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xr_man

fine tuning cam timing

10 posts in this topic

Any one know how to change the cam timing on a WR (426) using the standard cam sprockets...do they have to be pressed off (or one of them anyway) and moved to the new position, or is there another way ??

I have the standard WR inlet and a YZ 450 exhaust , and want to try a few different settings on the dyno (just a few degrees at a time)

Your help appriciated ...blar blar blar :applause:

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They are pressed on but you may want to loctite the sprocket into final position. Aftermarket cams are available with adjustable timing slots so you can fine tune the cam timing. :applause:

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Yer I know you can get after market cams with adjustable sprockets ... but I am incredibly mean , and just want to set up the standard ones !!

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Oh dear ....last time of asking .....can anyone help with info on adjusting the timing on standard cams / sprockets pls ?? :applause:

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Only way to change cam timing on the stock cam, less than 1 tooth, is to press the sprocket off and press it back on in a different position....it'd be a royal pain in the butt and you'd prob'ly have to tack-weld it to keep it on the cam. And good luck being sure it's where you want it...

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Only way to change cam timing on the stock cam, less than 1 tooth, is to press the sprocket off and press it back on in a different position....it'd be a royal pain in the butt and you'd prob'ly have to tack-weld it to keep it on the cam. And good luck being sure it's where you want it...

Actually this is the way the factory guys do it exclusively, I am fortunate enough to have a guy who builds engines for one of the major factory efforts as a friend, he is actually building my WR engine as we speak, and when we started this project I asked him if we were going to be using WebCams or HotCams and he said neither, he said that while both of these companies build decent product, nothing is as good as the OEM cam for durability and timing, the after market cams are pretty hard on the cam journals and can eat a head up in fairly short order compared to OEM.

He presses off the gear and presses it back on to degree the cam(s) in.

And the guys at the top of the heap he builds engines for do extremely well.

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thanks for the honest info .....do you know if the sprocket needs tack welding when put back on ?? I dont mind doing it but ONLY if its needed.....

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thanks for the honest info .....do you know if the sprocket needs tack welding when put back on ?? I dont mind doing it but ONLY if its needed.....

From what I understand it is about a .0015 in. interference fit, I think that works out to be about .031mm, so it is a fairly tight fit, I think since it is steel (both the sprocket and the cam shaft) they can stand a few on and off's without losing that interference fit, not something I would try with an aluminum to steel fit for exmple where the aluminum would start to go away.

I have had great luck with freezing one part and heating the other when it comes to things with interference fits (steering head bearing races and wheel bearings for example).

I will ask him tomorrow and post back, but he never mentioned anything about tacking the sprockets on, and stated that they will move the timing around from track to track depending on conditions.

I am fairly sure they have a few cams set up before hand so on location it is more likely a whole cam swap on the day rather than pressing gears off.

A good interference fit would suffice as the spring tension per valve is not that great, and also you will mostly be dealing with the exhaust cam (2 valves) rather than the intake (3 valves) which has 1/3 more tension due to the additional valve and spring right?

Good luck with your project.

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thanks....I will certainly have a play to start with as I have a spare exhaust cam (as fitted YZ450 one) and the idea of freezing the cam then heating the sprocket seems like a great one !! :bonk:

I'm going to check what the timing is at the moment, and then dyno the bike (its good to have a mate with a dyno shop !!) I will then try setting the timing to 110 degrees (what hotcams recommend for their cams) and then dyno it again ....if its better....I'll leave it alone ...if its worse ...I'll go the other way ....if anyones interested (or even if there not !!) I will post the results ....but dont hold your breath , it will take me a month or so to do the other jobs I am planning first :applause:

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