Author Topic: advance key question??  (Read 720 times)

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Offline Tattoo

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advance key question??
« on: December 22, 2017, 02:46:17 PM »
Im got a bike with Gear drive cams and a advance key. can't tell if the advance key is a 2 or a 4 ,nothing on the key is there a thickness I can go by or some other way? 

thanks.....
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Offline Ohio HD

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Re: advance key question??
« Reply #1 on: December 22, 2017, 03:08:01 PM »
Well, they're difficult to measure, to keep the offset side square in the calipers. The narrow side in the keys I've measured are 0.159". Then the 2 key measured 0.190" on the wide side. The 4 key measured 0.197" on the wide side. The measurement was as I said trying to keep the keys square in the caliper jaws, and not let the key cock sideways with the pressure of the caliper jaws. Hope this helps.
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Offline Tattoo

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Re: advance key question??
« Reply #2 on: December 22, 2017, 03:19:33 PM »
 :up: Thank you for the info it looks to be a 4.
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Offline Ohio HD

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Re: advance key question??
« Reply #3 on: December 22, 2017, 03:21:35 PM »
According to S&S a stock key is 0.188" x 0.150". I doubt these keys are all that precise, but, 4 is more likely.
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Offline Ohio HD

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Re: advance key question??
« Reply #4 on: December 22, 2017, 03:34:56 PM »
If you're really careful, you might be able to file the key down 0.006" - 0.007".   
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Online sfmichael

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Re: advance key question??
« Reply #5 on: January 01, 2018, 11:53:43 PM »
a wealth of knowledge you are Mr. Wottle  :smiled:  :up:
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Online tmwmoose

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Re: advance key question??
« Reply #6 on: January 02, 2018, 02:51:28 AM »
New in the package Woods had them colored blue and red on the ends , whether that held up in use I don't remember. Of course if you had the other one not being used on hand bingo , but probably not though in your case

Offline Ohio HD

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Re: advance key question??
« Reply #7 on: February 02, 2018, 10:58:09 PM »
And just to make this clear as mud. This is where the stepped keyway comes in. The 4 key I have measures about 0.011" of an offset. Drawing it all out, the math says it needs 0.013" of an offset, but close enough.  By the way, the 2 you see is really 4 at the crank.


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Offline Ohio HD

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Re: advance key question??
« Reply #8 on: February 03, 2018, 11:10:02 AM »
This is a scenario of a set of cams advanced by 4 at the crankshaft and the effect it has on the intake TDC lift. Keep in mind there is no set value that can be used to calculate the change on TDC lift when advancing or retarding a set of cams. The initial cam timing ground into the cam is what places the TDC lift, and then as well the shape of the specific cam lobe effects what that 4 crankshaft advance does to the TDC lift. So not just the 2 rotation of the cams (4 measured at the crank), but also the lobe shape is what gives the end result in TDC lift change.

I know many on here know all of this, but it helps some to see what is happening.

Also, the rotation of this rear cam is a gear drive set of cams. A chain drive rear cam would be clockwise.

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« Last Edit: February 03, 2018, 11:18:10 AM by Ohio HD »
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Online sfmichael

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Re: advance key question??
« Reply #9 on: February 03, 2018, 12:24:45 PM »
 :up:
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Offline 1FSTRK

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Re: advance key question??
« Reply #10 on: February 03, 2018, 01:32:34 PM »
Great info and diagrams thanks for post them.
« Last Edit: February 03, 2018, 04:04:31 PM by 1FSTRK »
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Offline 1FSTRK

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Re: advance key question??
« Reply #11 on: February 03, 2018, 03:17:03 PM »
OK
« Last Edit: February 03, 2018, 04:06:08 PM by 1FSTRK »
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Offline Ohio HD

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Re: advance key question??
« Reply #12 on: February 03, 2018, 07:02:17 PM »
This is a scenario of a set of cams advanced by 4 at the crankshaft and the effect it has on the intake TDC lift. Keep in mind there is no set value that can be used to calculate the change on TDC lift when advancing or retarding a set of cams. The initial cam timing ground into the cam is what places the TDC lift, and then as well the shape of the specific cam lobe effects what that 4 crankshaft advance does to the TDC lift. So not just the 2 rotation of the cams (4 measured at the crank), but also the lobe shape is what gives the end result in TDC lift change.

I know many on here know all of this, but it helps some to see what is happening.

Also, the rotation of this rear cam is a gear drive set of cams. A chain drive rear cam would be clockwise.

(Attachment Link)

I had to make some changes in the name of accuracy. I forgot to figure the rocker ratio into the equation. So the 0.208" TDC lift is actually then 0.237" TDC using a 1.625:1 rocker arm.

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Offline Ohio HD

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Re: advance key question??
« Reply #13 on: February 04, 2018, 06:22:20 PM »
Here are the dimensions of a 4 gear drive advance key. These are a really snug fit, and need to be filed carefully to fit. Paying attention to not file on a side that allows the cam and gear to recenter. A small hand held diamond file works well.


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