‘56 AJS model 30 600 twin

ILLF8ED · Jan 27, 2022

New to me project. The motor is very stuck. I have the heads off and have tried soaking the pistons in Marvel oil, Metal Rescue and currently using Kroil penetrant. I believe not only the piston rings are rusted to the cylinders, but also the cylinder skirts are stuck in the crankcase. I was able to remove the intermediate gear in the timing box, so I know the camshafts turn with no issue. To get to the under side of the piston skirts with penetrant…thinking of inverting the engine and pouring through the drain plug. Maybe even filling the engine with penetrant. The cylinder skirts on the AMC twins are very long making them even harder to unstick. Looking for someone with experience on these AMC twins…not really opinions based on working other engines.

Thanks

Time Warp · Jan 28, 2022

Maybe the infamous ATF and Acetone.
That looks like a very nice bike given its age.

mdt-son · Jan 28, 2022

Yes, tolerance is tight at the cyl skirts. Heat. Lots of heat at the barrels,one at a time; gentle heating of the c/case. Good luck!

mdt-son · Jan 28, 2022

A G11CS by the looks of it. Last year for the Burman B52 g/box.

ILLF8ED · Jan 28, 2022

mdt-son said:
A G11CS by the looks of it. Last year for the Burman B52 g/box.

Some previous owner put the 21” front wheel on it. In the AJS Matchless forum I was told the CS version didn’t come out until after ‘56. This has a working Lucas K2FC competition magneto on it also modification from a previous owner….nice. The magneto does not have a place for connecting a manual ignition advance and no auto advance I can see. Wondering if that means it has no advance mechanism.

ILLF8ED · Jan 28, 2022

mdt-son said:
Yes, tolerance is tight at the cyl skirts. Heat. Lots of heat at the barrels,one at a time; gentle heating of the c/case. Good luck!

I have been using a propane torch on the barrels and cases. I’m going to see if I can get some penetrant to the under side of the pistons/barrels. Then more heat as needed. Again my experience tells me go slowly…don’t break anything. Appreciate your reply and help.

Triton Thrasher · Jan 28, 2022

ILLF8ED said:
The magneto does not have a place for connecting a manual ignition advance and no auto advance I can see. Wondering if that means it has no advance mechanism.

It wasn’t very unusual to replace a broken auto advance with a solid gear, on twins.

ILLF8ED · Jan 28, 2022

Triton Thrasher said:
It wasn’t very unusual to replace a broken auto advance with a solid gear, on twins.

Huh, so it won’t break your leg trying to start when fully advanced? I don’t think there is room inside the timing case for the usual auto advance gear. These model 30s came with K2F manual advance mags.

Triton Thrasher · Jan 28, 2022

If there was no such thing as an AMC Twin with auto advance, then I suppose it’s more likely they fitted a magneto from another make of bike.

It probably will kick back, a bit, but it’s only a 600 twin. Won’t break anybody’s leg.

ILLF8ED · Jan 28, 2022

Triton Thrasher said:
If there was no such thing as an AMC Twin with auto advance, then I suppose it’s more likely they fitted a magneto from another make of bike.

It probably will kick back, a bit, but it’s only a 600 twin. Won’t break anybody’s leg.

Going back to the previous century before I started riding motorcycles…the urban myth was a Matchless 500 could break your leg or throw you over the handlebars if too advanced

baz · Jan 28, 2022

ILLF8ED said:
Going back to the previous century before I started riding motorcycles…the urban myth was a Matchless 500 could break your leg or throw you over the handlebars if too advanced

I heard it could break your thumb when your knee squashed it against the twist grip on kickback

Triton Thrasher · Jan 28, 2022

ILLF8ED said:
Going back to the previous century before I started riding motorcycles…the urban myth was a Matchless 500 could break your leg or throw you over the handlebars if too advanced

That’s the single cylinder Matchless G80/AJS Model 18. They do need to be retarded for kickstarting.

ILLF8ED · Jan 28, 2022

Triton Thrasher said:
That’s the single cylinder Matchless G80/AJS Model 18. They do need to be retarded for kickstarting.

Yup, a legend. When I was 16 the only Matchless I knew about was the 500 single.

Triton Thrasher · Jan 28, 2022

I had an AJS. It was a 1955 Model 20, that had a Model 18 single cylinder engine fitted. I liked it.

It definitely needed to be retarded for starting though, or else the kicking back was just as bad as they say.

mdt-son · Jan 29, 2022

ILLF8ED said:
Some previous owner put the 21” front wheel on it. In the AJS Matchless forum I was told the CS version didn’t come out until after ‘56.

Yes, I believe the CS model arrived for 1958. The bike has a roadster frame - the 21" is from a scrambles bike. As for the K2FC, it must have had an ATD. Pre-unit Triumphs had them, for instance.

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-Knut

Schwany · Jan 29, 2022

An ambitious undertaking.

A bicycle frame with a 600cc twin in it. Should be intoxicating.

The magneto should be driven with a straight cut or a chain gear. You should be able to get what you need for an AAU. Feked and others have a variety. I have a KF2C that was on my P11 when I got it. It has a chain driven AAU bolted to the short tapered shaft. Your magneto gear should be bolted to the tapered shaft unless somebody welded it on there. Then again, I've never owned an AJS G30, so haven't really got a clue what it looks like behind the timing cover. Might not be enough clearance in there for an AAU.

norton bob · Jan 30, 2022

Some of theses motors used wire wound pistons for close quiet running , I suppose the wire could get very grippy if rusty.

johnm · Jan 30, 2022

norton bob said:
Some of theses motors used wire wound pistons for close quiet running , I suppose the wire could get very grippy if rusty.

That's was early on. My dads 1949 AJS 500 single had a wire wound piston but he told me the skirt dropped off.

johnm · Jan 30, 2022

ILLF8ED said:
Huh, so it won’t break your leg trying to start when fully advanced? I don’t think there is room inside the timing case for the usual auto advance gear. These model 30s came with K2F manual advance mags.

Yes I actually owned a 1956 600 back when I was at uni. Mine certainly had the manual advance K2F mag. Almost certain you Will not get an AA unit in there. I remember the pinion was very hard to remove. I actually damaged the end of the mag rotor trying to remove it. You need a special puller which I had made. Havnt seen it for 40 years sorry

Other things I remember was the strange relief valve on the end of the drive side of the crank. Make sure it is complete and working or you will lose oil pressure to the big ends.

Mine had the AMC box. Pretty certain it was original. I understood 1956 was the first year for that box.

I used the bike a lot. . One Easter I rode it from Wellington to Cape Reinga and back. That was a decent ride back in 1973. Unfortunately the motor was destroyed by a woman who borrowed the bike and ran it out of oil. Bit sad.

Very important safety point. The front brake anchor on these AMC bikes is in tension and has a rather minimal amount of metal around the hole where it bolts to the brake plate. They break. Happened to me and I have seen at least one other. Especially dangerous if chromed or worn. Check carefully that it is in good condition.

NSU Max front brake anchors do the same thing. Some years have a grease nipple at the weakest point which really helps them break.

Don't remember much more sorry. It was almost 50 years ago. Good luck with the build.

ILLF8ED · Jan 30, 2022

’56 was the last year for the Burman Gearbox.
I saw the spring and small disc on the drive side end of the crank. The metal disc is a bit smashed so will need to file it or replace it.
As I get further into the rebuild, I will decide on the magneto and if I want a 19” front wheel.

‘56 AJS model 30 600 twin

.......back to the 70's.