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

[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................

[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.