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MG MGB Technical - High torque starter to fit 3 synchro engine

I have a 5 bearing B engine which has been modified to fit into my MGA. It has been fitted with an early 3-synchro backplate and flywheel to make it match with my 5-speed gearbox conversion.

I am looking to fit the engine with a high-torque pre-engaged starter motor but it is not so obvious (to me anyway) which starter motor will fit the 3-synchro set up.

So I thought that this forum may be the best place to ask about this.

I would appreciate any advice on this.

Cheers

Colyn

Colyn Firth

I just ordered the on from Moss, which was not configured for a 3 syncro set up. All I had to do was to rotate the mounting plate on the front of the starter to get the proper clearance. Cheers - Dave
DW DuBois

There's high-torque, and there's geared. Hi-torque are generally not much dearer than standard but geared are about twice the price. Standard and hi-torque have the motor in line with the pinion, geared have the solenoid in line, and it is generally bigger than the motor. Some geared have a moveable adapter plate and some have a fixed, and some of those come with one of the bolts already in place as the hole is covered by the motor/solenoid.

Original inertia starters for the MGB (Mk1 3-synch) and MGC have a 9-tooth pinion, pre-engaged for the MGB have 10 teeth (for some reason the V8 has 9 teeth even though it is pre-engaged), I understand you can get both in the geared. What starter did you use with the 3-bearing back-plate and flywheel? If that has been working without any problems then I'd count the teeth on that. However some people have said they have used a 10-tooth on a 3-synch, but any wear from mis-match might not be immediately apparent.

Paul Hunt

Thanks Paul
The term "high torque starter" sounds as if it would help turn over my "new" engine easier than the inertia starter I have now.

The car is presently fitted with a 3-bearing 1850cc MGB which has been dyno'd at 106 bhp and the inertia starter sometimes struggles a little when it is really cold although it is fine when it is warm.
This may be partly due to the single 12v battery I have on the car which looks like it would be more suitable for a Fiat Panda than a hi compression MGB engine.

So my "new" engine is going to be a 1950cc 18V engine with quite a lot more power and torque and I sort of expect that my inertia starter will struggle even more with this.

The 1950cc engine is fitted with a 3 synchro backplate and matching smaller flywheel in order to fit my 5 speed gearbox bellhousing.

So would the high torque starter be any better than the inertia starter Paul?

I have just been to look at my starter bendix and it has 9 teeth on it.

Much appreciate your help

Cheers

Colyn
Colyn Firth

Colyn, for your application, I would go with the gear reduction High Torque starter motor as it will provide more power to turn over your engine hot or cold. RAY
rjm RAY

Colyn,
Spinning the engine, or more especially difficulty spinning, can also be a product of poor battery and starter connections, high compression ratio, heavy cold oil, cold battery, worn or corroded solenoid contacts, current losses in the power lead, corroded earth strap and insufficient cold cranking ability from the battery. These days physical battery size isn't always an indicator of cranking ability!
3 bearing engines are easier to spin because of the fewer frictional losses. 5 bearings up the losses slightly, but power output doesn't increase the spinning difficulty unless you up the compression ratio.
Allan Reeling

Hi-torque are a bit better than the originals (inertia and pre-engaged), but the geared are miles better as Ray says. I did have one on my V8 for a while and the first time I used it my heart sank as it sounded like just the starter was spinning and not turning over the engine. I was gobsmacked when it burst into life as usual. They are one of those things where you gain on the swings and the roundabouts - they spin the engine faster but take less current out of the battery. The upshot is that there is less strain on the battery and more voltage left for the ignition. The only downside is the cost. Mine had to go back as the adapter plate was attached to the starter unit with three self-tapper and super-glue, and came loose within a few days, so I went back to pre-engaged, but these days they are attached much more securely and if (when?) I need another replacement I'll plump for geared.

But first check connection losses as Allan says. Measure the voltage on the battery POSTS (not the connectors) while cranking, then measure on the solenoid stud and casing. The difference between the two is what you are losing in the cables and connections. You should be able to get this down to less than 1v total losses. You may need an analogue meter for this as digitals may not give a consistent reading. For those with twin 6v batteries measure the voltage on the individual batteries and add them together then compare that with the starter reading. If the battery is outputting less than 10v then it is weak, unless there is something causing the starter to put more load on them than normal i.e. a tight engine.
Paul Hunt

Colyn. I have a similar setup as you with the Panda battery and B engine but had no problems with turning the engine and that was in the north of Sweden at –C very cold.
First winter there was to use a truck size cable from the battery to starter switch and the difference was amazing.
J Hughes

Colyn,
My '73 GTV8 now with a 3.9, originally had twin 6's now replaced by the same Panda battery mentioned by Mr Hughes. I also have a Wosp geared starter. No problem cranking. My other V8, 3.5 with 9.35 CR, has the original pre-engaged starter again with a single 12v battery, albeit a slightly higher CCA but no problem there either but all the cables, relays etc were renewed when I built the car. Check out all the possible sources of current losses and even double up the battery to starter lead with a jump lead and see if things improve.
Allan Reeling

Likewise, my V8 conversion uses a smallish single battery with the original V8 pre-engaged starter motor. But I increased the battery to starter cable to a bigger cross section and in seven years have never had the slightest difficulty starting, even in freezing temperatures.
Mike Howlett

This thread was discussed between 24/02/2016 and 27/02/2016

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