Tell Me Your Horror Stories of MX 4 Stroke Engines

Solid State

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Patman said:
I think it not important if it's 2T or 4T but what type of oil you use :p

That response was immature and clearly intended to take the thread off topic. Besides, everyone knows that 4Ts have a much higher top speed than 2Ts.
 

Okiewan

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Besides, everyone knows that 4Ts have a much higher top speed than 2Ts.
They do?
 

ellandoh

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way faster :laugh:

edit: pay no attention to the parts falling off that FOUR stroke :boss:
 

Rich Rohrich

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Birken Vogt said:
Anway I would like to elaborate on the question if it's not too late. Apparently they need frequent top ends and valve train adjustments. Has anybody tatered one by going too long on these.

Birken - If you had to pick a most common cause of expensive failures, ignoring the service intervals and running parts too long has to be top of the list. Lots of folks are convinced that the OEM service intervals are a scam to sell parts and have no basis in reality.

My personal experience with the current japanese 4t engines has shown me that respecting the service intervals makes for an overall very reliable engine in an MX application, especially with the 450s. The notable exception being the RMZ/KXF 250 engines. They seem to experience more "random appearing" failures. The 2006 KXF250 appears to be a bit more reliable, but still a far cry from what I would expect from a japanese OEM.

The oiling and cooling systems on these bikes don't seem up to the task of sustained dune riding or long distance desert work in my opinion. As they become better MX bikes, they become less flexible overall.

I hope this helps some.
 
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James

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Birken Vogt said:
Anyway I am curious to know if anybody has gone too long on a piston and have it get sideways and take out a cylinder plating for instance or maybe neglected valve adjustment and had something happen. I am familiar with the story of the RMZ camshaft I think it was. Any more like that would be good. Also do these motors just get "plumb wore out" when you ride the heck out of them. My idea of a good day is 2 or 3, 100 mile long rides. Which I have a hard time doing any more due to my ancient machinery it seems :p But that's all right because I also get tired more easily than I used to. It seems like most of the "kids these days" want to just ride their CRFs over some jumps for a half hour, then sit around camp talking about their new gear. They don't really put the hours on that they claim. Basically I am asking if anybody rides serious desert/long distance with these things. I realize they are MX bikes. But as often as I can keep it running I ride my CR500 on these types of rides and it is a MX bike too. If these things do just as well I might get one some day if I get sick of fixing the CR. It breaks stupid things like gaskets and hoses more than anything internal.

Birken
Here's my real-life non-engineering Non-professional-mechanic but 4 stroke owning opinion and obseravtion.

Most of the crowd I ride with has CRF450s and YZ250fs. For a good number of them, their maintenance schedule is somewhat haphazard and the valves get checked when "I think something is wrong because it won't start." or "why is it making that noise?" Unlike me, most of these guys ride one bike everywhere for everything. MX, trails, harescrambles, 100+ mile per day wide open jaunts in WV, etc etc. NONE of them have "tatered" their bikes. I think these CRFs and YZFs have held up surprisingly well. One guy is still on an 02 CRF450 that has been on MANY 100 mile day/200 mile weekends and I know that bike has been ridden HARD. I think he has replaced the valves once or twice. One guy is on a YZ250f that I cannot believe is still running considering all of the stories I have read about MX 4 strokes...but don't get me wrong...I know that motor will be "tatered" before all is said and done.

I think you said "2 or 3" 100 mile rides PER DAY? I don't know anybody that rides that much in a day. 200 miles on a weekend...maybe. After seeing how well their bikes have held up...I am seriously considering taking my YZ250f to WV...but the thought of revving the heck out of the motor for 100 miles a day worries me still.

Good luck!
 

CaptainObvious

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Asking for specific tragic 4T stories isn’t really a fair comparison.

I had a friend who had to spend over $1,000 to have a 2T repaired that had a c-clip installed incorrectly on the piston pin – from the factory. Piston, ring, crank, rod, cylinder and head all destroyed.

I bought my son a used KX85 this winter. When I began to disassemble the bike and noticed that there wasn’t a grease ring between the airfilter and airbox I knew there might be trouble. When I saw there was dirt all over the reeds I knew there was trouble.

Sure enough, piston, rings, renick’d cylinder and a rod kit…over $700 later.

Without proper maintenance, all motorcycles are expensive to own.
 

Birken Vogt

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James said:
I think you said "2 or 3" 100 mile rides PER DAY? I don't know anybody that rides that much in a day. 200 miles on a weekend...maybe. After seeing how well their bikes have held up...I am seriously considering taking my YZ250f to WV...but the thought of revving the heck out of the motor for 100 miles a day worries me still.

Out in the desert it can be a long ways to anywhere interesting so a lot of that time is spend riding at top speed down the road. So, it only takes a couple hours to rack up a hundred, and most of it is not very tiring to the rider anyway.

Birken
 
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