YZF motor maintenance and relability


19 replies to this topic
  • icebat

Posted July 08, 2005 - 09:59 AM

#1

I have a couple of questions being a two stroke guy thinking of swithing to a four stroke.

What is the major differences between the CRF and YZF motor and why does the CRF have so many issues?

What about adjusting valves? I have heard that with the CRF you have to remove the cam to adjust the valves, is this true of the YZF and RMZ?

I am really looking forward to the 2006 450 shootout!

  • grayracer513

Posted July 08, 2005 - 12:45 PM

#2

Yamaha came up with a simple, solid design in the first place when they did the YZ400F, and refused to compromise on it to appease their accountants. They shortcut nothing. When the decision was made to use titanium valves, they reviewed the advantages and the limitations of the material and again decided to use only very high quality materials treated to high standards. The result is what they have now, one of the most reliable pieces of racing machinery ever offered to the public.

Honda decided that they needed to be different, and came up with the "UniCam", which is innovative, I suppose, but the idea was to reduce the weight of the top end components, which it didn't really do very well. It did make the valve gear somewhat more complicated, though.

Their valve issues are mostly a matter of using a grade of titanium which is inferior to that employed by Yamaha, and then failing to coat them with Ti Nitride as deeply as Yamaha does. Their valve seats are not as hard either, from what machinists tell me.

The CRF also had (have?) a problem with the balancer shaft/bearing on the right side that is simply the result of the shaft not being hard enough, and the wrong type of bearing used.

As for valve adjustments, here's how it's done:

http://motoman393.th...ech/valves.html

Here's the same procedure for a 250F with pictures: http://www.thumperfaq.com/valves.htm

Note that you do indeed have to remove the camshafts in the YZF to do this job, but note too that it does not require a special tool to disengage and lock the cam chain tensioner, and that the removal of both cams from the YZF is a somewhat simpler operation to perform than the removal of the cam and tower from the CRF head. Another point is that you won't be doing much of it, anyway. My '03 has never needed a valve adjustment. I keep checking, but it's still not out of spec yet. :)

  • Chills

Posted July 08, 2005 - 01:03 PM

#3

Wow Gray,

Awesome reply...

  • MIGHTYMOUS327

Posted July 08, 2005 - 01:20 PM

#4

That's Sweet News. I Would Sacrifice Alot For Reliability.

  • Ga426owner

Posted July 08, 2005 - 03:53 PM

#5

Yamaha came up with a simple, solid design in the first place when they did the YZ400F, and refused to compromise on it to appease their accountants. They shortcut nothing. When the decision was made to use titanium valves, they reviewed the advantages and the limitations of the material and again decided to use only very high quality materials treated to high standards. The result is what they have now, one of the most reliable pieces of racing machinery ever offered to the public.

Honda decided that they needed to be different, and came up with the "UniCam", which is innovative, I suppose, but the idea was to reduce the weight of the top end components, which it didn't really do very well. It did make the valve gear somewhat more complicated, though.

Their valve issues are mostly a matter of using a grade of titanium which is inferior to that employed by Yamaha, and then failing to coat them with Ti Nitride as deeply as Yamaha does. Their valve seats are not as hard either, from what machinists tell me.

The CRF also had (have?) a problem with the balancer shaft/bearing on the right side that is simply the result of the shaft not being hard enough, and the wrong type of bearing used.

As for valve adjustments, here's how it's done:

http://motoman393.th...ech/valves.html

Here's the same procedure for a 250F with pictures: http://www.thumperfaq.com/valves.htm

Note that you do indeed have to remove the camshafts in the YZF to do this job, but note too that it does not require a special tool to disengage and lock the cam chain tensioner, and that the removal of both cams from the YZF is a somewhat simpler operation to perform than the removal of the cam and tower from the CRF head. Another point is that you won't be doing much of it, anyway. My '03 has never needed a valve adjustment. I keep checking, but it's still not out of spec yet. :)



AMEN GRAY

  • Satch0922

Posted July 08, 2005 - 04:48 PM

#6

here is a new one.... a friend had the oil pump go out on his 03 CRf and it trashed the crank. It took a month to get a crank for it.....they were on backorder....

WONDER WHY? :)

  • Hick

Posted July 08, 2005 - 05:25 PM

#7

I have a couple of questions being a two stroke guy thinking of swithing to a four stroke.

What is the major differences between the CRF and YZF motor and why does the CRF have so many issues?

What about adjusting valves? I have heard that with the CRF you have to remove the cam to adjust the valves, is this true of the YZF and RMZ?

I am really looking forward to the 2006 450 shootout!


Me too.

Second what Gray said, the YZF has a more traditional dual OHC setup, the CRF has the Uni-Cam w/ followers, and instead of 4 Ti valves aren't the exhaust valves steel?? Not sure...

Anyway the Uni-Cam arrangement results in less gyroscopic effect that resists attitude changes (read: leaning it into a turn) because their is a 50% reduction in spinning mass up there, one cam vs. two. The other weight of the rockers/followers (or whatever) probably weighs almost as much as another cam, but overall weight reduction wasn't the point. AFAIK the reduction in spinning mass was the reason for the Uni-Cam design. I doubt a company like Honda would go through the trouble of this just to be different, but hey, it's possible.

Any cam-over-bucket arrangement, which I assume the RMZ has in common w/ the YZF, will necessitate cam removal to change valve shims.

But I don't see how the the valvetrain design difference would have anything to do w/ the valve life issues CRF vs. YZ or RM. It would more likely be different cam profile, different valve seat material, different valve makeup/construction, or just cheap/overly weak valve springs.


Also, you don't need a special tool to deal w/ the Honda timing chain tensioner, I use a screwdrive and vise grips, or you can just remove it. Honda does list one in the manual but they tell you how to make your own as opposed to selling you one, and all the mfg.s have their "special tools" they try to sell you, chalk it up to whoever wrote the manual or is in charge of "special tool sales." Example, Yamaha wants you to buy a $75 tool to remove the crank, it is essentially a non-adjustable steering wheel-puller. I made my own out of all-thread and square tubing...

  • Hick

Posted July 08, 2005 - 05:33 PM

#8

here is a new one.... a friend had the oil pump go out on his 03 CRf and it trashed the crank. It took a month to get a crank for it.....they were on backorder....

WONDER WHY? :)



You should have seen the wait times on YZ/YZF 4th gear wheels in late '00.


GEE I CAN'T IMAGINE WHY THAT WOULD HAVE BEEN!


By the time I got rid of my '00 YZ, the guys at the NCY mail-order parts counter recognized me by voice alone (hint: I SPOKE WITH THEM OFTEN).


Example, Yamaha wants you to buy a $75 tool to remove the crank, it is essentially a non-adjustable steering wheel-puller. I made my own out of all-thread and square tubing...


GEE I WONDER WHY I HAD TO FIGURE OUT HOW TO REMOVE THE CRANKSHAFT???


:)

  • yz450supermo

Posted July 08, 2005 - 06:36 PM

#9

** marks up one..no, two explanation points for gray...well said.

  • grayracer513

Posted July 08, 2005 - 06:39 PM

#10

instead of 4 Ti valves aren't the exhaust valves steel?? Not sure...

Me either, but the intakes at least are titanium, and aren't very well executed by comparison

Anyway the Uni-Cam arrangement results in less gyroscopic effect that resists attitude changes (read: leaning it into a turn) because their is a 50% reduction in spinning mass up there, one cam vs. two. The other weight of the rockers/followers (or whatever) probably weighs almost as much as another cam, but overall weight reduction wasn't the point. AFAIK the reduction in spinning mass was the reason for the Uni-Cam design. I doubt a company like Honda would go through the trouble of this just to be different, but hey, it's possible.

Did Honda actually say that was the rationale for the Uni-Cam? Frankly, the cams don't weigh enough, nor are they large enough in diameter, nor spin fast enough, relatively speaking, to be a significant factor in the gyroscopic efect of the internal rotating mass. (They're probably less than a tenth the weight of the crank) Maybe technically they do, but I don't notice the difference in gyro effect going 4oz up or down on the flywheel weight. Sounds nice on the surface, but I don't buy it.

Any cam-over-bucket arrangement, which I assume the RMZ has in common w/ the YZF, will necessitate cam removal to change valve shims.

But I don't see how the the valvetrain design difference would have anything to do w/ the valve life issues CRF vs. YZ or RM. It would more likely be different cam profile, different valve seat material, different valve makeup/construction, or just cheap/overly weak valve springs.

Valve train design isn't their problem. But it does contribute to or detract from serviceability, and on the CRF, I think it detracts, because of how they laid it out. My opinion.

Weak valves are the cause of the premature wear issues. Springs would be a likely culprit in valve breakage episodes.

When I did the top end on my 250 in January, the valves were on back order, but we know there is not a major problem with valve durability in that model. Just bad timing I suppose, for doing an engine in winter when all the teams are doing theirs, or just a flaky parts system. It's not always fair to use that as an indicator of problems with a particular bike.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Hick

Posted July 09, 2005 - 12:28 AM

#11

Did Honda actually say that was the rationale for the Uni-Cam?


As I recall, yes they did, and the CRF feels much less top heavy than a 426. I don't have enough hours on a YZ 450 to have an opinion on this though as I realize the 450 is much lighter, and less top-heavy.

Frankly, the cams don't weigh enough, nor are they large enough in diameter, nor spin fast enough, relatively speaking, to be a significant factor in the gyroscopic efect of the internal rotating mass.


A camshaft spinning at 6k rpm is going to have a significant gyroscopic affect. Heck, a small wheel at 500 rpm is enough to feel w/ your bare hands. Try it.





(They're probably less than a tenth the weight of the crank)


True. But the crank is right at the center of gravity, so it has little gyroscopic affect w/ respect to attitude changes about the bikes axis. The cams are at least 50% away from center. A big difference w/ respect to an attitude change that is happening about the axis of the crankshaft .

Maybe technically they do, but I don't notice the difference in gyro effect going 4oz up or down on the flywheel weight. Sounds nice on the surface, but I don't buy it.


Again, the crank is right about the axis that the bike changes attitude about, so this isn't noticeable.

I've seen Husaberg literature that claimed that counter-rotating cams made the bike steer better. This argument is a bit outside my understanding of the nature of gyroscopic forces, and yet Husaberg sought it worthwhile to make this change.

I dunno.


Valve train design isn't their problem. But it does contribute to or detract from serviceability, and on the CRF, I think it detracts, because of how they laid it out. My opinion.


You could be right, but how, in your opinion, does their Unicam layout contribute to service/durability problems? I don't see any connection here.


Weak valves are the cause of the premature wear issues. Springs would be a likely culprit in valve breakage episodes.


One theory that folks much smarter than I have posted here is that weak springs don't allow sufficient heat transfer between valve and seat, and this buildup of heat in the valve surface leads to premature failure. This makes sense to me. This is a very popular bike w/ a fairly common problem, so far I've seen a lot of theories outside of valve material.

In fact the more reputable tuners focus not just on valve material but spring makeup. This doesn't explain how the YZ, using a single, non-conical spring and Ti valves, has almost zero issues in this regard. My own ignorant opinion is that the valve seats are too hard, but what do I know? (have you compared the price of a bare head, YZ vs. CRF???)

For '06 the literature states that the CRF has new valve seat material.

  • YZLEE

Posted July 09, 2005 - 06:32 AM

#12

Another theory about the valve issue.

A fellow posted awhile back, who owned a CRF, and said the air filter cage was of such a poor design that it was hard to get a proper filter seal. Thus allowing dirt in and accelerating wear on the valves, crank, etc.

  • grayracer513

Posted July 09, 2005 - 08:57 AM

#13

As I recall, yes they did, and the CRF feels much less top heavy than a 426. I don't have enough hours on a YZ 450 to have an opinion on this though as I realize the 450 is much lighter, and less top-heavy.

One reason for this is that the 426 is 20 pounds up on a CRF, and is more top heavy. Although a YZ450 is within 2 pounds of the Honda, they are 1 1/4' higher than a CRF. The other is steering geometery. But we're off point.

A camshaft spinning at 6k rpm is going to have a significant gyroscopic affect. Heck, a small wheel at 500 rpm is enough to feel w/ your bare hands. Try it.

...But the crank is right at the center of gravity, so it has little gyroscopic affect w/ respect to attitude changes about the bikes axis. The cams are at least 50% away from center. A big difference w/ respect to an attitude change that is happening about the axis of the crankshaft .

Again, the crank is right about the axis that the bike changes attitude about, so this isn't noticeable.

Gyroscopes do not resist being moved in any direction at all, vertically, laterally, or otherwise. Rather, they resist any change in the the tilt of the axis around which they rotate. The crank may or may not be at the center of gravity, but it still has to have its axis tilted to lean the bike, and being the heavier, faster turning mass, will have the most to say about whether it happens. The cams may contribute to the overall effect, but only in a very small way.

I've seen Husaberg literature that claimed that counter-rotating cams made the bike steer better. This argument is a bit outside my understanding of the nature of gyroscopic forces...

Mine too. I'd like to see someone explain that one. If they had said they wanted to shorten the overall length of the chain and narrow the channel it runs in, that would have made sense.

...how, in your opinion, does their Unicam layout contribute to service/durability problems?

Not durability. just serviceability. It's just harder to work on, to me. First, the allen bolts in the cam sprocket should be replaced with torx bolts. I've seen several complaints about them rounding out. Having to remove the sprocket is particularly annoying when using an indexable sprocket, because you have to reset it each time. Finally, the bores for the lifters are part of the tower. Because of that, lifters and/or shims may fall out of place when removing or replacing the tower, and it just seems like kind of a nuisance. And, the YZF chain tensioner is inarguably easier to deal with.


One theory that folks much smarter than I have posted here is that weak springs don't allow sufficient heat transfer between valve and seat, and this buildup of heat in the valve surface leads to premature failure.

In fact the more reputable tuners focus not just on valve material but spring makeup. This doesn't explain how the YZ, using a single, non-conical spring and Ti valves, has almost zero issues in this regard. My own ignorant opinion is that the valve seats are too hard, but what do I know? (have you compared the price of a bare head, YZ vs. CRF???)

For '06 the literature states that the CRF has new valve seat material.

I don't buy the heat theory. Heat transfer between two metals is not pressure dependent as long as the two parts are in full contact. Any spring with so little seat pressure as to allow the valve to not seat fully would also allow the valve to bounce as it reseated, which would produce extra wear. And more than one reputable cam grinder has stated that conical springs are not a good choice for engines like this.

Valve material and treatment is a major part of the problem. Not only Honda, but the Kawazuki 250F had troubles with this, too, and they are using the same DOHC design that Yamaha does. Titanium is not hard enough to be a valve face, and must rely of the extremely hard Titanium Nitride coating applied to it to be durable enough for the purpose. How well the coating wears depends on its quality, its depth, and the strength of the underlying titanium that supports it.

When I did the valve job on my 250F, the machinist showed me that the valve seats in the YZF head are quite hard, and wear very little. Only a slight touch up was required to restore them. The intake valves on the engine were seriously worn, but it took over 400 hours to do that, and most of that was without needing a valve adjustment.

Other things that may figure in are excessive clearance in the valve guides, allowing the valve to scrub the seat as they close. Or cam profiles without an adequately gentle ramp on closing.

Note that the steel valved YZF's from '00 back have even fewer valve issues than the current ones. They've had this right from the beginning.

I have priced out the two heads, and the CRF is much less expensive, but there are probably reasons for that besides a quality question. The YZF head is a much more complicated piece of machine work because it includes the lifter bores, the bores for two cams, and is machined for 5 valves instead of 4.

  • Hick

Posted July 09, 2005 - 10:14 AM

#14

Not durability. just serviceability. It's just harder to work on, to me. First, the allen bolts in the cam sprocket should be replaced with torx bolts. I've seen several complaints about them rounding out. Having to remove the sprocket is particularly annoying when using an indexable sprocket, because you have to reset it each time. Finally, the bores for the lifters are part of the tower. Because of that, lifters and/or shims may fall out of place when removing or replacing the tower, and it just seems like kind of a nuisance. And, the YZF chain tensioner is inarguably easier to deal with.




Good points, especially about the lifter bores, but I don't recognize any difference in dealing w/ the cam chain tensioner. Having said that, I think the YZ's is of a simpler and more robust design.


I have priced out the two heads, and the CRF is much less expensive, but there are probably reasons for that besides a quality question.


My (probably too subtle) point was that Honda priced the head cheaper because they consider it a service item (like a piston etc.). I have no evidence whatsoever to base this on other than the widespread intake valve problems and price of the head. Just tongue-in-cheek sarcasm from a somewhat disgruntled Honda owner.

  • Hick

Posted July 09, 2005 - 10:19 AM

#15

Another theory about the valve issue.

A fellow posted awhile back, who owned a CRF, and said the air filter cage was of such a poor design that it was hard to get a proper filter seal. Thus allowing dirt in and accelerating wear on the valves, crank, etc.



I've heard this theory, along with countless others, but don't really like it. The problem w/ the Honda filter cage is it is vastly over-engineered, making it nearly impossible, IMO, to not get a proper seal.

Anyway the seal on the '02 Honda between the boot ring and airbox was suspect, and many owners pulled it out of shape when removing the subframe/airbox/boot assembly from the carb etc. From this perspective it sounded like a nice theory until Honda fixed this issue for '03 and intake valves were still going south.


:)

  • MotoGoalie

Posted July 09, 2005 - 10:32 AM

#16

My (probably too subtle) point was that Honda priced the head cheaper because they consider it a service item (like a piston etc.). I have no evidence whatsoever to base this on other than the widespread intake valve problems and price of the head. Just tongue-in-cheek sarcasm from a somewhat disgruntled Honda owner.


Why fight it then, my brother?

Come put on a blue cape and become the superhero your momma wanted you to be.....come over to friends and family that will welcome you with talk about graphics changes and hop up goodies and you will no longer need to fear the Valve Reaper, or the Crank Wraith.

You are in safe hands with Yamaha.

Welcome friend. :)

  • johnmeasures

Posted July 09, 2005 - 01:35 PM

#17

My team runs YZ250Fs & the senior rider has moved to YZ450F as of tomorrow (Our 1st 450 race). The YZ250F valve clearances are fairly easy to check. I check every 15hrs max & they stay in tune quite well. Yamaha UK Race Team supplied my YZ450 & say they check their 450 valves every 2nd race meeting! Ther have been some problems in UK with YZ450/250 blowing the carbs off during the race so we run ours with additional restraints round the carbs. We also re-route the breather pipe because it clogs in the glorious mud we Brits race in & blows the blanking disc off the front of the cylinder

  • Hick

Posted July 09, 2005 - 02:11 PM

#18

Why fight it then, my brother?

Come put on a blue cape and become the superhero your momma wanted you to be.....come over to friends and family that will welcome you with talk about graphics changes and hop up goodies and you will no longer need to fear the Valve Reaper, or the Crank Wraith.

You are in safe hands with Yamaha.

Welcome friend. :)

:)

True, I'll likely be back on blue in '06 (or late '05, whatever). If it is half the lemon my '00 was I'll just grin and bear it like I did back then and wait for the '07.

I still miss that Yamaha handling.

  • grayracer513

Posted July 09, 2005 - 02:22 PM

#19

...Just tongue-in-cheek sarcasm from a somewhat disgruntled Honda owner.

It's really a shame, too, because the CRF is an excellent bike if you overlook the reliability issues. I would have one for junior right now instead of the 250F, and maybe even one for myself, if they were as durable as the YZF.

...(the breather) clogs in the glorious mud we Brits race in & blows the blanking disc off the front of the cylinder

John, have you not heard of these?
http://shop.thumpert...p/qmr-03dpb.htm

Completely cures that problem. Of course if the breather clogs, the half moons on the cam box gasket might be next, but they hold much better than that blanking blanking plug does.

  • johnmeasures

Posted July 12, 2005 - 01:32 AM

#20

[quote name=' John, have you not heard of these?
[url']http://shop.thumpertalk.com/product_p/qmr-03dpb.htm[/url][QUOTE]
Looks good, thanks. I have made a metal finger that holds the blanking plate down. Some British teams, Emberson/London Diamond Drilling for example, run without the breather pipe





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