Engine won't turn over

[mrgeido]

Hi Looking for some areas to explore.

My Jupiter engine won't turn on the starter with the spark plugs in. Some bits I have already checked:

replaced the battery with a high Amp battery.
Engine turns freely with a spanner on the crank pulley.
Engine spins on the starter with the spark plugs out.
Engine still doesn't spin with just the ignition disconnected (wanted to rule out the timing).
I've had the starter motor out and checked the brushes and cleaned the comm.

Do you think this could be a bad earth? I was thinking of disconnecting the starter and putting jump leads straight onto the motor to rule out all the wiring.
Could this be the valve timing , or the valves need setting? How is it best to check this.

any help appreciated as I'm running out of ideas. The engine did run and all fluids are present and like I said spins freely with the plugs removed..

thanks

Tim

[David Kemp]

My two bobs worth, cleaching every single contact including the earth(twice)!
If you have a solenoid try by passing, they do get old.
By pass the starter button, another source of voltage drop.

[Keith Clements]

Try using a volt meter. Saves a lot of time.

Is your car positive or negative earth? It might have been changed from standard.

Over 12 v across battery terminals .
run wire to engine earth . there should be 12v between this and the non earth terminal of battery. Normally neg. terminal.

press starter switch. No difference? then keeping the earth connection to your meter where it is check the voltage on the three terminals of the starter solenoid. you should have 12 v on one. if not the there is no feed from the battery. then press starter switch should get 12 v on both of the other terminals. if only on the small terminal then it is the solenoid that is gone. if not on small terminal then starter switch or ignition switch.
if there is 12v on all three then problem is cable to starter or starter.

if there is a bad earth then move the earth wire connected to you meter to the earth terminal of the battery and do the above tests again.
But also check the voltage on the starter motor casing when the starter solenoid is pressed.
if you get 12 v or anything more than 1v then you have a bad earth. Earth straps connected?

[mrgeido]

Thanks Keith and David

I'll have a look this evening and report back what I find, hopefully a dodgy earth which when found is easily fixed.

Tim

[mrgeido]

OK so I think electrical might have been a red herring. Checked all the voltages and connections and everything OK.
I tried a battery direct on the starter and again the engine turns over fine without spark plugs in but when the plugs are back in it turns about 1/2 a turn on the crank before the starter conks out and locks out. To free it I have to stop and take a spanner to the crank so that the starter disengages.

I have the rocker covers off and all is cycling through while the plugs are out, I ran it for a good 30 seconds but didn't want to damage the starter so stopped. When I put the plugs back in back to half a turn.

I think that it must be something mechanical in the engine? All I can think is that the valves aren't opening so that the piston is causing a vacuum that the starter cannot over come.

Any other ideas to try?
thanks in advance

Tim

[David Kemp]

Sounds like a chewed up ring gear. Or flogged out starter pinion.
Pull the starter out , rotate the flywheel and inspect by feel & sight.

[Alf Heseltine]

Try fitting the plugs one at a time, maybe you could then diagnose a guilty cylinder, if that is the problem.
Could be a slight coolant leak to cause a piston to lock up. You seem to have covered about everything else.

Alf.

[Srenner]

While the starter is out, check for side play in the shaft. Worn bushes allow the shaft to bind by cocking sideways. Wouldn't hurt to clean the commutator and brushes, as they wear grooves that can drop the power to spin the starter. And as noted above, check the condition of the engagement teeth on both the starter and the ring gear.

[mrgeido]

Latest update :

I checked the starter and ring gear. Both seem Ok, not perfect but nothing too bad, I stripped and cleaned the starter while out and there is very little side play. Also the engine turns over well with the plugs out so I don' think its just them, clearly they are not perfect but should be good enough to turn the engine over.

I then took Alf's advice and put the plugs in one at a time. The engine will turn over with plugs in cylinders 2 and 4. If I put a plug in either 1 or 3 then it really struggles and eventually stalls the starter.

At this stage I borrowed a compression tester and tried it in each cylinder:

1:140 psi
2:120 psi
3:140 psi
4:125 psi

I don't know if these are OK figures?
For me it does point to 1 and 3 being higher compression so perhaps this is adding to my issue?

Questions then:
Are the compression figures an issue, or should the starter be able to cope?
Is it coincidence that it's both cylinders on one head?
What could cause this and more importantly what is worth checking next, adjusting?

once again thanks all for your advice
Tim

[Alf Heseltine]

Hi Tim, to make certain it’s a head gasket leaking coolant, just drain the water coolant completely, refit the plugs & check the engine turns over. If that allows the engine to turn you have head gasket trouble. Check the oil for any sign of water
contamination. Good luck

Alf

[Keith Clements]

It may also be a sticking valve. I hope the starting handle has been used to turn the engine through 4 revs.

[Keith Clements]

I think your starter may not be delivering enough torque possibly due to a poor circuit to both battery terminals. Try some good jump leads from a new fully charged battery directly onto the starter.

[mrgeido]

Thanks Again for the replies.

Latest update. I've drained the coolant and tried again. No change, still won't turn over with plugs in 1 or 3 cylinder. So that would seem to rule out your suggestion Alf.
I've tried a battery and jump leads directly onto the starter and it is no change either.

Keith what do you mean by using the starting handle? Certainly the engine has been turned quite a lot using the starter dog and a large spanner. I've also been able to spin the engine fully with all the spark plugs removed and also with just plugs in 2 and 4 cylinders.

Everything is pointing to something wrong with the valves or head of 1,3 cylinder head. Before I remove the head is there any useful checks I can do with the valves? Watching them as I turn the engine over on the starting handle they all appear to open and close from the springs going up and down. I've not removed any of the valve train yet as want to check the obvious first.

What would anyone recommend for the next steps?

thanks

Tim

[Keith Clements]

Are they the correct reach spark plugs?

[Mike Allfrey]

Hi Tim,

I have just come into this concern.

My main suggestion is sound continuity at the earth strap from battery terminal itself (not the clamp) to chassis. Also, just as important, thoroughly check the earth strap from starter motor flange to the chassis. These are common areas of concern with diesel engines and we called it 'Domestic Science'. Ninety-nine percent of our winter call outs to farm tractors with similar symptoms were due to corroded connections or broken solder joints.

Maybe try another starter motor?

Another thought - the battery cables to starter solenoid and from solenoid to starter motor. These terminals can, due to unsupported vibration, break free at solder joints, but appear to be in good condition.

Another check, are the carburettor choke controls becoming hot while spinning the engine with plugs removed? If so, a poor quality earth connection some where.

Reference battery/solenoid cables - I use electric welder cable material. This cabling has fine copper wires and stout rubber insulation. It is far superior for handling starter motor loads. Heavier, maybe, more expensive, also maybe, but vastly more dependable.

This is probably too late,

Mike A.