Advice regarding starter.

[Pex]

As some maybe know I planned to uprate the front suspension but found a crack in the right engine frame. I have now dissembled all except the frame and thought I replace the starter with a new uprated high torque one while everything is easy accessible.
My engine block is not the original one, instead it’s from an xj6 which makes me worried if the new starter will fit or not.
SNG has two uprated high torque starters and one saying “USM003/1 for XJ6 will NOT fit E-Type 6-Cylinder cars, This motor will NOT fit E-Type 6-Cylinder cars. For E-Type please use USM003/1E.”

The starter isn’t mounted on the engine block so can I assume that USM003/1E will fit?
My M45G has 9 teeths if that means something.

[cactusman]

Others may disagree but the M45 was quite sufficient to start many an XK engine. Give it a clean and lubricate. Replace the brushes although I'll get they are fine. Possibly replace the solenoid....age and use does pit the closing contacts and lead to voltage drops.....the original set up is fine. Unless your starter really is past repair or the dog is badly worn then the original unit is more than up to starting an engine ....IMO....

[christopher storey]

And far more reliable than the modern so-called high torque replacements . I have a feeling that the SNG catalogue may be misleading - an M45 style starter will NOT fit a 3.8 XK engine,which had the old bendix inertia starters and a different sized and teethed flywheel , but should fit any 4.2 engine

[Pex]

Maybe you're right, still considering weight,size and the less load on the battery/electrical system.

I think I dissemble the old one first and see how worn it is before taking any decision but will probably have to pay a little extra later because of Brexit (vat, customs etc).

Could someone help me find a link or similar to a description how to "refurbish" the starter?
Never seems to find anything when I search probably because I don't use the correct search terms since English isn't my native language. I have books but I prefer some real pictures.

[mgcjag]

Hi Peter....it dosnt matter about your xj6 block its the bellhousing that the starter fits to and the flywheel it engages with....i can see you have a 4.2 bellhousing as it has the starter fixing holes recessed also you flywheel teeth look like a 4.2 which has 133 teeth.........As far as im aware SNG have the Powerlite starters.....I contacted Power lite recently about this problem.....there are 3 models available for 4.2 out with their suppliers......however they now only recomend 2 of these models the RAC 303 and RAC 303ms.......neither of these need a spacer between the starter and bell housing that you should have seen when you removed your existing starter.....the ms model above is for special situation and has an adjustable bracket to let you twist the motor body to different positions so really you want the RAC 303 model.............their 3rd model RAC 300 is still available and sold by some suppliers as suitable for a 4.2...but it has a longer throw out to the pinion so you must use the spacer also the electrical cable connections are on the wrong side and could possibly touch the block.........hope this helps..Steve....Ps service manual has a section on starter motor

[Pex]

Just the information I was looking for
I have long experience as an electrical engineer and based on my experience, less current is better, even if the original starter is enough and do the job
I found RAC 303 at Powerlites homepage but I can't find any information on which model SNG actually have so I will contact them and see which model "USM003/1E" represent.

[cactusman]

Less current is indeed good but then P=IV. V cannot be changed so reducing I will reduce the power produced by the starter and I fail entirely to see how this would increase the cranking speed. Both the old M45 and new starters are electrically similar. Stator and rotor windings and brushes...and while the modern units may be a bit lighter in terms of efficiency in converting electrical energy to mechanical work there is not going to be a vast difference....it would indeed be interesting to compare the current drawn by an old M45 vs a new replacement and do the same for engine crank speed....I'd suspect the differences would be marginal...

[mgcjag]

As far as im aware the high torque starters are permenant magnet gear reduction motors....so your not useing up amp to energise field coils so a saveing of 50- 60% in cranking amps....becaus of the gearing it will also spin faster....are they any better?...depends what you want to achieve....definatly lighter...Steve

[cactusman]

Permanent magnets would indeed make a difference....so long as they don't loose their magnetism over time....

[PeterCrespin]

FWIW, neither of my two different spare gear reduction starters shows any hint of magnetism (tested by dropping small steel washers all over the exterior).

[Series1 Stu]

Gear reduction starters are essentially identical in construction to direct drive starters, they simply use a smaller motor than runs at around 4 times the speed of a direct drive motor. This higher speed is reduced by a gearbox to around the same speed as a direct drive motor. This in turn multiplies the torque created giving roughly equivalent performance but from a typically smaller, lighter package that draws less current.

The main benefit of a gear reduction starter is that it is generally more reliable in cold weather.

There is no evidence to suggest the use of permanent magnets in any gear reduction starters that I have encountered.

Regards

[mgcjag]

Hi All....yes confused myself after looking at PMGR starters for another project....the standard offerings for E types are just gear reduction starters....but still offer a greater reduction in amps used.....Steve

[cactusman]

Then I return to my original observation....you need a certain amount of power to spin an xk engine sufficiently quickly enough to start. The book states the M45 draws around 200-220 amps at 1000 rpm and gives 8.3 lbs ft of torque with a voltage at its terminal of 10.2 to 9.8 volts....sufficient to start the engjne...the book also gives the lock torque as 22lb ft with the motor dissipating around 3.3 kW.

So the power generation is roughly 10 volts X 210 amps = 2100 watts with the engine spinning...you need around 2kw of energy to spin the engine....roughly....

The battery voltage is fixed so the power dissipated at the motor as mechanical torque plus heat from winding loses etc is directly proportional to the current draw. Whether you have a direct engagement starter or one that is geared down you need around 2kW of power to turn the engine so you draw around 200 amps...modern motors may be slightly more efficient yes.....but significantly reduced current draw....hmmmm....afraid I don't see how.

[johnetype]

So the power generation is roughly 10 volts X 210 amps = 2100 watts with the engine spinning...you need around 2kw of energy to spin the engine....roughly....

No, you need torque to spin the engine, 8.3 ft lbs or whatever. An electric motor wound the way a starter motor is will be much more efficient at 4 times the RPM hence the rationale for putting it behind the added cost and complication of a gearbox.

Whilst in theory an electric motor produces infinite torque at zero RPM, it also draws infinite amps at zero RPM and the losses are proportional to current I squared so in practice you need to be away from low motor RPM. It is all about efficiencies and minimising the current drawn.

[42south]

Hi
Check out this site, the original British starters.

https://www.classiccarperformance.com/c ... com?page=2

I got one for my S3 and they are most knowledgeable, down to correct one for the model year. It has performed flawlessly for 10 years.
Cheers

[cactusman]

Thanks John...good point....it would be good to see someone do a comparison and see just how much of a reduction in current draw is actually achieved though...anyone out there got a clamp meter handy?

[mgcjag]

Standard offerings for most high torque starters suitable for E type 4.2 are 1.4Kw units....But its not just about current draw they will spin the engine much faster.....plenty of technical spec data available on manufacturers websites if you need it...Steve

[288gto]

Thanks John...good point....it would be good to see someone do a comparison and see just how much of a reduction in current draw is actually achieved though...anyone out there got a clamp meter handy?

Hi Julian, when I fitted a Fosseway high torque starter motor I also fitted a fuse to protect the large cable from the battery to the starter, being unhappy that originally along with other swathes of wiring it has no fuse protection.

Admittedly not very scientific, but I gradually increased the fuse rating until it didn’t blow on cranking.

Results.

80amp will blow almost immediately
100amp will stand a few seconds cranking
120 amp seems ok

I might buy a clamp meter just out of curiosity now you’ve brought it up though.

[cactusman]

I will see what my old M45 set up uses next time I get the car out....I have a clamp meter...remember that any fuse should carry its rated current (essentially) for ever and will carry twice it's rated current for a considerable period of time....minutes....Depends a bit on the fuse construction. Only when you reach five or ten times it's rated current will it fail rapidly....again depends on the fuse construction. To me putting a fuse in the cable to the starter is probably not likely to afford a great deal of protection although no harm in it...remember though that any fuse is also a low value resistor so you will lose a few millivolts across it when under load..