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Bmc starter motor piston not rotating?


Tessy

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I recently changed my starter battery thinking it was causing my start issues but it wasn’t. Until today the situation deteriorated to the point I was getting just a click with no turning over, UNLESS I had the starter on charge above 14.5. Realising it still did this even after battery replacement, I tried giving the solenoid/ starter motor a few taps with a hammer prior to starting and this works. Presumably this means the piston is engaging (Clicking) but not rotating as it’s stuck? If that’s the case then why would the higher voltage work? After a few starts it now starts every time, but I doubt this will last. Ultimately I want to know what causes this, and weather or not the issue can be fixed without replacement?  Engine is bmc 1.8

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38 minutes ago, Tessy said:

I recently changed my starter battery thinking it was causing my start issues but it wasn’t. Until today the situation deteriorated to the point I was getting just a click with no turning over, UNLESS I had the starter on charge above 14.5. Realising it still did this even after battery replacement, I tried giving the solenoid/ starter motor a few taps with a hammer prior to starting and this works. Presumably this means the piston is engaging (Clicking) but not rotating as it’s stuck? If that’s the case then why would the higher voltage work? After a few starts it now starts every time, but I doubt this will last. Ultimately I want to know what causes this, and weather or not the issue can be fixed without replacement?  Engine is bmc 1.8

 

I would start by checking the wiring for good clean contacts. This may not be your problem, but it's a good place to start. It cured my similar problem a few years ago. 

 

 

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4 hours ago, Tessy said:

I recently changed my starter battery thinking it was causing my start issues but it wasn’t. Until today the situation deteriorated to the point I was getting just a click with no turning over, UNLESS I had the starter on charge above 14.5. Realising it still did this even after battery replacement, I tried giving the solenoid/ starter motor a few taps with a hammer prior to starting and this works. Presumably this means the piston is engaging (Clicking) but not rotating as it’s stuck? If that’s the case then why would the higher voltage work? After a few starts it now starts every time, but I doubt this will last. Ultimately I want to know what causes this, and weather or not the issue can be fixed without replacement?  Engine is bmc 1.8

 

I go with @Higgs for a first check but it sounds more like a solenoid contact fault and that can be straight forward burned/dirty contact but as you say when on charge it works I suspect there is volt drop on the  solenoid energisation circuit that includes the ignition switch.

 

As a test of this circuit get a length of mains 13Amp cable such as you may put on an electric fire or immersion heater. Strip all three conductors at each and twist them together so its in effect just one cable. Fix one end firmly to the start battery positive taking great care to prevent the other end touching any bare metal. Then firmly touch the free end to the connection on the solenoid that has a SINGLE thin wire on it. It's often a single 6mm blade. It should clunk and spin each time you do it. If it does then that implies volt drop on the energise circuit so if it's been fine in the past I would suspect the ignition switch has gone resistive but check all the ignition switch  terminals for cleanliness and tightness.

 

It might be undersized energise wiring but if so it should have been happening for years unless your start battery has a shorting cell so its down on voltage. What's its voltage first thing in the morning? If it's less than about 12V after standing overnight having been well charged then the battery is suspect.

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Agree with Tony but easy way is to short the 6mm solenoid terminal to the big terminal on the solenoid that is wired to the battery. If it works every time then its the wiring to the solenoid from the ignition switch or from the switch to the battery via the fuses.

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30 minutes ago, Onewheeler said:

If it's burnt or dirty contacts, the solenoid on the BMC is easy to remove and dismantle. A gentle rub with a small file might sort you out in a few minutes. Don't forget to disconnect the battery before trying!

 

Not if it's a later solenoid with a swage on the metal body holding the plastic cap on. If the plastic solenoid cap is over half an inch deep then its probably held on by nuts but if its shallow it may be swaged in place. If so I would think a new solenoid would be the easiest.

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4 hours ago, Tony Brooks said:

 

Not if it's a later solenoid with a swage on the metal body holding the plastic cap on. If the plastic solenoid cap is over half an inch deep then its probably held on by nuts but if its shallow it may be swaged in place. If so I would think a new solenoid would be the easiest.

I bow to your knowledge. The one on my 1.8 took ten minutes to dismantle for a contact clean. I did it without a manual on a fuelling pontoon!

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1 hour ago, Onewheeler said:

I bow to your knowledge. The one on my 1.8 took ten minutes to dismantle for a contact clean. I did it without a manual on a fuelling pontoon!

 

Yes, easy to do on the nutted on version. I have done those  in situ  up river. Its the rarer modern version that is near impossible to get the cap off/.

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34 minutes ago, Sir Nibble said:

Take careful note of the orientation of you take the contact cap off the solenoid. If the cap goes back on the solenoid upside down it won't work. (Or refuse to stop working!)

I was thinking that I had forgotten to say that yesterday, pleased you have. Plus the need for a soldering iron - not a toy, gert great big one. Quick on and off. Seen too many attempts with a toy iron people use for electronics.

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2 hours ago, Tony Brooks said:

I was thinking that I had forgotten to say that yesterday, pleased you have. Plus the need for a soldering iron - not a toy, gert great big one. Quick on and off. Seen too many attempts with a toy iron people use for electronics.

Certainly a serious iron. I use a 100W for my benchwork.

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