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jonsson_

09 yz450 intake advanced 1tooth

11 posts in this topic

Changed cam chain a few hours ago, apperently the bike have been running with the intake cam advanced 1tooth... How much room for error is their with these engines?

Only fired it up after the change of chain so I havent rode it, should it make a big difference? Seems weird when it have been running great.

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Advanced, as in rotated one tooth counter-clockwise from the correctly aligned position? I'm surprised it survived it. If it had been two teeth advanced, it would have bent all three intakes first thing.

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Ooppss sorry typo! Retarded, intake cam was 1 tooth clockwise. When exhaust ligned up correctly the marking on the intake cam was below the edge of the head. Are you still as surprised it survived then?

I´ve ran it for 18hours since I bought it and according to seller the piston had 4 hours on it when I bought it so a total of 22hours with the cam like this.

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Depends on which way, on the old YZ426/WR426 the difference was that the WR camshaft were 1 tooth off compared to the YZ, This to make the motor a little less agressive.

Don't know how this is on the newer bikes but as it actually ran you probably havent broken anything. So just put the camshaft back in the original position.

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Yeah, I know about the older 426s but I´ve got no idea on this one? I put it back like it´s supposed to be and it started up and ran great on the stand. Im interested in knowing more in detail how it should change the powerband. It´s been running great. Its 2 weeks since I rode it last time, If its not a big difference I´m not sure I will notice it. I dropped the needle 1# when I had the tank off so now I have 2 changes at once. Not good! IF I notice a change I wont know if its needle or cam :smirk: Hopefully Gray or someone else will share their knowledge about the cam timing.

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These bikes will run with the intake one tooth retarded, but not very well. In general, retarding the intake cam only will widen the powerband and decrease the peak power. However in the cam world the difference between a very tight lobe separation and a very wide lobe separation is only 10 degrees. Going one full tooth is simply too much of a change to be doing as a "performance mod". Changing the degree of a man as little as 2 degrees will make a pretty noticeable difference in the power characteristics of the engine, both to the rider and on a dyno. You should definitely be able to tell a difference in how the bike runs by changing the intake timing one whole tooth.

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I´ll go riding in a few hours if the rain stops... Will know by then. But it hasnt run bad, kinda weak lowend(for a big 4st) and better topend. And coming on throttle from closed have been yerky feeling and not smooth.

so, KJ what you´r saying I should´ve been low on power but with a good wide powerband?

I found this at compcams.com:

Advancing Retarding

Begins Intake Event Sooner Delays Intake Closing Event

Open Intake Valve Sooner Keeps Intake Valve Open Later

Builds More Low-End Torque Builds More High-RPM Power

Decrease Piston-Intake Valve Clearance Increase Piston-Intake Valve Clearance

Increase Piston-Exhaust Valve Clearance Decrease Piston-Exhaust ValveClearance

Is this applicable to the yz?

What your saying KJ is that 1 tooth is WAAAY to much change to do. Do you know how many degrees 1tooth might be?

According to the list from compcams I should have much better lowend now.

EDIT: I cant post that list readable!! If you cant read it here it is http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx

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Here's a little better discussion of lobe centering/cam timing and its effects:

http://www.muzzys.com/articles/lobe_centers.html

Since the intake opens as the piston approaches TDC on the exhaust stroke, advancing the cam brings the valves closer to the rising piston. Retarding on the other hand would increase clearance.

KJ makes a valid point (as usual) regarding moving the chain over the sprocket vs. re-indexing the cams. Most tuners change the cam timing only 4-5 degrees or less either way, and as he said, 10 is pretty much the most you'd hear about. Since there are only 32 teeth on the cam sprocket, and the cams turn at half speed, each tooth moves the cam 22.5 degrees vs. the crank.

But the fact that it was retarded raises a question: did you really assemble it wrong, or did the cam seize momentarily and cause the chain to skip over the cogs? When you reset it to the correct timing, be sure you carefully inspect the cam cap bearing surfaces for signs of scoring, and be very careful in reassembling the cap and torquing it down.

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Remember that the camshaft bracket should be torqued down in a criss cross pattern and only to 20 Nm or you will see excessive wear on the bearing and probably something worse.

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Gray I took a picture of it before removing the cams and old chain. Cams bearings and camcaps were in perfect shape. Put the caps back on very gently letting them fall into their position.

Eliass, oh yes always criss cross.

Ran the bike for 20mins today and the low end is alot better! Traction was bad so topend I couldnt tell any difference. But the transition from chopped throttle to open it up again is SOOO much better. Before I was annoyed with how abrupt it went from coasting to accelerating. It was either on or off. Really bad when you NEED throttle control in tecnical slow sections. Stall rpm is alot lower then before. 180 brakeslide turns is so smooth!

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I´ll go riding in a few hours if the rain stops... Will know by then. But it hasnt run bad, kinda weak lowend(for a big 4st) and better topend. And coming on throttle from closed have been yerky feeling and not smooth.

so, KJ what you´r saying I should´ve been low on power but with a good wide powerband?

I found this at compcams.com:

Advancing Retarding

Begins Intake Event Sooner Delays Intake Closing Event

Open Intake Valve Sooner Keeps Intake Valve Open Later

Builds More Low-End Torque Builds More High-RPM Power

Decrease Piston-Intake Valve Clearance Increase Piston-Intake Valve Clearance

Increase Piston-Exhaust Valve Clearance Decrease Piston-Exhaust ValveClearance

Is this applicable to the yz?

What your saying KJ is that 1 tooth is WAAAY to much change to do. Do you know how many degrees 1tooth might be?

According to the list from compcams I should have much better lowend now.

EDIT: I cant post that list readable!! If you cant read it here it is http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx

Yes those are a rule of thumb when it comes to cam timing changes, though more things come into play as with most things. However, that list is referring to the normal cam timing change of only a few degrees, not a huge change like being one tooth off. When the lobe separation angle gets as large as you had it, who knows how the engine will act , I'm surprised it ran without breaking up to be honest. Since it did run smoothly, odds are it would be lacking a significant amount of low end power (as you have commented on). I doubt you would have seen an increase in top end power with the incorrect timing you had simply because I think the rev limiter would kick in before an RPM high enough for that lobe separation angle to be optimal (near where your peak power would be). Basically your engine would have to rev insanely high for a lobe separation angle that large to work well, so in reality you would see a loss in power across the whole RPM range of the engine's capability with the intake retarded one tooth like yours was.

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