Upgrading Starter: Fitting Powerlite hi-torque starter motor.

A recent battery failure during the cold weather reminded me of just how much juice the original Lucas starter required. I fitted a new battery, but to preserve its life, and hopefully improve starting I decided also to fit a Powerlite Hi-torque starter motor. This is one of the cheaper Hi torque motors, I don't think its the geared type which cost rather more. The distributor has to come out for access to the starter motor so if you are contemplating fitting electronic ignition then this is probably a good time to do it. I am (or rather I was), but it turned out I have the wrong distributor so this will have to wait for a later post. 

Raise the front of the car on ramps to assist access from below and disconnect the battery.

Since I am removing the distributor its important to set the motor at a known position so I set it at tdc on compression in no 1 cylinder. The rotor arm is then pointing at no 1 spark plug lead

Motor at tdc...

 Distributor-rotor position

rotor arm points at no 1 plug lead- in my case up at 45 deg and towards the front of the car

To preserve timing on the distributor- (in case of early abandonment of the swap), I removed the distributor by releasing the 2 distributor clamp-to-block bolts NOT the distributor timing clamp. I'm coming at this car from a Lotus- remember all those gags about access in those... the necessity of adopting the "lotus position"???- Well I can now officially confirm that access to the distributor and starter on the MGB surprisingly is even worse! Given the amount of space in the engine compartment, it is truly astounding how all the components have been arranged to block access to each other! Best I can recommend is a short and thin 7/16 ring spanner.

Distributor- adjustment screw top but do not release this one

Removing both bolts lets the distributor pull out giving improved access to the starter beneath

Distributor removed- dipstick also out

 The starter is held by 2 bolts- the upper also retains a cable clamp

Starter upper bolt and attached cable clip

 The lower starter bolt is virtually inaccessible- I can't even photograph it from above or below! I found that it can just be be reached using a small 9/16 socket on a long wobble bar extension. Luckily it wasn't tight.

Check the starter connections- these are all made to the solenoid part of the starter and are positioned underneath the motor. They appear at first sight chaotic. There are 4 ring terminals to the main starter terminal post. One of these is the battery cable- I'm not sure what the others are. There are also two spade connections; 1 of these (the larger in the black plastic cover) is the solenoid energising trigger, the second (green/white wire) supplies full voltage feed to the coil for the "cold start" system for starting. The Powerlite unit doesn't have this second  12V take-off and the makers' suggest simply leaving this second wire disconnected and do without the cold start boost. I'm not really happy with this so I will return to consider it later... probably earlier if I have starting problems.

Starter connectins- 4 ring terminals on main post and 2 spades

second view

9

Third view- spades clearer here?

 Disconnecting these wires was straightforward.  solenoid trigger

Disconnecting both spade temrinals

I tied the 4 ring terminals together with a cable zip tie so I remembered to reconnect them all.

 I removed all wires before loosening the lower starter motor bolt and removing the starter itself.

This is the new starter- It has a single spade triggering connection in addition to the main copper terminal. Note that although it is smaller and lighter than the original , It is a different shape and this will complicate fitting.

Side view copper contact on top, spade contact on side

End view

The starter has a plastic drive gear- which isn't great but this was by far the cheapest starter I could find and I guess this price saving has to be reflected somewhere. Note that the fitting holes are different- one is a simple hole for the bolt whilst the other is open making it a slot.

Front view plastic drive gear; hole-and-slot mounting points

I assumed that the slot mounting is to be fitted downwards so that the weight of the starter will hold the motor on. It has the added advantage that the lower (and inaccessible) bolt doesn't necessarily need to be taken out completely in order to remove/refit the starter. However there are two problems with this- firstly the design of the new motor means that it has several bulges on the side, when positioned this way up against the block, the new motor blocks access to the bottom mounting bolt more effectively even than the original! Access is now virtually impossible and you need to get the bolt in to close to the right depth before slipping the motor onto the stud to minimise the number of turns needed to tighten it after installation.  You can just reach it approaching horizontally underneath the motor using a 9/16  1/4 drive socket on a  long extension wobble bar and turn it, but you can't really exert much force. If anyone knows a better way please let me know.

The second problem is that this moves the terminal to the top of the motor and although the solenoid trigger and three of the ring terminals can cope, the battery lead is annoyingly just a cm or so too short. Normally this would not be a problem since I could slacken the mounting clamps underneath the body and ease the cable through for a cm or so. However, in my case I have just spent some £500 having the under-body professionally cleaned and sealed (Rustbuster of Spalding). This has coated the cables and clamps in sticky goo. As I doubt they removed the cables and pipes to treat behind them, they have effectively sealed the starter cable, fuel pipe and brake pipes to the under-body.

Starter cable in underbody clamp. Note the black goo now sealing it to the body

If I were to move the cable I would break this seal, potentially allowing rust-promoting water to sneak in behind the cable and rot the body along the cable line. I don't therefore want to move the cable and this means I will need to crimp on a short extension at the solenoid end.

NB although both bolt access and cable length problems are solved by installing the starter the other way up, you cannot do that because in this position it blocks the distributor so its essential to do it the harder way!

A word here about battery/starter cables because I found it confusing. There are 2 types of cable commonly used in this application: battery and welding cable. Both are bundles of copper strands inside an insulating coat. Welding cable has a finer strand which means firstly, its more flexible and secondly, more of the interior cross-sectional area is actually occupied by copper. Consequently, a welding cable can take a higher current than a battery cable of the same nominal internal copper cross section. Welding cable also has a higher quality of insulation and so is sometimes considered preferable for locations subject to weathering. However the MGB uses battery cable. For most cars battery cable of 16mm2 cross sectional area (110 amp) is fine- but for cars with the battery at the rear, the intrinsic resistance of a  long cable run could reduce voltage at the starter. So to keep cable resistance down cars like the MGB use 25mm2 battery cable (170amp).

Joining lengths of cable, or adding new terminals can be done using solder-on or crimp-on terminals. I use crimp-on as I find it nearly impossible to get enough heat into a thick copper cable to melt solder without also melting the insulation! I use a cheap hydraulic crimper from eBay as it can be used in position on cables fitted to the car. I think the secret is to crimp first using a bigger dye. I use the 35 size, and then do a second crimp using the dye of the correct size (25). I should also add that buying terminals can also be problematic in terms of both size and amperage capacity. My advice is always buy cables and terminals matched by cross-sectional area only. Some  suppliers only describe their terminals by cable diameter. This is often of no use since its not clear if they are talking about the internal cross sectional diameter of the conductor bundle or the whole cable including its insulation. Other suppliers use an AWG size which doesn't help at all, or give only an amperage figure for the cable and this is often confused with welding cable of the same diameter. This approach does reduce choice of suppliers, but at least you know that everything should fit. If there is a choice of amperage rating for the terminals I always buy the highest amp rating at the size I need. I bought a length of 25mm2 battery cable and joined it to the original using butt-join crimp connectors and added a new eyelet terminal. The joins are then covered in two layers of heat-shrink tubing. I needed to extend the cable by 25 cm to reach the starter post terminal. Be careful not to over tighten the connections to the solenoid post- it is copper and easily stripped!

I obtained some advice on reinstating the cold start system from the MGB owners club- I am indebted to Paul Hunt for the link to
http://www.mgb-stuff.org.uk/coilboost.htm where I obtained the relevant diagram reproduced below.



This method adds a new starter relay to work in tandem with the existing relay. The existing starter relay is one of two cylindrical relays that operate the starter and ignition circuits. Both are located on the inner wing on the right hand side and there is room to mount the new relay beside them.  NOTE I found that the original source (link above) was wrong, at least as it applied to my MGB, because it described the starter relay as connected to the brown/white wires. This is incorrect, that is the ignition relay! The starter relay is connected to the red/white wires. You must connect the new relay to the starter relay as you want to supply the 12V coil feed only during cranking. If you use the ignition relay you would be supplying 12V to the coil at all times that the ignition is on with presumably drastic effects on the 6V coil.

Given the confusion in wire colour its tempting to try and identify these relays whilst the battery is connected by assessing how they are supplied with 12V and under what circumstances they output that voltage. All I can say is DON'T! Be VERY careful with these relays! They feature live (brown) connections in ridiculously close proximity to earth (black) connections and they are not fused. Do not even think of touching anything here unless the battery is disconnected. I omitted this and a momentary flash contact meant I'd melted a good 6 inches of earth wire and had to unpick the loom and replace it! Luckily there was no more melting beyond the first 6 inches and no other wires were damaged. I strongly suggest that you rely on the wiring diagram.

I bought a new 30A  switching relay with a plastic base which accepts the spade terminals and holds them in position- minimising the chances of an accidental short.

New relay in position with wired base. I used a piggy-back connector to pick up a 12V output from the starter relay (energised when the ignition switch is turned to "start") and feed this via a red wire to both the relay activation (terminal 85) and switched power in (terminal 30). Relay activation earth (terminal 86) was connected to the chassis using the relay mounting screw to avoid over stressing any of the existing earth wires. Switched power output was connected via a green wire from terminal 87 to the existing coil boost wire formerly connected to the old starter motor.
Note the unpicked loom! I have ordered more cloth loom tape to rebind the loom in this region.

I tested the operation of all these wires off the car to make sure everything behaved as expected, and tested again on the car to check that the green wire was only live during cranking. Finally  the green wire was connected to the coil feed via the existing spade connector and I made a last check of the insulation round all the new spades I had fitted.

In view of my mix up with the distributor I opted at this stage not to fit the Powerspark unit but simply cleaned, lubricated and reinstated the points distributor fitting new points, condenser, plugs and plug leads.

Reassemble and re-time and everything so far OK. Cranking performance is much improved.