Author Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50 (Read 245185 times)

HondaMan · « **Reply #1200 on:** June 29, 2015, 10:17:16 PM »

Ah, the notorious "spark wobble"!

The culprit here usually is: a slightly bent points shaft that mounts the spark advancer, which makes it sit ever-so-slightly not flat against the end of the crank. This makes the points cam, which has a bit of play in it, alternately wobble first 'away' from the points on one revolution, then as it gets pushed to (your) right when it opens the 1-4 set again, the clearance shifts 'toward' the 2-3 set on the next revolution, advancing the timing for one revolution. Then this cycle starts again. If left this way for a LONG time, it causes the foot of the points cam to wear in an arc, and then the only solid solution is to replace the advancer or mill the base flat and make some shims of the same amount, tricky stuff to do (but often needed on the Honda Twins of the 350/360 genre).

The "fix" is to align the points shaft. Sadly, this requires both a dial gage and the removal of the whole points plate...it has to be less than .002" out-of-round (and is fairly easy to get perfect) to fix this issue.

..unless the points cam is already worn, then it's a different issue?

A word to the sage: this bending happens when the big nut is turned CCW (backward) with the sparkplugs still in the engine. This lifts the advancer off the base opposite the dowel, bending the shaft (specifically while adjusting the 2-3 points set with a static light). It literally can happen in one backward turn! Before I figured out that I was CAUSING this to happen (in about 1973) on bikes I was tuning up, I had to 'fix' a lot of them in those days, before I got smarter.

But, now you're smarter, too!

Bill/BentON Racing · « **Reply #1201 on:** June 30, 2015, 06:49:47 AM »

Rafi, most awesome work my man, you've done more than well! What Mark said, think Restoration Fan and Stella have same problem. Ron, I'll help you check runout, Bill
And Rafi, you have moved the bar way higher than it was! K,

HondaMan · « **Reply #1202 on:** June 30, 2015, 04:36:45 PM »

Quote from: Bill/BentON Racing on June 30, 2015, 06:49:47 AM

And Rafi, you have moved the bar way higher than it was! K,

Boy, that's no lie! I can't turn on my computer in the garage, or my bike might slap me....

edwardmorris · « **Reply #1203 on:** June 30, 2015, 08:17:28 PM »

Thank you, thank you ALL, yet again, for the kind words, I cannot express my gratitude for the help and support throughout, I'm sooooo close to begin enjoying long rides on the gorgeous Indiana roadways!

I did do the static timing with the plugs out, the clearance on the pistons is pretty tight (or at least I'm not strong enough

to turn it with the plugs in). I did however have to turn it CCW slightly a couple times

Anyway, what's done is done, and it looks like I'm going to have to pull the plate regardless of whether I swap out the points/timing shaft or 'fix' it. I do have a dial gauge, so I will test the runout first and see how bad it it. The wobble is only on the 2-3 side and is very very little, but, I am able to see it. Since I now have the plate timed nicely, will marking a small dot on the base and on the crankcase work to get it back relatively close to the original position?

Bigger question is, how exactly do I go about 'fixing' the shaft if the runout is more than 0.002"??

Davez134 · « **Reply #1204 on:** June 30, 2015, 09:17:39 PM »

That's what I do when I have to remove plate, I make a couple marks to get it back close.

As far as fixing the runout in shaft, rotate engine (I raised rear tire off ground and used that to turn engine forward) watch for where dial gauge is highest. Give the shaft a tap in direction 180 degrees away from gauge. Repeat until runout is within spec. I also tried moving dial gauge to different angles to the shaft just to make sure.

SOHC4 Cafe Racer Fan · « **Reply #1205 on:** July 01, 2015, 06:38:39 AM »

Rafi,

Your bike was instantly nominated and seconded for Bike of the Month. Please post an acceptance of the nomination in the BOTM thread, or the Earth my stop rotating.

Don

Stev-o · « **Reply #1206 on:** July 01, 2015, 06:49:25 AM »

Quote from: CB750 Cafe Racer Fan on July 01, 2015, 06:38:39 AM

Rafi,

Your bike was instantly nominated, seconded and declared the winner for Bike of the Month.

Fixed that for ya, Don!

754 · « **Reply #1207 on:** July 01, 2015, 12:33:08 PM »

That is such a sweet motorcycle.. Same as my first 750 but much much nicer.
Well done Rafi, a whole extra raisin pie for you..

SOHC4 Cafe Racer Fan · « **Reply #1208 on:** July 01, 2015, 01:44:01 PM »

Before any of that happens by way of majority vote, Rafi has to accept his nomination.

Justin · « **Reply #1209 on:** July 01, 2015, 01:45:36 PM »

Quote from: HondaMan on June 30, 2015, 04:36:45 PM

Quote from: Bill/BentON Racing on June 30, 2015, 06:49:47 AM
And Rafi, you have moved the bar way higher than it was! K,

Boy, that's no lie! I can't turn on my computer in the garage, or my bike might slap me....

hahaha, awesome

love a good build thread and the inspiration and knowledge of so many of you fine chaps.

edwardmorris · « **Reply #1210 on:** July 01, 2015, 03:38:54 PM »

Thank you, all, its very overwhelming how great and positive the reception has been for my first build. Sorry I'd been cooped up in a conference for the past two days and wasn't checking in. I'll head on over and accept the nom on behalf of everybody that has helped me build it.

HondaMan · « **Reply #1211 on:** July 01, 2015, 04:55:00 PM »

Quote from: edwardmorris on June 30, 2015, 08:17:28 PM

Thank you, thank you ALL, yet again, for the kind words, I cannot express my gratitude for the help and support throughout, I'm sooooo close to begin enjoying long rides on the gorgeous Indiana roadways!

I did do the static timing with the plugs out, the clearance on the pistons is pretty tight (or at least I'm not strong enough to turn it with the plugs in). I did however have to turn it CCW slightly a couple times Anyway, what's done is done, and it looks like I'm going to have to pull the plate regardless of whether I swap out the points/timing shaft or 'fix' it. I do have a dial gauge, so I will test the runout first and see how bad it it. The wobble is only on the 2-3 side and is very very little, but, I am able to see it. Since I now have the plate timed nicely, will marking a small dot on the base and on the crankcase work to get it back relatively close to the original position?

Bigger question is, how exactly do I go about 'fixing' the shaft if the runout is more than 0.002"??

Once you figure out a way to make your dial gage clamp on to the engine (that's the hard part!), you add 2 nuts on the threads of the long bolt and lightly jam then together: this is where you will tap it with a hammer to move it (so the threads survive). Then use the gage to see where the "high" side is, then (laboriously) back the gage away, tap on the shaft a little, re-gage and check again. It's a PITA, but the shaft bends pretty readily, so it doesn't take more than a couple of times around to get it straight.

754 · « **Reply #1212 on:** July 01, 2015, 06:15:13 PM »

Ordinary guages are cheap they can survive the bounce.. I would leave guage in place, put drift on nuts and tap carefully or just push firmly and see if it goes....try for 1/2 of indicated runout..

edwardmorris · « **Reply #1213 on:** July 01, 2015, 09:09:39 PM »

Quote from: 754 on July 01, 2015, 06:15:13 PM

Ordinary guages are cheap they can survive the bounce.. I would leave guage in place, put drift on nuts and tap carefully or just push firmly and see if it goes....try for 1/2 of indicated runout..

I do a magnetic base, came in really handy when truing the wheels, well worth the investment for a ride that holds a line steady

Looks like I have my work set for the long weekend (not as long for me but I do have some time off!), I'll try the firm push method first, its a brand new shaft so I'm hoping it isn't too far outta shape. Thanks for the help guys, this independence day I might just get my first loooooong ride!

harisuluv · « **Reply #1214 on:** July 01, 2015, 10:38:50 PM »

Wow amazing build. I had no idea what you had been up to! Awesome.

evanphi · « **Reply #1215 on:** July 02, 2015, 07:11:03 AM »

FWIW, Rafi... I had the same issue with 2/3 stuttering and tapped my shaft back into within 0.002" of perfectly straight. It can be done!

754 · « **Reply #1216 on:** July 02, 2015, 08:05:41 AM »

Try a small hammer handle (wooden not end against nuts)for the pressing, first try pushing with palm of hand, if that is not enough, then tap on the hammer with another hammer.
It should not take much force to bend the stud.

Godffery · « **Reply #1217 on:** July 02, 2015, 12:00:15 PM »

Well done in deed. Outstanding attention to detail !

rickmoore24 · « **Reply #1218 on:** July 02, 2015, 12:47:00 PM »

WOW WOW WOW WOW WOW WOW WOW WOW!! BEAUTIFUL WORK!

Sam Green Racing · « **Reply #1219 on:** July 02, 2015, 01:29:04 PM »

Rafi, the fact that you remembered and thanked all the people that helped you is awesome, please let me thank you for all you did for me, I really am honored to call you MY FRIEND.

Sam.

Restoration Fan · « **Reply #1220 on:** July 02, 2015, 05:15:20 PM »

Raphi,
Your's is one of those threads I keep going back to...just to look at the photos. Can't say it enough times. You did a damn fine job.

Ron

HondaMan · « **Reply #1221 on:** July 02, 2015, 06:49:57 PM »

Rafi: keep that one locked up when you're not home!

edwardmorris · « **Reply #1222 on:** July 02, 2015, 10:43:22 PM »

Quote from: HondaMan on July 02, 2015, 06:49:57 PM

Rafi: keep that one locked up when you're not home!

Conference is done, made it home with some sunlight left, so took it out for a spin without touching anything since that last "wobble" situation. Bike ran worse than it did with just static timing

Will be starting over tomorrow AFTER checking the runout and stuff, hoping to have better news soon, and that loooooong awaited long ride!

edwardmorris · « **Reply #1223 on:** July 02, 2015, 10:45:30 PM »

Quote from: Sam Green Racing on July 02, 2015, 01:29:04 PM

Rafi, the fact that you remembered and thanked all the people that helped you is awesome, please let me thank you for all you did for me, I really am honored to call you MY FRIEND.

Sam.

Sam!! Glad that you're still hanging out with us. Knowing all you guys here, the honor truly, is MINE!

Johnie · « **Reply #1224 on:** July 03, 2015, 05:59:13 AM »

Raf you just set a pretty high standard there. Wow...I am speechless at the detail and bling. Every aspect of that bike just POPS out at you with those great pics. We can all see the detail and effort you put into this...now the big question...how does the wife like it? My hat is off to you man!!! Excellent...what is next?

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Author Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50 (Read 245185 times)