Author Topic: Points cam orientation - does 180° make a difference? (Read 4303 times)

sweet_baby_james · « **on:** July 12, 2013, 12:23:50 PM »

I've put the points back onto my 78 550k after dumping the Dyna-S ignition. Since I bought the bike with the Dyna I had to source a points cam for the advancer. Now, obviously the advancer rotates with the crank shaft, and hence so does the cam. The cam has one high point on it which drives the points. So, what would happen if the cam were installed on the advancer 180° out? There doesn't seem to be anything that will stop this from occuring? Would this mean that the 1-4 would be making when the 2-3 points should be making (ie. the 1-4 points would make when cylinders 2 & 3 are in the position to fire)?

I hope that question makes sense!

Thanks

Xnavylfr · « **Reply #1 on:** July 12, 2013, 01:43:28 PM »

Your question make perfect sense! You are correct to think , if it is 180 out , then 2/3 plugs would fire when 1/4 should ! BUT I've been informed on this forum ,you can't time these engines 180 degree out of time?

?
If the CAM is set with #1 TDC on timing mark and your points cam was set to open #2/3 points and you DON'T do any wire swaps I DOUBT it will run!!

I'm not from Missouri but someone would have to show it will RUN!!!

Xnavylfr(CHUCK)

dave500 · « **Reply #2 on:** July 12, 2013, 02:09:21 PM »

the igniton can be set up 180 out,the cam cant,just swap the blue and yellow over at the points or coils,they have index marks,pretty hard to spot if you dont know they are there,the hitachi rotors dont have that hole,you use the logo instead.

Xnavylfr · « **Reply #3 on:** July 13, 2013, 06:28:38 AM »

Thanks Dave, I knew those point cams had an index mark somewhere to show center of high point but my eyes are not what they used to be. I'll start using a 10X magnifying glass.

Xnavylfr(CHUCK)

sweet_baby_james · « **Reply #4 on:** July 15, 2013, 08:21:17 PM »

Wow, I would never have spotted that. Thanks.

James

neilc · « **Reply #5 on:** July 16, 2013, 05:30:33 AM »

doesn't the dowl on the back of the advancer set it in the correct position?

trueblue · « **Reply #6 on:** July 16, 2013, 05:43:49 AM »

Quote from: neilc on July 16, 2013, 05:30:33 AM

doesn't the dowl on the back of the advancer set it in the correct position?

Yes it does, but the points cam can be put on the advancer mechanism 180 out.

74750k4 · « **Reply #7 on:** July 16, 2013, 11:37:04 AM »

When you can see the dimple for maximum cam height position to adjust the points, the Big nut, and the 10mm securing nut, have to be off. If you try to adjust the points with those off, it will be innacurate, as the cam will be able to wobble, and is pushed to the side by the points rubbing block, without the nuts on the end of the shaft... so, you will need to mark the shaft somewhere, where you can see it, assemble, and THEN set the points...

crazypj · « **Reply #8 on:** July 16, 2013, 12:39:49 PM »

When the advancer backplate isn't drilled for assemble there is usually a cutway to indicate corret position ('dimple at 3:00 o'clock position)

There is also a tiny 'dot' punched into the end of points cam, it's just about visible at 5:00 o'clock position, some are even 'lighter' than this one and real hard to see

(btw, this isn't for CB750

)
I'm pretty sure there is no mention of these marks in any service manual or bulletin?

sweet_baby_james · « **Reply #9 on:** July 16, 2013, 02:03:50 PM »

Might be worthy of a place in the FAQ section. I haven't seen any mention of this in any manuals.

sweet_baby_james · « **Reply #10 on:** July 16, 2013, 05:55:14 PM »

Is that dimple the high point on the cam? I am using that as a reference for setting the gap. It looks like it is a little bit off the high point on mine.

James

dave500 · « **Reply #11 on:** July 17, 2013, 01:31:45 AM »

might be worth dialing that to see?it might be a precision mark?if its a rainy weekend ill have a tinker with it.

crazypj · « **Reply #12 on:** July 17, 2013, 09:21:30 PM »

Quote from: sweet_baby_james on July 16, 2013, 05:55:14 PM

Is that dimple the high point on the cam? I am using that as a reference for setting the gap. It looks like it is a little bit off the high point on mine.

James

Nope, it's for assembly only

HondaMan · « **Reply #13 on:** July 17, 2013, 10:41:03 PM »

Quote from: crazypj on July 16, 2013, 12:39:49 PM

When the advancer backplate isn't drilled for assemble there is usually a cutway to indicate corret position ('dimple at 3:00 o'clock position)

There is also a tiny 'dot' punched into the end of points cam, it's just about visible at 5:00 o'clock position, some are even 'lighter' than this one and real hard to see

(btw, this isn't for CB750 )
I'm pretty sure there is no mention of these marks in any service manual or bulletin?

Not a word!
I used to look for it in every manual. Then, in a blank-brained moment, I took pix of it for my Tuning Appendix G in my book, but left out the text that pointed out the orientation. Duh...!

Darren Jakal · « **Reply #14 on:** May 12, 2018, 03:15:56 PM »

Sorry about bringing this back, but does anyone have a picture that shows these marks?

I'm on an old Mac and can't update my browser without a whole lot of potential problems with the software I'm using, so I don't have a photobucket fix.

Dam photobucket #$%*ed up a lot of great threads.

Cheers, dj

evinrude7 · « **Reply #15 on:** May 12, 2018, 06:49:17 PM »

darren here are the photos that were in the replies above which you could not see.

dave500 · « **Reply #16 on:** May 12, 2018, 08:34:38 PM »

here ya go.

Deltarider · « **Reply #17 on:** May 12, 2018, 10:45:49 PM »

For some reason, most photos don't open. Hence here mine. The 'marks' (in the pic at 5 o'clock position and white encircled by me) should face eachother after reassembly. I understand the Hitachi version has a logo there instead of a hole.

Darren Jakal · « **Reply #18 on:** May 13, 2018, 08:36:43 PM »

Hey thanks for the replies.

This place is great.

cheers, dj

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Author Topic: Points cam orientation - does 180° make a difference? (Read 4303 times)