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Author Topic: Spark Advancer CB750F  (Read 1639 times)

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Offline Porscheguy912

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Spark Advancer CB750F
« on: March 14, 2009, 11:45:32 PM »
Hello all,

I'm rebuilding Macm2010's bike on here. A 1976 CB750F
When we got his bike it had a bad issue with Cylinder #1; It was almost frozen.
When i went to look at it, it kicked over about one revolution (i was doing a compression test) then it froze. I took off the points cover and used a wrench on the end nut. That worked for a bit but i noticed that the nut was loose.

Anyway, 6 months later i'm putting the engine back together and i realize that the nut is loose again and i tighten it but it still moves. Turns out the two pegs that protrude off of the spark advancer to mesh with the end nut have sheared off and are stuck in the nut.

Any ideas on fixing this or should we try to find a used one? -Are they the same for all the 750s or specific per year/K and F?

I thought maybe just welding the nut on to the the advancer?
Here are the pics:
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Current: 1978 CB750F3
Past: 1974 CB550K

Offline Sweep

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Re: Spark Advancer CB750F
« Reply #1 on: March 15, 2009, 07:12:31 AM »
You would need a new one.  I found one on ebay for myself a while back for my '76 750k.  You either need a new one or you need to get an electronic ignition system that does away with it such as the Dyna 2000.
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'76 cb750K Wiseco 836|ape crank/head|Carillos|CR29s|Dyna 2k|Kerker
'74 Norton Commando Fastback w/belt and bells

Offline meb1948

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Re: Spark Advancer CB750F
« Reply #2 on: March 15, 2009, 08:08:59 AM »
There's a spark advancer on Ebay right now with a Buy It Now price of $22.50.

http://cgi.ebay.com/ebaymotors/honda-cb750-1972-timing-advance-05350_W0QQcmdZViewItemQQcategoryZ35595QQihZ019QQitemZ290302814214QQrdZ1QQsspagenameZWDVW

The part numbers is the same between the '72 750 and the '76 750F.

Mark.
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Mark
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Offline Porscheguy912

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Re: Spark Advancer CB750F
« Reply #3 on: March 15, 2009, 11:13:00 AM »
Quote from: meb1948 on March 15, 2009, 08:08:59 AM
There's a spark advancer on Ebay right now with a Buy It Now price of $22.50.

http://cgi.ebay.com/ebaymotors/honda-cb750-1972-timing-advance-05350_W0QQcmdZViewItemQQcategoryZ35595QQihZ019QQitemZ290302814214QQrdZ1QQsspagenameZWDVW

The part numbers is the same between the '72 750 and the '76 750F.

Mark.

Well since its cheap..... ;D
Thanks!
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Current: 1978 CB750F3
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Offline MacM2010

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Re: Spark Advancer CB750F
« Reply #4 on: March 16, 2009, 10:15:36 PM »
All your spark advancer belong to us.
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WHALEMAN

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Re: Spark Advancer CB750F
« Reply #5 on: March 17, 2009, 05:25:30 AM »
If someone really put that much torque on that nut to shear off hardened steel pegs I would be very suspect about twist or the staightness of the thin shaft. Dan
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Offline lordmoonpie

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Re: Spark Advancer CB750F
« Reply #6 on: March 17, 2009, 01:29:13 PM »
Quote from: Porscheguy912 on March 15, 2009, 11:13:00 AM
Quote from: meb1948 on March 15, 2009, 08:08:59 AM
There's a spark advancer on Ebay right now with a Buy It Now price of $22.50.

http://cgi.ebay.com/ebaymotors/honda-cb750-1972-timing-advance-05350_W0QQcmdZViewItemQQcategoryZ35595QQihZ019QQitemZ290302814214QQrdZ1QQsspagenameZWDVW

The part numbers is the same between the '72 750 and the '76 750F.

Mark.

Well since its cheap..... ;D
Thanks!
If you don't get it I have a unit you can have for postage and packing cost only(from the UK, about 8-10 bucks?) - it's minus the bob weights and sleeve but you can re-use those off your existing sheared one. The centre and plate is what I have left from my cobbling around for the CR750 ignition. Let me know if you want it, I accept paypal  ;D
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Offline Porscheguy912

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Re: Spark Advancer CB750F
« Reply #7 on: March 17, 2009, 05:11:50 PM »
Quote from: WHALEMAN on March 17, 2009, 05:25:30 AM
If someone really put that much torque on that nut to shear off hardened steel pegs I would be very suspect about twist or the staightness of the thin shaft. Dan

I had the same thought Dan.
It looked ok, but i will check it.
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Current: 1978 CB750F3
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Offline Porscheguy912

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Re: Spark Advancer CB750F
« Reply #8 on: March 17, 2009, 05:15:49 PM »
Quote from: lordmoonpie on March 17, 2009, 01:29:13 PM
Quote from: Porscheguy912 on March 15, 2009, 11:13:00 AM
Quote from: meb1948 on March 15, 2009, 08:08:59 AM
There's a spark advancer on Ebay right now with a Buy It Now price of $22.50.

http://cgi.ebay.com/ebaymotors/honda-cb750-1972-timing-advance-05350_W0QQcmdZViewItemQQcategoryZ35595QQihZ019QQitemZ290302814214QQrdZ1QQsspagenameZWDVW

The part numbers is the same between the '72 750 and the '76 750F.

Mark.

Well since its cheap..... ;D
Thanks!
If you don't get it I have a unit you can have for postage and packing cost only(from the UK, about 8-10 bucks?) - it's minus the bob weights and sleeve but you can re-use those off your existing sheared one. The centre and plate is what I have left from my cobbling around for the CR750 ignition. Let me know if you want it, I accept paypal  ;D

Thanks Lord Moonpie! but i believe the one on evilbay has already been purchased by Macm2010 and will be ready for installation upon arrival. Hence The Quote, "All your spark advancer belong to us!"

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Current: 1978 CB750F3
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Offline Porscheguy912

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Re: Spark Advancer CB750F
« Reply #9 on: March 25, 2009, 05:34:54 PM »
So Here are Some Pics.
The one on the Left is the one that came out of The 1976 CB750F.
The one on the right is the one we got from ebay. The ebay one is from a 72' 750.
The new one is smaller than the old one.
Mark, you mentioned that the part numbers are the same. Will this one work? Its so much smaller!

Thanks!
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Current: 1978 CB750F3
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Offline Alan F.

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Re: Spark Advancer CB750F
« Reply #10 on: March 25, 2009, 08:39:38 PM »
You could bolt it on and break out the old timing light. At worst it would advance earlier or later compared to the original unit.
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Offline lordmoonpie

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Re: Spark Advancer CB750F
« Reply #11 on: March 26, 2009, 04:53:08 AM »
Yes it will work. The dished end of the crank that this fits into is smaller on later models by a fraction of a millimetre. I had the opposite problem to take a K3 advancer and fit it onto a DOHC crank end. I had to stick the advancer in the lathe to trim down the circular boss with the timing pin in that you show in the photo. Now fits like a glove and times up perfectly :-)
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