. After disassembling, found the piston, cylinder and head toasted, and the crank blew apart taking out both case halves.

Glad it happened in the driveway and not on the track. Needless to say, I check the damn throttle all the time now.

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5/11/2020 6:45 AM

1995 CR125. First bike I bought new and I had about 6-8hrs on it. She took a shit and bogged in a corner and lost all compression. I took the top end apart and found a circlip came out and ruined the cylinder. Engine had never been apart and the bike was brand new basically. Honda told me to pound sand. Oh well....

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5/11/2020 6:48 AM

On my 99 RM125 I fell over in a corner because I lost power. Thinking it was my fault I tried everything to get the bike to restart. Pulled the cylinder and found the ring locating pin popped out and ended up on top of the piston allowing the ring to turn and lose enough compression to not run. Other than some marks in the head everything was fine so I threw another piston in and got out there for the second moto.

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2018 KTM 250sx
Instagram CamaroAJ

5/11/2020 7:10 AM

I bought a used RM250 and the thing was wicked hard to start and would foul plugs. Went through everything and all checked out OK. One time while looking through the back of the carb when the subframe was off I noticed the slide was higher than it should be. The issue ended up being a too short cable. Just enough to mess things up.

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5/11/2020 7:24 AM

Phillip_Lamb wrote:

at a local track on yz125 the spark pluc tip broke off, rattle in the cylinder then out the exhaust pipe. Lost a ton of power and bike wanted to shut off like losing fuel. was able to ride back to truck where it died

later pulled the head off and it only had minor damage. replaced the piston, sanded the head a little and raced the rest of the season

I had the same thing happen in 83 on a 1983 RM250. It gouged up the top of the piston and the cylinder head but no other damage!

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5/11/2020 8:02 AM

Post-Vintage cross country racing a '79 Yamaha IT175. Fell on a muddy downhill, and took a couple minutes to get myself righted and back on course. After the crash, the bike ran terribly, could barely keep it running at low rpms.

At first I figured it must have flooded lying there the way it did, and I figured it would clear out shortly. It didn't. So then I thought the assumed flooding must have fouled the plug. So I stopped trailside to change it out. That would fix it, right? It didn't. Still ran like crap. Could barely keep it running, and stalled several times. It would refire, but barely ran.

It was the last lap, so I just cut it short and headed back to the pits and loaded. During bike cleaning, I discovered that the choke lever had somehow been depressed- likely during my crash. How that happened I have no idea. But raise the choke, and Kablam, runs like new.

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5/11/2020 8:04 AM

Hearing about a stuck throttle, some old guys will remember the 78 RM 250's had aluminum slides. Had mine stick at the top of the uphill jump at Rawhide Park.

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