Timing the Magneto on your Matchless G12CSR

I read the manual on re-timing the ignition on the big twins (non-Norton). Here is my mild re-write with some extra thoughts.

To re-time the ignition – Twins (Magneto Models). Before proceeding to time the ignition, check the breaker point gap, which should be from .012” to .015”. Ensure that this is done first, as it will affect the advance point if you do it after.

Loosen the nut from the magneto driving gear, and release the gear from the tapered end of the magneto shaft with the correct extractor (part number 015374 – also used for the small crankshaft gear if that ever needs to be pulled).

Remove the inlet rocker cover and spark plug from the off-side cylinder (that’s the right-side of the bike). Insert a rod into the spark plug hole, or if you have it, a dial indicator gauge (if you’re really cool), or a spark plug timing tool as is available on eBay or other outlets (see pic).

Turn the engine in its normal direction until you have found top dead centre after the inlet valve has closed.

Hold the rod in the plug hole, and mark the rod where you can see it register, or mark your dial indicator, adjust the tool, etc… Take out the rod if you’re using it, and mark it higher up 3/8in (9.5mm) for the 500/600cc twins, or 11/32in (8.7mm) for the 650cc models. Put the rod back in (you DID keep it at TDC, right?) and rotate the engine backwards until the higher mark is at your registration point.

Put the ignition control lever on the handlebars in the fully advanced position.

DO NOT Disturb or move the engine. Turn the magneto in a clockwise direction (looking at the contact breaker side, not the shaft side. Keep turning until the contact breaker points are just about to separate as the fibre block moves against the cam.

You can use a piece of cigarette paper or similar super-thin paper between the points to do this, or a test lamp. When it separates, you’re at the exact right position. Press the magneto driving gear back in and lightly tighten the securing nut.

Recheck the timing by repositioning the piston and then tighten everything down. You can check with a degree wheel if you have the engine far enough apart.

3/8” = 39º 11/32” = 35º

And Bob’s your Uncle.

No photo description available.

Matchless Twin Oil Pump Wet-Sumping fix

Matchless G12 Twin Oil Pump Wet Sumping fix, Step by step with instruction download

Since I have the engine of my ’61 G12 apart, I looked up the “Wet Sumping Fix” for Matchless Twins that involves adding O-Rings to the shafts around the input side of the pump. I decided to video the steps I took to share. The instructions on how to do this are in the Jampot Archives or I updated their copy here.

First, you need to remove the input side of the oil pump. While I’m sure you could do this while the pump is on the engine, I think it’s just easier to pull everything, take it apart, clean it and then put it back on the bike.

You only have to do the input side of the pump. There are “two pumps” on the oil pump, one that puts oil “into” the engine from the external sump, and another that takes oil “out of the engine and returns it to the external sump. We are only concerned with the input side. It is the smaller of the two, and is located on the intake side of the engine. DO NOT MIX THESE UP when reassembling.

This first video, I have disassembled the pump and I’m preparing the plate that will be counterbored:

Preparing the Input Pump plate for counterboring

Plate, ready for counterboring. I explain what gets machined, and what to skip.
O-Rings, Honda parts.

Once you have the plate all nice and clean and flat, you can get your 9/16 counterbore with 7/16 pilot and prepare your drill press (I guess you can do it hand-held in a pinch, but depth is critical. Make sure the depth is equal to the width of the O-Ring).

Counterbore installed, preparing to clamp everything down!

Once you get everything together, clamp everything down into a vice, line stuff up, check twice to make sure the pilot goes in and out of the hole smoothly so the cut will be correct. Use the depth gauge on the drill press to make damned sure you don’t go too deep. It’s better to go shallow, then check with a decent set of vernier calipers. I did this. It ended up being 1/128 in short, so I was able to just touch it one more time to make it perfect!

Everything aligned and ready to go.
First one complete
1/16 in. depth. I initially drilled it 1/128 short, then measured with my calipers
Action shot of the last counterbore on the back side of the pump plate.
Finished cutting, time to de-burr and clean.
Assembled, showing external O-Ring that will fit on the camshaft-side.

That’s about it. Follow the steps in the instructions, and I hope the videos explain the step-by-step procedures and break it down for you.

1960 Matchless Spares (Searchable)

I had the recent opportunity to need the 1960 Matchless Spares book, available free from the AJS/Matchless Owners Club Archives (http://archives.jampot.dk/).

Since they were an optical scan, I took some time using my OCR tools and made them searchable. They are available here. If anyone from the club would like to upload them to the archives they are more than welcome to. I only ask that they be freely distributed.

You can download it here:
https://www.chasingmotorcycles.com/wp-content/uploads/2020/12/1960_Spares_List_M_G3_G3C_G80_G80CS_G9_G12_G12CS_G12CSR_searchable.pdf