T3 Bosch Starter Motor Overhaul

[injundave]

This job was necessitated after I had to abort a 4-day trip because of a faulty starter motor. I have previously seen that many people do not seem confident to complete routine maintenance on these motors, hence this tutorial. The Bosch is a very simple piece of machinery. It consists of an electric motor with a solenoid mounted above it and a lever connecting the two. When the start button is pushed the solenoid pulls the lever which moves a small gear on the end of the armature shaft into mesh with the ring gear on the flywheel. At the same time, the motor revolves, turning the engine over and, hopefully, causing it to start. When the button is released the solenoid reverts to it's "rest" position, assisted by a spring. The lever disengages the two gears and all is good with the world.

Over a period of time the internals can become dirty and the starter motor will not work as it should. Maintenance involves stripping and cleaning and is easily accomplished with 13 and 10 millimetre spanners, wrenches to you yanks, and a screwdriver or two.

The first thing to do is to remove the starter motor from the bike. Disconnect the battery and then the two cables at the solenoid. One is a push on terminal and the other requires a spanner or socket. Undo the two bolts holding the starter to the flywheel housing. The top one screws into the housing, the bottom bolt has a nut on one end. Lift the starter clear. The rest of the work is done on the workbench or a table and a vice is some assistance although you can manage without if necessary. Clean every part as it comes off. Use only a cleaner which evaporates and leaves no residue behind.

Remove the second cable from the solenoid (the one which disappears inside the starter motor) and note which way the solenoid is oriented. On mine the push on terminal is on the inside of the solenoid when mounted on the bike.



Remove the two countersunk screws holding the solenoid to the starter motor.



Remove the bolt and nut running through the solenoid holder of the starter motor. This screw locates the aforementioned lever.



With a bit of jiggling remove the solenoid and lift it clear of the end of the lever.



Clean the solenoid thoroughly using something like brake cleaner, which evaporates and leaves no residue. Then lubricate with a non-drying, spray on lubricant and work the solenoid plunger in and out against the spring to ensure the lubricant penetrates well.



Set aside then remove the end cap,



the circlip and any spacers.





Remove the long screws holding the brush cover to the body and remove the cover.



Mine was stuck to the body so both came off together.



Remove the rubber bung



and withdraw the armature and lever.



Separate the two and clean thoroughly. Set the lever aside.



 Inspect the armature. The bit at one end, with a lot of copper segments, is called the commutator. If the small slots between the segments are clogged with dirt, use a thin blade to score gently, removing the dirt. If there is a groove worn into the segments they can be machined smooth in a lathe using a very sharp tool and  very light cuts. The slots will probably need to be scored again after this operation.



Clean thoroughly and wipe with a clean cloth.



Separate the brush cover from the body, if it has not already separated.



Inspect the brushes for wear. If they need to be replaced you will require a large soldering iron. If you are not confident doing this an auto electrician will do the job reasonably cheaply.



Insert the armature back into the body with the commutator at the end with the brushes.



You can clearly see the springs which locate the brushes against the commutator in this shot. The easiest way to get them out of the way is to pull them out with needle-nose pliers and locate them against the metal brush holder, thus removing pressure from the brushes and making them easier to fit into place.



When you have them in place, replace the brush cover,



the spacer and circlip.



Place a blob of grease into the end cap and replace it also.



Also grease the following three places.







Reassemble the lever onto the armature



and grease the bush in the large solenoid mount.



Place the solenoid mount onto the armature with the lever in place. Don't forget to replace the rubber bung. There is a small slot in the end of the body which locates the rubber bung so you can't do it wrong.



Insert the two long screws through the end cap, through the body and into the solenoid holder. If all is well everything will line up and you can tighten the screws.



Place the slot in the end of the solenoid plunger over the end of the lever and use it to line up the hole in the lever with the bolt hole in the solenoid holder. Replace the bolt and tighten as well as replacing the two countersunk screws holding the solenoid in place.



Reconnect the cable from the starter motor to the solenoid and fit and tighten the nut.



Install the starter motor back onto the bike and reconnect the two cables. Reconnect the battery and try the starter. If all is well the starter motor should have a new lease of life and should work well. Mine did.

[jacksonracingcomau]

 :+1

My 2c added

Brush & bush kits are only $10,  bushes just tap out and in

Solenoid also comes apart easily for proper clean, just unsolder end, dismantle, clean, reassemble and resolder wires.

Built by people who intended them to live forever, just like the whole bike.

[redrider]

Ditto on the solenoid disassembly and I used nail polish for alignment marks. The solenoid has the copper contacts that carry the high amp current. Every time the contacts make or break, sparks occur which both erode and burn them. Clean and burnish them for maximum current flow.

Great tutorial. 

[azguzzirep]

Looks not so bad for being 40 years old!

The Bosch starter is a lovely piece of machinery! Simple and dependable.

If you are in the Phoenix/Glendale AZ area, Gen-Star is your local Bosch parts/repair place.

Tom

[dilligaf]

Thank you sir.  Enjoyed it. I'm not going to be able to ride for the next two months so now would be a good time to overhaul mine.  ;-T Naw.  :wife: I'll just wait until they quit.  :BEER:
Matt

[Kiwi_Roy]

Great tutorial ;-T
The last two Bosch starters I stripped down had a rubber washer sandwiched between the outer part of the NDE bearing and the end cap, I was surprised to see it there.
Yours is either missing or it never came with one
I think it must be to keep water out of the cap, an "O" ring would do the same job.

I was taught to leave the commutator if it has that hard black finish, it will never wear.
Don't forget the black rattle can paint job.

I sent you a PM

[Groover]

Thanks for making this thread. I'll reference it when I do mine.

[Chuck in Indiana]

Thanks for making this thread. I'll reference it when I do mine.

Yep, great resource. Thanks!   ;-T

[Antietam Classic Cycle]

http://www.thisoldtractor.com/moto_guzzi_loopframe_starter_and_solenoid_repair_-bosch-.html

[Tom]

 :+1 Thanks.  That's how I work on mine.  ;-T

[Stevex]

Had mine apart last year and gave it a lick of paint at the same time.

[jacksonracingcomau]

Or ceramic coat

did that in June 2012
Came up pretty good today


Worth the money IMHO

[SED]

Great post - thanks!  I'll be referring to this when I work on mine.

[Kiwi_Roy]

Am I the only one that noticed what was really wrong with the starter ???

[Tom]

Yeah....probably. ;)

[Kiwi_Roy]

Then take another look at the pictures, see who spots the problem ???

[Kiwi_Roy]

 



 

Focus in a bit :-\

[Matt Story]

Then take another look at the pictures, see who spots the problem ???

Bump

As most of us are uninitiated to inner assembly of a starter, I would hazard to guess most are at a loss here.  I'd do a lot better if I could hold it in my hand.

How about a clue? or just spit it out.

Matt

[Chuck in Indiana]

First guess. Carbon from the brushes packed into the segments of the commutator?

[Kiwi_Roy]

Look at the steel of the armature, see anything there?

How do you think it got so polished at one end?

[pete mcgee]

I see 2 issues.
1 its had water enter it and has a layer of surface rust on most surfaces.
2 the rotor has contacted the stator, one or both of the end bushes have worn allowing the contact.

Hows that?

[Kiwi_Roy]

I see 2 issues.
1 its had water enter it and has a layer of surface rust on most surfaces.
2 the rotor has contacted the stator, one or both of the end bushes have worn allowing the contact.

Hows that?

Right on, look how nasty the shaft looks at the armature.
The friction is stopping it from spinning
A good Kiwi fix would have been a strip of beer can between the shaft and bushing, it would go like that for ages  ;-T

[Chuck in Indiana]

That was instructive. Thanks, KR.. ;-T

[Tobit]

Thanks for the great write up and pics.  I have two or three Bosch starters needing service and will get right on it.

KR, yep, I noticed the polished armature and chewed up shaft.  Good to know also that the bushings are available.  That's what both my worn starters need.

Tobit

[Tobit]

Anyone do business with EMI?  I've found a kit with brushes, bushings and brush springs.

http://www.euromotoelectrics.com/Starter-Tune-up-Kit-BMW-MG-BO157-TK-p/bo157-tkplus.htm

Tobit

[Charles in Lake Charles]

I've bought a number of items from them and have always been very satisfied.

[Tobit]

 ;-T

I'll let my son and daughter repair the two I have under the bench.  Good exercise in hands-on electro/mechanical work and I can just "direct."  They'll both be driving soon so they need to know how things work beyond in-dash infotainment.

Tobit

[Tom]

Anyone do business with EMI?  I've found a kit with brushes, bushings and brush springs.

http://www.euromotoelectrics.com/Starter-Tune-up-Kit-BMW-MG-BO157-TK-p/bo157-tkplus.htm

Tobit

 ;-T  John is a good vendor to work with.

[injundave]

Roy was quite right, on closer inspection the bushes were flogged out. I ordered some new ones and, when they arrived, soaked them in oil for a few days prior to installation. I also polished both ends of the armature with some fine emery tape and got most of the scuff marks off.

The first time there was some minor hesitation then the (cold) engine fired up. The next time I tried, I touched the start button and the engine was running before I even heard the starter motor turn over. Fixed this time.

Thanks Roy for pointing out what should have been obvious.

[Kiwi_Roy]

A quick way to get the oil to impregnate the bronze bush is sit it on the tip of your index finger, fill it with oil then squeeze with your thumb
the oil oozes out the pores in the metal.

It's not that obvious, I didn't spot it straight away either. You should be good for 100,000 kM now, glad I could help.