Hot starting

[robertj]

I have an old bukh 20 which run like a sewing maching.
I have one problem when hot the starter will not engage/work other than the click of the solenoid.
After 1/2-1hr it will turn over fine.
Any ideas?

 

[ruaridhmaccallum]

One or more of the carbon brushes may be corroded in place in their holders, i.e. they don't get pushed onto the commutator by the spring. I have seen this exact behaviour in more than one starter where this was the cause. As they engine heats up they seem to lose contact with the commutator, but they get enough back as it cools down to make it work again.
If you are able, strip the starter and clean / free up everything, re-assemble and test before writing it off as anything more serious.
R

 

[oldharry]

I dont remember whether its pre-engaged or bendix on those engines. Does the starter motor spin without engaging? If so the bendix is not working properly, usually due to corrosion or muck on the shaft. It may be possible to clean it up enough to keep it going for a while. Remove the starter. The cog which engages with the flywheel should be free to move up and down the shaft on its spring. Clean any muck or rust off the shaft, and see if that helps. Otherwise you need an auto repair specialist to dismantle it and do the job properly.

If the motor doesnt spin when the solenoid clicks, then there is either an internal fault in the motor - just possibly brushes sticking - or a bad contact in the external wiring - less likely as that usually shows up on cold start when its on full load.

If its a pre-engaged starter, the solenoid will be mounted on top of the motor. If it just clicks and does nothing else, it needs a new one.

Before spending money, just check the starter cable terminals at the battery and the starter, and importantly, the negative return terminals from the engine.

 

[neil_s]

It might also be the contacts in the solenoid that need cleaning. You can get to these by removing the bakelite cover over the end of the solenoid but you need a soldering iron to undo the electrical connection first. If it is the brushes, you can often get the starter to work by rotating the pinion a little bit with a finger. Keep the starter key with you while doing this, though! Having had this trouble myself, I now take the starter and alternator off my engine and keep them in the warm and dry during the winter.

Neil

 

[cimo]

I dont remember whether its pre-engaged or bendix on those engines. .

bendix.

 

[oldharry]

bendix.

Thanks - thought so.

 

[robertj]

One or more of the carbon brushes may be corroded in place in their holders, i.e. they don't get pushed onto the commutator by the spring. I have seen this exact behaviour in more than one starter where this was the cause. As they engine heats up they seem to lose contact with the commutator, but they get enough back as it cools down to make it work again.
If you are able, strip the starter and clean / free up everything, re-assemble and test before writing it off as anything more serious.
R

The starter was new about 4 years ago so should be ok brush wise.
It will spin fine when cooled that's what I cat understand.
The motor seems fine will investigate wiring/connections soon.

 

[ksutton]

Heat in and around your engine compartment transferred to the electrical wiring is the key to your answer. The warmer the wiring gets the higher resistance in the wire. I will guess that the wire feed from your starter button or key switch which energies your starter solenoid has border line ability to pull in the solenoid when hot. If everything has been previously working without problem and the problem has crept up on you, you may have increased resistance due to a deteriorating connection. If after all connections are checked and cleaned or renewed you still have a problem, you can install a remote 12v relay located closer to the starter solenoid.

Next time it wont start hot, and presuming you can get to your engine starter motor easily, try jumping the heavy starter + wire to the + connection of the solenoid with a short piece of wire and see if it starts.

I had an identical problem, which began a few weeks after I installed an engine hour meter run feed in the 12 volt key switch feed to the starter button. The small power draw from the hour meter was enough to upset the starter solenoid feed and cause the no start problem only when the engine was hot. A 12 volt 30 amp relay energizing the solenoid remotely, fixed the problem.