Matchless G15/45

Matchless · Dec 4, 2023

Here are a few pictures of a bike I started building twenty odd years ago, & finally got around to finishing this last summer. I have always thought that the G45 was one of the best looking race bikes of all time, so I built a road going version.
The bike was purchased as a very scruffy, bodged up racer, but what I wanted was the frame. Most of the bike including the engine was scrap, so was disgarded. As nothing was available off the shelf I set about making damn near everything, including the engine plates, top yoke, swan neck bars, brake & gear levers, footrests, inlet stubs, belt guard, chain adjusters, the list goes on.
The frame which was out of line when I aquired it, was sent to P&M for Steve the frame builder to sort out.
The engine is the very rare g15/45 750, which came back from the U.S. Nigel at NRP made a very nice exhaust system to my requirements.
I had it running briefly this summer & will drag it out next spring once I get time.

Fast Eddie · Dec 4, 2023

Wow Martyn, that is class !

baz · Dec 4, 2023

Matchless said:
Here are a few pictures of a bike I started building twenty odd years ago, & finally got around to finishing this last summer. I have always thought that the G45 was one of the best looking race bikes of all time, so I built a road going version.
The bike was purchased as a very scruffy, bodged up racer, but what I wanted was the frame. Most of the bike including the engine was scrap, so was disgarded. As nothing was available off the shelf I set about making damn near everything, including the engine plates, top yoke, swan neck bars, brake & gear levers, footrests, inlet stubs, belt guard, chain adjusters, the list goes on.
The frame which was out of line when I aquired it, was sent to P&M for Steve the frame builder to sort out.
The engine is the very rare g15/45 750, which came back from the U.S. Nigel at NRP made a very nice exhaust system to my requirements.
I had it running briefly this summer & will drag it out next spring once I get time.

Very very nice

Hortons Norton · Dec 4, 2023

Super job on it!!

Matchless · Dec 5, 2023

Thanks all. I'll post more next year once I've ridden it.

N0rt0nelectr@ · Dec 6, 2023

What a beautiful bike. Very well done. Thanks for sharing.

mdt-son · Dec 8, 2023

Nice, Martin! Have you considered ABSAF G12 big fin alloy barrels? It would make the engine look more like a G45.

Extracting more power off the G12 or G15/45 requires the cylinder heads to be substantially modified. Routing of the oil lines detracts from the overall clean lines, I think.

- Knut

Onder · Dec 8, 2023

What does it weigh?

Triton Thrasher · Dec 8, 2023

mdt-son said:
Nice, Martin! Have you considered ABSAF G12 big fin alloy barrels? It would make the engine look more like a G45.

Extracting more power off the G12 or G15/45 requires the cylinder heads to be substantially modified. Routing of the oil lines detracts from the overall clean lines, I think.

- Knut

Popular lore says more power should not be inflicted on the 750 Matchless engine.

Matchless · Dec 8, 2023

mdt-son said:
Nice, Martin! Have you considered ABSAF G12 big fin alloy barrels? It would make the engine look more like a G45.

Extracting more power off the G12 or G15/45 requires the cylinder heads to be substantially modified. Routing of the oil lines detracts from the overall clean lines, I think.

- Knut

I have looked at them, but I think they would be a bit spendy. As it is the engine cost me a kings randsom, & still needed a full rebuild. Luckily Russell motors had some +0.020" pistons in stock. Everything else apart from the top end gaskets is the same as the 650 version.
If funds were unlimited I wouldn't have used 750 Honda forks & BSA/Triumph conical hubs.

Matchless · Dec 8, 2023

Triton Thrasher said:
Popular lore says more power should not be inflicted on the 750 Matchless engine.

I totally agree with that statement. They do seem to have been reasonably reliable though, as they had the SG iron cranks & the larger oil pumps, but the crankcases are simply over bored 650 types & look to be on the very limit. The heads are the same casting with slightly different machining in the squish area. I have a pair of race kit cams but decided not to fit them.

Matchless · Dec 8, 2023

Onder said:
What does it weigh?

I haven't weighed it yet, but I'd guess around 320/330 lb.

mdt-son · Dec 8, 2023

Triton Thrasher said:
Popular lore says more power should not be inflicted on the 750 Matchless engine.

Provided you do the usual upgrades, the only weak point I can think of is the head studs. There appears to be a solution. A Matchless enthusiast in California races them.

- Knut

baz · Dec 8, 2023

Matchless said:
I have looked at them, but I think they would be a bit spendy. As it is the engine cost me a kings randsom, & still needed a full rebuild. Luckily Russell motors had some +0.020" pistons in stock. Everything else apart from the top end gaskets is the same as the 650 version.
If funds were unlimited I wouldn't have used 750 Honda forks & BSA/Triumph conical hubs.

Why the preference for honda 750 forks?
Do they work/damp better than other Japanese forks from that ere ? Cheers

Matchless · Dec 9, 2023

baz said:
Why the preference for honda 750 forks?
Do they work/damp better than other Japanese forks from that ere ? Cheers

The reason for using Honda 750 forks is because I had some, & secondly they look similar to the AMC comp. type. Obviously it would be better to have the real thing if money was unlimited.

Fast Eddie · Dec 9, 2023

Matchless said:
The reason for using Honda 750 forks is because I had some, & secondly they look similar to the AMC comp. type. Obviously it would be better to have the real thing if money was unlimited.

I’m no AMC rivet counter, but I never gave the forks a second glance as they just looked ‘right’ to me.

acotrel · Dec 13, 2023

When I sold my 500 cc Triton back to my mate for $5000 , it had front and back 7R hubs, which cost $5000 each if somebody wanted them. The bike was cannibalised for the hubs - ended up with Commando wheels. The 7R hubs were dangerous - they have strange snail cams and rollers, pushing the brake shoes. I am a bit dubious of anything Matchless.

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