Blown Up 4 Strokes

[M5-]

My KTM went down at the end of this year and I have read about the odd other random engine failures here and there. I'm just curious as to how many motors have actually grenaded from snow biking. I'm at the crossroads of rebuild it vs go CR500. Was it just bad luck that I had an issue or is it too hard on the 4Ts revving the pi$$ out of them for days on end.


M5

 

[Teth-Air]

What year and engine?

 

[05900]

Usually rev the piss out of 'em no matter what..maybe it is temp related or maybe it was just time?

What happened,when ??

 

[partypete]

I used stainless intake valves on my crf which probably aren't supposed to be revved to the limiter all day long. Long story short a valve broke off and trashed the rest of the engine and I switched to a cr500 lol.

 

[Uncle si]

Yes. I don't know if 2t is the answer either. Adequate track seems to reduce engine demands a little.

For now I am running a Kx500 with a 146x2.5 track and checking everything very frequently. No plans for cams for this guy!

My KTM went down at the end of this year and I have read about the odd other random engine failures here and there. I'm just curious as to how many motors have actually grenaded from snow biking. I'm at the crossroads of rebuild it vs go CR500. Was it just bad luck that I had an issue or is it too hard on the 4Ts revving the pi$$ out of them for days on end.


M5

 

[noob]

4 strokes are a strong motor, but always thought the snow bike setup was running them to the max. I had a 2moto kit, and if there was more then 2 foot of snow you had to hold that thing wide open. Sure looks like the timbersled kit is night and day better, but still gonna be hard on the bike.

 

[tomk]

I had a Wr that threw a rod, I rebuilt it and the one of the valves went cause I didn't have the head re done, all together it cost me $1400 and a lot of head aches sold it and bought a kx500, rebuilt it once for $180 right after I bought it, haven't touched it since
No valve lash to check and shim, and I change the tranny oil twice a year, never going back for four stroke turds

 

[summitboy]

Interesting topic. I do believe the snowbike kit is murder on these bikes. If you think your gonna slap on a 12,000rpm KTM 4 stroke and get more than 2 seasons u may be delusional ha ha. They were never designed to be held WOT for 4 hours.

One problem with the 4T is cost to rebuild. It's gonna be 2-3000 bucks unless you really know what your doing. A CR500 is very easy to rebuild and is cheaper. Sub 1000 isn't to hard to achieve. That's piston, rod, truing the crank. Pretty simple.

The 500 has way, more power ! LOL

 

[Hawkster]

Yes. I don't know if 2t is the answer either. Adequate track seems to reduce engine demands a little.

For now I am running a Kx500 with a 146x2.5 track and checking everything very frequently. No plans for cams for this guy!

Not trying to be an a$$ but your taking a machine out of it's element . With any of these kits it renders the bike virtually exhausted in a much shorter life span , as if they didn't already have a short enough one spoken by the warranty they come with . It's the nature of the beast , accept them for what they are .
Old school isn't such a bad thing

 

[thejean]

I just bought a KTM 450 for next season and now all this debate? You guys are killing me!

 

[sidehillsam]

In the world of "too many skis" there have been way more 800 Polaris 2 strokes pulled back to the truck verses the Yamaha 4 strokes.

 

[summitboy]

In the world of "too many skis" there have way more 800 Polaris 2 strokes pulled back to the truck verses the Yamaha 4 strokes.

HAHA that's funny. Let's keep the P word out of this forum ! We are talking about old school Honda/Kawi/Ktm engineering here. Not some poorly built 800 motor that has a junk crank, poor EFI system, and built out of tin foil.

Let's stay on track ha ha.

Neither the 2T or the 4T will be reliable long term. Both are to under built for this type of torture long term. I like the 2T for cost,simplicity, lightness, and most importantly Power. Will it out last a 4T ? Who knows. I can say I have seen more 4Ts down/damaged than 2Ts this year, but I'm the only one with a 2T

 

[sodahucker]

Did you have the valves installed by a shop or did you do it yourself? I know a lot of guys talk about just throwing in SS valves without any kind of head rebuild. I'm interested because I just had my CRF head redone in the shop, wondering if I need to worry about it more than I am. I stuck with the Ti valves though.

 

[partypete]

Ive had shops just put valves in and they always wore out quickly. I sent this head to racers ER/ fastheads to get seats cut and rebuilt. About 25 hours later it broke. I think your good with titanium valves because stainless cause so much stress on the valvetrain at max rpm.

 

[M5-]

Usually rev the piss out of 'em no matter what..maybe it is temp related or maybe it was just time?

What happened,when ??

A little back ground. KTM 450 08, rode it for like 6 years one season as a snow bike still ran pretty good even after that. I decided it was time to rebuild the motor so I sent it to one of the best KTM guys around. I had everything done to the motor including a 520 big bore, valve job, single sump conversion all oiling and cam updates yada yada yada. The bike ran really strong but it wasn't cheap. These motors are built for desert racing which can't be all that easy on them either. Sounds like it may have eaten a bearing, it still runs but has an awful knock, it could be the wrist pin don't know yet. It's back at the KTM hospital. This thread isn't meant to be about my engine warranty etc. I just want to know what guys are experiencing now that we've been at this a few years. I can't afford a new 4T motor each season.

M5

 

[Hawkster]

These motors are built for desert racing which can't be all that easy on them either.

M5

Proper valve lashing is really important on overhead v-twins and fours so is it possible the hard SS valves needed a break in check up ?

Used the Vs' as an example since I've worked with them

 

[summitboy]

I dont believe it was valve failure. I believe its a rod bearing. Most likely the top. M5 ?

 

[M5-]

Proper valve lashing is really important on overhead v-twins and fours so is it possible the hard SS valves needed a break in check up ?

Used the Vs' as an example since I've worked with them

It wasn't a valve failure, I forgot to mention I did a valve set after break in, only one valve was marginally out. I'm almost certain it was a con rod bearing which kinda blows cause we installed a brand new con rod from KTM. Valves are Ti in the KTM.

M5

 

[thejean]

Con rod bearing would be no different than in a 2T I wouldn't think. Could also be a lot of gas in the oil causing premature bearing failure, which is primarily a 4T problem.

 

[Crash&Burn]

Lost a main rod bearing on a 06 ktm450 just recently as well. Ridden hard for 4+ years as a snowbike and longer as a dirt bike. Everything but the bearing still looks great, valves have only been adjusted a total of .006 since new. My failure is suspect to be from lots of fun hrs and hard days with a few overtemp times I'm sure due to lots of snow and a few trips towing others out (lol). It sucks to be broken but just like anything mechanical it will break. Just time for a re-buld for me i guess. A friend i ride with had a ktm450 (02 or 03) rode it hard for 4+ years as a snowbike with no motor issues and did less maintenance on it than is done on mine. (Luck of the draw i suppose) . Just some info for ya since you asked, good luck on the repaires.