680 motor: which cam?

15 replies to this topic
  • Mikie1

Posted May 18, 2005 - 05:52 PM


I'm putting my bike back together now... cylinder bored, re-nickasiled to a 102.4mm (680cc), 11:1 piston, Carillo rod, Edelbrock carb (standard bore), Barnums pipe. I've decided to stick with OEM valves, springs & rockers (after discussion with Bruce Ogilvie) and a HotCams cam, since they're designed to work with the OEM parts.

But... my dilemma is this: Should I put in a Stage I or a Stage II cam? Everything I've read says I'll lose bottom end and mid-range with the Stage II, but will have a raging top-end. One race shop says that I'll gain everything I would have lost with the Stage II cam back, with the extra displacement and higher compression, and that I'll have an arm-stretching top end. Another shop says the bottom will still be soft, but the mid and top-end hit will be too hard with the Stage II cam. Another says the bottom and mid hit would be too hard with the Stage I, and I won't realize the potential of the Barnums pipe with just a Stage I cam.

My normal riding style is to use the torque/ meat of the powerband most of the time. I want the bike to stay easy-to-ride. I would actually like it a lot (I think....) if it just stayed about the same as stock, or maybe just a little more down low & mid-range, but had a big top-end hit & pulled like a freight-train right up to the rev limiter.

Any thoughts/ feedback?

  • EliJoe

Posted May 18, 2005 - 06:06 PM


My opinion: I wouldn't worry about "too much" bottom end, if that is what you like. Just get a Tera-Flex! I would think with the big bore and high compression, a Stage 2 may be the way to go, though. Cams are cheap...buy two, then you'll know. If it were me, I would do the Stage 2, and if the bottom end was insuffecient, I would get a Stage 1 and sell the Stage 2.

  • Mikie1

Posted May 18, 2005 - 06:29 PM


Ha! Funny you said that... that's what I did- I bought both! Plus, you confirmed what I was thinking about the Stage II.

Anybody with some experience with a Stage II in a 680, or even a 650 with 11:1?

  • BWB63

Posted May 18, 2005 - 08:13 PM


I have BarnumsPro mid cam. More lift and more duration then the HRC or stage I cam. I also have 102.4 piston (680cc) 3mm oversized intake and the Edelbrock bored over to 40mm X 42mm (from stock 36mm X 42mm) and I will tell you that the big bore more then makes up for what you think you will lose.

Losing bottom end is relitive to one cam to the next.

I made more torque everywhere with the bigger cam, no loss but, I made a lot more in the higher RPM's compared to what I gained in the bottom rpm's. In other words you may not pick up much at all in the bottom with the stage two compared to the stage one cam but, will pick up more later in the RPM's. The jump in torque with the 680 piston is so much that you gain Horsepower everywhere what ever cam you put in it. The part that makes it hard to compare is the bigger intake valves I have. That should have been a loss in bottom end but, I gained everywhere with that also. I run lean with the #19 needle at 3,000rpm with the Edelbrock so, I have to mod a needle for my bike. I had no loss with the Mikuni TM40


Check out the torque chart down by the red comaro.

You will have so much more low end with a 680cc kit you won't know what to do with it all :)

  • mikekay

Posted May 18, 2005 - 08:41 PM


'stage two'

add hardened rockers and the HRC cam chain/gears/sliders--a must. The stock chain cant handle that motor.

  • BWB63

Posted May 18, 2005 - 10:06 PM


What ever cam you put in, check the piston to valve clearance. Clay test and I think it's should be no less then .060"
Also, degree in your cam.

  • frankstr

Posted May 19, 2005 - 05:02 AM


What ever cam you put in, check the piston to valve clearance. Clay test and I think it's should be no less then .060"
Also, degree in your cam.

Smart, Always check piston to valve clearance and always dial in your cam.. :)
Clearance should be .060 on intake and.090 on ex.....

  • BWB63

Posted May 19, 2005 - 05:11 AM


I do not know the lift of the Stage one and Stage two cams but, Barnum's cams have extra lift so, the valve guides have to be decked. Mine were decked .030. This is a must with some cam's or the valve guides will be pushed down. But, it sounds like the cam's you are going to use have a standard lift?? My piston also had to be milled to make room for the valves.

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  • Mikie1

Posted May 19, 2005 - 06:46 AM


Uggghhh! Will check it carefully... The HotCams say they're made to be used with stock components- a straight bolt-in. Not sure whether that holds true with the 680 piston or not. Stage 1 lift is 9.2mm, 254 degrees (intake) & 9.2mm/ 251 degrees (exhaust): Stage II is 9.6mm/ 265 degrees (intake), 9.5mm/ 260 degrees (exhaust).

Stage I is supposed to be a real close copy of the HRC cam, which doesn't require shortening guides. Stage II intake is .4mm more lift (about .016), and exhaust .3mm.

To check the guides, do I just have to make sure the rockers don't hit them and/or the seals? So, basically I just put it together & turn it over real slow, right? If I torque everything down per specs to clay-check the piston-to-valve clearance, then do I need another new head gasket for final assembly? Errrggghhh! I had to special-order this one.

If the cam sprocket isn't slotted, how do I "degree in" the cam? I imagine the shop that's helping me with the head (new guides, seals & minor "clean up" of the valve seats) has a degree wheel... What do I need to look for?

  • BWB63

Posted May 19, 2005 - 11:05 AM


No you can use the same head gasket but, you don't torque it down all the way the first time. You are not putting any water in it, and leave the spark plug out. If the stage two is more lift then an HRC I would check and make sure the valve retainers don't get close to the guides. I am sure while the bike is reving high the valves float some. I would call and ask if you should deck them or not. Easy to do. I would worry about the piston clearance. It is a different then stock piston.

  • bootlegger2

Posted May 22, 2005 - 03:35 AM


where do you a adjustable cam gear for these things
i didnt think you could degree in a cam with out one

  • BWB63

Posted May 22, 2005 - 07:33 AM


where do you a adjustable cam gear for these things
i didnt think you could degree in a cam with out one

you remove enough from the area that has no spline teath so, you can move the sprocket one or two you can move the the cam time 4 degree. Most stock xr650r's are off almost that. Big difference in how they run. Most of the after market cams Include adjustable cam timing sprocket

This is from someone XR650R motard page:

The valve timing of the engine with the HRC cam installed was determined with a dial indicator and a degree wheel as shown in the photos below:

Posted Image


I decided the best strategy to preserve low end torque without sacraficing too much top end would be to time the cam so that it would lead the crank by 3 degrees (relative to HRC spec values).

In order to advance the cam 5.7 + 3.0 = 8.7 crank degrees (4.3 degrees on the cam) I used a vernier relation between the cam spline (22 teeth) and the cam gear (38 teeth). I had to remove the filled in tooth on the cam spline with a dremmel tool. Then I advanced the cam 2 spline teeth, and retarded it 3 gear teeth for a net advance of 4.31 cam degrees, close enough to the 4.35 degree goal.

The possible cam spline / gear vernier relations are shown in the cam timing vernier table. All values are in cam degrees and values within +/- 10 degrees are bolded.

  • bootlegger2

Posted May 23, 2005 - 03:25 AM


That Is A Great Idea I Think They Should Come With Adjustable Timing Gear So You Can Dial It In And Help Take Up For The Chain Slack You Will Be Getting Down The Road
I Will Save This Info For A Friend Of Mine Getting Ready To Do The 680 Kit Cheap Adjustable Timing Gear

  • frankstr

Posted May 23, 2005 - 05:11 AM


I can see I'll have to get a new degree wheel when I redo my engine... :)
My 18" one is going to be too big I believe after seeing those pics.. :D

  • bootlegger2

Posted May 25, 2005 - 03:33 AM


the 9" one i have may even be to big for this

  • Billahjack

Posted September 02, 2009 - 07:06 PM


Did anyone grab a copy of that chart from the Scottsworld link? Its inactive now.


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