Timing Mark on Rotor Not at "T" Mark on Case When Pistons are TDC

[UncleBuck]

It's actually about 180° away. As best I can figure the PO (everyone's favourite person to blame) had the engine apart, and the rotor didn't get set back to the right position.

Does that even make sense?

I definitely have not been able to start the engine. If I back off the toothed nut holding the points shaft on the the cam shaft, I can adjust the timing until the points separate just about TDC, and I could probably fudge it so they separate back at around the F mark on the rotor (15° BTDC?). However, backing off that nut and trying to adjust things is how I got into this mess in the first place. Wish I'd checked to make sure the pistons were at TDC with an ever-loving straw through the spark plug opening before assuming they were at TDC because the marks said they SHOULD be at there.

Now, I'm pretty sure the right answer is to open things up and make them back to factory.

What kind of mess is this going to be to sort out? I can probably hack my way through this making small adjustments until the bike starts. I'm thinking there's probably a smarter way.

Any thoughts?

 

[Grinder]

Are your timing marks aligned on the mechanical advance side of the rod? There are two hash marks that need to line up for proper timing.

 

[grizld1]

Grinder, the man is talking about the timing marks on the alternator.

UncleBuck, the alternator rotor is keyed to the crankshaft--assuming the key is in place. If the PO had the rotor off, neglected to reinstall the key, and just stuck the rotor back on the shaft and torqued it down, the rotor mark could easily be 180* off. It's easy enough to check; make, buy or borrow a proper thread-on puller, spin the nut off, pull the rotor, and look.

 

[Grinder]

I know, just seemed unlikely that the rotor would be off unless the po was a real dumb ass. The advance is easy enough to mess up if you don't know.

 

[jd750ace]

Normally we do not "assume" but when it comes to unknown previous owners, it often applies. Follow the advise of the great Ronald Reagan with regard to the Soviets: Trust, but verify.

 

[UncleBuck]

Grinder: Yes, I have been careful about those hash marks on the advance side of the rod. I have made that mistake previously, but I eventually found a comment rearding that in another thread. So, yea, that's a fair comment. To clarify, to PO said the engine had been done over so it ran more like a 750, and the carbs had been done too, so it was more like an 850. Dumb ass sounds about right. Then again, it ran when I bought it, so he knew at least more than me.

grizld1: That keyway is the kind of advice I was hoping to hear about. I'll get in there and check it out. Seems like it probably won't be in there given how far away from where it should be the rotor is. Is that just a normal parallel key, or is it something unusual?

jd750ace: Yep. Not the first time I've made that mistake. I like "yer man" Reagan's take on it.

 

[Grinder]

If the rotor slipped on a running motor, it should still run providing nothing else was touched. Granted it would be impossible to time using the marks but it should still run.

 

[5twins]

Do you have all the locating pins in place on the advance rod and cam? There are 3, one on each end of the advance rod and one for the advance unit that locks it into the proper position on the cam. I have no idea what you're talking about when you mention a toothed nut holding the points shaft on the cam shaft. If you're missing any of the locating pins, the points cam, the little disc on the advance side, or the advance unit could be in any position but the correct one and your timing could be anywhere but where it should be.

 

[grizld1]

Look, guys, the man is talking about the pistons being somewhere around BDC when the rotor mark lines up with the TDC mark. The only way that's going to happen is if the rotor is out of place.

UncleBuck, the keyway takes a woodruff key--half-moon shaped.

 

[Grinder]

Understood, all I'm saying is a slipped rotor won't cause the motor not to run unless the owner tried to readjust the timing with the rotor in the wrong position.

 

[Brian902]

It's a 78 XS650 so the key doesn't matter for running purposes, but nice to have for timing purposes.

Buck, key falls out pretty easy when rotor is removed, PO probably didn't notice because when re-installed everything would have still worked.

Sloppy PO.


TDC
Easy way to find it; 1-remove both plugs 2-rotate crank counter clock wise until intake valve of left cylinder opens and closes 3-continue rotating until, using a straw or screwdriver down the plug hole, you feel the piston come to top.
You are now ROUGHLY at TDC. Both exhaust and intake valves should be loose on the left cylinder.

Gif file needs to be opened with Internet Explorer, otherwise it comes up as a black screen. Save to your computer and then open with IE if it doesn't work here.

 

[UncleBuck]

5twins: I've definitely had the marks on the advance wrong; see attached photo (red circles are hash marks in wrong position, red arrow shows "toothed nut"). This has been now corrected, after reading a post you wrote in another thread. I appreciate the advice on the pins. I have noted the pins on either end of the advance rod; I haven't noted the pin for the advance unit. I'll have to look.

grizld1: In the thread on doing a PMA conversion, punkskalar uses a modified 5/8" x 3/16" woodruffe. When I check the rotor to see what's going on, I'll measure the keyseat to see what it needs to be from factory. I'll hunt around some local shops. Worst case scenario, I'll ask the mold maker at work to help fabricate something.

Grinder: You are describing the exact problem. The owner (me) tried to set the timing with the rotor in the wrong position. I get what you mean - if I hadn't tried to set the timing, it would probably still be running. As sloppy as it is to drop the key, if the PO knew it wasn't there, they probably could have dealt with it, and the slipped rotor not caused them an issue.

Brian902: You've got much nicer reference images than I do! One of the boys at work is an amateur road racer; he suggests chopping up an old spark plug, and fixing in some kind of bolt that will contact the piston before TDC. With that plug in place, gently rotate the crank CCW, and mark the position where it stops against the bolt. Then gently rotate CW and mark the position where it stops against the bolt. The point halfway between your marks is TDC.

 

[grizld1]

Be careful with that piston stop. The technique you're describing is fine in a 2-stroke or side valve cylinder, but if you try that full rotation number on a OHV 4-stroke you may eat up a valve. There are a lot of ways to skin this cat. Your best bet is to use a dial indicator and a degree wheel. Set the indicator up on a piston crown at a given drop BTDC, record degrees, pull back the indicator plunger so side load doesn't lock it up, rotate over TDC, take a degree reading ATDC, and find your midpoint. Really, the simplest solution is to install the rotor correctly!

 

[UncleBuck]

I may be in a bit of trouble here.

I can see no sign of any pin that would lock the advance onto the the cam.

Please see attached photos.

 

[jkocr2]

The pin should be in that hole in the top of the cam..

 

[5twins]

I think you may have found the problem. While the advance unit is off, you can verify the cam timing in relation to the timing marks. Here's a link .....

http://www.650motorcycles.com/CamTiming2.html

Face the pin hole in the cam straight up or straight down. The rotor mark should be on T.D.C.

 

[UncleBuck]

So, the plan to get back to running form is:

1. Pull the rotor
2. Key the rotor
3. Tighten it down
4. Pin the advance (red arrows in attached photos)
5. Tighten it down
6. Check points as per manual
7. Kick 'till it hurts?

Both the pin and the key should be snug, but not press fits, yes?

 

[grizld1]

You got it. But if you follow up the static timing (step 6.) with a strobe after you get the motor fired, you'll make a repeat of the hurtin' part of step 7. less likely in the future.

 

[UncleBuck]

What a happy coincidence! Timing lights are on sale at Princess Auto!

 

[XSLeo]

My old timing light got to a point where the clamp on pick up was getting pretty bad. It would work fine at idle but when reved up it wouldn't.
I went up to Harbor Freight and picked up one of there cheapies. Works great, not quite as bright as the old one but works at all rpms.
The wires that hook it to the battery and the plug wire are not very heavy so I have to be careful where I let them hang. Keep them away from the exhaust.
Leo