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MG MGA - High Torque/Pre Engaged Starter Motors

I was most impressed with Barry Gannon's high torque starter motor performance whilst I was over in Oz. It got me thinking about my starting performance. I have always had indifferent starting on my A despite doing complete electrical continuity checks that have included all the usual cable connections, various starter switches and 3 different starter motors. The starter always spins well when engaged, but frequently (about once in 10 starts) suffers from the nashing of teeth - yes, one option is that the ring gear is getting worn although it looked quite reasonable when I had the engine out a couple of years ago.

So, I have started making enquiries about these high torque / pre engaged starters and have got somewhat confused. Could someone enlighten me in simple terms how they work.

I spoke with the MGOC on Friday and was told the following:

1. With my MGB 1800 engine and 5 speed box (high starter position) I could not use an MGB pre engaged starter. The technician could not tell me why but suggested the ring gear had a different number of teeth on my MGA 1600 flywheel.

2. The high torque starter for the MGA is listed as an inertia type, but he was unable to tell me if the motor engaged the gearbox side of the starter ring or the engine side. I suspect the latter but need clarification.

Am I wasting my time spending money on one of these starters, or am I better pulling the engine and replacing the ring gear or rotating the fly wheel?

All thoughts and advice welcome.


Steve Gyles


those starters are just nice! Using mine since 2006.
They work from the opposite side so it might be necessary to grind the theeth on the starter ring. Just give it a try.
The grinding can be done with the engine in situ as you got a lifter...


The technician is an ass.

All MGA/B through 18GB (3 synch box) have 120 tooth flywheels, and inertia starters.
Anything after 18GB (67) (4 synch box)had 127 tooth flywheels and fat pre engaged starters.

Your conversion might be either, but I suspect the earlier. Assuming you used either an MGA or 18G/GA/GB backplate, it must be so. Whatever, the starter position is determined by the mounting plate, and positions the starter centerline relative to the flywheel gear. You must use an early pre 68 backplate with a 120 tooth flywheel, and a late 68-on one with 127 teeth. Since the teeth are of the same form, the teeth should engage properly if the starter will physically mount and fit. Inertia starters engage from the rear, and pre-engaged from the front, and the flywheel teeth are chamfered to suit. However, reported experience says that the hi torque starters, which are all pre-engaged, work just fine despite the chamfer being "wrong".

Some of the conversion starters have mounting plates which let you index the starter to various positions, helping with clearance problems that come up in various mixey-matchey combos.

Pretty certain Barney has a good bit on this.

FR Millmore


My engine is a late 1800, 5 bearing.

My recollection from 12 years ago is that I used a 1600 backplate. I had it reamed to accept the 1800 crankshaft rear seal. I think I have the 1800 flywheel. I remember weighing it 2 years ago and it matched MGB specs. Could that be my problem - using an MGA starter with an MGB flywheel?

What confused me with the MGOC advert was that the MGA High Torque starter was listed as an inertia, but the photo suggested it was front engagement.

Steve Gyles

If you used an MGA backplate, then you have the 120 tooth flywheel, the ring gear of which is exactly the same for MGA/B. Flywheels are identical so far as the starter is concerned. You need a starter suitable for MGA, only to clear distributor etc.
MG felt that the 1800 could use a bit more oomph, so MGB to 18GB were fitted with a different starter, bigger and with a more complex drive, but MGA ones fit and work. You might expect it to be a bit lazier. After the 18GB, the pre engaged starters were fitted with the bigger flywheel/gear.

FR Millmore

I have also an MGA with an MGB engine (1950 CC high compression ratio) and a 5 speed gearbox.
The flywheel is an MGA type.
As FR Fillmore said, the inertia starterd motor engage from the rear and the High Torque pre engaged from the front. It seems that it could spoil the theet.

I have any problem to start my engine with the standard MGA starter motor with a good battery.
SD Dubois

Ok. The MGOC Accessories catalogue lists the MGA as a hi torque inertia starter. I have attached the photo from the catalogue. Unless I am mistaken it looks like it engages from the front.


Steve Gyles

I have no clue what they are talking about, and they have less. Maybe they mean that the original one WAS inertia. All starters I've ever seen that have the solenoid mounted integrally are pre engaged. That means that the solenoid engages the drive before it turns the power on for the starter motor. And yes, that one certainly comes in from the front.

Pictured unit does not appear to have the means to re-index the starter relative to the mounting plate, which may or may not be an issue on your conversion.

FR Millmore

Early B and MGA flywheels are not identical, as one has three locating pegs for the clutch plate, the other has just two. Otherwise they are dimensionally the same, but the B one is lighter.
dominic clancy

Thanks Dominic. My flywheel is certainly lighter than the A. I also run the MGB clutch assembly.

I looked up the Hi Torque starter on the Moss site. Their version looks very much the same as the MGOC. No mention of that dreaded 'inertia' word. Looks like a pre-engaged system as FRM describes.

Steve Gyles

Quote: "Flywheels are identical so far as the starter is concerned." Unquote.

FR Millmore

Is the MK2 1622 flywheel also heavier than the early B?
J H Cole

Lightened flywheel was introduced during MGA MK-II production in September 1961 at (e)3708. After this the MGA flywheel is same as early MGB flywheel except for number of alignment pins for the clutch cover.
Barney Gaylord

1 - high torque starters may be nice but they aren't necessary, I've used stock MGA for years

2 - if you want to use a pre-engaged style of starter on an 18GA or 18GB engine using the early style rear engine plate, the cheapest solution is to just bolt in a starter out of a Morris Marina. It is identical to the MGB starter of the pre-engaged style, and it doesn't matter that it pulls in the opposite direction from the way it goes in the MGB, nor that the bevel entry on the flywheel teeth is on the 'wrong' side of the flywheel. Just bolt it on, it works.

The reason I say to use a Marina rather than MGB pre-engaged starter is that the Marina has the solenoid on the upper side. The stock MGB has it low down where it will foul the MGA frame.

A picture of it bolted to a 5 main block (ignore the Twin Cam head up top) can be seen at

Bill Spohn

This thread was discussed between 26/03/2012 and 28/03/2012

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