Mountfield R28M ride on Mower not starting (Again!!)

sujsuj

Section62 said:

Starter motor most likely, we need the make and model of engine to confirm.

Meanwhile, stop trying to start it until you've found and repaired the fault.  The "vibrating" sound is quite likely to be the starter gear trying to grind itself into dust... if so that could become a replacement rather than a repair.

Please have a look at my latest post with photos titled 'What is that sound?' I'm not sure if it confirms your diagnosis or points us in a different direction. Thanks again!

sujsuj

WIAWSNB said:

SS, have you tried jump-starting the mower yet? 

By far the easiest first step, and could point to the cause.

I’m in the process of buying new jump start cables. When I upgraded my car, I was confident I wouldn’t need them for the foreseeable future, so I sold them during my house move. Now I find myself needing a set again — time to source one. Thanks!

sujsuj

WIAWSNB said:

First check that the engine is not seized.

This, however, is usually down to either a flatish battery, bad HD cable connections from the battery to the starter, or possibly the starter/solenoid itself. 

Easy way to check is to 'jump' it. Is the mower battery 12V? And do you have jump-leads, SS? If so, try jumping from your car battery (taking all the usual precautions). If the mower now fires up cleanly, then assume the mower battery is feeble. But if the same noise occurs, then check the mower battery, and all the HD cables and connections from the battery to the solenoid and starter motor (these last two may be part of a single unit).

It sounds like a pulsing solenoid rather than the actual starter motor - a bit of a classic early-morning soundtrack in the 60s and 70s

The wee key switch is 'light-duty', and cannot carry the hefty current being drawn by a starter motor. So, they fit a relay - the 'solenoid' - in between this switch and the starter motor. The key switch is strong enough to handle the few amps required by the solenoid, and this then 'clicks' audibly as it closes a couple of much heftier switching contacts inside. This heftier switch can then handle the 100+ amps drawn by the powerful starter motor as it turns an engine.

If the battery is weak, however, or if the cable connections are poor and not allowing a full current to pass, what often happens is that the key switch engages the solenoid as before - which clicks - but then the large current demanded by the starter 'pinches' the battery current, and it isn't enough for the solenoid to remain enagaged - it therefore clicks again as it releases. Once it releases, the starter is not getting its supply, so there is now enough for the solenoid to engage again - click. But, once it engages again, the starter does youknowwhat all over again. So, the poor solenoid just pulses like this.

I've added a photo with the battery details — it's a 12V battery. Based on the tests I carried out today, I'm wondering if your diagnosis still holds, or if things are pointing in a different direction now?

Thanks again for your continued help!

will have to try out other things mentioned here based on your feedback to my latest tests today. thanks

sujsuj

Section62 said:

ButterCheese said:

...

I'd then take the starter motor out and put on a bench; apply power and see if the bendix drive is fully extending.  It could be that it's partially jammed and not engaging fully with the flywheel.   Could be what the grinding noise is

sujsuj, first things first - make and model of the engine so we can confirm what type of starter motor it has.  There are lots of variations in small engines fitted to equipment like lawnmowers, and different types of starter motor.  There's no point removing the starter motor and applying power to check the bendix drive if your model doesn't have one.

E.g. If your starter motor is a constantly-engaged type then it is unlikely to be that making the noise and the relay/solenoid would need to come under the spotlight first.  Remember that taking things apart which don't need to be taken apart can cause new (and often expensive) problems.

If you do take the starter motor out to test it (and this applies to any medium or high-torque motor) then make sure you have it firmly bolted or clamped to something solid before applying electrical power to any part of it.  If you don't secure it, the body of the motor is likely to attempt to rotate rapidly in the opposite direction to the armature and potentially go spinning across the bench, or the workshop floor. (Newton wasn't wrong about this).  Never just lay a motor on a bench or floor and connect power.  The forces involved can be enough to do some quite serious damage - to the motor, to you, and/or to the workshop.

not sure my latest finding still points to starter issue.>? please confirm. thanks

sujsuj

WIAWSNB said:

SS, have you tried jump-starting the mower yet? 

By far the easiest first step, and could point to the cause.

This is the next step based on inputs my todays's test outcome/photos. I need to source jump cable from amazon. thanks.

sujsuj

Section62 said:

WIAWSNB said:

SS, have you tried jump-starting the mower yet? 

By far the easiest first step, and could point to the cause.

Although every time that key is turned there is potential for more (potentially expensive) damage to be done.  Attempting to jump start with a fully charged larger capacity battery might work.... or it could just do (potentially expensive) damage more efficiently.

There are some steps - such as checking the engine turns over freely by hand (done safely) - that would be wise to do before attempting a power crank again.

Which direction should the engine’s flywheel rotate during starting? Based on my latest test results, do you think this points to a different conclusion?

sujsuj

WIAWSNB said:

Just one single, one-second turn required.

Please elaborate? Thanks

Section62

sujsuj said:

One striking observation from my attempt to start the engine: in the image-3 below, you can see a vertical shaft (marked as I) with teeth that rotates — that's the sound you hear when I turn the key. However, I noticed that this shaft doesn’t engage with the second set of teeth (marked II) , which I originally thought it was supposed to turn. The two sets of teeth now seem to be on different levels, so the vertical shaft is spinning freely without connecting to the second gear.

Is this just how these engines are designed to work, or could this be the clue you’ve been waiting for?

We need a video of that - one quick key-turn is all you need.  Your 'I' is the end of the starter motor with the pinion which engages with the flywheel gear 'II' when the starter motor is operating.  The pinion on 'I' should go upwards so it is level with the gear on the flywheel.

Are you saying you hear the noise and see the pinion ('I') rotating?

sujsuj

I'm fairly certain the noise is coming from the toothed shaft (marked 'I') as it rotates. However, I couldn’t see it moving upward. I’ll try to get a video tomorrow, though it might be a bit tricky.

When the mechanism was stationary, I tried pulling it up, and it seems the top of the shaft can be lifted—it’s spring-loaded. What I still need to confirm is whether the teeth also rise to the same level as point 'II' and engage to rotate the large wheel.

WIAWSNB

sujsuj said:

Which direction should the engine’s flywheel rotate during starting? Based on my latest test results, do you think this points to a different conclusion?

Ok, good devlopments - very useful to have exposed the top of the starter motor.

On the engine direction Q, I think you have it right, but I am not certain. I'm basing it on the angle of the fan blades, and assume they catch the air from the centre - ie draw it in from the vent on the top of the egnine cover - and then blow this cooling air over the engine, and eject it out from below. I think that makes more sense, as to draw the air in from below would risk having it full of grass clippings! But, I don't know for sure.

The fact that you can turn that blade by hand (always with sparkplug lead disconnected for safety) suggests the engine is not seized - more good news. How far you can turn it - have you managed at least a whole turn? 

If you remove the sparkplug itself, it'll be easier again to turn, so possibly worth doing. Don't leave it out, tho', in case rain or dust gets in there.

Ok, fuses. Fuses are electrcial safety devices. They should not blow unless there's a fault, but sometimes they do - tho' rare. If that 10Amp fuse blows again, then I suggest do not replace it, because twice would suggest a fault - a short circuit somewhere. It has given you a warning.

The 25Amp fuse, I am guessing, does supply the starting system, but not the actual starter motor - becuase that will draw around 150+ Amps - a shedload - when it's spinning. The cable to the starter motor will be found to be the thickest on the mower for this reason, and is unlikely to be 'fused' at all. I am guessing that the 25A fuse supplies the solenoid, which is likely to be the device that's making the noise (tho' not definite).

You've removed the 25A fuse? And it was not showing any signs of black marks from arcing, carbon, damage, heating? If not, I'm guessing it's fine. Trace the wires to this fuse as far each way as you can, and check any connection you find.

The starter motor. You have analysed what it does very well. The large toothed ring under the fan is the 'starter ring gear', and is part of the engine. The small toothed gear on the end of the starter motor is the 'starter pinion' gear.

As you've surmised, the two don't currently 'mesh'. It's designed that way, or else the starter motor would always be spun by the running engine, which would wear it out. That 'pinion' only jumps up and engages with the starter ring when you actually crank-start your engine. Once you release the key, it jumps back down under spring pressure.

Two ways to make that pinion jump up. The first if it's on a spiralled 'screw' thread on the starter motor shaft. In this case, once the starter motor turns, the pinion is fired up that spiral like a nut on a spinning bolt, but much faster - instantly.

The other way is that it's fired up by the same solenoid that engages the hefty switch that powers the starter.

You can check which it is by repeating what you did before - try and lever that pinion upwards again, using a piece or wire or similar to pull it up. If it firmly turns as it goes up, and turns back in the opposite direction when you release it, then it's a 'screw' type. But it it lifts up straight, and pops back down again, then it'll be solenoid controlled. Most likely.

Phew.

Ok, could you take some equally good photos of that starter motor from the side, please? Try and show how it's attached - there will be obvious bolts. Also, look very closely at all the cables that go to it. Take photos of this too, please.