2 stroke vs 4 stroke engine lifespan

[SMOKEU]

I've been looking around on Trademe at various modern dirt bikes, and I've seen that a lot of the 4 strokes are having top end rebuilds at relatively frequent intervals, and I've seen that some of the 2 strokes are going for a huge number of hours before needing a top end rebuild. So are the modern, highly strung 4 strokes in need of frequent top end rebuilds? How much longer would a 4 stroke last than a 2 stroke between rebuilds, assuming that both are maintained well and use good oil?

[vr4king]

And here we go again folks:yawn:

[blackdog]

Just as important, you failed to ask the difference in cost between rebuilding a 2t and a 4t top end.

[bogan]

Depends how you ride it. As a rule of thumb, 2Ts require more frequent top end rebuilds but a 4T rebuild costs more.

[mossy1200]

some of the 450s (eg yzf)4strokes are needing valve adjusting every 15hrs and top ends every 30hrs while 2 strokes top end 80 odd for average rider.

Enduro version of yzf is wr450 which with a lower state of tune last alot longer between rebuilds

[flyingcr250]

Ive done over 150+ hours on my 4t and the valves are still well within spec, i usually do pistons aboit every 80 or so hours, frequent oil changes and air filter cleaning will prolong any motors life weather it be 2t or 4t, as for cost, who cares about that??

[cheese]

To be honest if you can DIY its about the same price. If you pay for it to be done, you will be stung. You can just pay to get your valves checked by a local bike shop.

Time wise its about the same intervals.

[scott411]

some of the 450s (eg yzf)4strokes are needing valve adjusting every 15hrs and top ends every 30hrs while 2 strokes top end 80 odd for average rider.

Enduro version of yzf is wr450 which with a lower state of tune last alot longer between rebuilds

the race 250F's are like that by none of the 450, even top 15 national riders in NZ get at least 50 hours out of 450 pistons, most of them more, and none of the 450s are hard on valves because not many people can rev them that hard,

MZ 250 2ts in race conditions need pistons at around 35 to 40 hours, and 125's were 15 to 25,

the big difference is with four strokes, if you do not do them when due it can get a whole lot more expensive fast,

[gammaguy]

there are many laws of physics,the one that applies to this question would be this one:

THE CANDLE THAT BURNS TWICE AS BRIGHT BURNS HALF AS LONG.

Do the math................:blink:

[ktm84mxc]

Wud have to agree with Scott if buying new a 250f - 50 hours, 450-100 hours if being raced at mx , being trail ridden you could add in 50% hours as your generally less at full throttle.
Most Mx four strokes use titanium valves these require regular servicing for prolonged life, the enduro models WRF,CRFX, RMX, EXC use stainless steel valves and have longer service intervals .
Some riders can get huge hours on there bikes, were as some just can't it's all about how you treat them.
Two strokes Scott is right in the hours under race conditions for MX , in enduro/trail biking you can easily add 50% to the hours, my KTM 300 a piston at a 100 hrs is normal but cleaning the power valve assembly shud be done every 50 hours.
The pistons cost about the same 2 verses 4 on the same size engines the costs creep up when a four stroke needs valves etc.

[barty5]

some of the 450s (eg yzf)4strokes are needing valve adjusting every 15hrs and top ends every 30hrs while 2 strokes top end 80 odd for average rider.

Enduro version of yzf is wr450 which with a lower state of tune last alot longer between rebuilds

Shit who told you that i got 80hrs out of my yzf450 did the rings then a piston at 115hrs and reset the valves they where only just out bike was stolen at 144 hrs and other than oil and filters etc that all that was ever done to it. And yes it did get a hard time. as cheese said if you can do it your self the cost is about the same.

[Crasherfromwayback]

Shit who told you that i got 80hrs out of my yzf450 did the rings then a piston at 115hrs and reset the valves they where only just out bike was stolen at 144 hrs and other than oil and filters etc that all that was ever done to it. And yes it did get a hard time. as cheese said if you can do it your self the cost is about the same.

Probably an owners manual. And without wishing to seem rude...I wouldn't buy one of your old bikes going by your service history.

[CRF119]

Valves wear out because people don't know how to clean and re oil air filters correctly! I spray silicon inside the rubber boot before the carb this catches any dust that may get through. Between filter changes i wipe it with a white rag, If i see any on there then i know i didn't do my filter properly. (Ive never had any dust past the filter) But plenty of bikes that ive worked on are coated in dust past the air filter. One so bad he could have grown plants in side the carb boot.

Once the valves start getting out of spec throw them away because after that they will just keep streching

I brought my 08 CRF450 in October 07.

Every 5 hours i change oil unless it was a hard ride on clutch and engine

Every 50 hours i do rings

Every 100 hours i replace the piston

So far i am at 180 hours a valves are still sweet.

I also brought the bike new so i have one more set of rings left before i have to start paying for rebuilds. So so far its been cheap as to maintain.

[pete.ktm]

got a '06 KTM 450 EXC, got it at 80 hours and just coming up to 300 hours. ridden pretty easy on trail rides.

up till now only regular maintenance; oil, air filters and valve adjustments every 30-50 hours which i do myself.

last adjustment the intake valves had no adjustment left which is a known thing on this model.

i pick it up tomorrow and i'll be $2k poorer. and thats with me buying the valves and piston off ebay and them doing a few other little bits.

sounds a lot but $2k for 4.5 years and 220 hours worth of fun is probably a pretty good investment.

but gotta admit i was thinking about a 2 stroke or a reliable jap 450 when they quoted $2k just coz the intake valves were gone.

[scumdog]

If you're talking about road bikes?

Well I've only ever had one top end rebuild including pistons/rings.

But then old Harleys don't need jack-shit in the way of maintenance.

About 4 spark plugs in 100,000km plus oil & filter changes.

[flyingcr250]

got a '06 KTM 450 EXC, got it at 80 hours and just coming up to 300 hours. ridden pretty easy on trail rides.

up till now only regular maintenance; oil, air filters and valve adjustments every 30-50 hours which i do myself.

last adjustment the intake valves had no adjustment left which is a known thing on this model.

i pick it up tomorrow and i'll be $2k poorer. and thats with me buying the valves and piston off ebay and them doing a few other little bits.

sounds a lot but $2k for 4.5 years and 220 hours worth of fun is probably a pretty good investment.

but gotta admit i was thinking about a 2 stroke or a reliable jap 450 when they quoted $2k just coz the intake valves were gone.
My 2011 ktm 350 blew up last sunday, fucked cams, cam bridge, head, piston and cylinder $4100, and yep im going back to a 2T...

[jt119]

My 2011 ktm 350 blew up last sunday, fucked cams, cam bridge, head, piston and cylinder $4100, and yep im going back to a 2T...

injoy you tube till the bike gets here

[pete.ktm]

My 2011 ktm 350 blew up last sunday, fucked cams, cam bridge, head, piston and cylinder $4100, and yep im going back to a 2T...

damn that was probably going to be my next bike.

but i was going to wait for the 2nd year model.

was there a reason it exploded?

[gammaguy]

If you're talking about road bikes?

Well I've only ever had one top end rebuild including pistons/rings.

But then old Harleys don't need jack-shit in the way of maintenance.

About 4 spark plugs in 100,000km plus oil & filter changes.

Like I said

Bright candles-short

Dim Candles-Long


sir,you have a very long life candle between your knees

[barty5]

Probably an owners manual. And without wishing to seem rude...I wouldn't buy one of your old bikes going by your service history.

there is no point doing piston etc etc if they arnt needed everything measured up fine and oil and filter where always done every 5-6 hrs so dont see the problem.

[Crasherfromwayback]

there is no point doing piston etc etc if they arnt needed everything measured up fine and oil and filter where always done every 5-6 hrs so dont see the problem.

I agree with you 100%. But I think you're extremely lucky getting away with not doing valve adjustments until you got to the hours you state without serious trouble. Dunno if your model YZ has titanium valves or not, but if it has, valve spring replacement is a must too. The titanium valves are so light they get away with running very light valves springs, which lose tension very easily with heat...and can easily fail letting a valve clip the piston.

An RMZ450 (and lets face it, all the Jap brands are very similar) manual will tell you to replace the piston @ 10 hours. Now we all know they're covering their arse by saying so, and it's a total waste of money doing so. But once you get up over 50-60 hours...you're running the guantlet big time in my opinion. But hey...if it works for you, then all good.

Makes my used 450's a good bet for buyers though. As I've never run more than 20 hours on top ends. And I do the oil and filter every single time I ride them.

[Jinxycat]

Ive done over 150+ hours on my 4t and the valves are still well within spec, i usually do pistons aboit every 80 or so hours, frequent oil changes and air filter cleaning will prolong any motors life weather it be 2t or 4t, as for cost, who cares about that??

like to retract that statement??

[flyingcr250]

like to retract that statement??

*hangs his head in shame*

[CRF119]

If you're talking about road bikes?

Well I've only ever had one top end rebuild including pistons/rings.

But then old Harleys don't need jack-shit in the way of maintenance.

About 4 spark plugs in 100,000km plus oil & filter changes.

Road bike engines last much better because the pistons have a much larger skirt and most of its cruising.

Harleys don't ware out because they are decedents from the tractor family

[ding322]

Man you guys are worring me with all the talk of maintenance and rebuild intervals etc so then I did the manly thing and consulted the manual for the RMz and thats just made it worse :crazy:

Manual states Piston and ring replacement at 12 hour intervals. But that is for top end MX i guess.

[SMOKEU]

Man you guys are worring me with all the talk of maintenance and rebuild intervals etc so then I did the manly thing and consulted the manual for the RMz and thats just made it worse :crazy:

Manual states Piston and ring replacement at 12 hour intervals. But that is for top end MX i guess.

Yours should do at least 4 times that mileage if you look after it properly.

[motor_mayhem]

I agree with you 100%. But I think you're extremely lucky getting away with not doing valve adjustments until you got to the hours you state without serious trouble. Dunno if your model YZ has titanium valves or not, but if it has, valve spring replacement is a must too. The titanium valves are so light they get away with running very light valves springs, which lose tension very easily with heat...and can easily fail letting a valve clip the piston.

An RMZ450 (and lets face it, all the Jap brands are very similar) manual will tell you to replace the piston @ 10 hours. Now we all know they're covering their arse by saying so, and it's a total waste of money doing so. But once you get up over 50-60 hours...you're running the guantlet big time in my opinion. But hey...if it works for you, then all good.

Makes my used 450's a good bet for buyers though. As I've never run more than 20 hours on top ends. And I do the oil and filter every single time I ride them.

I have an 06 manual thats says do them every 50 hours and I did the one on my 06 450 at 80 hours and it was all good. That's only my experience/sample of 1 though.

It seems very reasonable to put stainless valves in your 450 as honestly has there ever been anyone short of perhaps top level racers who fully utilise the power of them?

[Crasherfromwayback]

It seems very reasonable to put stainless valves in your 450 as honestly has there ever been anyone short of perhaps top level racers who fully utilise the power of them?

I used mine a lot for motard and road racing...so you do have them at full throttle/revs way more than you would in the dirt.

[Crasherfromwayback]

I have an 06 manual thats says do them every 50 hours

I'd be surprised. My '05' manual states every 6 races or 12 hours, as does the '08' book.

[Crabby]

Harleys don't ware out because they are decedents from the tractor family

Concrete Pump family too :wings:

[057rxz]

And here we go again folks:yawn:
AHAHAH so true...the battle will never stop... people just dont get that its a preference.. if you can be bothered with a 2t then go for.. I LOVE THE FUCKORS ITS WHY I OWN 2 OF EM... soon to be ONE!! but if your not familiar with shiz and just wanna play get a lumpy 4 batt. IMO no hate to 4t owners... i love 4t's aswell its why i OWN 3

[057rxz]

got a '06 KTM 450 EXC, got it at 80 hours and just coming up to 300 hours. ridden pretty easy on trail rides.

up till now only regular maintenance; oil, air filters and valve adjustments every 30-50 hours which i do myself.

last adjustment the intake valves had no adjustment left which is a known thing on this model.

i pick it up tomorrow and i'll be $2k poorer. and thats with me buying the valves and piston off ebay and them doing a few other little bits.

sounds a lot but $2k for 4.5 years and 220 hours worth of fun is probably a pretty good investment.

but gotta admit i was thinking about a 2 stroke or a reliable jap 450 when they quoted $2k just coz the intake valves were gone.

450exc's are fuckn work horses... i love those bikes!! should have never sold my 525. Sigh! but now i own a cr500 so fuck you! ahahah jk jk

[Crasherfromwayback]

Two ticks mate :-)






You're wearing that picture out mate. Unlike the bikes in it.

[del-solider]

You're wearing that picture out mate. Unlike the bikes in it.

:shutup:

This man speaks the truth!

[Blagger]

You're wearing that picture out mate. Unlike the bikes in it.

Give it up, Crasher - haven't you twigged that Stylo doesn't actually own any bikes at all and is only trolling?
The guy's a spankcarrot apartment-dwelling eedjit who's found a bunch of pictures of some vmx 2ts.

On to the subject in hand - do I get the feeling that 4ts are getting higher in compression and performance and 2ts have followed suit?
I'm way behind the curve but when I get off my ancient 2-wheel sofa and get on my mate's CRF450 it feels like it's gonna blow at any moment.

To me the elephant in the room is the gradual change from a 250 being a gutless starter bike to a 250 being a respectable dirt weapon (2t or 4t) - I reckon it was the MX crowd wringing every last drop out of the cc's available that did it.
Keeping in mind that F1 cars are, so I hear, about 2.5litres- the new KTM MX bikes being 150cc size isn't that surprising.


Everything is being pushed to it's limits,2t and4t, as an earlier poster said, it's getting to be purely a matter of personal taste these days.


I've got an old fat thumper and I would LOVE a 2t as well.
Also I'm teaching a skinny runt how to ride and I'd like a trials-type 2t small bike for her



Oh fuck it, I just want a double garage full of bikes

[scott411]

Give it up, Crasher - haven't you twigged that Stylo doesn't actually own any bikes at all and is only trolling?
The guy's a spankcarrot apartment-dwelling eedjit who's found a bunch of pictures of some vmx 2ts.

On to the subject in hand - do I get the feeling that 4ts are getting higher in compression and performance and 2ts have followed suit?
I'm way behind the curve but when I get off my ancient 2-wheel sofa and get on my mate's CRF450 it feels like it's gonna blow at any moment.

To me the elephant in the room is the gradual change from a 250 being a gutless starter bike to a 250 being a respectable dirt weapon (2t or 4t) - I reckon it was the MX crowd wringing every last drop out of the cc's available that did it.
Keeping in mind that F1 cars are, so I hear, about 2.5litres- the new KTM MX bikes being 150cc size isn't that surprising.


Everything is being pushed to it's limits,2t and4t, as an earlier poster said, it's getting to be purely a matter of personal taste these days.


I've got an old fat thumper and I would LOVE a 2t as well.
Also I'm teaching a skinny runt how to ride and I'd like a trials-type 2t small bike for her



Oh fuck it, I just want a double garage full of bikes

by this post i do not think you have really followed motocross for a while, 250cc racing was the preimer class from the mid to late 80's on, the 450's only came in as four strokes were allowed a higher limit to race in this class from the late 90's, again the 125's was seen as the feeder class and thier limit was 250cc for the four strokes,

the four strokes rev a shit load higher than the 2 stroke machines they replaced,

250cc trail bikes are still learners bikes, as they have always been, we do not really have the big bore 4 stroke dirtbikes anymore (TT500, XR600 etc) due to the fact that 450cc bikes put out way more horsepower than most people can use now,
(I know there are a few euro exceptions, but these are getting smaller as well)

[Jay GTI]

My 2011 ktm 350 blew up last sunday, fucked cams, cam bridge, head, piston and cylinder $4100, and yep im going back to a 2T...

Fark, that's not good reading... :blink:

I've had a few issues with mine, currently doesn't like shifting from 1st to 2nd, but I put that down to the monkey dealer mechanic who had the gearbox apart in the last recall. Being an early production bike, I was expecting a few teething problems but while I think KTM know how to put an engine together, I'm far more concerned about the work done under factory recall.