Decomp pin grind



9 replies to this topic
  • Duderino

Posted January 08, 2014 - 05:30 PM

#1

I've looked and but can't find this out: Are you grinding the pin in the cam or removing it then grinding? I can't seem to figure out how to get the pin out seems pressed in...and grinding in place scares me because the cam lobe is right next to the pin and I don't want to nick it.

Thanks,

Mark

  • still2smokin

Posted January 08, 2014 - 08:04 PM

#2

This is what you are looking for .....

http://www.thumperta...d#entry11015098

 

Grind the pin with it still installed in the cam.

 

Careful though , I went just a smidge to far and made it super hard to start....... smoked the cables from the batt to the starter.

Luckily I had another cam from an exploded motor.  For $180 bucks it is worth it just to buy the yzf cam .


Edited by still2smokin, January 08, 2014 - 08:06 PM.


  • KennyMc

Posted January 08, 2014 - 10:54 PM

#3

I've looked and but can't find this out: Are you grinding the pin in the cam or removing it then grinding? I can't seem to figure out how to get the pin out seems pressed in...and grinding in place scares me because the cam lobe is right next to the pin and I don't want to nick it.

Thanks,

Mark

I believe this guy left his in.

http://www.thumperta...0f-cam/?hl=cams



  • Duderino

Posted January 09, 2014 - 12:32 AM

#4

Thanks, I left it in. Took off just under 1mm....9ish, my digital calipers took a dump on me right as I was finishing.

I got some metal duct sealing tape and put a few layers over the cam love so I wouldn't nick it.

Got a polishing kit for my dremel and went to town. I ground check, ground checked... Went very slow. Got close, shaped the side, not touching the top, overall surface. Got down to .8mm ish and used a 220 paper sanding disc and kept shaping, got a nice done then touched the top surface down with paper to about .9mm.

Then I used a small polishing wheel with polish and polished that thing almost like a ball bearing.

The surface, while polished did have some light "turtle shell" appearance but not much.

I did buy a nice sanding/polishing kit from Lowes that would have done a better job but it didn't have the right mandrel with it... It had some rubber flap wheels and some scotch wheel that propably would have done a better job. Or using a couple more finer paper sanding wheels...but that's all I had.

It's in a relatively low abuse function...other than light oil on start up, so I'm hoping my imperfections will be tolerated!!

Got it fired up, could get estart to fire it cold, but I didn't go through my normal pre-start ritual so not sure how it will do cold. But...once warm E-Start works like a champ!!!! Hell ya! Never did before.

I'm gonna try to go abuse it Friday so I can report back if everything goes well because u no there's others lurking that want YZ cams but don't want to loose e-start.

  • Krannie McKranface

Posted January 09, 2014 - 06:29 AM

#5

I'm still totally lost on this whole deal...

 

1 tooth retard on the stock exhaust cam, on years 2007 and later? ...but it requires the pin to be ground?....so that is going from 13 to 12 between the cams?

YZ exahust cam, standard timing, or retard? ....still grind the pin?



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  • grayracer513

Posted January 10, 2014 - 09:21 AM

#6

If the cam is retarded and the pin not modified, then the timing of the reseating of the exhaust valve by the decomp pin will also be retarded by the same amount.  Remember that in matters of event timing in engines, "retard" means "to happen later".   One tooth on the YZ/WR cams results in a change of 22.5 degrees of crank rotation.  The exhaust valve on the '06 YZ450 is reseated at right around 20-25 degrees BTDC.  I don't have specific specs for the various WR grinds, but I imagine they would be quite similar.  If the cam is retarded, and the exhaust vale reseating is retarded by the same amount, the valve would not reseat until TDC or just after, and you would have no compression.  Because of that, all other things remaining the same, the pin needs to be shortened to allow the valve to close up sooner if the cam is retarded.

 

That is the reason that the pin on the first 3-4 years of the WR450 was so much longer than the one on the YZ450 cam.  The two camshafts ('03-'05 YZ450F and '03-'05 ('06?)) WR450 were the same cam shaft that simply had the gear repositioned when it was assembled.  The WR cam timing was more advanced, which would mean the valve would also reseat sooner, which would increase cranking compression to beyond what the e-start can deal with, so they built the WR cams with longer pins to begin with.

 

After, and perhaps including, '06 (don't recall for sure just now), the cam grind profile was altered on the WR450, and retarding them as used to be done with earlier models is not something that I've followed very thoroughly.  It's best to evaluate the results that have been obtained by those who have tried it. 



  • Krannie McKranface

Posted January 10, 2014 - 08:37 PM

#7

Ok, that's is what I remember: post 2006 exhaust cam retiming does not have the same postive effect as earlier years did.



  • Duderino

Posted January 12, 2014 - 02:33 PM

#8

Did a hard 3 hour ride with no issues...well, other than me getting bucked off with a hard hip/shoulder/head auger in!!

I must say having E start is fantastic and I am pissed at myself I didn't do this a long time ago!!! It's the way the bike was when I bought it (2 yrs ago) so this is the first E start for me ever, I'll never go back. But I am getting fat, old and lazy.

My bike is an '08 with YZ cams (don't know timing). Took me about three hours at a low-speed,beer drinking, putter pace that included a lot of check and recheck, grind and recheck. Could be done quicker.

  • WRF-Rowdy

Posted June 03, 2015 - 08:06 AM

#9

If the cam is retarded and the pin not modified, then the timing of the reseating of the exhaust valve by the decomp pin will also be retarded by the same amount.  Remember that in matters of event timing in engines, "retard" means "to happen later".   One tooth on the YZ/WR cams results in a change of 22.5 degrees of crank rotation.  The exhaust valve on the '06 YZ450 is reseated at right around 20-25 degrees BTDC.  I don't have specific specs for the various WR grinds, but I imagine they would be quite similar.  If the cam is retarded, and the exhaust vale reseating is retarded by the same amount, the valve would not reseat until TDC or just after, and you would have no compression.  Because of that, all other things remaining the same, the pin needs to be shortened to allow the valve to close up sooner if the cam is retarded.

 

That is the reason that the pin on the first 3-4 years of the WR450 was so much longer than the one on the YZ450 cam.  The two camshafts ('03-'05 YZ450F and '03-'05 ('06?)) WR450 were the same cam shaft that simply had the gear repositioned when it was assembled.  The WR cam timing was more advanced, which would mean the valve would also reseat sooner, which would increase cranking compression to beyond what the e-start can deal with, so they built the WR cams with longer pins to begin with.

 

After, and perhaps including, '06 (don't recall for sure just now), the cam grind profile was altered on the WR450, and retarding them as used to be done with earlier models is not something that I've followed very thoroughly.  It's best to evaluate the results that have been obtained by those who have tried it. 

You are talking about retarding a WR cam, right? The ones with the longer, more rectangular decomp pin.

That longer decomp pin has to be ground down some so that when retarded, it behaves decompression-wise exactly as the ronded YZ pin, right agian?

 

That would mean, dropping an OEM YZ cam into a WR would not need any grinding, just nicely aligned punch mark will do, true? :thumbsup:

 

Then why did my WR'2012 not like the freshly purchased '06 YZ cam?  The E-starter happily chruns away, apparently seeing no compression. :foul:

 

I'm a little lost here. As the '06 YZ cam does have the rounded pin, I can't grind it down further, thus where's my compression?


Edited by WRF-Rowdy, June 03, 2015 - 08:07 AM.


  • grayracer513

Posted June 03, 2015 - 08:28 AM

#10

The fact that the pin is already shorter and rounded compared to that of the WR is not a clear indication of whether or not it will work right.  The thing to check is the point at which the exhaust valve reseats as the decomp pin comes out of contact with the lifter.  In a Stock Yz450, this happens at about 20-25 degrees BTDC.  You'll need a degree wheel for this.  If it were me, I would check to see where this point was with a stock WR cam and try to duplicate it as much as possible. 

 

I haven't done any such conversions on the later WR, so I can't give a more definitive answer, but if I'm not mistaken, I believe the '06 ex cam does need a little bit removed from the pin to work correctly in the WR, although I'm not certain as to exactly why it should. 






 
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