Reasons for doing cam mod?


15 replies to this topic
  • wc426mx

Posted May 18, 2005 - 11:00 AM

#1

I want to know what all reasons you guys had for doing the cam mod? Was it just ease of starting, changed power delivery, both, or something else?

I need to explain these reasons to a friend who is installing my 450 cam. He's doing the work for free :) , but he's more of a hi-perf. auto guy, and he just wants to understand my reasoning. Any help is appreciated. Thanks!

  • YZ250F_Rider

Posted May 18, 2005 - 11:37 AM

#2

The first time you kick it over without going thru the TDC ritual, it will be self explanitory.

  • Rick_Graham

Posted May 18, 2005 - 11:46 AM

#3

It simplifies the starting procedure. It will allow you to bump start on the fly. There really is no downside to this mod.

  • grayracer513

Posted May 18, 2005 - 12:49 PM

#4

Apart from the already stated facts that it will eliminate the starting "drill", and you can bump start it like a 125 without having to coordinate the comp release with the clutch, a lot of guys say that the 450 exhaust cam delivers a heftier, more linear power curve that pulls floor to ceiling without a "hit" along the way.

Be sure you get it timed right. The only mark on the 450 cam that's usable in the 426 is the one that would be at 12:00 in a 450. Set it 14 pins from the 12:00 on the properly timed 426 intake.

  • BigDesto

Posted May 18, 2005 - 01:02 PM

#5

I did mine after my bike didn't start @ Adelanto GP in 03, barely got it started before the next group took off :)

  • cowboyona426

Posted May 18, 2005 - 03:26 PM

#6

Ease of starting and better power delivery.

  • wc426mx

Posted May 18, 2005 - 03:53 PM

#7

Besides offset metric feeler gauges, what do I need? Is a ft. lb torque wrench okay, or do I need an inch lb torque wrench? Harbor Freight has a 1/4" drive inch lb torque wrench (20-200 inch lbs). Is this what I need? :)

Thanks.

  • 642MX

Posted May 18, 2005 - 04:00 PM

#8

I did mine when I replaced the piston, It seemed like the thing to do and I didn't want to hook the compression release back up.

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  • cowboyona426

Posted May 18, 2005 - 04:20 PM

#9

The cam cap bolts use such a low torque rating, that I didn't even bother trying to stuff a torque wrench in there.

  • wc426mx

Posted May 18, 2005 - 04:28 PM

#10

The cam cap bolts use such a low torque rating, that I didn't even bother trying to stuff a torque wrench in there.

I think it's something 7.2ft/lbs on the cam cap bolts? Is that right?

  • cowboyona426

Posted May 18, 2005 - 04:36 PM

#11

I wouldn't know, I didn't torque them :) What I did was crank on the bolts a little ways, then back them off until the cam can spin freely in the journals.

  • grayracer513

Posted May 18, 2005 - 04:48 PM

#12

A torque wrench is critical. Conventional thinking is that improper tightening of the cam caps is the major cause of seized cams, as it leads to distorted caps. The manual calls for 7.2 ft/lbs (87 in/lbs), but I consider that too high, as do a couple of other guys on the forum, and Yamaha has reduced the torque specs considerably for the '05's. I use 75 in/lbs (6.2 ft/lb). An inch pound wrench is usually require only because a ft/lb wrench is tricky to use at those low values. A 1/4" beam type will fit onto any of the bolts without an adapter, and you can get a higher quality tool cheaply if you use one of that type as well.

Offset guages are unnecessary. The flat ones as thin as you use here will flex right into place without problems, and although metric guages would be cool, I still use English ones with the metric equivalent marked on them. You could just convert the specs to English measure, too. Inches = mm divided by 25.4, so .10mm is .0039", or .004". I use a .004" and .006" on the intakes, and a .007" and .010" on the exhausts.

  • wc426mx

Posted May 18, 2005 - 05:00 PM

#13

A torque wrench is critical. Conventional thinking is that improper tightening of the cam caps is the major cause of seized cams, as it leads to distorted caps. The manual calls for 7.2 ft/lbs (87 in/lbs), but I consider that too high, as do a couple of other guys on the forum, and Yamaha has reduced the torque specs considerably for the '05's. I use 75 in/lbs (6.2 ft/lb). An inch pound wrench is usually require only because a ft/lb wrench is tricky to use at those low values. A 1/4" beam type will fit onto any of the bolts without an adapter, and you can get a higher quality tool cheaply if you use one of that type as well.

Offset guages are unnecessary. The flat ones as thin as you use here will flex right into place without problems, and although metric guages would be cool, I still use English ones with the metric equivalent marked on them. You could just convert the specs to English measure, too. Inches = mm divided by 25.4, so .10mm is .0039", or .004". I use a .004" and .006" on the intakes, and a .007" and .010" on the exhausts.

Thanks everyone for the replies!

grayracer513, you said you use a .004" and .006" on the intakes, and a .007" and .010" on the exhaust. I'm camshaft illiterate, could you elaborate on this? What measurements are you referring to? Thanks.

  • grayracer513

Posted May 18, 2005 - 06:39 PM

#14

Thanks everyone for the replies!

grayracer513, you said you use a .004" and .006" on the intakes, and a .007" and .010" on the exhaust. I'm camshaft illiterate, could you elaborate on this? What measurements are you referring to? Thanks.

.004" and .006" equate very nearly to .10mm and .15mm, the spec for the intake valve clearances. Unless I'm wrong, the specs for exhaust valve clearance are .17mm to .25mm, which roughly equals .007" to .010". Not exactly, but the difference is way too small to matter.

  • wc426mx

Posted May 18, 2005 - 07:00 PM

#15

Okay. I totally understand now grayracer513. I appreciate your help. I should get the cam installed tomorrow, but I doubt my Yamaha dealer will have the correct shims in-stock. I'm afraid I'll have to end up ordering the shims, and waiting a little bit before I can ride the finished product.

  • myoung

Posted May 18, 2005 - 08:20 PM

#16

Well, I love the fact that the bike is now almost impossible to stall, where as before...........:)

I almost never use the clutch anymore even when turning on a track or negotiating tight stuff on trails. Add that to the drill free starting, smooth increased power delivery, and bump start ability and there's really no down side to the swap. Hell, I don't even remember the last time I needed the hot start. Sure the Hotcams would probably give more horsepower, but the power improvement I got from the 450 cam seemed such a great improvement that I couldn't justify the cost of going to a Hotcams set-up, especially since they took so long to get their cam released and I already spent my money on the 450 cam. :D





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