The pampered BMC - advice on starter motor issue please!

[mikeakc]

Some of you may have read the 'pampered BMC overheating' thread. The help here was instrumental in getting it sorted and Nell now reads a comfy 75 when ticking over so thanks for that! The next issue is an intermittent issue I've been ignoring for a few years...

On turning the key in the ignition the starter motor clunks but doesn't turn the engine over. It sounds exactly like the problem in this video <(click on the words) at 1:12 seconds (the pinion fires forward but doesn't rotate).

Based on this video I finally bit the bullet and purchased a new starter motor for £135 a couple of days ago (they're starter and solenoid combos - the old solenoid came off with the old new unit, the new unit has a new solenoid built on it). The old one looked to be the same age as the boat (1979)! During removal I cleaned up every terminal on the wires and battery isolator switch. On fitting the new starter motor, the engine roared into life first time. Hooray, problem solved I thought. However, the second time I tried to fire up I had exactly the same issue as before! Extremely frustrating. Verbal spanners were thrown.

The only thing playing on my mind is that at the bottom of the drum of the starter motor there is a terminal bolt which is unused. It's the bolt I'm pointing to in the image below. On my old starter motor this terminal was connected to a battery cable but the battery had long been removed so this connection was doing nothing. This redundant cable was in there for 7 years of happy boating so I doubt it's the root cause but could it be that there isn't enough earth (I don't know what I'm talking about) which makes it intermittent?

Could anyone shed some light on what I should try next please?

Many thanks in advance!
Mike

 

[William_H]

The bolt you identified would be for connection of a negative wire from battery neg. terminal. However there should be similar (heavy) wire from battery negative to the engine block so completing the circuit via the mounting of the starter. So not likely to be your problem however you should check for condition both the negative wire from battery and the positive from battery probably via a isolation switch.
If you have jumper leads for your car you could use them to run firstly a lead battery negative to that bolt on the starter then also try a lead from battery positive to the terminal on the starter (blue wire?). If either of these fix the problem then you can track back to find a bad connection in either negative or positive supply.
The cylinder on top of the starter is a solenoid. It has a coil which when energised with trust the pinion gear into the fly wheel ring gear and at the end of it's stroke will make heavy contacts to provide 12v to the starter motor. Possibly those contacts are dirty so you hear the thrust into ring gear but don't get starter turning. This possibility would be fixed by removing whole starter and having ti over hauled by an auto electrician or dismantle it yourself.
The solenoid takes quite a large current. (like 10 amps). In some cases the key switch and light wiring are not good at delivering this current. This may result in solenoid not pushing hard enough to make high current contacts. Check the light wiring and switch. However in some cases it is easier to fit a relay near the starter which takes a small current via the key switch but whose contacts can carry the larger current to the solenoid. You can check by bypassing this circuit by connecting with a wire or screw driver the main battery supply to that terminal I think with the red wires to activate directly the starter. (you might get a fright) Just make sure there I amn not certain of connections to starter key switch. ol'will

 

[Boater Sam]

The feed to your solenoid from the key switch is insufficient. Either bad switch or connections or cable that is borderline thin. This is limiting the current to the solenoid which is why it clicks but does not slam the solenoid far enough to engage the starter contacts in the back of the solenoid. A common problem. You did not need a new starter.

 

[MisterBaxter]

Just had exactly this problem on a BMC engine on a narrowboat. It was fixed by replacing the key switch. It would also be worth inspecting the wiring to and from the key switch for condition, connections and spec.

 

[mikeakc]

The bolt you identified would be for connection of a negative wire from battery neg. terminal. However there should be similar (heavy) wire from battery negative to the engine block so completing the circuit via the mounting of the starter. So not likely to be your problem however you should check for condition both the negative wire from battery and the positive from battery probably via a isolation switch.
If you have jumper leads for your car you could use them to run firstly a lead battery negative to that bolt on the starter then also try a lead from battery positive to the terminal on the starter (blue wire?). If either of these fix the problem then you can track back to find a bad connection in either negative or positive supply.
The cylinder on top of the starter is a solenoid. It has a coil which when energised with trust the pinion gear into the fly wheel ring gear and at the end of it's stroke will make heavy contacts to provide 12v to the starter motor. Possibly those contacts are dirty so you hear the thrust into ring gear but don't get starter turning. This possibility would be fixed by removing whole starter and having ti over hauled by an auto electrician or dismantle it yourself.
The solenoid takes quite a large current. (like 10 amps). In some cases the key switch and light wiring are not good at delivering this current. This may result in solenoid not pushing hard enough to make high current contacts. Check the light wiring and switch. However in some cases it is easier to fit a relay near the starter which takes a small current via the key switch but whose contacts can carry the larger current to the solenoid. You can check by bypassing this circuit by connecting with a wire or screw driver the main battery supply to that terminal I think with the red wires to activate directly the starter. (you might get a fright) Just make sure there I amn not certain of connections to starter key switch. ol'will

Lots to try there Will, thank you for the advice and time, I'll report back!
Mike

Just had exactly this problem on a BMC engine on a narrowboat. It was fixed by replacing the key switch. It would also be worth inspecting the wiring to and from the key switch for condition, connections and spec.

The feed to your solenoid from the key switch is insufficient. Either bad switch or connections or cable that is borderline thin. This is limiting the current to the solenoid which is why it clicks but does not slam the solenoid far enough to engage the starter contacts in the back of the solenoid. A common problem. You did not need a new starter.

 

[mikeakc]

Just had exactly this problem on a BMC engine on a narrowboat. It was fixed by replacing the key switch. It would also be worth inspecting the wiring to and from the key switch for condition, connections and spec.

That sounds like a nice easy fix. I'll certainly investigate this one as soon as I get the chance. Thank you!

 

[mikeakc]

The feed to your solenoid from the key switch is insufficient. Either bad switch or connections or cable that is borderline thin. This is limiting the current to the solenoid which is why it clicks but does not slam the solenoid far enough to engage the starter contacts in the back of the solenoid. A common problem. You did not need a new starter.

I suspect you may be right about not needing a new one. The old one was very, very old so perhaps a new one could be considered an investment?! I'll keep the old one, might even try to sell it on ebay! Cheers.

 

[lustyd]

Be careful until you sort out any bad connections, the additional current from any voltage drop can destroy your starter wiring so use it sparingly until you're sure it's fixed.