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General Category >> Rubber Side Down! >> Cam Timing, Part Deux
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Message started by Armen on 10/15/16 at 11:04:09

Title: Cam Timing, Part Deux
Post by Armen on 10/15/16 at 11:04:09

So, I'm scratching my head trying to figure a simple way to make small adjustments in the cam timing. I start to write a program to poke more holes in the cam sprocket (only the teeth are hardened, the rest can be drilled). Figure I'd do three sets of holes for 1, 2, and 3 degrees of cam timing-which would correspond to 2, 4, and 6 degrees of crank timing. Of course, there are three holes-two for the cam bolts, and one for the locating pin.
But, I am shiftless and lazy.
So, I buy another crank sprocket and take a look. Sure enough, there are 19 teeth for the cam chain and 22 teeth for the crank splines.
WooHoo!
360 degrees divided by 19 teeth is 18.947 degrees per tooth for the chain sprocket.
360 degrees divided by 22 splines is 16.364 degrees per tooth for the crank splines.
So, if you advance the chain timing on the crank sprocket by one tooth, and retard the crank sprocket 1 tooth on the crank splines, you end up with 2.58 degrees of advance. A nice amount if one is dialing in the cam timing. Not good enough for a race engine, but good enough for a street bike.
Especially if you are dealing with a used cam chain. Might be the ticket to bring the cam timing back to stock.
;)

Title: Re: Cam Timing, Part Deux
Post by verslagen1 on 10/15/16 at 11:10:21

Nice... and you can check that with a degree wheel against the top of the head.

Title: Re: Cam Timing, Part Deux
Post by LANCER on 10/15/16 at 11:48:34

So are you drilling new holes for the pin ?
I have a few extra cam gears, would you be willing to drill some for me for some $$ ?

Title: Re: Cam Timing, Part Deux
Post by Armen on 10/15/16 at 11:53:53

Hey Lancer,
Nope, I'm not touching the cam sprocket. Or doing any machining.
All the changes are done by moving the crank sprocket. The chain is advanced one tooth on the crank sprocket, and the sprocket itself is retarded one spline on the crank.
Make sense?
Told you I'm shiftless and lazy ;)

Title: Re: Cam Timing, Part Deux
Post by norm92de on 10/15/16 at 11:56:40

Nice discovery. Ain't science wonderful. :)

How much did you decide .070" of cam chain stretch retards the cam timing?

Title: Re: Cam Timing, Part Deux
Post by Ruttly on 10/15/16 at 12:08:40

Armen , Curious with your finding and have a question. If you did that to a brand new engine with no wear would that still have a good result.

Title: Re: Cam Timing, Part Deux
Post by Ruttly on 10/15/16 at 12:15:19

Armen, Next question. Will ignition timing need to be adjusted as well ?

Title: Re: Cam Timing, Part Deux
Post by LANCER on 10/15/16 at 13:24:26

Are you doing this based on having a stock camshaft ?

Title: Re: Cam Timing, Part Deux
Post by norm92de on 10/15/16 at 14:31:58

Armen,
I just did a few calculations and I think your figures are off. The total advance of the cam is 10.765 degrees. A bit too much to correct for a worn cam chain.

Title: Re: Cam Timing, Part Deux
Post by norm92de on 10/15/16 at 14:40:57

Armen,
My numbers are correct except for the direction. The cam is retarded 10.765 degrees! :-[

Title: Re: Cam Timing, Part Deux
Post by Armen on 10/15/16 at 16:20:19

Hey Norm,
How did you get to those numbers?

Title: Re: Cam Timing, Part Deux
Post by Armen on 10/15/16 at 16:21:28

Answers:
Verslagen figured out the cam timing change with a stretched chain. I'd ask him.

Don't think I'd change the ignition timing.

As far as doing this on a stocker, advancing the timing usually moves the power band lower in the rev range. Considering how early the motor signs off, I doubt you'd want to lose any more top end.
Try it and see. Just do the usual piston-to-valve clearance checks.

Lancer-I was offering this as a way to make a relativley small change in cam timing. Either with a stock or hot-rod cam.

Title: Re: Cam Timing, Part Deux
Post by Armen on 10/15/16 at 16:34:25

Norm,
Just so that we are on the same page:
On the crank sprocket, move the chain one tooth to advance the timing. There are 19 teeth on the crank sprocket.
360 degrees divided by 19 is 18.947 degrees per tooth.
Retard the crank sprocket one tooth on the crank splines.
There are 22 splines on the crank.
360 divided by 22 is 16.364 degrees.
By advancing the timing 18.947 degrees and retarding it 16.364, you have a net advance of 2.58 degrees.
Measured at the crank, which is how most cam timing is given.
Unless I had another brain fart :o

Title: Re: Cam Timing, Part Deux
Post by norm92de on 10/15/16 at 17:39:21

Armen,
We are indeed talking at cross purposes.
What I thought you said was advance the crank sprocket one spline, then retard the cam chain one tooth.
What you have just described is different. Advancing the cam chain one tooth. Then retarding the sprocket one spline will indeed result in an advance in timing of 2.56 degrees at the crank and an advance at the cam 1.28 degrees.

I think you have achieved what you wanted. It will be more than enough to compensate for a worn chain. :)

Congratulations. We on this site are sure doing things Suzuki never thought of.

Norman.

Title: Re: Cam Timing, Part Deux
Post by Dave on 10/16/16 at 03:03:57

Well done! ;)

Title: Re: Cam Timing, Part Deux
Post by Armen on 10/16/16 at 05:17:36

Thanks :)

Title: Re: Cam Timing, Part Deux
Post by justin_o_guy2 on 10/16/16 at 05:29:13

Flippin Wow,, what an elegant answer..

Title: Re: Cam Timing, Part Deux
Post by thumperclone on 10/16/16 at 14:54:21

would moving the pick up coil have any advantages?

Title: Re: Cam Timing, Part Deux
Post by Armen on 10/16/16 at 17:28:21

Hey Thumperclone,
This whole thought exercise was about trying to correct cam timing caused by either manufacturing tolerances or cam chain wear.
Because the bike uses a crank trigger ignition, the ignition timing pretty much stays put.
Having said that, I've played with ignition timing on a few bikes. On Airhead BMWs, a few degrees of ignition timing can make a noticeable differences in how the bikes run.
On our SR500 racer, I spent a bunch of time trying different ignition timing settings and running the bike on a Dynojet dyno. Honestly, it made almost no difference at all advancing or retarding the timing.
As for the Savage, try it. You can modify the ignition trigger mounting and get a little bit of adjustment there. There are offset keys made to modify timing. The trick is to find or make one. Of course that means pulling the alternator.
On our Bultaco racer, one ignition we used made away with the key and had you move the rotor on the crank taper to adjust the timing (PITA).