A reason to follow service intervals for RMZ & KXF 250 owners

[Rich Rohrich]

The new breed of four-strokes have much shorter service intervals than the old XR style bikes we are used to. Despite the service interval recommendations in the manual a lot of folks who are racing these bikes are choosing to ignore them.

Under the heading a picture is worth a thousand words here's a graphic example of what tends to happen when you run the stock valve components too long. These pics are from a KXF 250 that I worked on yesterday.

If the springs and valves would have been changed more in line with the service intervals this wouldn't have happened. As a result the head is destroyed beyond repair, the barrel is junk, and the rod was bent and a bunch of other pieces are now scrap. Take specific note of the exploded tappet/bucket in the cam side view. Luckily the rider didn't get hurt when it let go. The interesting part is, with all this carnage the cam journal without an oil groove that people are worried about is in perfect condition.

The moral of the story is, if you are racing a 250F invest in an hour meter and pay attention to the service intervals.

Click the links below for the full size hi-res versions of the pictures

KXF Head & Piston
KXF Head close up
KXF Head broken bucket
KXF broken valve

 

[Rich Rohrich]

While we are on the subject of reliability there is something that I have been meaning to address on these engines for a while but up until now it has been fairly speculative on my part so I have been reluctant to say anything. The main bearings in the KXF/RMZ engine are pressed into the cases with a very light interference fit, but unlike most designs of this type there is no locking plate in the case to keep the bearing secure. Keep in mind this engine has no counter balancer so there tends to be a bit more crank mass than say a YZF250 and as a result it looks like it subjects the main bearings to a different type of load than a counter balancer equipped engine.

The point is, more and more it looks like as these engines get a lot of hours on them the main bearing saddle in the case looks to be loosening up and allowing the main bearings to move around. This looks to be especially prevelant on the ignition side. Red loctite usage and carefull installation of new bearings looks like a temporary fix, but long term these engines when raced will probably wear the cases to the point of needing complete replacement.

Eric and I are looking at the possibility of using a bearing and lock plate setup similar to what Yamaha and Honda are using in the hopes of keeping folks from having to treat case replacement as part of their annual maintenance. As we work more on this I'll pass along any info I can. In the mean time pay particular attention to the main bearings when you are doing your crank maintenance.

 

[VintageDirt]

I tell ya, some people...:)

But seriously, Rich I bought an hour meter and I can't for the life of me find maintenance intervals in hours. Is it my 3rd grade reddin compenshin or somethin else. Maybe you could list the important intervals in hours. :worship:

 

[Chili]

Ok time for the hot seat Rich. We are probably giving in to the lure of the darkside for LazyBoy for next season. He really isn't fond of the handling of the Yamaha's so we had kind of ruled out the YZF. Honda really doesn't have a dealer locally that supports our MX scene so I had always preferred to spend my money going yellow or green and supporting what I felt were superior dealers for my needs. Based on the bearing issue do you feel there will still be more reliability/design issues with the KXF/RMz even if you are anal about your maintenance intervals? Based on the Green/Yellow issues this year I had pretty much decided to go red for 05 but everytime I go out to the Zook dealer I leave wondering/hoping the bike is better for 05 and worth a risk so I can support the dealer.

 

[JUSTRIDE415]

I printed these pictures to give them to my suzuki riding buddies!

 

[Rich Rohrich]

Doug - I've owned a whole bunch of Suzukis over the years and loved each one, but at the risk of annoying people and being branded a Suzuki hater I'll tell you what we have told our other customers. Based on the way things stand today I would strongly advise AGAINST this bike if it is going to be raced/ridden hard on a consistent basis. There are far too many design and quality control issues to recommend it. It seems to be a nice bike for trail riders and slow pokes, but racing one will prove to be very expensive.

Now, down the road we'll have a systems solution to the valve issues from Kibblewhite (springs, valves and tappets) so the valve issues should go away. Suzuki is claiming to have fixed the transmission and cooling system problems for 05, so that's a plus.

If you decide have Troy race one I would suggest buying a spare head and setting it up with the Kibblewhite parts so it can be swapped out at the first piston change (15-20 hours) . You can easily sell off the spare OEM kitted head. Past that if you get used to the rather intense service requirements and roll the bikes over every year you aren't likely to run into any of the long term issues and will have a pretty nice bike. What new issues will crop up with the 2005s remains to be seen. I was really disappointed with how this bike turned out. I really had high hopes for it.

Unfortunately seriously racing any of the new 250Fs can be seriously expensive but this one pushes it a little too hard.

Maybe ochster will see this and share some of his experience with the bike. He was wrenching for a national level rider and has some really good insights on the issues that come with racing the RMZ.

I tell ya, some people...:)

But seriously, Rich I bought an hour meter and I can't for the life of me find maintenance intervals in hours. Is it my 3rd grade reddin compenshin or somethin else. Maybe you could list the important intervals in hours. :worship:

Wes - I'll try and put together a list of stuff for the various bikes. Good idea. :cool:

 

[Chili]

Maybe ochster will see this and share some of his experience with the bike. He was wrenching for a national level rider and has some really good insights on the issues that come with racing the RMZ.

Thanks for the reply Rich. That's pretty much where we were at but I keep trying to find excuses to support this dealer.

As for ochster did he switch riders? because I thought Ryan raced a CRF this summer instead of the zook.

 

[Rich Rohrich]

As for ochster did he switch riders? because I thought Ryan raced a CRF this summer instead of the zook.

I haven't had a chance to talk to him lately. Maybe they switched brands for the reasons we just discussed.

I'll send him a PM and ask him to jump in on this thread.

 

[ochster]

Rich has summed up the yellow/green versus other colors dilemia very well. Putting that aside the RMZ is a great handling and very competitive bike.

Oversize radiators on the 04's are a must with fast riders and hot climates using a 1.6 or 1.8 cap. The oem radiator shrouds limit flow out the back of the radiator. A couple of stragtegically placed holes/slots helps. As does spacing the radiators out from the frame 1/2"-3/4". We use aluminum spacers and longer bolts with a longer connecting hose on the top. At a minimum do the spacing and holes/slots with a Boyesen water impeller kit and 1.6 cap, it works. We have had good luck with Race Kool from Precision Automotive, or 80-90% water and 10-20% antifreeze. Water pump seals are short lived, keep a spare or two. Headgaskets are notorious for leaks even when new. All the fasteners on the engine cases will loosen up regularly. The fastener quality is very poor, do not over torque. This is why many have leaking center cases and right side covers. Safety wire the drain bolt, its already drilled. The flywheels have been known to seperate. Do a visual check by pulling the left side cover occasionally, you will see damage to the magneto if the center is coming loose. They do use oil when rode hard, 2-3oz. in 30 minutes is common under race conditions with a higher compression piston. A hinson clutch cover will give you added capacity and delete the cover window wich some have broke. The rear shock linkage will bend bolts under hard moto. If your going have the frame powder coated, weld up all the gussets (especially at the stem head) and reinforce the steering stop. It's tiny and when it shears it takes out the frame and fork leg. The airbox is held to the subframe with two bolts up top by the seat, locktight them. The plastic tabs on the airbox break frequently. The intake boot on the carb is loose on most all bikes when new. The band clamp (at the head) stretches and bottoms before tightening in short order. Some have lost carbs, we safety wire the carb forward to the head and use a quality clamp. The hot start cable plunger in the carb is brass. Moisture will get in thier and corrode it solid to carb body in very short order. Undo the silly plastic nut and pull it out, apply some lube (I use silicone grease), do it frequently. Be very careful rethreading the plastic nut. If you do cross thread it or ruin the brass plunger, there is a kit for this that includes everything on the end of the cable for $20. Many overtighten the valve cover bolts and pull the threads out of the cam towers. Thier is a fair amount of CDI problems, not a bad idea to carry a spare.

Rich and Kibblewhite is on top of the valve situation. It will be nice when the kits are ready next month. Bronze seats and frequent tappet and oem valve replacements for precaution have been working very well. Kibblewhite did just set me up with thier new bucket design, very nice. We have never had any cam journal issues.

There have been shifting issues. Mostly related to shift pawl plate wearing a groove into the pawls, and worn/ bent forks and shafts. But still some are just notchy compared to others. Rich is right about the lifespan of centercases.

Ryan Abrigo picked up a private Honda ride, he may be with Motosport outlet for 05'. I have been wrenching for Cole Siebler since the outdoors. We were actually trying to secure some help for a privateer supercross team, but it's tuff to round up $60,000-$85,000.

 

[Chili]

Thanks for the info Mark, I think we'll just go red or blue until they sort things out with the RMz. Good Luck with Cole, he looks like a heck of a rider. Seems his injuries probably cost him his spot on the Samsung team last year as I think he was one of the most talented riders they had.

 

[Rich Rohrich]

Ochster - Thanks for the VERY complete rundown of the RMZ issues you've had to deal with. This one will be going into the archives for sure. :worship:

Best of luck to you and Cole in the coming season. As always if there is anything we can do to help you guys just holler. :cool:

 

[ochster]

Just replaced a flywheel and ignition on a bike with less than 6 hrs.on it. The inside of the flywheel seperates. Symptoms are it just stops running, you lose spark. It was a 04' RMZ.

 

[slideways11]

Interesting thread. Wouldn't it be nice if you could buy box motors from Suzuki and the other manufacter's. With the maintenence required to keep the new 4 strokes going it only makes sense. What would it take to run off a 1000 or so extra engines for these guys ? I am sure there is a market for them.

 

[brentl]

Rich ...... if we're talking about 450 4 strokes.....

In deference to your and Eric's experience and exposure to failed engines.....

Which 450 has the least troublesome/most reliable head/engine package?

I'm shopping fo a new bike ;have an RM250 now.
Trying tochoose between the big three for ' 05.

I am planning to race about four times a month, moto only.


Thanks for any opinions !

 

[Rich Rohrich]

In deference to your and Eric's experience and exposure to failed engines.....

Which 450 has the least troublesome/most reliable head/engine package?

I'm shopping fo a new bike ;have an RM250 now.
Trying tochoose between the big three for ' 05.

I am planning to race about four times a month, moto only.


Thanks for any opinions !

Totally stock, the Yamaha has the edge. If you put stainless steel valves and a proper spring kit in the CRF450 it has proven to be a really solid performer as well. If you race them hard they all wear out eventually. ;)

 

[brentl]

Thanks Rich

Really appreciate Your comments !!

 

[CaptainObvious]

But seriously, Rich I bought an hour meter and I can't for the life of me find maintenance intervals in hours. Is it my 3rd grade reddin compenshin or somethin else. Maybe you could list the important intervals in hours. :worship:

Wes - I'll try and put together a list of stuff for the various bikes. Good idea. :cool:

Me three Rich.

 

[drgsin]

WOW!!! After reading all this, WHY would the average weekend warrior race anything but a 2 stroke??? New top end once a year, simple maintenance, I dont think there's a chance of 2 strokes dying out. Once the reality of what it actually costs to keep 4 strokes running hits people where it hurts they'll be flocking back to the pre-mixers.

 

[john3_16]

I guess this thread puts to rest the idea that all brands are built with an equal amount of quality and longevity.

I keep hearing

"it all depends on how you maintain it"

well, yes this is true but you have to assume all things being equal you then realize some bikes are built better than others.

Looks like if you want the most reliable 4 stroke motor then you've gotta get a Yamaha.

 

[Buckholz]

Actually, the most reliable 4 stroke engine is probably an XR400..... or a Dodge slant 6.

Probably a gross oversimplification, but the more HP/displacement, probably the quicker it wears out and the more finiky the engine is. The 250 mx 4-strokes are the most high strung off road engines, thus they fail sooner.

The trails were littered at this years ISDE with failed 250 four strokes....

 

[john3_16]

Actually, the most reliable 4 stroke engine is probably an XR400..... or a Dodge slant 6.

Probably a gross oversimplification, but the more HP/displacement, probably the quicker it wears out and the more finiky the engine is. The 250 mx 4-strokes are the most high strung off road engines, thus they fail sooner.

The trails were littered at this years ISDE with failed 250 four strokes....

Well, you're probably right!

Maybe I should of said of all the racing 4 strokes the Yamaha is the most reliable.

 

[drgsin]

I agree. Yamaha has to be considered #1. It came in 2nd in just about every magazine test last year, and now we're finding out that Hondas (which were #1) and Kawazukis are blowing up motors left and right. These bikes are sooooo close when it comes to riding differences that cost of maintenance, I would assume, would be a big factor in purchasing decisions. Apparently not though, Honda outsells them all! Go figure!

 

[cujet]

Suzuki has some work to do or it seems they will sell far fewer bikes. Maybe not, but I cannot see the logic in $6000 going down the drain right away.

As the 4 stroke bikes mature, riders will demand a certain level of reliability and durability. Sometimes this is achieved through solid engineering, but it looks to me like the quality of the components has to improve. Yamaha has made it work fairly well for years now. There is just no reason for some of these failures with today's bikes.

Chris

 

[john3_16]

Went to the shop today and we saw a brand new RMZ250F on the floor with that looked as though coolant was leaking right where the head meets the cylinder...I mean there was alot of coolent that looked dried out all over the right side of the motor...And it was a brand new bike sitting on the showroom floor...

 

[tyesai]

Just get the 2 banger, I almost bought a 4 stroke because me and my friends ride mostly trails, but I got the 2 stroke because I figured maintenance is much simpler and less expensive, looks like I figured right.