1978 R100S ignition timing issue

[nicholas]

Hi thanks for the advice guys. I am not sure I am going to spend any more time with the mechanical systems, I'll probably look at fitting a Boyer system. The current one looks good as it has two sensors which contribute to cancelling out "run out"... I'm going to take off the timing cover and have a look at the chain, probably replace it as I'll be in there anyway. I am not sure my hack of the points has actually worked, or if the cam sprocket/chain is a tooth off... I cannot seem to redline the bike at what appears to be full throttle.... Ah the joy of discovering a bikes history.

With respect to getting an ignition system that runs off the crank, wouldn't it be better to use the cam given that it also drives the valves etc.... better to out of sync together than off of the crank?

[Major Softie]

With respect to getting an ignition system that runs off the crank, wouldn't it be better to use the cam given that it also drives the valves etc.... better to out of sync together than off of the crank?

A crank triggered ignition is more accurate. A cam triggered ignition is subject to the slapping of the cam chain, so as the chain wears, the timing fluctuates more and more.

[Pattern14]

Going with the Boyer ignition from Motobins was my choice about 17 years back, and has run perfectly ever since. I Keep the original set up in the tank toolbox ( mine is ex police ), as points will always get you home, even if they don't run as well. On the accuracy of ignition systems ie crank vs cam mounted, the wear on the timing chain does have an influence for sure. With nearly 800,000klm on my bike, I have replaced the timing chain 4 times, before I realised it was the wear on the sprockets that was the problem. With each successive chain replacement, the crankshaft sprocket in particular wore a little more until it became a real pig to start, and would kick back, breaking starter motor housings and other such delights. The Official BMW suggestion is to replace the whole set up , not just the chain, to avoid this very problem, but of course, very few of us do, and the "experts" told me it was just the company trying to get me to spend more money on parts.......Timing chain replacement came at more frequent intervals, as new chain on worn sprockets means chain wears faster etc. I made my share of live and learn mistakes, and when I eventually replaced the whole timing system, the change was amazing. With factory fresh sprockets and chain/tensioner, the motor got that whole "born again" feeling. By all means get a reputable mechanic to look at the timing chain and sprockets just for peace of mind if the boyer ignition does not fully fix the problem. Either way, I hope it works out for you.

[George Ryals]

With a degree wheel and a dial indicator you can determine if your chain is a tooth off without dismantling the front of the engine.

[nicholas]

Going with the Boyer ignition from Motobins was my choice about 17 years back, and has run perfectly ever since. I Keep the original set up in the tank toolbox ( mine is ex police ), as points will always get you home, even if they don't run as well. On the accuracy of ignition systems ie crank vs cam mounted, the wear on the timing chain does have an influence for sure. With nearly 800,000klm on my bike, I have replaced the timing chain 4 times, before I realised it was the wear on the sprockets that was the problem.

Wise words, thanks Pattern14. Its funny, I mentioned the sprocket issue to my friend (mechanic) and he said the same thing, they generally do not ware. If I can find a new set for my bike then I'll change them and know that I'll never need to worry about it again.

I like the idea of a backup ignition system, seems that the crank driven ones the popular option...can anyone recommend a mature system like the Boyer? The reason I am still considering Boyer is that its been around for a while now and is a tested system.

[nicholas]

With a degree wheel and a dial indicator you can determine if your chain is a tooth off without dismantling the front of the engine.

That sounds promising, I don't own these tools, but happy to buy or find someone who does. Can you share a little more information on how to go through this process?

Sorry I'm still learning about motorcycles and the principals of ignition systems.

[George Ryals]

http://www.lunatipower.com/Tech/Cams/Ho ... eACam.aspx

This link describes how to do it using a part of a v-8 block. You can do it on your engine with the front cover and one valve cover off. You'll need to search around to find the specifications on the cam in your engine.

[esman100]

I'm going to chime in because I had a very similar problem setting new BMW points a few years ago. Kurt already mentioned that they could be bogus and they very well could be. I think it was 4 or 5 years ago that BMW out-sourced them and they had about an extra 1.5mm length to the fiber board which put the timing past the slots. It drove me crazy until I figured it out and then it was confirmed later by the dealer that sold them to me that they had a bad batch. I've been getting good BMW OEM points the last few years from Hans at Huckey's and they have all been good. Han's does carry another brand of points that I have no experience with that are less money, but I'm content with the OEM. Other than that, I have never had issues with points and actually prefer them and would recommend that you give it another try with a known good set.

[nicholas]

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.

I think I am going to take this route, many thanks for the heads up. I am better off avoiding any issues with the cam shaft and timing chain given I have the option. I'll keep the points system as backup and might even order another set of points to eliminate the possibly of bad points, but it could also be the ATU...

Do you know anyone who has gone down the crank timing systems, pros and cons? I've seen a few threads of people having issues with the electronics with these aftermarket systems...hence my apprehension to go with a brand that isn't well known.

[nicholas]

Hi All, I fitted a Boyer in the end, I spent a whole weekend fabricating brackets for the blue box, new and smaller coil and routing the new wires. I found once I connected my electric speedo I couldn't turn off the ignition so had to re-wire taking power from the ignition key as opposed to the 7A +12 line that came from the battery.

I set the timing using the advance, and it seemed in more realistic ranges (i.e. not out of adjustment like with the points) I need to check the image of the DOT on the flywheel with an expert as I am not sure if I am seeing the "double image" as a whole the bike seems to start easier, but the overall performance feels exactly the same as the old points setup. The new coils and blue box do not add or change the feel of the bike. I am thinking I could have just replaced the points given that looks the obvious culprit. I am not riding the bike at present as I am busy trying to plan my relocation to Australia, but I am not done with this and intend to tinker a bit more with the bike back in Melbourne.

One thing that I did notice when I took it for a test ride was that rear drive is now making a rattling noise, I don't think it is related to the ignition...and more so a string of bad luck.

Thanks all!