Timing advanced too far? Will I hole a piston?

[650Fool]

Hi,

Thought I'd throw this out to anyone rather than dump this on RetiredGentleman.

Question: How far to the left of the advance mark can the timing be before damaging the piston?

Background: I just finished a top overhaul on a stock '77D with 28k. The points and backing plate were clean and still serviceable. The bike was running very well for a few miles until the advance mechanism backing plate retaining nut loosened itself and the cam pin fell out. While dealing with that, I came across RG's advance weight tang peening tip, and tried it (I also clipped the new springs as they were too loose). It worked great! Bike never ran smoother. Initially I had used the static method to set the timing at idle and left the rest to itself because the bike ran so well to redline. RG was very kind in reminding me to check the timing with a timing light to ensure the spark wasn't advanced too much at higher rpms (excessively advanced timing = holed piston). Hooked up the timing light and at idle, the timing was exactly centered between the two marks on either side of the "F". Sweet, huh? Rolled the rpms up to 3500 and the timing moved to a spot 1/2" to 3/4" LEFT of the full advance mark, giving the appearance of too far advanced. Bike still sounds very good. If it matters, the mark shown by the strobe didn't really move off idle until around 3000 rpm and it jumped out past full advance suddenly, in a second or so. Rotated the points base plate to time idle at the right hand mark beside the "F" hoping to retard the timing closer to the advance mark and still get a decent idle. The advance moved in to about 1/4" LEFT of, but still beyond full advance. The bike ran okay, but the idle wasn't as good. I did not recheck point gap. I rotated the base plate back where it was and the timing settings returned to their original positions relative to the marks. I then pinned one of the advance weights to full out (the other moved with it the same amount) and static timed both points. Without doing any adjustment, both were 1/8" - 1/4" to the RIGHT of the full advance mark, indicating very good advance I have put about ten miles on the bike since the overhaul. Running Iridium plugs which I have not checked for color. 87 octane with no pinging or sounds of preignition (not that I would necessarily recognize it unless it was really bad). The bike, as it sits, is a sweet little rocket that wants to GO.

So any advice will be appreciated... Is it safe to run? Only the weights showed any wear, but should I replace the entire advance mechanism? Should I replace the mechanism, lose the points for a PamCo and cross my fingers? (I think I know the answer to that one, but I haven't done enough reading to understand how the PamCo will prevent holing a piston in this case) I will do the PamCo sooner now rather than later, but I really want to know what the heck is going on.

BTW, I do value two cents, so THANKS for any help (and/or humorous comments)!

 

[Grinder]

Somebody else will chime in here I'm sure but your advance should not be comming on all of a sudden. It should be a smooth transition from idle on up. Did you pull and regrease the advance shaft? I wouldn't take a chance of advancing past the mark but that's me. I did the Pamco a while back and would never go back to points.

 

[650Fool]

Somebody else will chime in here I'm sure but your advance should not be comming on all of a sudden. It should be a smooth transition from idle on up. Did you pull and regrease the advance shaft? I wouldn't take a chance of advancing past the mark but that's me. I did the Pamco a while back and would never go back to points.

Hi Grinder,

I pulled and miked the shaft during the overhaul. I might not have been generous enough with the grease on installation (wasn't sure where it would end up, bushings, not bearings, too!). I agree on the smooth transition (glad I mentioned it), hadn't thought of the grease though, Thanks! I just finished reading an "advanced" discussion among Cheftay, Grizld1, pamcopete, and Sundie. I'm thinking a new advance unit and a regrease so far (I'm sold on the pamco too, just don't want to spend until the engine is broken in/proven). Maybe the good idle/bad advance is due to a worn ATU cam pin slot...

Thanks so much for responding!

 

[grizld1]

The pin and slot are there only for alignment during assembly.The slot doesn't wear against the pin; it's the stepped nut that holds the ATU rotor in place on the camshaft, not the pin. If the nut loosens, the pin will damage the slot severely, often breaking a chunk out of the ATU. If you run the engine with the ignition too far advanced, detonation will occur, and you'll hole a piston.

 

[650Fool]

Hi Grizd1,

I was thinking the pin and slot were responsible for holding alignment, thanks for the update on that thought! The nut definitely came loose enough for the plate to come forward and the pin to fall out (it was resting inside the cover!). Fortunately the plate stopped moving and retarded the timing. There didn't apear to be any damage to the pin, cam, or plate. Symptom as it all loosened while riding was the appearance of, and steady increase in, popping from the exhaust when letting the power go to idle and engine braking to decel. On restart, the bike idled okay but would just huff-huff when throttle applied without a load. Stalled immediately when clutch let out. That's when I took the advance cover off and found the loose nut etc. Used locktite AND a punch with a 2.5 lb sledge to whang the nut back on after the fix. Also marked the nut and plate with a sharpie to check for movement periodically (why didn't Yamaha left hand thread that thing?). Bike ran great for a few miles after that and I parked it for the night. Then read RG's timing advice... Yikes! The bike is parked until I know why the timing is so far advanced while zeroed in on idle. Thanks a bunch for replying, and especially that older post on an advance problem.

Cheers!

 

[retiredgentleman]

650Fool;

For timing the engine, pay no attention to where the timing appears to be with "static" method (VOM or test light). It does not show the true timing. The only true timing is with a timing light.

If the timing light shows its going past the full advance mark at 3500 rpm, then you may not have peened the tangs (ears) enough. The tangs must be a tight fit in the slot of the slotted disk. You should try to achieve that with your original ATU parts. If unable then you may have to buy new parts.

As to your timing being delayed and then rapidly jumping to full advance.................I experienced the same thing. I had removed my stock springs and replaced with springs from Mikesxs. Finding them loose, I also cut off 1 coil. I would have a real dead area as I tried to accelerate, then all at once the weights would fly out causing a surge in acceleration. This was anything but smooth and not acceptable.

My solution was to remove the springs from Mikesxs and re-install my OEM stock springs. The result was a nice smooth acceleration!! (Never throw out stock OEM parts removed from your bike)

I have found many items that Mikesxs sells that are similar to stock but they just don't work like stock OEM items. The ATU springs that they sell do not have the correct tension, and that is why the timing advance is not linear.

Another item from Mikexs that does not work properly, is the carb intake manifolds. They are not the correct size and cause air in leakage. I'm also back to using my OEM stock manifolds.

 

[xjwmx]

I wouldn't stray too far from what they're telling you is correct timing, but if there's no preigntion there won;t be any preignition damage. To hear what it sounds like, put it in 5th when you should be in 2nd and get on the gas. Some xs650s are more prone to knocking/pinging/preignition than others. I rode one the other day that seemingly wouldn't knock for anything.

 

[650Fool]

Hi retiredgentleman,

Great tips! I did find Mike's springs loose and cut them. I DID save the old springs, although I don't know if they were stock, they seemed to work. I'll put 'em back on and see what happens with the timing. I'll also pull the rod and regrease it (hope nothing falls out on the way!). So static timing is just to get points ball park (so the engine can run well enough to do the dynamic timing)? I guess I'm not familiar enough with the 650 yet to realize it could run better still. Acceleration during the little riding I have done has been smooth and rapid, no apparent surge. I peened the tangs from .138/.141" to about .161" on both and they seemed snug. As mentioned directly to you, I did have to file the tips down to get them to rotate properly in the slotted disc. I'll try peening a bit more as I've nothing to lose, then plan on replacing the weights as I'm sure fatigue will shorten the life of the tangs. I can only hope the new parts are well fitted. Good advice on holding onto apparently worn out parts!

Thanks to other posts, I got my intake boots (and carb diaphragms) from JBI and am very happy with them (the boss knows his ___ from a ___!).

THANKS yet again for your help!

 

[650Fool]

Hi xjwmx,

Nice to hear from you... I generally enjoy your reparte immensely!

Okay... I thought I might be able to get away with like an eighth of an inch or so beyond full advance, but, going by the marks, it really is off. I rode about five miles, riding like I stole it, to break the engine in... I have the title. During that ride, all was bliss, no funny sounds, plenty of smooth power on demand as fast as I could crank the throttle. Only sign of (potential) preignition so far is that full advance timing is too high. I did not lug the engine because I read that's a "no-no" on break-in, but a short burst won't hurt and, as you say, should reveal impending doom. I'll replace the weight springs first and see what happens, then try lugging it in fifth regardless to see what happens (then run higher octane gas for awhile, it might matter).

Since the engine is smooth otherwise, what do you (all) think about the idea of bending in the stop tabs for the weights to prevent them from advancing so much?

Thanks so much for the detonation check idea! See, this is why I like these bikes so much...

 

[retiredgentleman]

Yes, the static timing is just for ball park accuracy. Always use a timing light to read the true timing.

If the the removed springs you have are OEM, they will do a better job for you. I'm always amazed at the quality of the OEM parts (made in Japan) on these bikes. Mikexs parts all seem to be made in Tiawan....................some parts are OK but others just have no quality.

Don't bend the stop tabs on the ATU. They are brittle steel and will break off.

I would not lug the engine in 5th gear just for a test.................its about the worst thing you can do to these engines. Just get the timing set correctly and you will have no detonation and no chance of engine damage.

 

[xjwmx]

I would not lug the engine in 5th gear

You do it. Fess up...

With cars the age of these bikes, a good way to set the timing by advancing it until you get knocking and then backing off until you don't. By those standards a timing light can have you way off. You can knock earlier than you should due to carbon build up for example. Or you can knock later due to lack of compression.

 

[5twins]

When you lube the advance rod, you're not really lubing the rod (just grease it lightly), you're lubing the bushings it turns in. If you look closely at the outer bushing on each end of the cam, you'll see it has grooves in it. Clean them out and fill with fresh grease. This will give you a reservoir of grease to keep the rod lubed for many years to come. The factory recommends a grease with moly in it. I use VW CV joint grease because it has a very high moly content.

 

[gapper]

So are you greasing the advance rod? I just installed a pamco and never did I read anywhere about grease!

 

[650Fool]

I happened to have a new timing light around, so I'm good there. I just never used it because my CB500 with Dyna S runs very well (can't even remember the last time I checked it). I always had luck with various Hondas static timing with just a light bulb... I must have been blessed cuz the pistons survived. I don't want to ruin that run here! besides, since I'm taking medication now to prevent flicker vertigo, I might as well start doing proper timing. With regard to electronic ignition, I had unpleasant experiences with them during their retail infancy and generally prefer points since they work fine for a non performance rider. The Dyna S has changed my mind, but fooling with points on an unfamiliar machine will help me understand and trust it, then move on to electronic.

RG - I don't want to lug the engine and will do whatever I can to fix the problem before it gets to that point. I can't rule it out as diagnostic tool, despite its crudeness. I just don't understand what's causing such excessive range in the timing, but I am starting to get a sense of what might be happening. Grizld1 did hint in another post the advance mechanism is brittle, and I forgot, so Thanks again for trying to save my bacon. If I can't get the tangs any tighter, how about gluing thin spacers in increments onto the inside edge of the stops to reduce the advance, does that seem viable in theory? I have read a lot here and learned to take Mike's with a grain of salt, some stuff is great other stuff not up to snuff. I actually prefer MMM, but he's not always available and some of the stuff is same as Mike's. I agree with pamcopete, though, in that both companies, despite any shortcomings, serve a valuable service to us.


xjwmx - See what I mean? But I don't think RG lugs his machine, not even close. Being an old guy myself, we don't have enough time left to continuously screw around with these machines without also riding them...

5twins - I read this on another of your posts... AFTER having rebuilt the top. I know this is elswhere, but if I just remove the advance unit, the cam pin, and move the points felts out of the way, the rod will pull right out the points side without any parts falling off inside the cam, then go back in the same way after lubing? How about a moly/AMSoil synthetic grease 50/50 mix? BTW, the wheel spacer worked great! The back end is now moving in the same direction as the front. Thanks for your help on that! On to steering bearings...

 

[650Fool]

Hi Gapper,

Your question was for the others, I'm no mechanic, but I would grease the rod if only to prevent rust/pitting.

 

[xjwmx]

xjwmx - See what I mean? But I don't think RG lugs his machine, not even close. Being an old guy myself, we don't have enough time left to continuously screw around with these machines without also riding them...

I don't see what you mean. I don't even know what you're talking about

I suggested lugging the engine so that you could hear what knocking sounded like after you said in the op that you weren't sure you could recognize knocking. It has been misconstrued into my saying to do it habitually or something.

My point was that, at least with old car engines, you can advance the timing until you get knocking. Then back off until you don't. The factory specs are not always optimal for those old engines.

 

[grizld1]

650Fool, timing advancing too far with rpm's up after being dialed in correctly at the idle mark indicates that the tips of the bobweights are worn. New ones are available only with a new ATU assembly. A good quality repro is sold by Mike's XS for a very reasonable price.

If you want to try correcting the advance curve, don't do it by knocking/bending the limiting tabs on the ATU. They're brittle, and even if you can't see it, you'll start a fracture that will have a tab falling off in less (usually much less) than 1K miles. Pamcopete has suggested a quick fix; slipping shrink tube over the tabs. I'd regard that as a temporary measure, for use until a new unit arrives. For a more permanent fix, remove the bobweights and smack the tips with a hammer until they spread out to 4 mm. (.160").

In the absence of a dyno, fine-tuning the advance is best done by reading the spark plug electrode. Too wide a clean-burn line (as read after a high-speed run) means too much advance. See Gordon Jennings' classic article on plug reading at www.strappe.com . At ~10.25:1 static CR on pump gas, I never found it necessary to go more than 2* inside the factory setting. On a stock motor at the factory marks, you won't have any issues with elevated compression that 92 octane gas won't cure.

 

[5twins]

You don't have to remove the whole advance unit to get the rod out, just remove the little disc with the notches that the advance weights hook into. Then the rod can be pulled out the points side, points cam still attached. I lightly smear grease on the entire rod for protection against rust. The only part the needs grease for lubrication really is the 2 ends of the rod and that's mainly provided by what's held in the bushings.

 

[650Fool]

Good morning!

xjwmx - By "see what I mean" I was referring to your comment to RG about not ever lugging his engine. I like reparte as long as it ain't mean! (It wasn't). I understood immediately what you meant by suggesting lugging for me to clearly hear what detonation sounds like if it was present (you took me back to a '63 F150 I owned that was on its last legs). I appreciate any help. Thanks for the smiley, too, I don't know if Teebs woulda done that.

Grizld1 - THANKS for commenting! I peened the weight tangs out to just over .061" (credit RG) and they seem pretty tight. The profile was, of course, distorted but I don't think that would effect range, just how it gets to full advance. I will order a new advance unit from Mike's today. I was reluctant until you mentioned the quality was okay - thank you! In the meantime, I'll try the shrink tube trick to see if that nails the problem. I think it will because the problem is the advance range is just too large, 10-15 deg. over by eyeball, and effectively "moving" the stop should narrow it. I know Pete's just scratching his head over all this discussion. Thanks for the comment regarding a shortening of the stock advance range, I know XSjohn allowed a narrower range for lower compression engines but I'm not planning any mods like that. Do you recommend 650s run a higher octane fuel generally? I read somewhere in a Honda forum it may tend to load up the valves, but probably misunderstood.

5twins - Cool, I'll remove the cam pin too! I did lightly grease the rod, but I'm pretty sure I was afraid to do the bushings well, thinking grease might get into the valve train and plug up oil passages. I don't think it can as the bushings are in the cam and the cam is sealed at both ends. I think I'll remeasure the rod cams as excessive wear on the advance end will widen the advance range.

AWESOME!

 

[retiredgentleman]

I see typos by grizld1 and 650Fool with respect to the bob weights tang (ears);

Its not .060" or .061".

Just for correctness, I found mine at 0.156" and peened them to 0.168".