1978 R100S ignition timing issue

[nicholas]

Hi, just bought this bike and trying to workout the potential cause of my problem. When I got it the points were not fitted correctly and slipped off the day I bought the bike. After getting them back on I discovered that it wasn't right, I tried setting the timing statically and with the strobe at full advance, in either case the bike was running too advanced. This is my first points BM so after some research I discovered that the points could be bad/wrong (cheap Chinese), my cam could be bent or my timing chain had been replaced and is a tooth off... I looked at the CAM and it seems OK and haven't had a chance to whip off the timing cover to see if the notches are not aligned (if they are still on there...) I did read about opening the holes on the points plate to get the right adjustment... so I did this. I now have the static timing almost spot on, but I also had to grind the base of the points....so with my hack it seems to be running OK. Anyone seen this before and know what the real cause may be? I'm not happy with my hack, someone suggested going to Boyer, but I am not sure this will really solve the underlying problem.

Any thoughts or suggestions would be greatly appreciated

[Kurt in S.A.]

Nicholas -

Sorry you had so many things to deal with off the bat. IMO, the "hack" wasn't really necessary. With proper points (might want to try some new ones from say Motobins) and gapped correctly, there should be no reason to open the holes up on the backing plate. A very small change in points gap makes a big difference in timing. I suspect you either had bogus points (again, you should just buy new so they won't be a problem going forward) or you didn't set the point gap at the proper point of engine rotation.

Taking the timing cover off is not really a standard general tuneup step. It usually takes heat and also requires special washers/gaskets to put back on. Not to mention that you need a special bolt in order to remove the rotor. Removing the stator also has some pitfalls if you don't do it right. But removing this cover is not really needed.

Get some new points and condenser and start over. Things should go easier than that.

Kurt in S.A.

[nicholas]

Hi Kurt, thanks for your second reply to my other BM problems. So I set the points gap about a million times, .40mm with the opening at its widest point as I rotated the crank. Once the gap was set, I rotated the flywheel (crank) until the gap opened (light turned on) and it was way off...too advanced. So with the strobe at full advance, again same issue...I needed to retard the base and it was all the way retarded. Now the owner before me I think had given up as he was a bit sheepish about all these issues and apparently took it to a reputable place and they fitted new points (I think) and a new condenser...and when I opened it up, it was all the way retarded. So after my issue attempt I took the bike to my friend who is a professional mechanic and he was a bit puzzled too... I might get him to help me with the timing chain... maybe someone whipped it off the bike in the 36 years it's been on the road.. who knows? But with a duplex chain, they get about 200k miles? Mine is on 59k and if wrong say worst case 100k....but I'll need to investigate.

Again, I am really not experienced with this stuff...and I assumed it was the points/points plate too...but when I called Motorworks in the UK the guy there reckoned I should ditch the points and just go boyer... if I do have a rubbish points system then its a no brainer I am happy to upgrade to hall effect, my R80 has that and apart from the oil pressure light is a sweet ride.

Thanks again for your thoughts and advice, I'll find some time next week take off the timing cover...hopefully the sprocket if off and I can fix the issue...otherwise I'm back where I started.

[Pattern14]

Have you looked at the centrifugal advance unit? These are often the culprit when timing becomes problematic. had to deal with this issue a number of times with my own and mates bikes. Elongating the holes is what a previous owner had done on one of them, and we swapped parts out for those that were known to be good, with no real improvement. New points condenser etc, etc..... The "experts" back then told us that the timing chain had " jumped a tooth" and all sorts of crap, and needed this that and the other. It was pure coincidence that we put a brand new advance unit on it, from a bike that had been written off the day after the owner had bought it, and was selling it for parts. Problem solved instantly. So before you start pulling things apart, put brand new points, a new condenser, and see if you can try a low mileage or preferably new advance unit. Sometimes the little springs can cause the problem too when worn and stretched, but it is often that the whole centre section is worn from use, inadequate lubing of the felt, and plain old age.. The advance unit is actually more expensive to buy new than the complete Boyer CDI system, which is why most people don't bother replacing the worn mechanical advance mechanisms. Maybe you can borrow one that you know is in good shape just to eliminate this possibility. Let us know how you get on.

[nicholas]

Hi Pattern, they are some wise words, thank you. It had occurred to me that the ATU may have been worn, but I am not experienced enough to understand the impact of gradual mechanical ware. So you think the cam would still be OK, just the ATU could be knackered? I have a mate with a 1978 R80, perhaps he'll let me try his unit...

I'd prefer to stick with the points system as it keeps my bike free from black boxes and can be repaired on tour..... but if I can only get used parts or aftermarket Chinese versions then perhaps the Boyer is better solution, being cheaper and maintenance free is a plus.

Are there any CONS for switching to Boyer over persevering and getting my points system working? The guy at Motorworks made it sound like a black box with one set timing, not sure if that is a good or bad thing... He was pretty sure it would solve my problems.

But if my ATU is out, is it just the springs? They can be replaced, or do you think the inner tube that mounts on the cam is worn, id think the latter as the springs wouldn't affect the static timing, right?

Thanks again for sharing your experiences, I am pretty sure its my ATU, I find it hard to believe that my robust duplex chain has been replaced with such little miles.

[Kurt in S.A.]

I have a Dyna III unit on my /7 but the downside of that is that it retains the ATU...so if that's the basis of the problem, it would still be there. The Boyer has a built-in advance curve (I thought there were more than just one?). The Boyer is a good choice when/if someone snaps off the small nut on the end of the camshaft.

What about considering some of the crank-mount ignition systems? The Alpha and Omega come to mind. The current points system (as well as Dyna and Boyer) have a wasted spark system and can lead to imbalance or differential timing. The Dyna can adjust that out...I suppose the Boyer, too. But the crank-mounted ignition systems only fire once per crank rotation, thus eliminating the differential timing issue. Some aftermarket systems discussed here:

http://www.largiader.com/articles/ignition/

But a good points system is really nice to have...simple and easy to trouble shoot.

Kurt in S.A.

[Duane Ausherman]

"But if my ATU is out, is it just the springs? They can be replaced, or do you think the inner tube that mounts on the cam is worn, id think the latter as the springs wouldn't affect the static timing, right?"

You can observe the wear on the ATU cam by eye. I have seen a very few that were made with an error on the cam grind, and it will look perfect. Swap it out and all is OK again. If the cam shows some wear, the usual downside is that it will grind off the rubbing block quickly.

Those ATU are quite reliable. They can be very worn and work perfectly well for a long time. Get yourself two sets of springs, one to use and a spare.

[jagarra]

I once had a auto mechanical advance failed at early life on a Norton I had. It was solid on the nose coming out from the can shaft, the problem was that where it fit onto the hub that allowed it to rotate was sloppy. You could grab the lobe that operated the points and wiggle it side to side and make the points open and close from the side action. I have had binding pivot points on them where the weights would stay in position and not return properly they just stayed where they landed. Give that auto advance a good once over.

[Snakeoil]

I don't mean to hijack this thread, but it is along the same topic and year bike so I thought it would fit.

I'm brand new here so please excuse me jumping in without a proper intro. I will do that at the end.

Bike is '78 R100/7. Noticed that on the ACU the pivot holes for the weights are very large relative to the pivot pins. Also, the weights are not held in tight by the springs, but actually dangle a bit before the springs have an effect on them.

Is this normal? Bike supposedly has only 13K miles and I bought it from the original owner. Even got the original purchase receipt. Just seemed odd to me that there would be that much slop in the ACU pivots.

Intro:
I'm a new R100/7 owner with plenty of gray hair. Been riding and wrenching as long as I can remember. Had K-bike about 10 years ago but could not keep it at a legal speed and the 55mph buzz drove me nuts. Sold it. I have a number of vintage bikes of various brands and would almost rather wrench than ride. But once I'm on the bike I'd rather ride.

Again, sorry to jump in here. But I tend to believe in keeping similar subjects in the same post for the next guy looking for a complete answer.

Thanks and regards,
Rob

[Duane Ausherman]

Snakeoil said, "..........the weights are not held in tight by the springs, but actually dangle a bit before the springs have an effect on them."

Nobody can tell you the answer by this forum. The amount that they can be loose and work well is a wide spectrum. Someone that has worked on dozens of them can get a close answer. As I said before, replace the springs and try it.

Use your strobe light to watch the flyweights move out and then back in. They must operate smoothly and not jerk. You can't usually see it on the flywheel, as the timing is between the "S" and the "F" so you don't have a reference point to trust. Watching the advance unit gives one plenty of reference.

In fact, one can time the bike quite accurately without a strobe light, but one can't usually see a sticky advance without it.