Author Topic: Advance unit has sex? (Read 2538 times)

mycb750k6 · « **on:** June 09, 2010, 06:27:03 AM »

So I was replacing my points plate with a new Honda NOS. When I pulled the old one off I noticed the advance unit was also really groddy and the cam rusty. So I pulled that off too and cleaned it. Then I pulled the cam off the advance unit and cleaned and lubed inside it and then reassembled. When I tried to start all the engine would do is pop and back fire. So I pulled the advancer off again and pulled the cam off again and reassembled 180 rotation and the bike ran fine. I still don't understand why it makes a difference. Visually it looks the same each way - FWIW.

markb · « **Reply #1 on:** June 09, 2010, 08:47:03 AM »

I discovered that too when I was trying to set the timing after rebuilding. Couldn't get the points to open at the "F" mark. Did the same thing, took it apart and rotated the cam 180 degrees and no problem. I didn't remember this cam being loose on previous motors so maybe its not usually an issue. Maybe it makes a difference because the followers on the point arms are not at 180 degrees apart.
Mark

mycb750k6 · « **Reply #2 on:** June 09, 2010, 08:59:17 AM »

Yeah you may be right but the next time I take it apart, I'm definitely going to mark it so I can put it back together correctly the first time because you really can't tell visually. Oh and since my advancer back plate was really corroded as well, I found it useful to clean up the 1-4 and 2-3 T and F back plate marks with steel wool and then go over them with a fine black felt pen so then show up more clearly through the peep hole - big difference - FWIW.

fastbroshi · « **Reply #3 on:** June 09, 2010, 08:59:25 AM »

That's got to be it Mark. If they were it would fire if it were 180 out because of the wasted spark design of the ignition right?

Deltarider · « **Reply #4 on:** June 09, 2010, 10:14:11 AM »

Quote

... but the next time I take it apart, I'm definitely going to mark it so I can put it back together correctly

Actually it is marked, supposing your advancer is similar to the one on the 500/550 series. There is a tiny carve in the rim of the cam of the advance unit. Make sure that after reassembling that tiny carve (it is very small indeed) faces the little hole in the advancer unit. There is only one such hole and it's located under where it says "TEC". That's the correct way to assemble.

Bodi · « **Reply #5 on:** June 09, 2010, 10:30:32 AM »

The points must contact their cam at 180° apart or else if you could adjust the timing to be correct the dwells would be very unbalanced. When you install the cam the "wrong" way so it's 180° out on the advancer, each cylinder gets a spark 180° off where it needs to be. One is at just before BDC of the intake stroke with the intake valve slightly open: if the mixture ignites it blows fire back through the carb. The other is before BDC on the power stroke (an unfired power stroke) when the exhaust valve is opening, it may fire and "whuff" through the exhaust.

HondanutRider · « **Reply #6 on:** June 09, 2010, 12:08:08 PM »

Bodi's not "whuff'in" anything...he's right on.

Deltarider · « **Reply #7 on:** June 09, 2010, 11:06:27 PM »

Quote

... but the next time I take it apart, I'm definitely going to mark it so I can put it back together correctly

I wrote: Actually it is marked, supposing your advancer is similar to the one on the 500/550 series. There is a tiny carve in the rim of the cam of the advance unit. Make sure that after reassembling the tiny carve (it is very small indeed) faces the little hole in the advancer unit. There is only one such hole and it's located where it says "TEC". That's the correct way for assembly.

Well... is the 750 advance unit similar in this respect? Has someone checked?

Grnrngr · « **Reply #8 on:** June 10, 2010, 12:27:00 AM »

I just got out my box of leftovers from my 750 Dyna install...my cam has a mark on it..

Frankenkit · « **Reply #9 on:** June 10, 2010, 12:36:41 AM »

Mine did the same thing when I took it off to clean/lube and forgot which way it went. I thought it was a given, then, when it worked just right when reversed?

dave500 · « **Reply #10 on:** June 10, 2010, 12:47:01 AM »

the points themselves arent mounted at 180 degrees apart.reversing the cam will retard one set and advance the other set ,being a little bit very wrong,further to which the opening on each pair will be the degrees difference as per the off mount off each set of points ,thus being wrong more,or wronger,i think.umm?wheres the sex part ?

Frankenkit · « **Reply #11 on:** June 10, 2010, 12:54:42 AM »

not sure, it's been a long time since I've removed it.

Grnrngr · « **Reply #12 on:** June 10, 2010, 01:35:38 AM »

When I saw the title I thought for a moment maybe some "Special Ops" guys got leave or something...

Frankenkit · « **Reply #13 on:** June 10, 2010, 01:45:35 AM »

Yeah I'm getting really tired and have started reading it as "Sex unit has advance?"
... so I'm calling it a night.

dave500 · « **Reply #14 on:** June 10, 2010, 02:20:16 AM »

cant find the sex unit in my parts catalouge,umm,has anyone got the number?i asked the girl at the honda parts counter and she gave me a free slap in the face!

Deltarider · « **Reply #15 on:** June 10, 2010, 02:33:53 AM »

For the 500/550 series it is 30220-323-154 or 30220-323-005 for the whole unit.
(First one is made by Toyo, the other by Hitachi.)
We're discussing the cam, that can be separated after prying open the arms. In the rim of that cam, on the side, should be a eenie teenie tiny mark.

Bodi · « **Reply #16 on:** June 10, 2010, 06:23:58 AM »

The points assemblies are not mounted 180° apart but their cam follower faces MUST be 180° apart. The points assemblies are mirror images, and both mount "upwards". It may look like they are not 180° apart but if you think about the engine crank configuration and the single points cam lobe you will understand why the followers can't be any other angle and accept that the appearance of not being opposite is an optical illusion.

raymond10078 · « **Reply #17 on:** June 10, 2010, 06:33:46 AM »

As found in the service manual . . . .

mycb750k6 · « **Reply #18 on:** June 10, 2010, 07:08:54 AM »

OH I should have said CB750. Sometimes I think that's the only SOHC bike out there but I've never had the 550s or 500s so sometimes forget.
Anyway here's my advance unit from a K0. Perhaps that bulls eye at the bottom of the unit is important. I don't know what else it could be. Anyway I don't see the same example in the 750 manual.

As far as the sex part goes I meant; it only works one way or it has a specific orientation or I just like sex, I don't remember now.

Deltarider · « **Reply #19 on:** June 10, 2010, 07:35:00 AM »

OK, here are the marks (see pic).
Bodi, with all due respect, but we're discussing something else here.

mycb750k6 · « **Reply #20 on:** June 10, 2010, 07:41:35 AM »

I see them, I see them - yay!
Thanks.

Frankenkit · « **Reply #21 on:** June 10, 2010, 08:35:25 AM »

ah. this is the 650 unit:
http://cgi.ebay.com/ebaymotors/1980-Honda-CB650C-CB-650-Ignition-Advance-Unit-/150452479633#ht_582wt_940
looks a little different...
almost harder to tell...

754 · « **Reply #22 on:** June 10, 2010, 09:07:32 AM »

I am not finding that hash mark hard to see at all..

750 has 2 types of advance units.

IF you are high-lighting your numbers or marks.. use white or tellow paint.. not black..

HondanutRider · « **Reply #23 on:** June 10, 2010, 10:02:13 AM »

Quote from: mycb750k6 on June 10, 2010, 07:41:35 AM

I see them, I see them - yay!
Thanks.

Ya musta taken the bag offa yer head.

Deltarider · « **Reply #24 on:** June 10, 2010, 10:11:25 AM »

Quote

IF you are high-lighting your numbers or marks.. use white or tellow paint.. not black..

Nailpolish is best (I advise pearl) for oldfashioned neon strobes. With xenon light you don't need any paint at all.

News:

Author Topic: Advance unit has sex? (Read 2538 times)