Reliability and rebuilding of 4 stroke

mafrif

Member
Mar 2, 2004
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Right now im riding a 00 cr250. My next bike will most likely be a crf 450, ive heard alot of good things about them, and ive talked to people who have a yz450 and cr450, and they reccomend the crf. But my whole deal is rebuilding these darn things. My buddy bought a 01 426, he was always being cocky about me working on my bike and him doing nothing to it. Wasnt much longer that his bike took a crap on him and quit running. Took it to the dealer because they suck to work on, he got a new piston, an overall rebuild, and the bill was over a 1000 bucks. This bike is only 3 years old. On my 2 stroke i could rebuild it over five times, and tear apart the cases and replace the entire crank for this price. And i can do most of the work. When we race we are dead even, front wheels within a foot the entire time. I am geared slightly lower, but i dont need to go 90 mph. Also, when these bikes get to be 10 years old, and only worth 1000 bucks or so, people will buy them, the motor will quit running right, and they will have to spend a grand on the motor when the bike is only worth that.

How many of you 4 stroke owners have rebuilt your bike?
how many hours do think it had on it?
How much was it to fix?
What went wrong with it?
Is a 4stroke the answer?


Thanks for your thoughts

Chad
 
B

biglou

That's a lot of questions for one thread! If you search out each question, you'll find all kinds of answers, although they will vary...

Best bet is to follow the manual, and maybe make adjustments to their recommendations as you feel comfortable. The new 4-stroke MX'ers are not nearly as maint-free as you might think. And some good preventive maint. will go a long way toward the reliability of these bikes.
 

Moto Squid

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Jul 22, 2002
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biglou said:
And some good preventive maint. will go a long way toward the reliability of these bikes.

:thumb: a buddy of mine has an 01 yzf426 and had to do a complete top and bottom rebuild last year. He rarely changes the oil, or checks/maintaines anything else. Just rides. His wife has a 250f...I'm just waiting for that thing to go :|
 

Patman

Pantless Wonder
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Dec 26, 1999
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Rich assures me that I'll need the DHH light on my bike before it needs rebuilt because the sun will have burned out. Then again it's an XR :laugh:
 

ben.handasyde

Member
Jan 28, 2004
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Yz250f wouldn't last long either a priced a top end (all new valves ,valve springs and new cam chanin and piston and ring that was $550US all up. thats a lot of money.
 

DEANSFASTWAY

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May 16, 2002
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Yeah theyre starting to get problems, gotta remember though the CRF YZF are racing four strokes .Sort of like Patman added XRs seem to last forever a tribute to the state of tunre theyre delivered in . Just consider those old harleys that the army used to ride they were designed to take a byullet to the cases and still run . Actually these days everything is expensive Gas $1.85 milk $2.89 ciggys $6.00 new Chevy pickup $30k new chevy with diesel eng @$40k its all relative . I really like two strokes and four strokes as well.
 

CRSpeedy

Member
Nov 24, 2002
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I think if ppl are buying 4 strokes because they are cheaper to maintain, they are probably making a mistake unless they plan to get a new one every couple of years. I think there are just too many high speed moving parts, especially in the 250Fs at 13000 rpms. I really like them, but they scare me.
Seems like if 1 little part goes bad, it can take a bunch more with it. JMO
 

Patman

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Yup one little piece CAN take a lot of expensive pieces with it. Hence the need for regular maintenance. Sometimes that regular maintenance calls for replacing things that are a little spendy when they are not broke but have seen their service life. Most folks seem to ride until something breaks and then complain about it where if they had just replaced things and kept all the adjustments within spec they might very well have never seen any problems. It's not just XR's that are reliable as anvils but they seem to need less work to stay reliable.
 

TheJunkMan

Member
Jul 9, 2003
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I agree PAT with the XR's friends of mine have the evil quad version but they are tough as nails and so what if the 400 only makes 28hp at the wheels. but I am not sure you could say that about the current HIGH perf. thumpers. in this case I would take an XR style motor over a CRF style.
 

Patman

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I'm pretty sure if folks kept the valves adjusted and replaced everything from the spark plug to the crank assy when it was needed that even the high performance thumpers could be pretty reliable.
 

Rich Rohrich

Moderator / BioHazard
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Jul 27, 1999
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Patman said:
I'm pretty sure if folks kept the valves adjusted and replaced everything from the spark plug to the crank assy when it was needed that even the high performance thumpers could be pretty reliable.

Absolutely. That's the key, following the service intervals. Once you shake out the new model teething problems (like the KXK/RMZ riders are experiencing) the only folks who have usually have major reliability issues are the ones who try to stretch the service intervals well beyond the recommendations and break parts. The same things happen every day with two-strokes but the end results tend to be less dramatic. 125 two-stroke riders have been fragging motors on a regular basis since the first Elsinores hit the shores. Nothing new about that.
These same guys are now buying four-strokes and wrongly assuming they can be even less aware of service intervals.
Assuming you know more about the fatigue life of parts than the manufacturer can be an expensive gamble, as these guys have clearly been finding out. :cool:

Four-stroke or two if you wear parts out they will evetually break so it's in your best interest to maintain your engine before some part of it blows through the cases. :thumb:
 

truespode

Moderator / Wheelie King
Jun 30, 1999
7,978
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I had my 01 YZ250F last me 2 years without a problem. I replaced the top end once. It then went to a new owner for a year with no problems.

My 03 CRF450 has been pretty easy too. I had an issue with the front fork that seemed to be a bit freakish but nothing with the engine. I put a new piston in it after 15 months. Bike runs very well.

I change the oil and air filter religiously. Some people look at my air filters and think the dirty ones are still new :) I also check my valves regularly and they have always been within spec. I went with SS intake valves just to be safe and so far they have held up extremely well too.

Ivan
 
Mar 3, 2004
53
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i think rich hit the nail on the head. people grenade 2 strokes all the time. now those people are buying fourstrokes, and to compound their problems, they have misconceptions about these new thumpers. if your thinking XR.. you got it backwards. Its a race bike, think of it as one, and the rest of your mindset should follow suit.
 

mud_dawg

Member
Apr 1, 2004
5
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well i own a 98 yz 400 f had the engine down last fall for the 2nd time.We rebuilt the crank. bored, new piston and rings,
top end bearing,gasket kit and crank bearings.now i work at the shop so i only pay cost, but did not cost much more then it cost to redo any of the 2 smokes i have or do own,I have only used bel ray exr 20-50.change the oil every ride.i hill climb the bike and it is my main play bike. i do not think thats bad at all after 5 1/2 years of good ridding.Now i think i may be some what lucky because i have heard of and had to work on some horor story thumpers.i do not think they are any better or any worse then the 2 strokes.

oh wait i did have to replace the counter shaft seal last spring i had a little dribble now and then(lol)


MUD RULES !!!!!
 
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