Starter problem on 1974 R90/6

Recently since a top end my starter doesn't want to immediatly turn over. It acts like my old Harleys did but only when warm. Hit the starter and there is a delay before it starts to crank. I usually have to bump it a couple of times to get it to turn over.

The top end is new, valves, pistons, guides etc, I never had this issue before the rebuild. I have replaced ground and cable to the starter and cleaned connections.
The battery is new. When the engine is cold it will turn over easily and continue to turn over for several seconds with (with gas off so it won't fire).

So far it has never failed to start without a little coaxing.

I am considering the ND starter conversion from Motoraad Electric $350, The EU electric starter for $175 (probably Chinese), and having the Bosch rebuilt.

Any advice welcomed.

My original Bosch started getting slow to crank last year (lasted 33 years and 100,000 miles- not too bad)... I considered rebuilding it, or possibly replacing it with either the EME starter or the ND starter. Rebuilding the Bosch at a local starter shop was about the same price as purchasing the EME starter. I ultimately ended up buying the EME based on a few posts here and a short discussion with John at EME. I also liked the idea of less weight, less electrical draw, and better cranking speed. I might well have gone with the ND starter if I'd have had the money, as it has also gotten good reviews here on the forum.

The EME starter is definitely smaller and lighter, and is an easy installation. It cranks faster than the Bosch did when I replaced it, but no faster (that I can tell) from the Bosch earlier in its life, before it wore out. I don't know about the electrical draw (having not measured it), but I suspect it draws less than the Bosch did based on how quickly the battery seems to recover. Time will tell how it holds up- I kept the Bosch in case I ever decide I need to rebuild/reinstall it.

[QUOTE=dpmonk;835616]Recently since a top end my starter doesn't want to immediatly turn over. It acts like my old Harleys did but only when warm. Hit the starter and there is a delay before it starts to crank. I usually have to bump it a couple of times to get it to turn over.

The top end is new, valves, pistons, guides etc, I never had this issue before the rebuild. I have replaced ground and cable to the starter and cleaned connections.
The battery is new. When the engine is cold it will turn over easily and continue to turn over for several seconds with (with gas off so it won't fire).



Any advice welcomed.[/QUOTE]

Try double checking to make sure your static timing is spot -on correct. If the spark occurs too early, the explosive force of the fuel/air igniting expands before the piston can get over top. That would bear on why the motor is more inclined to hesitate when warm. That is why some Harleys pause before the cylinder compression pushes thru, more so when warm. And,.... it doesn't cost a dime to confirm your static timing. You have nothing to lose.

[QUOTE=James.A;835811]Try double checking to make sure your static timing is spot -on correct. If the spark occurs too early, the explosive force of the fuel/air igniting expands before the piston can get over top. That would bear on why the motor is more inclined to hesitate when warm. That is why some Harleys pause before the cylinder compression pushes thru, more so when warm. And,.... it doesn't cost a dime to confirm your static timing. You have nothing to lose.[/QUOTE]

Interesting idea. When I went back to points from a deceased Omega (funny, the end) and after only about 10k miles, I static timed then checked timing with light and it was good to go. Since then I have only adjusted points gap and checked with timing light, so it certainly wouldn't hurt to take a looksee. It doesn't feel like that is the problem since the odds are you aren't getting spark at the exact same time the starter button is pushed but nothing to lose.

I base my theory on this part of your original text....[QUOTE=dpmonk;835616] When the engine is cold it will turn over easily and continue to turn over for several seconds with (with gas off so it won't fire).
[/QUOTE]
"....so it won't fire"
I first observed this phenomenon in an Airhead when I went to help "CRAZYDRUMMERDUDE" with his 1974,R90/6. His bike had broken 2 starter motors and the cause turned out to be a shock wave created by an extremely advanced static timing.
Anyone remember when that was going on?
Essentially his timing was so far advanced that when the spark arrived, the air/fuel mixture would ignite and violently stop the piston in its upward travel driven by the starter motor. Shock wave ensues, nose casting of the starter eventually breaks. I doubt that your problem is as serious as that, but,.... Please check it out.

If you can get your hands on a BMW Factory Service Manual, there is an illustration of how to set up a load/ draw test in the electric start section.

I have to wonder if the advance unit may be sticking, which would cause the static advance to be too far on startup. Without having access to the Bosch greases, I use Superlube grease (which I found at harbor freight) sparingly on my advance mechanism and it seems to help. Checking the static timing may confirm if this could be happening.

[QUOTE=James.A;835923]I base my theory on this part of your original text....
"....so it won't fire"
Essentially his timing was so far advanced that when the spark arrived, the air/fuel mixture would ignite and violently stop the piston in its upward travel driven by the starter motor. Shock wave ensues, nose casting of the starter eventually breaks. I doubt that your problem is as serious as that, but,.... Please check it out.
.[/QUOTE]

I really am feeling stupid. Decided to go ahead and install new points and reset timing. But I am unable to get it quite right. Every time I set it and tighten plate down it moves on me. This is something I have done many times but I am ready to give up static timing and put the timing light on it and go from there.

later, well never mind, after my whine, I went back and instead of trying to set the s mark in proper place and adjust the backing plate to it, I rotated the motor and adjusted the timing until when the light came on I was at the S mark. Took all of two tries. Now on to the timing light to check it tomorrow.

[QUOTE=dpmonk;837443]I went back and instead of trying to set the s mark in proper place and adjust the backing plate to it, I rotated the motor and adjusted the timing until when the light came on I was at the S mark. Took all of two tries. Now on to the timing light to check it tomorrow.[/QUOTE]

This is the exact procedure that I employ. The kick starter, with the plugs out to defeat compression, make it pretty easy. If the point gap is close to right, and your battery is good, your bike should start right up. If not, I'm a doofus but you still haven't spent a dime needlessly on starting circuit components.

On any real BMW motorcycle with points you can easily and quickly check static timing hot or cold without any light as follows:

Required to have normal or not seriously damaged hearing

Remove plugs and lay on cyl so they will fire when points open - keep the gap end away from the open spark plug hole so you do not ignite the gas vapors coming out

Turn on ignition and rotate engine slowly by squeezing end of kick pedal against footpeg
or rotate engine by bumping rear wheel in top gear

You can clearly hear the tic when the spark occurs even if you do not see it

S mark should be in the window

You are right on. I could hear the spark at the points but didn't always get a light. Finally figured it was the continuity light and not the nut holding it. Spent $10 on a coulple of 1893 bulbs and socket. Attached alligator clip on one side and battery terminal on the other with enough wire that I could use as a cont. light by clipping on to condenser or a little worklight by connecting to positive side of battery.

Checked with timing light and the s mark was perfect and Full advance mark good too.

Tomorrow will ride and get the engine good and warm and see if I am still having problems with the starter when bike is hot or if this cured it. My gut tells me I am going to have to do something with the starter.