Starter motor does not always engage.

[rovertone]

Originally Posted by SD1too

Richard tells us that his starter motor is screaming because it's not engaging with the engine. As Jon says, this is an unusual failure mode for a pre-engaged system. The way to make progress is to remove the motor assembly for an internal examination as I said in my first reply. Alternatively, a quicker but more expensive repair would be to fit an exchange unit. Over to you Richard.

Simon

Or it could be engaging with the flywheel but, with intermittent slipping of the bendix clutch, the shaft is being driven without taking the bendix/flywheel with it. That's what was happening with mine.
As said previously I managed to get a new assembly from a company in Ireland but I've been looking again and whilst I can find listings on ebay there are none specifically listed for 75's.
See attached link below where the seller lists starter numbers (scroll tight down) and see whether any matches the number on the starter and/or contact the seller.
In my posts I have assumed we are talking about an original Denso starter, if the OP has an aftermarket replacement then it's doubtful if any such parts would be readily available and an exchange unit might be the best option but as Simon has said maybe that's the best option anyway.


https://www.ebay.co.uk/itm/191967408544

[Arctic]

Hi Jon.
i was happy to find you found the thread readable, but not so happy that you thought it did not help with regarding why perhaps the OP may gain some insight to how the starter works, so this link may well cover that for the OP and you.

https://www.autoelectro.co.uk/starter-motors

[COLVERT]

Originally Posted by Arctic

Hi Jon.
i was happy to find you found the thread readable, but not so happy that you thought it did not help with regarding why perhaps the OP may gain some insight to how the starter works, so this link may well cover that for the OP and you.

https://www.autoelectro.co.uk/starter-motors

Thanks for that info.---HOWEVER ( sorry. lol. ) It does not explain how the one-way clutch works or why it's needed.



so------here is why.-- As the engine starts the speed of the fly wheel greatly exceeds the that of the pinion gear.--The one-way clutch stops this energy being transmitted into the starter motor and potentially wrecking it.---------10,000 rpm plus being a tad too fast for it.---

[Ducati750cc]

Originally Posted by COLVERT

Thanks for that info.---HOWEVER ( sorry. lol. ) It does not explain how the one-way clutch works or why it's needed.



so------here is why.-- As the engine starts the speed of the fly wheel greatly exceeds the that of the pinion gear.--The one-way clutch stops this energy being transmitted into the starter motor and potentially wrecking it.---------10,000 rpm plus being a tad too fast for it.---

Errrrr no it doesn't, what makes you think it does ?

[SD1too]

We seem to have lost the attention of the OP who hasn't logged-on for ten days now.

Originally Posted by COLVERT

There's a one-way clutch at the gear end of the starter motor. This is the part that has to be replaced to make things work correctly

Hi Jon. RAVE refers to this as the "overrunning" clutch. Since the OP describes the fault as the pinion intermittently not engaging with the ring gear, could you explain how you believe that this clutch can be responsible as I've never inspected its operation closely?

Many thanks.

Simon

[COLVERT]

Originally Posted by SD1too

We seem to have lost the attention of the OP who hasn't logged-on for ten days now.

Hi Jon. RAVE refers to this as the "overrunning" clutch. Since the OP describes the fault as the pinion intermittently not engaging with the ring gear, could you explain how you believe that this clutch can be responsible as I've never inspected its operation closely?

Many thanks.

Simon

I'll explain how it works in a later post having just read yours at 20 past mid-night.---Will take quite a few words to explain how it works.-----It's not like any clutch you could imagine.

[Ducati750cc]

An excellent video showing how a starter motor roller clutch operates and what it comprises of :


https://www.youtube.com/watch?v=uzM9MxFp75c

[SD1too]

Thanks very much Bill for posting that. It is indeed an excellent explanation and much more professionally presented than the average YouTube video.

Thanks also for your offer Jon but you've been relieved of the need for a thousand words!

Simon

[COLVERT]

Originally Posted by SD1too

Thanks very much Bill for posting that. It is indeed an excellent explanation and much more professionally presented than the average YouTube video.

Thanks also for your offer Jon but you've been relieved of the need for a thousand words!

Simon

That's OK as I've been ill and into hospital three times.---After being beaten up by big and very strong daughter.----


Still have the scars to prove it.