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MG MGA - Rebuild starting problems

I'm starting a new thread as my oil priming one was solved but I am having real trouble getting my MGA with a Derrington head started.

The main symptom was that when the ignition was on the starter motor stalled or only turned the engine over very slowly. Without the ignition on the starter turned the engine over at approximately normal speed. It felt as if as soon as it tries to fire the starter motor stalls and the engine is trying to go backwards and stops suddenly.

This morning I assumed if it was an ignition timing issue. I found the ignition timing was set at 10 degrees BTDC so I reset it at 5 degrees before TDC on No 1 cylinder and have checked all the ignition leads into the distributor cap. That all seems fine with the correct firing sequence and the ignition set when No 4 inlet and exhaust valves are rocking, this should be no 1 TDC firing stroke.

Now I find that with the ignition on the starter will turn the engine over at normal speed initially but stalls when I think it is trying to fire and it doesn't start.

So I am really puzzled why the starter stalls when I think it is trying to fire.
I have been through different starter switches, cleaned the engine earth lead and used two batteries in parallel and I can't make it any better. I could retard the ignition more but I'm not sure that is the right thing to do.

Any ideas?



John Francis

Compression ratio too high?
Steve Gyles

Are you sure that the plug leads are connected in the 1342 sequence?
Dominic Clancy

Did the distributor drive shaft drop back into the correct position? It is really easy to install the gear incorrectly, ask me how I know this :^)

This could really mess up the timing of your engine.
See link to Barneys page on this. http://mgaguru.com/mgtech/ignition/ig103.htm

Also, did you fit a new distributor? The reason I asked is that a good few years ago, I fitted a brand new one, it had the usual offset dog but when I installed it, the rotor arm was miles away from the position it had been with the old one and the engine would not run.

I had to rotate the distributor over 30 degrees to get the engine to fire up at all.



It turned out that the dog on the new rotor shaft had been fitted in a completely wrong position and I sent it back to the suppliers.

(You could try rotating the dizzy and see if you can find a position where the engine fires)

Cheers
Colyn




Colyn Firth

IIRC, you can get a good indication that Number 1 cylinder is approaching TDC when both the Number 1 cylinders exhaust and inlet valves are fully closed.
When they are both closed at the same time, that cylinder is on the compression stroke.
(you could insert something (carefully) into through Number 1 sparkplug hole to get a good idea of TDC, or use a dial gauge to be spot on)

Sorry if you have already done this all this stuff John, but it may be worth double checking.

Best of luck

Cheers
Colyn
Colyn Firth

I am pretty sure the leads and distributor are correct. I checked according to the workshop manual with valves on no. 4 cylinder rocking giving TDC no 1 cylinder on firing stroke and took the plug out to check it was TDC which I can see visually. I double checked the rotor arm position and the leads to the cap, all are in the right place and sequence.

Steve I don't know what the CR is. When Peter Burgess tweaked the head for me in the spring I forgot to ask him to measure the volume of the head chambers. It is possible the CR may be high as the head came off a racing Wolesley 1500 and I have not run it before on my engine. Peter has suggested retarding the ignition a bit more which I will try in the morning. I think the CR and timing could be the problem. I just hope it runs OK and is usable as I have put a lot of work into all this!

John Francis

Well, so long as you are looking at the valves on cylinder number 4 rocking when you check the TDC and NOT valve number 4 rocking, then you should be about right John.

Have you tried to see if the engine will turn over on the starter with the plugs removed?

You may be able to check the compression pressure one cylinder at a time if you remove all the plugs and use a compression tester on one cylinder. (Don't forget to jamb the throttles wide open when you do this so that you get the max air-fuel mix into the cylinder)

I expect that with a Derrington alloy head, you will be running around 10.5 to 1, or more.

My cast iron head runs at about 9.5 to 1 and shows around 175 psi. You may get more than that with your higher ratio but I would give Peter Burgess a call to ask him if he knows what your compression gauge should show.

Best of luck

Colyn

Colyn Firth

I ran a Derrington head with 11:1 compression for years. No problem turning over or starting (geared starter). I’d get someone else to check all the items others have raised, sometimes you get too close to the problem you cannot see the wood for the trees. Happened to me once where i had the plug leads crossed and checked it several times but didn’t pick it up.
Mike Ellsmore

Same here Mike ,I had one on an 1800 with 10.5 and had 15 deg static timing and it started without kicking back--
It's not a compression issue if it winds over fine with the ign off--it's ignition
If it's on 10 deg(or5) it shouldn't kick back-
IF No1 plug wire is in the correct position as stated, and lined up with the rotor at tdc with No4 valves rocking, then No4 plug lead 'must' be on the wrong cylinder
If 2-3 were crossed over it won't make it kick back, it has to be No4 crossed with either 2 or 3

willy

OR
If you are timing it statically which I guess you have to be ,what method are you using
I've seen examples of it being done on the wrong side of the lobe by turning the dizzt the wrong direction
You could hook a timing light up to it and get someone to crank while you check it that way
Then if you wanted to check if no4 is on the right plug ,hook your timing light to no4 instead of 1 and it 'should' flash on the same timing mark as no1---If it doesn't then you've got em crossed there somewhere
William Revit

Thanks Willie and Mike. As always really useful experienced input. I thank everyone else too!

However, I checked it all again today. Adjusted the distributor so I can use the micrometer thumbscrew to set igniting between 7 degress BTDC and after TDC. I set the ignition statically with a light as in WS manual.
Tried various settings with same result all the time - motor stalls or slows a lot after a few revolutions.

I tried switching the leads around, no difference. Then took all the plugs out and ran it to see if I could see the firing sequence in the dark. The sequence seems to be fine, 1342.

So I have ordered a new high torque starter just to see if that makes a difference. That gives me a few days to shut the door on it and forget about it! I think I will go play with my newly acquired yacht to take my mind off it!
John Francis

It might seem daft but I would try swinging it on the handle, if you still have the original dog on the front. It would at least see how difficult it is to turn. Depending on your strength you might need a strong armed youngster to do this. I can certainly start my ‘standard 1800’ engine on the handle and I am feeble and in my 70s.

Good luck.

Paul
Paul Dean

John

I can see where you are going with the high torque starter. I presume you are talking a pre-engaged version?

One of the main benefits is that it bypasses the starter switch with the heavy load. The battery cable connects directly to the starter. The switch then just becomes a very light load carrier for the solenoid in the starter motor.

The symptoms you are suffering at the moment could in part be due to the heavy load through the starter switch and you are suffering carbon build up in the contacts through arcing. This was certainly the case with me and my high torque pre-engaged starter solved everything, including starter switch longevity.

Enjoy getting an armful of oil. I presume you are aware the oil filter needs to be removed as part of the removal/fitting process?

Steve
Steve Gyles

If the starter motor turns the engine over normally but then kicks back with the ignition on I would be very wary of trying to swing it on the handle.

Malcolm
Malcolm Asquith

Hi Malcolm, exactly, I tried it once! Luckily just a sore wrist for an evening this week. A big mistake. Thumb tucked back as well.
John Francis

John
I'm a bit confused about the starter
Wasn't it spinning over normally without the ignition on---or was that with the plugs out
If the plugs were in, it still points towards an ignition or timing issue--to me
I'd just retard the timing back just to see what happens
Is the distributor the same as pre Derrington
Was anything else changed during the head change-
like rotor ,cap etc
William Revit

John
I'm a bit confused about the starter
Wasn't it spinning over normally without the ignition on---or was that with the plugs out
If the plugs were in, it still points towards an ignition or timing issue--to me
I'd just retard the timing back just to see what happens
Is the distributor the same as pre Derrington
Was anything else changed during the head change-
like rotor ,cap etc
I know you know what you're doing but just for another set of eyes, maybe a pic of your cap (if you can see it) and where the leads go--Bit of a big ask to get at it but we might see something-?
Wouldn't mind a look at the conversion anyway
cheers
William Revit

IT STARTED!!
Hooray, high torque starter motor and wired it as pre engaged and it started pretty easily. Its sounds rough as anything but at least it goes. Now I can spend some time adjusting things so it runs a bit more smoothly although I have a suspicion it will have that kind of feeling and sound whatever. I'll post some pictures soon.
John Francis

John,
pleased to hear that it is running now at least.

If I were you I would run it in for a while to make certain that is run in and then take it up to Peter Burgess to have it set up on his dyno.

That's exactly what I did with my 1950 cc engine to get the Weber DCOE set up on his dyno and he has transformed the car, worth every penny.

All the best
Colyn





Colyn Firth

Good stuff John, well done
Wrecked my theory of what was going on, but if it started , then all good
Keep smiling
willy
William Revit

I was a bit worried when you said that you were going to try a Hi Torque starter John, I have had quite a few really bad experiences with them.

The first one I fitted started up the engine just fine, but when I released the button (I have a starter solenoid on my car), it wouldn't disengage and you could hear the motor being spun over by the engine. I adjusted it and refitted it a few times but I couldn't solve that problem. I ended up giving to a friend of mine.

I think the problem is that my engine has a mix of parts to make it work, a High-Gear 5-speed bellhousing for an early 3 brg MGB, but this is fitted to a 5-brg MGB engine, which must complicate the alignment for a High Torque starter motor.

I mentioned it to Bob West when I was there a couple of years ago and he pulled three slightly different Hi Torque starters out of a cupboard and said "These are supposed to fit your engine, see if one works for you"

Back home I measured up to see which one would fit and gave it a try.
This almost caused a disaster, when I pressed the starter button the starter didn't operate but I heard loud click, a very loud whine and could smell very hot insulation! Releasing the starter button didn't change anything and so I leapt to turn off the battery kill switch.
The starter motor seemed to be in a dead short condition and when I checked, the battery cables were really hot and both the starter solenoid and the battery isolator switch were partially melted!

The battery cable seemed to have survived but there was an obvious burn area at the point the point where the earth lead attached to the chassis down near to the battery tray.

So I fitted a new battery isolator switch, a new starter solenoid and went back to the original inertia starter, which I have continued to use since then.

Let us know how the crossflow engine goes when it is sorted.

At least this experience helped me to find a poor connection of the earth lead to the chassis at the battery tray. (it had been painted over)

Cheers
Colyn





Colyn Firth

John
Just inquisitive--what cam have you got in him
William Revit

This thread was discussed between 15/10/2020 and 20/10/2020

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