Roller Cam In The XR650R?


16 replies to this topic
  • Kawabuggy

Posted October 30, 2007 - 08:11 AM

#1

I am considering stepping up to the XR650R and was wondering if they have "roller" cams in them...?

By this I mean do the followers that ride on the cam use a wheel, or are they just solid tappets as is found in the XR600R?

That is one thing about the 600 that I don't like. Having had to replace all the rockers, shafts, cam, and some valves already, I would prefer to sell the bike now that those things are new, than to have to replace them again later. If the 650R has a better valve train arrangement, it's just one more good reason to make the switch.

  • Denn10

Posted October 30, 2007 - 08:21 AM

#2

dont think their into overhead rollers yet wonder if it would even be an advantage?

  • martinfan30

Posted October 30, 2007 - 08:25 AM

#3

oh hell ya, anytime you can reduce valvetrain friction you get a quicker revving engine. plus less strain/wear and tear.

  • LeadDoggy

Posted October 30, 2007 - 08:34 AM

#4

Roller tips work wonders too......

  • cleonard

Posted October 30, 2007 - 08:40 AM

#5

I've never heard of a roller rocker arms for any of these engines. Doesn't mean that it does not exist. Reduced valve train life is one reason that I'm still on the stock cam. The increased power from aftermarket cams and high compression pistons come at the cost of reduced life.

I guess that I have been lucky. My engine has countless hard miles on it. I did have to have some valve work done a couple of years ago, but the cam and rockers are still original.

  • Kawabuggy

Posted October 30, 2007 - 09:31 AM

#6

I saw a write up recently where someone had torn into the top of a single cylinder 4 stroke-and it was equipped with roller followers on the cam. I don't remember if it was a Honda CRF450, a KTM or what-but I am sure it had roller followers.

Roller cams have been around since the 50's. I am amazed that this technology has not trickled down to the motorcycle industry yet. I know Harleys use roller cams-why not the jap bikes?

The ONLY drawback to roller cam equipped engines is the possibility of the roller follower coming apart and spilling needle bearings inside the engine.

The plus side is lower engine temperatures, less drag, less friction, increased engine oil life, faster revving, you can use bigger valve springs for better valve control at higher RPMS to stop valve float, longer cam life, shorter intervals between valve jobs due to better valve control-MORE HORSEPOWER!

That list could go on for a while. The aftermarket should step up and produce kits to retro fit roller cams. Think your XR is reliable now? Now imagine that same engine without any of the valvetrain issues they experience. Priceless.

  • SniperTeamBravo

Posted October 30, 2007 - 09:37 AM

#7

The only reason for a roller on the lifter on a pushrod motor is is lessens friction between the lifter, and the cam shaft. There is no reason for it in a motorcycle valvetrain because they except for Harleys, are overhead cam motors. An overhead cam motor has the friction dealt with by the design of both the follower, or rocker arm landing, and the oiling capability of the system.

The ammount of friction on an overhead cam motor at the point of contact may be as much as 100 times less than a pushrod motor. Therefore no roller mechanics are necessary.

Not only that, but one of the boggest horsepower robbers in a overhead camshaft system is weight, so adding a roller system would be counterproductive. The japanise companies take great strides on their race motors like the CRFs to lessen weight at the grams level, so adding ounces to each point would be going the wrong direction.

BTW, I've been inot hundreds of motorcycle motors and not one has ever had rollers on the rockers. I assume you might gain some reliability of the valve train with roller tips, but you would loose high rpm performance and probably revving quickness since the VT would be heavier.

  • rmhrc630

Posted October 30, 2007 - 12:22 PM

#8

sniper that is an awesome response!!! I actually dont know which part you guys are mentioning but I think you cleared up the essensce of the question!!

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  • Billahjack

Posted October 30, 2007 - 02:41 PM

#9

A roller adds mass to the sytem which makes it more difficult to follow the cam proffile at high speed. You end up having to run a higher valve spring rate with thicker rockers. The design will snowball into a heavy mess in order to take the stress at 9000 RPM. Your valves and seats will wear out fast with the high spring rate.

Proper oiling makes it so the metal rocker surface doesn't touch the metal lobe surface on the cam during operation. If I remember correct, its called a hydrodynamic wedge.

If you want to reduce friction, look into offsetting your crank shaft 1mm to make the rod straighter on the combustion stroke. Yamaha is doing this on their sport bikes. This reduces the friction between the piston skirt and the cylinder during combustion.

  • bigredxr

Posted October 30, 2007 - 04:02 PM

#10

I saw a write up recently where someone had torn into the top of a single cylinder 4 stroke-and it was equipped with roller followers on the cam. I don't remember if it was a Honda CRF450, a KTM or what-but I am sure it had roller followers.

Roller cams have been around since the 50's. I am amazed that this technology has not trickled down to the motorcycle industry yet. I know Harleys use roller cams-why not the jap bikes?

The ONLY drawback to roller cam equipped engines is the possibility of the roller follower coming apart and spilling needle bearings inside the engine.

The plus side is lower engine temperatures, less drag, less friction, increased engine oil life, faster revving, you can use bigger valve springs for better valve control at higher RPMS to stop valve float, longer cam life, shorter intervals between valve jobs due to better valve control-MORE HORSEPOWER!

That list could go on for a while. The aftermarket should step up and produce kits to retro fit roller cams. Think your XR is reliable now? Now imagine that same engine without any of the valvetrain issues they experience. Priceless.


The KTM 640 LC4 engine uses roller rockers according to the specs on their website.

  • scalejockey

Posted October 30, 2007 - 07:43 PM

#11

look at the crf's the uni cam design has single roller on the exhast side.

  • Thumpmeister

Posted October 30, 2007 - 07:58 PM

#12

How about we just get rid of the valve train as a whole???

http://www.coatesengine.com/csrv.html

  • martinfan30

Posted October 30, 2007 - 08:59 PM

#13

very interesting... kind of a hybrid reciprocating/wankel engine almost.

  • Billahjack

Posted October 31, 2007 - 07:15 AM

#14

look at the crf's the uni cam design has single roller on the exhast side.


I just saw that on a HotCAMS advertisement in Dirt Rider. The roller is very close to the rocker arm pivot. They basically redesigned the standard rocker arm for a roller system that can follow at high speed. It probably has a 4:1 (or so) lever ratio unlike the XR rockers due to the roller location so close to the pivot. This means that the cam lobe lift is only 1/4 of the valve lift due to the lever ratio. The result is that the roller moves less distance in a cam revolution and has lower maximum speed during movement.

If you put the rollers on a 1:1 rockers (cam lobe moves the rocker follower same distance as valve opens), then the system gets too heavy for high RPM.

  • gialinn

Posted October 31, 2007 - 07:19 AM

#15

The did that alread long tima ago it's called a 2 stroke

  • gialinn

Posted October 31, 2007 - 07:21 AM

#16

I have seen hundreds of old air cooled non rollor rocker motors go thousands and thousands of mile just fine. Proper maintanance with good oil with be much better for you than a trick drive train. Although good quality aftermarket standard rockers would be nice. I bet they could save wieght and improve quality of them.

  • Denn10

Posted October 31, 2007 - 09:50 AM

#17

The only reason for a roller on the lifter on a pushrod motor is is lessens friction between the lifter, and the cam shaft. There is no reason for it in a motorcycle valvetrain because they except for Harleys, are overhead cam motors. An overhead cam motor has the friction dealt with by the design of both the follower, or rocker arm landing, and the oiling capability of the system.

The ammount of friction on an overhead cam motor at the point of contact may be as much as 100 times less than a pushrod motor. Therefore no roller mechanics are necessary.

Not only that, but one of the boggest horsepower robbers in a overhead camshaft system is weight, so adding a roller system would be counterproductive. The japanise companies take great strides on their race motors like the CRFs to lessen weight at the grams level, so adding ounces to each point would be going the wrong direction.

BTW, I've been inot hundreds of motorcycle motors and not one has ever had rollers on the rockers. I assume you might gain some reliability of the valve train with roller tips, but you would loose high rpm performance and probably revving quickness since the VT would be heavier.


thats exactly why i said i wonder if it would even help out all, i know it does on my modded SBC 350 in my truck BUT thats not overhead cam.





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