WR450F'12+ How to grind a YZ cam for e-startability

[WRF-Rowdy]

Topic has been discussed well, everyone should know by now that a YZ-cam has a longer decomp duration (almost no compression to work against)

However, a WR-cam needs some intake charge to be left inside the combustion chamber to actually fire up the engine. 

 

Reason is: on good kick will have the decomp pin retract, on both bikes.

But the slow churning of the e-start does require a decomp setting,

perfectly balanced between "no-compression at all" and "way too much for the e-start to overcome"

 

To be able to add compression to the YZ exhaust cam we need to trim the decomp pin down so that the cam's decomp pin

will close the exhaust valve at exactly the same amout of "degrees before compression TDC" as the WR cam was doing.

 

That very moment when the decomp pin stops touching the exhaust valve bucket has to be found.

 

I was using a slab of flat aluminum, app. 20mm high, so the cam's gear is clear of the working table's surface.

I wanted to simulate the valve clearance as well.  So I searched for a sturdy material that would be 0.2 mm thick.

I used a piece of hard plastic I found in my errm... garage (note: never clean up your place, last day's garbage might be todays tool ? )

 

The Process:

1) lay the cam onto the flat aluminum, having the lobe close to the decomp pin (precisely the lobe's backside) touch the 0.2mm strip.

Then the aluminum would be where the valve bucket's surface normally is, one clearance away from the cam.

 

2) press down at the cam with your finger, behind the 0.2mm strip, so that the cam now rests on strip and far end

 

3) while you keep pressing down the cam, somehow note the position of the 9 'o clock punch mark

  (that is the only thing telling us how the cam will be installed).

 Rock the cam back and forth to find the exact decomp pin contact position.

  As that position is somewhere in the air, hard to reference against, I picked the 3rd tooth left of the 9 'o clock mark instead,

  because that tooth points nicely at 9 'o clock when viewed from sprocket side, and colored it black with some felt tip marker.

 

4) create a reference.  I used the cam's packaging box and marked the exact position of the 3rd tooth.

   (weight down the box or use something more sensible ? )

 

5) grab the YZ cam, find the 3rd tooth left of the 9 '0 clock punch mark, color it black.

 

6) now when you position the YZ cam at "decomp pin touches simulated bucket" you will see how far the 3rd tooth is OFF of the marking on the reference box.

 

7) grind it down, frequently rechecking, until the third tooth is exactly at the mark.

 

8) use a 1000 (or 800?) grade sand paper to smoothen the scuffed surface.

 

9) really clean the YZ cam very, very well, reassemble and enjoy the e-start working with the YZ cam

 

Total time, includung photo documentation: 2 hours.

 

Notes:

Make sure you know which punch mark is the "9 'o clock" type. (see pichtures)

The 0.2mm strip could be any material as long as it won't budge when you hold down the cam.

I know that one could use another strip at the far side lob to make the cam parallel to the "bucket simulator", but I simply didn't want to be anal about it.

WARNING: altough the decomp pin looks indestructible your dremel grinder will work through it like butter! Be very gentle. Look at the scars I made and do better.

The pin cannot rotate more than 30° around its movement axis. So I only took off material at the bucket touching side.

I was worried that reducing the overall lift of the pin might make the decomp less effective. And I only wanted to fix the decomp detachment point, nothing else.

WARRRRNING: 1mm is WAY TOO MUCH!  That must be the number for triming the huge WR cam's pin, I only took off 0.4mm at best!

 

Most important: Even when you ducktape the bearing you will contaminate it with particles, audible if you turn it by hand.

I did take the cam to the tap and rinsed it generously with hot(!) water until all oil, grease and grime were gone.

I excessively spun the bearing while holding it into the streaming water.

Don't forget to actuate the decomp pin a coupe dozen times while douching it. Dry well with a hair dryer.

Result should be that when given a good push with your thumb it should keep spinning for 10 seconds flat!

Don't get to axious because a completely dry bearing when held at an angle might develop a rattling sound comming from the fact that the balls change race.

If you hold the cam vertical either way it should be spinning w/o any other sound than "wheeeeeeeeezzzzzz". no rattling!

 

edit:

just took it outside and verfied the result:

started up "cold" (~28°C currently) in gear firt try.

stopped a mile later and restarted fine in gear.

deliberately stalled it with the rear brake and it still fired up in gear!

I like that. Feels like success to me.

 

 

left WR'12 right YZ'06

 

flat elevated surface, with valve clearance simulator

 

End-Of-Decompression position of the WR'12 exhaust cam

 

End-Of-Decompression position of the unmodified YZ'06 exhaust cam

 

app. 0.4(!) mm of grinding later

 

after polishing off the edges

Edited June 12, 2015 by WRF-Rowdy

[chu]

Thanks for sharing.  I might give it a try one of these days.

[WRF-Rowdy]

Starting in gear is an interesting topic. I had a hard time in the first week of riding to start the stock WR'2012 in May.

Even when hot every second time it would require three attempts.  Demonstrably three, not two and not four.

I had been setting the CO to +8 like everyone was suggesting.

 

Back home I recalled how I had dialed in the idle mixture of my WR400F and the '03 WR450F:

I'd lower the idle speed to ridiculously low and searched for the rich end of the mixture screw

and the lean end where the engine would quit and when smack into the middle. 

Idle back to sensible and happy starting for over a decade.

 

I found it interesting that YAMAHA actually deployed some kind of fuel cutoff mechanism into the EFI version,

which made for super silent engine braking (no fuel injected, doh) until app. 4000 rpm where the backfiring would start with a tame "pfft..tiff..pff.tt".

 

However the prefectly starting '03 would go "whamm... bang... PAmmm,..samm.. bang"  when one used a lot aof engine braking.

 

So now I tried to set CO w/o looking at the numbers, just lowering the idle speed to extremely low values

with the CO setting mode active, playing with CO towards rich and towards lean until the engine would die.

 

I did end up with -6 as CO setting!  Helped a lot with e-starting in gear.  No idea why. 

And of course when engine braking and  rpms drop below 4000 she now does "whamm...pss..tss. bang.tss.bang".

 

Now after todays YZ cam grinding I habitually torture the e-start:

Every start is in gear, cold and hot, and up to now each of them was first push.

I'm really happy as a camper, the '12 now starts in gear as fine as the '03 did!

 

Of course it is hard to tell what influence the YZ cam has, I think the backfiring increased a little,

but as above 4000 rpms it is completely silent (the '03 would backfire ear shatteringly) it's ok for me.

Edited June 13, 2015 by WRF-Rowdy

[grayracer513]

I found it interesting that YAMAHA actually deployed some kind of fuel cutoff mechanism into the EFI version,

which made for super silent engine braking (no fuel injected, doh) until app. 4000 rpm where the backfiring would start with a tame "pfft..tiff..pff.tt".

 

Standard practice for EFI gasoline engines. 

[FORMA MOTO]

The pin depth is not consistent from one YZ EX cam to another.

 

We proved this comparing (3) new OEM 2007 YZ EX cams.

 

All the pins protruded at different distances.

 

THAT is the issue with this issue.

[chu]

It doesn't really matter what size the pin is before you grind it as long as it's the right size after you grind it.

[FORMA MOTO]

It doesn't really matter what size the pin is before you grind it as long as it's the right size after you grind it.

 

Noshet Sherlock...

 

I was pointing out that the endless discussion on exactly much to grind the pin is pointless, as every pin is different.

It's not about measuring the amount removed, it's about measuring the amount remaining.

[chu]

Yeah, that and it's kind of hard to grind a precise amount off a small, dome shaped object freehand with a dremel tool. 

The height of the pin just determines how much the valve is lifted.  It's how it ramps down that determines when the valve closes.  Some things are easier to eye up on a crude jig than to measure with calipers.

Edited June 13, 2015 by chu

[chu]

Can you adjust the CO while the engine is running?

[WRF-Rowdy]

Sure! That's the reason why the tool displays the rpms while in CO adjustment mode.

 

While you lower/richen the CO setting you can watch the rpms change in real time. 

Edited June 13, 2015 by WRF-Rowdy

[WRF-Rowdy]

We proved this comparing (3) new OEM 2007 YZ EX cams.

 

All the pins protruded at different distances.

Sounds very unlikely for a company whose production quality allows one

to drop an '05 YZ cam where a WR '12 cam was installed, w/o reshimming!

 

I'd assume YAMAHA would be manufacturing two, max, three types of decomp pins:

- the square ones for all the WRs

- the lower, rounded ones for all YZs

- and maybe something different for the quads.

 

If their YZ decomp pins are variing by a releavent amount and the WR pins would too,

then it would a lottery if one's WR would fire up by e-start or not.

 

On the other hand why should they ship WR cams with precisely machined pins and YZ cams with varying pins?

 

How much difference are we talking?   Height or pin shape, too?

Edited June 13, 2015 by WRF-Rowdy

[chu]

Sure! That's the reason why the tool displays the rpms while in CO adjustment mode.

 

While you lower/richen the CO setting you can watch the rpms change in real time. 

 

OK, my lean best idle seems to be around -9 or -8.  I'm gonna try that for a while and see how it goes.  Ignition has to be off to get into CO mode but you can start it up once you're in CO mode.  Can't believe I never thought of that.

Edited June 13, 2015 by chu

[FORMA MOTO]

Sounds very unlikely for a company whose production quality allows one

to drop an '05 YZ cam where a WR '12 cam was installed, w/o reshimming!

 

I'd assume YAMAHA would be manufacturing two, max, three types of decomp pins:

- the square ones for all the WRs

- the lower, rounded ones for all YZs

- and maybe something different for the quads.

 

If their YZ decomp pins are variing by a releavent amount and the WR pins would too,

then it would a lottery if one's WR would fire up by e-start or not.

 

On the other hand why should they ship WR cams with precisely machined pins and YZ cams with varying pins?

 

How much difference are we talking?   Height or pin shape, too?

 

Should but don't. For the YZ application it doesn't matter if they are precision lengths.

[RockerYZWR]

So since we've ID'd the requirement for the correct dimension of cam base circle plus pin length...uh, what is it?  That would answer the questions that come up a lot about this. 

[chu]

If you do it this way, you mostly just grind the right side of the pin.  From the picture it doesn't look like much was taken off the top.  It looks like it would be hard to get an accurate measurement.

[WRF-Rowdy]

So since we've ID'd the requirement for the correct dimension of cam base circle plus pin length...uh, what is it?  That would answer the questions that come up a lot about this. 

Won't work that way.

- can't measure precisely enough

- height is not the issue here, shape is

 

Personally, I would assume grinding down the whole YZ-pin (giving it a square profile like the WR-pins have)

to a height that will close the valve at WR e-start time, you might end up with a very small total pin height, not lifting the valve off its seat to decompress enough.

 

 

That pin can only rotate for app. 60°, so when the cam is rotating

there is a pin side which starts to press against the bucket and a side that guides the bucket back in place.

 

What you want to opt for is grinding the "trailing pin shoulder" to a height, where the valve closing-time is correct (WR-ish)

while leaving the max. pin elevation as unmodified as possible to maintain decent valve lift.

 

If you look at an YZ decomp pins from the side it's a cylinder with a spherical cap on top:

https://www.thumpertalk.com/uploads/monthly_07_2013/post-274936-1373066657924.jpg

 

What you might want to achieve by grinding is create a flat plane from the highest point of the pin

reaching to the location where the cylindrical section starts, but only on the trailing side!

(trailing side is the left, when looking alongside the cam, sprocket at far, end pin on top)

 

Hard to describe but when you place it on the cam-grinding-tool I describe here in post #1

you actually can see which part of the pin is touching the valve's bucket right before detatching from it.

That is NOT the highest part of the pin, but a point near the start of the cylindrical section.

Edited June 14, 2015 by WRF-Rowdy

[WRF-Rowdy]

From the picture it doesn't look like much was taken off the top.  It looks like it would be hard to get an accurate measurement.

Exactly! both your, statements are true.

[grayracer513]

I think that what you will find if you want to spend a whole lot of time researching is that the pins on any given YZ model protrude the same distance from center on all of the cams for that particular year model. The portion of the cam from which the pin protrudes is not a critical dimensioned area of the camshaft, and that is where the variance is apt to be found.

[WRF-Rowdy]

I think that what you will find if you want to spend a whole lot of time researching is that the pins on any given YZ model protrude the same distance from center on all of the cams for that particular year model. The portion of the cam from which the pin protrudes is not a critical dimensioned area of the camshaft, and that is where the variance is apt to be found.

I'd say the protrusion, when measured from the polished lobe's back side to top of pin, will be as precisely identical as anything else on this cams is.

I'd agree with you that when measuring from the crude, unpolished body of the cam to the pin's top one might find different values.

Edited June 16, 2015 by WRF-Rowdy

[alstar250]

...Of course it is hard to tell what influence the YZ cam has...

 

Hey awesome job and just wanted to say thanks for posting this. Now what I really wanna know is. hows the power? What mods have you made (i.e exhaust, tuner / map settings) and what do you think of the YZ cam?