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how many have had your motor blow up???

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I have .. and from posts here, and on a few other dirtbike forums, a few replies lead me to believe this is something one can expect to happen regardless of your maintenance habits...

here's the post regarding my situation, specifically:

https://thumpertalk.com/forum/showthread.php?t=263459&page=1&pp=10

myself, my bike is/was an 83 honda xr350r ... just bought the bike a couple month's ago... my first bike/dirtbike. I got to ride the bike for one weekend... I changed the oil after ride like you're supposed to, and I broke the oil drain housing. JB weld didn't work, so I had the cases separated, and replaced the left side case with another one, at a very reputable shop.. I put the motor back together, with some new replacement parts like cam berings, rings, gaskets, seals, all according to specs and procedures exactly as described in the shop manual for this bike..

I started the bike up, and a new noise that wasn't there before I had all this work done on the bike, started coming from what sounded to be the clutch cover area. I had heard that noise on other bikes before and read posts saying it may be normal, so I let the bike warm up, and then revved it up to around 3000rpm for roughly 5 seconds or so, and there was a bang, then oil everywhere, and pieces of the case on the garage floor.

this being my first experience with dirtbikes, I have to say the fun I had on them was awesome, but &%$#@!? is this what I can expect, no matter how much money I spend, or how much maintenance I perform???

what I'd like to know is, out of all the people who frequent this forum, how many of you have had your motor blow up on you? and by blow up, I mean, just that, or had some other catestrophic motor disaster happen to you, either on the track, trail, or like me, in the damned garage 5 minutes after putting everything back together...

I'd like to know the year, make and model of your bike, any symptoms you noticed, what you think went wrong, and what you did about it...

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i rebuilt my 01 rm125 about 6 month ago id say and i rode it yesterday and it needs to be done again..i might be able to get away with jus rings i gotta see when i pull it apart

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Oh yeah, mine blew up TWICE!!

Damage1.jpg

2001 KTM 520SX.

It should never have happened, but my dumb self didn't heed a service bulletin that was out, nor did I stop and check the bike out after a terrible time starting and a noise for 20 seconds when it DID start.

I was in a hare scramble, making a pass for first, coming up to a small double (35 foot or so) on the MX track leading into the woods. I got right beside the current leader, first lap, and went to take the inside over the double, and just before the face, she locked up.

The Automatic decompression nut had come loose and jammed in the cam chain, causing it to snap and cause this catastrophic failure,

Damage? Head (Obviously) four valves, cam chain, timing gear.

ALl parts and back together, by me, in one week.

I then proceeded to blow it up again three weeks later, as apparently I didn't tighten down the one exhaust adjuster nut enough, and it backed off and did the same thing.

Damage? 2 valves, cam chain, and a woodruff key. Whoops! 🙂

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I melted the piston in my 2000 rm 80 two years ago, there was a hole in the coolant hose, and it all drained out. And I used that bike to get from my house to my friends house, so 6th gear pinned out on the road....you get the idea. Anyways I tore the top end apart, and the piston was melted. It's a pretty cool lookin piston though.

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Put a hole the size of a dime in my piston on my old YZ250. I needed race fuel and I didn't know it.🙂 It blew the 2nd time I took it out.

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I had a bearing on a piston pin seize. Not major in itself...until you factor in that the rod broke and ejected itself through the front of the engine. I found another used motor cheap and just swapped the whole thing out. I will never use Pennzoil again.

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OK I had a 96 XR 400 which was highly modified I put a 426 piston in it with 12:1 compression what I did not realize with this being my 1st bike in 15 years (and 1st 4 stroke ever) was that with great power comes great resonsability!! (thanks Uncle Ben for the cool quote) Never boost your compression that much without reinforcing the bottem end.. All I was doing was riding a lil flat track with my 4 year old racing some brats on XR 70's and wham locked up..Broke my connecting rod whick is now jammed in my cylindar!! I am parting the XR out and bought a 2 stroke!! 🙂

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I had a bearing on a piston pin seize. Not major in itself...until you factor in that the rod broke and ejected itself through the front of the engine. I found another used motor cheap and just swapped the whole thing out. I will never use Pennzoil again.

What did that happen on? A motorcycle?! Pennzoil in a bike??

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My '02 KTM (Kan't Take Much) blowed up real good after about a year of excellent maintenance. It's the only four stroke I've been able to waste. The tranny on my WR 2 stoke crapped out after about a gazillion miles, that's OK. The Husky, Yamaha and '80s Honda 4 strokes I've owned have been indestrucktable. I did seize many a small bore 2 stroke back in the 80s both Suzukis and Hondas. 🙂

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Your oil level could have been way too high and caused pressure, in the future you don't have to change the oil every ride. Every 5 to 10 rides would be fine.

The only way that would cause such a failure is if the breather vent was clogged, pinched or otherwise obstructed. Even then, it would take a tremendous amount of pressure to do that much damage. Usually, a gasket will blow first.

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Just got done rebuilding mine....had a valve drop and contact the piston.

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84 XR250. I never had so much engine trouble. Sucked water (and evidently dirt) into the motor, and it started to burn oil. Changed the rings, but evidently forgot to tighten the bolts that hold the cam gear to the cam. After a while, the cam gear cam off, broke the timing chain, and pretty much blew the entire top end. I did have it running pretty good for a year or so, modified some after the repair. Then during one trip to Silver Lake, it lost a valve keeper climbing the dunes. Bent a valve, broke the valve stem. After repairs I could not keep a set of rocker arms in the bike for more than one ride. It would just eat them like candy.

Other than that, my wife siezed a lower end rod bearing on a '91 KTM 125MX. It had sat for so long I think things got a little rusty in the bottom end, so it was no suprise.

My WR400 needed a big end rod bearing after 2500 miles, but it never blew, just got noisy unitl I got it fixed.

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I have never seized a motor but many of my friends have. Almost every time I have seen someone seize there engine it has been there fault. Many times they had it pinned in a low gear or had improper gas mixture 🙂

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my 50 (88), i was riding and fell over throttle got stuck for 2 seconds and all of a sudden the engine stopped i took it apart the engine shattered into 8 peices the barrel cracked broke a valve and destroyed the valve seats

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I posted this question in the xr250/400 forum, but perhaps y'all may know..

on a 4 stroke, when installing the cam, is it possible to install the cam on the wrong TDC?

I mean, when I put the cam in, I was bang on TDC, and the cam gears were lined up perfect, and the cam lobes were down, as the manual shows... But I've read in some of the sticky's and forum posts about when adjusting valves to make sure you are on the right TDC stroke ..

To me, when you are putting the cam in, there is no way to know what stroke you are on, and to me it shouldn't matter... what determines the stroke? isn't it the cam? TDC is TDC right? I can see it when adjusting valves, you don't want intake valves opening during the exhaust stroke, but that's determined by the cam lobes ..

so is it possible to screw up a cam install??? could that be the reason for that gear to have punched its way out?

all the people I talk to about this personally, who saw and experienced the bike before I had the left side case replaced, are positive something wasn't done right when the bottom end was put together... more and more I'm inclined to agree, cause I see no other reason for it to crap out like that...

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Ok, I MAY be wrong - but TDC is just before the spark ignites the fuel.

The cam needs to have released the intake and ready to hit up the exhaust ports, but if your ignition is set wrong (Crank is in the gas expulsion "TDC", not the compression TDC), you will have a really screwed up engine.

THe crank does have two TDC's, although one is not true - and the cam chain keeps the cam in timing with the crank.

CHeck for a mark on your flywheel that goes by your ignition pickup in the ignition side of the case. THe mark should be at the pickup as the piston is at TRUE top-dead-center. Install the cam this way.

I HOPE this is correct for your bike - it's been a while since I did mine, and the XR may be quite different in how it's set up.

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I bought a '91 KTM 300 two years ago. Second day I had it a connecting rod bearing went out. But, the guy I bought it from helped pay for the parts to rebuild it. :applause: Then, the only part we didn't replace broke. The power valve broke into three pieces. Got a new one, slapped it back together, and I still use it as a spare.

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THe crank does have two TDC's, although one is not true - and the cam chain keeps the cam in timing with the crank.

CHeck for a mark on your flywheel that goes by your ignition pickup in the ignition side of the case. THe mark should be at the pickup as the piston is at TRUE top-dead-center. Install the cam this way.

True for the most part. The important (and correct) thing is that the crank is lined up with the "T" of "F" at the index mark on the case. You can see these marks in the small hole on the top of the left side case cover. The larger hole below it is for turning the crank to align everything.

I bought 2 XR200R's ('84 & '85 - the RFVC, 2 carb models) from a guy who had them in boxes in his basement in ME. I put the better motor together and put it in the '84 frame, with a complete bike left over for spare parts. Yes, I had to put the engine together. The tranny of one was together and the other was in pieces (guess which one I used??).

After a year of riding and racing HS in FL, I decided to try some paraffin-based synthetic oil in the ole girl. Well, she liked it - too much. All the familiar noises changed, and everything just felt different. Good, but different. She ran cooler and quieter, but I didn't learn this quick enough.

So, I'm coming out of the woods at our club's riding area prepping for an upcoming HS, thought I was in 3rd and downshifted to 2nd, when I heard the most God-awful racket down there between my legs. Turns out I was in 2nd and shifted to 1st - going just a bit too fast. Sucked an intake valve thru the piston, which destroyed the piston and the cylinder wall where it protrudes into the case. I had to tear that motor down, split the cases and clean all the pieces-parts out of the tranny gears.

The good thing was, I had another jug, piston and head in a box back home. The bad thing was, that jug was dinged and had to be bored out, so I had to order an oversized piston and rings.

Missed the race, btw.

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