Small diesel starting problem

Nov 25, 2018 Last reply: 7 years ago 56 Replies
C

We have a Stiga mower with a Hatz 1B50 diesel engine. When cold it starts easily as long as the battery is in good condition. However it's near impossible to re[start] when it's hot.



It has a fairly standard car style (but smaller) starter motor which has a pinion that engages on teeth in the outer rim of the flywheel. What happens when it fails to start is that the starter motor engages and turns the motor, the motor fires once and that disengages the starter pinion and the motor fails to continue rotating, it bounces back off the next compression cycle.



Is this a symptom of a weak/broken spring in the starter motor?


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N

Is it a Bendix, or pre-engaged?

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H

The engine is pre-igniting. Happens when the engine is hot. This means it goes backwards. Try a different make of fuel. (Less volatile)

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N

Also suggests wear on the pinion if that kicks it out.

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C

It's a diesel, I know it can still pre-ignite, but it's not really a 'typical' diesel problem is it? It's mostly run on red diesel as we also have a Kubota diesel and an Iseki tractor.

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C

When I looked at it a while ago it all looked amazingly un-worn.

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T

How do you normally stop it? Can you arrange to get it turning over with no fuel being injected?

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C

It has a stop solenoid of some sort, it's probably a fuel cut-off but

*might* be a throttle close one I suppose.
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T

My vintage of agricultural machinery has mechanical linkage to the injector pump:-) You can get the engine turning and then send some fuel. You could try interrupting the solenoid feed with a second switch.

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A

Is this one with a speed control on the engine block which also acts as a stop, i.e. it cuts the fuel if the speed control is rotated fully anti clockwise?

If so see if the engine spins freely with the control fully off and strat rotating clockwise once it's spinning (much as Tim L suggests)

AJH

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M

Carbon build up in the head causing pre ignition when hot. Perhaps it needs a de-coke.

Mike

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C

I'm not sure how the engine stop works, I need to take a look.

Yes, if I can spin it up with no fuel or 'stopped' by other means (such as throttle closed) it might work as several people have suggested. I'm off for a few days but when I come back that will be the first thing I try.

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C

Is this something that actually happens with diesels? ... and it's hardly 'hot' when it still won't start, just vaguely luke warm.

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T

Diesels can coke up, yes.

In general on simpler diesels the failure mode is carboned up valve seats that reduce compression.

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V

What sort of diesel has a throttle?

Andy

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T

Model aircraft ones :-0

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M

They all do, I imagine. Perhaps you're confusing 'throttle' with 'choke'? (I know they sound like similar things.)

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T

Nope they may have a throttle control but unlike a petrol engine there isn't a butterfly valve controlling the air intake. Engine power is governed by fuel injection.

Tim

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