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 Post subject: Crank/Primary Gear modified Keyway
PostPosted: Fri Jun 29, 2018 2:07 am 
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Joined: Sat Aug 04, 2012 2:01 am
Posts: 179
Location: Ventura, California
Has anyone had an offset keyway made for the upper crank/primary gear to correct the synchronization of the upper and lower cranks?

I believe it would require an offset of about .020" or .5mm to correct the 2+ degree difference at TDC of the cranks. Any feedback would be appreciated... Thanks!


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Fri Jun 29, 2018 2:14 pm 
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Joined: Fri Nov 18, 2005 6:15 pm
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Location: Wisconsin
Maybe. I'd have to look to see if I have an extra.

If I do, it corrects 2.5 degrees.


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Fri Jun 29, 2018 2:56 pm 
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Joined: Sat Aug 04, 2012 2:01 am
Posts: 179
Location: Ventura, California
Thanks Jeff - that would be great. Hard to measure exactly, but it does look like a correction of 2.3-2.6 degrees is needed.
If you do have an extra, let me know what I owe you and if I can PayPal you the money... shipping would be to Ventura, CA 93003.


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jun 30, 2018 8:21 am 
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Joined: Fri Jul 28, 2017 4:23 pm
Posts: 80
Location: Stratford Upon Avon UK
I've never heard of this before. Does it make a noticeable difference?

Sent from my HTC Desire 530 using Tapatalk

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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jun 30, 2018 9:16 am 
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Joined: Thu Jan 26, 2006 3:56 pm
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Location: la belgique
It does ,but the crankkey is diffrant for all motortypes

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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jun 30, 2018 11:26 am 
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Joined: Fri Nov 18, 2005 6:15 pm
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Location: Wisconsin
Look what I found!
Image


Last edited by Jeff B on Mon Jul 02, 2018 1:09 pm, edited 2 times in total.

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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jun 30, 2018 11:36 am 
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Location: Wisconsin
Linx wrote:
I've never heard of this before. Does it make a noticeable difference?

Sent from my HTC Desire 530 using Tapatalk


The cranks being out of time gets some of the blame for uppers being more likely to seize. Personally I did it for reliability not performance.


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Fri Jul 06, 2018 11:59 pm 
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Joined: Thu May 17, 2018 10:19 pm
Posts: 9
I am doing another goofy motor and I'm gonna check this and definitely want them the same


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jul 07, 2018 1:43 am 
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Joined: Sat Aug 04, 2012 2:01 am
Posts: 179
Location: Ventura, California
A few pointers learned during the process of syncing up the cranks:

* Check for TDC in degrees many times to accurately come up with the difference in degrees that the rear crank is retarded in respect to the front crank. Be sure to rotate in the correct direction of rotation at all times. Did I mention to check this multiple times?

* Now that you know how many degrees behind the rear crank is compared to the front crank, you can calculate the amount of offset required.


My rear crank was almost 2-1/2 degrees out. After many measurements, checking for accuracy, I was able to determine it was actually 2.3 degrees out. The calculation formula is as follows and based on the crankshaft diameter at the key being 25mm:


25mm x pi (3.14159) to get the circumference of the crankshaft = 78.539mm

Divide the circumference (78.539mm) by the total degrees (360) = .21816mm circumference per degree

Multiply circumference per degree (.21816mm) by the number of degrees the upper crank is retarded, or behind the front crank - in my case it was 2.3 degrees:

Final equation is .21816mm x 2.3 degrees = .50176mm offset required (just shy of .020")


* The stock key seems to be a little loose and allows for some of the inaccuracy - just be aware while assembling and measuring.

* The OEM key is of hardened stock - Rockwell Hardness measures at 27RC. BE SURE to use hardened stock for your key (most standard key stock is not hardened and designed to be the failure point or shear. You will want to match the hardness of the OEM key.

.........------7mm------
........____________
.......|..................|.....................|
........|..................|--0.5mm..........|
.........|_................|_..................|
...........|..................|...............7mm
0.5mm - |..................|.................|
...........|___________|................|

...........-------7mm--------

.......--------7.5mm---------


The OEM key is approx 7mm square stock. To create the offset key, you will need to start with larger stock, cutting down to a rectangle of 7mm x 7mm+offset required (.5mm)

--Start with 7.5mm stock, cut the top-to-bottom (height) dimension to 7mm

--Cut into the side-to-side dimension 1/2 way (3.5mm), the amount of required offset (.5mm) - width

--Do the same on the other side cutting into the other 1/2


Hopefully this help with figuring out how much offset is required to sync the rear crank to the front crank. Do not use an offset key on the front crank as the ignition timing is sync'd with the front crank and syncing the rear crank corrects the timing and TDC of the rear crank.


Last edited by Bengt Weil on Sat Jul 07, 2018 5:17 pm, edited 1 time in total.

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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jul 07, 2018 3:22 am 
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Joined: Sat Nov 12, 2011 10:50 pm
Posts: 204
Location: Adelaide, South Australia
Hi I had offset keyways made up for my projects. Bill Wilson tuned engines wanted to make
sure everything was right. Keyways were wire cut to the angle of the crank. Picture of the
keyway on my street fighter build.
Cheers Ron.


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jul 07, 2018 12:28 pm 
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Joined: Fri Nov 18, 2005 6:15 pm
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Location: Wisconsin
Your drawing implies that both sides of the key are square and parallel. Clearly one side should be rotated the ange of your offset.


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jul 07, 2018 1:25 pm 
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Location: la belgique
When rear crank hit tdc later then the front the upper crank is retarded but ignition is advanced
And dus prone to seizures as Jef mentioned already

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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sat Jul 07, 2018 5:27 pm 
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Joined: Sat Aug 04, 2012 2:01 am
Posts: 179
Location: Ventura, California
Quote:
Your drawing implies that both sides of the key are square and parallel. Clearly one side should be rotated the ange of your offset.


Heck, that drawing from the keyboard was hard enough (square & parallel)! You are correct, the drawing is a "simplistic" view.

In the case of my offset key (to correct for 2.3 degrees), when machining the .5mm offset, the key must be set at a 2.3 degree angle to the cutter when cutting one of the two "offsets", as well as to correct for the side opposite the angled offset cut to keep the two edges parallel. I believe any good machinist will know how to properly create an offset key (I would hope...).

I have edited my "drawing" to perhaps show the included 2.3 degree angle and the parallel surfaces. The .5mm offset occurs at the center point of the key and angles in or out from that center-line accordingly. Hope that makes it a bit clearer for all.

This attention to detail and fit is a vast improvement on the OEM key, which is loose enough to cause some slight rocking within the keyway. If one examines the original key, you will actually see the pressure marks of the crank shaft and the gear rotating and leaving slight wear marks on the key (this is where lack of tolerance adds to the problem of crank synchronization).

On another note, I have heard of people creating their own offset keys through the use of larger key stock, a vise and a file and apparently, that works as well...

Thanks again to Jeff B. for pointing out the rotational factor of correctly creating an offset key.


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sun Jul 08, 2018 1:18 am 
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Joined: Thu May 17, 2018 10:19 pm
Posts: 9
Yes a retarded crank is a advanced ignition


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 Post subject: Re: Crank/Primary Gear modified Keyway
PostPosted: Sun Jul 08, 2018 3:46 am 
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I used a programmable ZEELTRONIC instead with 2 separate sensor inputs and ignition timing being programmable for each cylinder individually. It requires 4 separate coils of course. This solves the issue of too advanced timing of the rear. Of course having an offset key is the ideal solution


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