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MG MGB Technical - Starting Problem

Hi to All and Happy new year

Here's my problem, just rebuilt my 68 roadster fitted a new 063 440ah battery last week and have been cranking the engine over without ht leads to get oil pressure up on gauge, trying the lights etc etc. because of all the above put my new battery on charge yesterday and today thought i'd go into the garage and start up the car (first time in 25years) so in i go check the timing, connect everything up to the coil and dizzy turn ignition on then go for start and all i get is s/motor engageing and trying to turn the motor but thats it, my fisrt thought was the battery is still not charged so i connected up my booster box and still the same, does anyone out there have a idea as to what the problem might be.

Even though the starter motor is a new one from MGOC could there be a problem with it?

Cheers Pete (frustrated)
PJ Thompson

Pete - Next time you try starting the car with the battery fully charged, hold the leads of a voltmeter directly on the battery terminals (not the cable clamps) and see how much the voltage drops when cranking the starter. The battery voltage should not drop significantly while cranking - I wouldn't expect it to drop below 12 volts. Next, try cranking the starter with the voltmeter leads attached to the starter terminal and ground, again looking for a voltage drop. It is my guess that you have a bad connection or a flaky battery cable. I have had battery cables develop corrosion up under the insulation, causing a large voltage drop whenever I tried to crank the starter. You might find some help in my article, Electrical Connection Preparation in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

Also inspect the ground strap running from the right motor mount to the engine. These are sometimes missing or poorly connected which will cause the symptoms you are experienceing. RAY
rjm RAY

Hi Dave
Thanks for your reply I will try your suggestions out on Saturday.
I do'nt i'll be in a fit state tomorrow after the new year celebrations.
Happy and prosperous new year to you

Regards Pete
PJ Thompson

Hi Ray
The earth strap is new as is the body shell and the bolts that hold it to the body and motor, ive checked these and they are tight, thanks for your reply
Regards Pete

Happy new year :)
PJ Thompson

"The battery voltage should not drop significantly while cranking - I wouldn't expect it to drop below 12 volts."

What battery are you running, David!? Typically battery voltage will drop to 10v on a *good* conventional battery, unless you mean spinning it with the plugs out rather than trying to start it. If less than that the battery is not fully charged or faulty.

Put the meter between the 12v terminal of the one battery and the earth terminal of the other if you have twin 6v batteries, then between the solenoid stud and the starter body. Ideally you should only see about 0.5v less at the starter terminals than at the battery posts, and that is the voltage lost in the cables and connections. If you see approaching 1v or more than it is worth using the voltmeter in various positions in the cranking circuit to see where the worst connections are and cleaning them up. Also check the link cable by measuring between its two posts (on a low voltage scale if manually switchable).

Not sure what you mean by 'without HT leads', normally you would take the plugs out to spin the engine to get oil pressure putting minimum load on the battery, and disconnect the coil leads to prevent random sparks.

Not in gear is it?
P Hunt

Hi All

Just been in the garage to carry out some tests and getting some weird results,

First with a voltmeter on the battery posts when attempting to crank the motor the voltage dropped from 13.6V to 7.5V.

Second with the voltmeter on the starter where the battery cable connects and earth on the chassis when attempting to crank the motor the voltage dropped from 13.3V to 5.4V and the starter is VERY warm!!!!

Obviously there's a problem but where ????

Regards Pete

PJ Thompson

Pete. Voltmeter probes, if connected to the terminals of the battery (rather than to the clamps that go on the terminals) showing a drop from 13.6v to 7.5v indicates a bad battery. (If reading taken on the clamps, it may indicate a bad/dirty connection.)

Battery voltage dropping to 5.4v at the starter indicates bad/dirty connection at the battery and/or bad cable from the battery to starter.

Also good to check the condition and contact of the ground strap as Ray suggests. But, get the battery tested before your next test.

As to battery voltage drop on starting, I agree with Dave DuBois on this. Here in the US, a battery which dropped to 10V on cranking would be be considered a bad battery. My non-MG mechanic did a battery test and got one of my batteries to drop to 11.5v under a 400 amp load and considered the battery good, noting that the load he put on the battery was more than you would see when cranking. He considers less than 11.0v when cranking to be a bad battery which will, normally, not crank over the starter on a cold engine.

Speaking of cold engines and winter months, what oil do you have in the engine?

Les
Les Bengtson

Thanks Les
I will get the battery tested its 3 months old,
as for the engine oil its sae30w for running in the engine (when i can get it started).

Regards Pete
PJ Thompson

Pete. Good show with the battery testing. I have seen three month old batteries go bad. It might, also, be worthwhile to pull the starter and have it tested. Here in the US, the quality of the "rebuilt" electrical items is variable. I had several bad starters on one vehicle, including one which tested bad right out of the box.

The 30 weight oil may be a little heavy for winter use. I have only used it in summer myself. Back when I lived in cold weather country, a switch to 10W-30 in winter months was indicated for better starting. There was, a number of years ago, a regular here who was a petroleum engineer living in Canada (last name of Wilson, Paul Hunt may remember his first name). His suggestion for testing the flow properties of oil in winter was to put several quarts in the home freezer over night, then, pour them out the next day. If one poured more easily than the next, it was a better oil for starting in winter. Worth a thought.

Les
Les Bengtson

hello Pete

The engine turns over by hand ok ? (I know you mentioned it was turning over without the ht leads to build up oil pressure recently)


Silly suggestion.... but the engine is not seized ???

Dave
dave bignell

Hi Dave

I hav'nt tried to turn it by hand, its a freshly built motor with new oil.
I will take the plugs out tomorrow and try this though

Regards Pete
PJ Thompson

Firstly 13.6v is way too high for a battery unless it is on charge, it should be about 12.8v normally maybe dropping to about 12.5v with the ignition on. A cranking voltage of 7.5v is way too low and indicates a discharged battery or a knackered cell. A further drop to 5.4v at the starter shows 2v is being lost in one or more connections between battery and solenoid. That on its own would be enough to cause an overheating motor, even more so with only 5.4v being available. Motors don't follow Ohms Law when it comes to voltage and current like a resistor does, with a motor the fast it turns the lower the current it draws and hence the cooler is stays. With bad connections the reduction in motor speed causes *more* current to flow, so heating the motor more, not less due to the increased resistance as one might expect.

First sort out the battery, you should be getting 10v at the posts cranking with plugs in. Then start testing for small volt drops post to clamp, clamp to cable, cable to body, body to earth strap, earth strap to engine i.e. all on the earth side, and much the same on the 12v side to see the biggest drops which will give you the biggest improvement when sorted.

Can't recall the Canadian you mention, Les, nor the oil test.
P Hunt

Pete,

any updates re your starting problem ?
dave bignell

Paul. The Canadian was Bob Wilson, originally from Calgary and, later, in Solvang, California. He decided on the use of Mobil 1 oil because he drove his GT year round (in Canada) and it still poured easily after a night in the freezer while petroleum based oils were considerably more sluggish.

Les
Les Bengtson

Hi Dave
Problem not sorted yet, hav'nt had time to get in the garage. This coming weekend is when ill next get in there and will let you know how i get on, thanks for asking.
Paul thanks for the info ill carry out a few test the weekend

Regards Pete
PJ Thompson

Have you checked ignition advance? Way too much advance will kick back against the starter, 'kind of' seems to struggle to tuen the engine over. easy to check - advance the distributor 45 degrees anti-clockwise (I think..., it's late, and cold) and see what happens. Might not start (possibly way too retarded now) but might turn over.
N
Neil22

Easier to disconnect the coil and crank it without any HT.
P Hunt

Easier, yes.

But if it does turn over, then you'll need to reconnect at the coil and turn the dizzy to confirm that was the issue. So why not just do it anyway. And anyway, he said that th engine turned with the HT leads disconnected...

N
Neil22

If it doesn't turn over with no sparks then it obviously isn't over-advanced timing, so by disconnecting the coil you haven't upset the timing, which presumably has already been set statically for its first start.
P Hunt

Hi All
Dave is spot on the engine is seized, ive pulled the motor out today and it seems No 3 big end is siezed.
there is side ways movement on No's 1,2 & 4 big ends on the crank no 3 is solid, ive taken 1 & 4 pistons out but can't turn the crank to get at bolts on 2 & 3.
Anyone have any ideas why this happened?
When i built the motor the crank turned freely after torqing the mains and big end bearings.

Regards Pete
PJ Thompson

Now that's a bummer! Hard to see how you could do that if all was well on assembly, but it has to be a lubrication failure, or a big piece of garbage lodged in that bearing. Or the shell came adrift in the rod - where they checked for fit and roundness? How much cranking did you do? Assembly lube should be enough to run 5 minutes without oil!
Maybe that if you can even get one rod bolt loose you will be able to turn it.

FRM
FR Millmore

Pete,

Sorry to hear about that. Can you pull the main caps and lift the crank out (with 2 & 3 still attached) so that you can reach the 2 & 3 big end nuts? If you try that, have some wood, rags, or such handy to protect the crank journals.

I realize you have a zero miles engine, but you mentioned the car was dormant for 25 years. Was the engine rebuild recent or many years ago?

Charley
C R Huff

FRM
It Is a bummer and i will loosen one bolt on each big end and see if it will turn.
I cranked the engine probably 6 or 7 20 second bursts and got oil pressure gauge up 70 lbs.
Maybe there was'nt enough assembly lube on this bearing ( im begining to doubt everything i do at the moment)
Charley
The motor was rebuilt 6 months ago i will try this method if the above does'nt work

Thanks and regards
Pete
PJ Thompson

Got to be a blockage in the feed to that one bearing, or just possibly the clearance was way too small. If you could crank it enough to get 70psi oil pressure, then that should be more than enough lubrication. I take it 1 & 4 had plenty of oil in them? If not maybe it is a blockage in the main feed.
P Hunt

Hi All
Ive since rebuilt this motor, as you know No3 big end had locked up due to myself bruising the crank journel when inserting the conrod and piston into the bore.
The motor now runs beautifully as of 30 minutes ago and im so chuffed.
Thanks for all your help and comments

Pete
PJ Thompson

This thread was discussed between 31/12/2009 and 24/02/2010

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