Auto Decompressor with an aftermarket cam


19 replies to this topic
  • tobinbakner

Posted November 13, 2007 - 04:47 PM

#1

Can you still get the HRC cam from Honda for the XR650L? I’m concerned about the loss of the auto decompressor. I was reading a Clymer manual on the XR600R and L to learn about the decompressor when I read it has a kickback decompression feature to lesson the force of the kickback. Now you may think that this wouldn’t matter on an electric start motorcycle but Suzuki didn’t use a torque limiting gear in the 98 and early 99 DR650 and if the engine kicked back badly during a start up it would crack the case. I’m wondering if the XR650L might suffer the same problem if the engine kicked back without the auto decompression feature. Unfortunately the only aftermarket cams I see either come without the decompressor or are hard welded. I don’t mind that but my understanding is that you should then have the rocker arms hard welded too. This adds significantly to the cost. Are there any online sources for the HRC Cam? Alternately does anyone know of an aftermarket cam that still uses the auto decompressor and isn’t hard welded?

Thanks

Tobin

  • Billahjack

Posted November 13, 2007 - 06:52 PM

#2

Try service honda. I ordered a XR605R HRC cam from Service Honda without ordering the entire power up kit. Just find the part number and see if you can order it from them.

  • martinfan30

Posted November 13, 2007 - 08:00 PM

#3

i dont think that is an issue. the hotcam i installed doesnt have a decrompressor(as you know). it cranks over fine and doesnt "kick back" on the starter.

i have never heard of this as an issue for the L.

  • tobinbakner

Posted November 14, 2007 - 08:20 AM

#4

My understanding is this, For the Suzuki the kickback is fairly rare. People have put thousands of miles on their bikes and never had a problem, but if the kick back occurs it will break the gear bearing bosses for the starter motor. Suzuki did put in a torque limiting gear in 99 to fix the problem. Perhaps there is another mechanism in the XR that prevents this, but in looking at both the Factory Honda manual and the Clymer manual I can’t find it. It looks like the only thing that reduces the kickback is the reverse decompression cam on the camshaft. Of course if the kickback never occurs the whole thing is moot. Does anyone know of a way to find out what HRC parts are still available or to find out the part numbers? I can’t find any on the web. I can try contacting service Honda but I don’t see anything on their website that shows any HRC parts.


Thanks

Tobin

  • BWB63

Posted November 14, 2007 - 10:11 AM

#5

Hot cam is not a regrind so, you can not install the auto decompression back on. XR's only, Barnum's, Web cams are regrinds and you can re-install the auto decompression if you took it off your stock cam before you turned it in as a core. Web cam and most other regrinds have very hard cam lobes and need to run hardened rockers. I run Barnum's regrind and he assured me I did not need hardened rockers.........I am not so sure now but, next time I rip it all apart I will find out.

  • tobinbakner

Posted November 15, 2007 - 02:14 PM

#6

I emailed service honda and they said all they can get is the HRC XR650R hop up kit. I have a feeling the XR650L cam is no longer available. I didn't see any parts for the XR650L at Barnum's website. I wonder why they need to make the face on reground cams so hard? I'm also wondering if it would be possible to machine the Hot Cam to accept the auto decomppressor. It looks like all it would need is an oil hole, a hole for a locating pin, and the hole for the spring.

Thanks

Tobin

  • Frank ZX

Posted November 15, 2007 - 03:08 PM

#7

i dont think that is an issue. the hotcam i installed doesnt have a decrompressor(as you know). it cranks over fine and doesnt "kick back" on the starter.

i have never heard of this as an issue for the L.


No problems with my XRL.

  • Brtp4

Posted November 15, 2007 - 05:48 PM

#8

Tobin,

These guys have it:

http://www.megacyclecams.com/

Also, I haven't poked around this yet, but it seems it might have a lot of info:

http://www.thumperpa...ners/Honda.html

Let me know what you find on the cam.

BP

  • crmc33

Posted November 16, 2007 - 04:57 AM

#9

For Info,
the latest 650L hotcam has the sprocket carrier built in so you cant fit the decompressor.
Sounds like your best bet is a call to megacycle. Im in the UK, Phil Joy reground my std cam with the HRC profile. Its stellite welded but Phil says welding the followers isnt necessarily needed with his cam as running simialr material for cam and followers isnt always good.. and I trust a man with decades of race cam experience! I had mine done as they werent looking very good, and with the 'iffy' oil supply issues of the XRL, I think its safest to get them welded!

I think kick back causing damage on the XRL cases is unlikely but Ive not had that much experience of running them with a starter (I remove mine for the track for instant engine respse :thumbsup:)

  • tobinbakner

Posted November 16, 2007 - 03:11 PM

#10

Megacycle cams and Webcams both hard weld your stock cam and regrind to their specs. This usually requires you to run hardened rockers. I’m not sure why it is necessary for them to use such hard material when welding the cam. Unfortunately this raises the price of the cam significantly. Webcams told me $428.00 not including shipping. I’d definitely consider the $140 for a hot cam but I’m not sure about $428. It’s interesting that the hot cam now comes with the sprocket holder. I can only assume it’s pressed on like the factory. It could still be possible to add the decompressor if it is removable. I wonder why they added it? It must add a decent amount to the cost. The main reason I’m interested is I’m paranoid. Suzuki added a torque limiter back to the DR650 because it cracked the case. Honda has always had it. Is it merely left over from the XR600R so it won’t break your leg when it kicks back? I don’t know. I’m guessing 99.9% of the time it won’t kick back. Some time though it is likely that everything will come together and it will happen. Maybe the Honda cases are stronger and it will take the kick back. If it was just the starting decompressor I wouldn’t be worried because as long as the starter turns it over it doesn’t matter. It’s the reverse decompressor that has me concerned.

Thanks

Tobin

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  • martinfan30

Posted November 16, 2007 - 03:16 PM

#11

my hotcam i just installed will not accept the decomp device.

  • valvesrule

Posted November 17, 2007 - 12:23 AM

#12

Hotcams are pressed on sprocket flange with key only no splines like stock cam. All Webcam and Megacycle cams are hardwelded. Even though you can get the decomp on a core reweld, the extra duration of the cam lowers cranking compression enough for it to be unneeded unless you jack up the compression ratio with a popup piston. Megacycle has billet cams also but I don't know what the hardness is on them. I suspect they are hardened too so they will hold up to high valvespring pressures.

  • tobinbakner

Posted November 19, 2007 - 07:13 AM

#13

That's depressing. I suppose as long as the diameter of the shaft and the distance between the back of the sprocket and the cam lobe are the same it would still be possible to have it machined but it appears that it would be very problematic. I've tried looking to see if any big bore thumpers don't use some sort of kick back torque reduction. The KLR and suzuki both use it in their 650 and 400's. Apparantly yamaha had to add it to the wr450 because it would break the woodruff key. The more I look the more concerned I get that you need it.

Thanks

Tobin

  • absynth01

Posted November 20, 2007 - 09:01 AM

#14

I've had problems with my 04'650L. It did backfire once when punchin it in a dirt parking lot. Unknown at the time it blew the carb off the boot!!!! I noticed it after I got it home because the notch on the boot and carb were seperated. I also got it started once and it reved like it was out of gas. That made me look at the intake/gas. Now my problem is it wont start after riding it for 2 months no problems. It sat for 3 weeks and runs the battery down within a short time. Makes me wonder how much more the starter is working with the hotcam? It also doesn't help with my headlight upgrades! I have a new moose powermax gel, and is recharging now
10.5-1 piston, hotcam, rod, bearing/bushing kit, big gun evox, uni, airbox mods, clutch, valves, xr's only carb, clarke tank and other stuff.

  • martinfan30

Posted November 20, 2007 - 09:49 AM

#15

I've had problems with my 04'650L. It did backfire once when punchin it in a dirt parking lot. Unknown at the time it blew the carb off the boot!!!! I noticed it after I got it home because the notch on the boot and carb were seperated. I also got it started once and it reved like it was out of gas. That made me look at the intake/gas. Now my problem is it wont start after riding it for 2 months no problems. It sat for 3 weeks and runs the battery down within a short time. Makes me wonder how much more the starter is working with the hotcam? It also doesn't help with my headlight upgrades! I have a new moose powermax gel, and is recharging now
10.5-1 piston, hotcam, rod, bearing/bushing kit, big gun evox, uni, airbox mods, clutch, valves, xr's only carb, clarke tank and other stuff.


the battery dies while cranking? this happened upon starting after sitting 3 weeks?

  • tobinbakner

Posted November 20, 2007 - 04:53 PM

#16

The backfire I'm talking about would only occur during startup or shutdown. Since you were running at the time sounds like you have or had lean condition for some reason. If I understand correctly the backfire occurred and blew the carb off. You fixed that and rode it for 2 months without any problems. now all of a sudden after not riding it for 3 weeks, you went to start it and it won't start. The 2 problems may or may not be related. Have you checked for spark? Your description does make it sound like it's not getting enough fuel but I always check for spark first. Your description says you have an xr's only carb. I don't know if it has provisions for cold starting but if it does you might make sure they are working properly. After that check to see if it is getting fuel.

Tobin

  • absynth01

Posted November 20, 2007 - 06:37 PM

#17

Yeah somthings goin on here. I just installed fatbars, and rox dampening risers. I was just checkin my controls but couldn't get it started. Going to change plug tomorrow. It has been fairly maintenance free with those exceptions, but they are big. Any one else have hard start problems with the cam and piston. Seems like it works to crank more than my other bikes. First e-start thumper. Not first built motor with e-start.

  • martinfan30

Posted November 21, 2007 - 08:39 AM

#18

Yeah somthings goin on here. I just installed fatbars, and rox dampening risers. I was just checkin my controls but couldn't get it started. Going to change plug tomorrow. It has been fairly maintenance free with those exceptions, but they are big. Any one else have hard start problems with the cam and piston. Seems like it works to crank more than my other bikes. First e-start thumper. Not first built motor with e-start.



check the battery and its connections.

  • tobinbakner

Posted November 21, 2007 - 02:49 PM

#19

If the problem started right after you installed the fatbars and risers, you might check out the wiring to the handlebars. A short in either the clutch switch or the kill switch could create the problem.

Tobin

  • absynth01

Posted November 21, 2007 - 08:29 PM

#20

It was just being a bitch in this cold weather.





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