Converting 500 Twin to 600.

Information relating to the Matchless G11 or AJS Model 30 600cc twin
BruceB
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Converting 500 Twin to 600.

Post by BruceB »

I have a 58 AjS twin engine here, would I be right in thinking that if I use the bottom end from this and put on 600 heads, barrels, pistons and valve rods it would be essentially be a 600?
If this is correct do I need to avoid particular years because the bottom end is 58?
Ignore bolt on ancillaries like carbs etc, I am talking about the basic engine parts within the casings and barrels etc


Or am I talking nonsense and this simply wouldn't work? :D
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
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dave16mct
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Re: Converting 500 Twin to 600.

Post by dave16mct »

Yes 600 heads, barrells and pistons will fit your 58 500 bottom end. Go for 57 or 58 heads as I think they had bigger valves. Also use 57 or 58 manifold and carb (the 56 used same carb and manifold as 500).
Dave.
BruceB
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Location: INVERNESS-SHIRE UK

Re: Converting 500 Twin to 600.

Post by BruceB »

Does the throw of the crank match?, trawling around reading throws this up as a possible issue.
I need to completely rebuild the engine anyway as it is in bits and am still deciding whether it would be worth just looking for another motor or just selling the 500 parts needing swopped and buying the necessary 600 parts.
While I am not particularly bothered about rivet counting when I come to build I would prefer it was as correct as was practicable and have a 600 rather than a 500 if it wasn't too difficult.
I have a 78 Honda Superdream I am about halfway through and a Cyclemaster to follow so it will still be a little while before I break open the boxes and start working on it. It would be good to start looking for the odd part though while there is no delay trying to find them.
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
Groily
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Re: Converting 500 Twin to 600.

Post by Groily »

Stroke is same (at 72mm); balance factor would be slightly different with 600 bits on top.
You may also read about differences in cranks for the early 500s compared to later - but you should be able to make whichever you want on the bottom half you have.
BruceB
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Location: INVERNESS-SHIRE UK

Re: Converting 500 Twin to 600.

Post by BruceB »

I have now managed to acquire a set of 56 G11 cases, barrels and pistons. This should allow me to build a 56 G11 engine from the 58 G9 engine I have in the boxes with the rest of the bike. The gearbox and frame numbers say it is a 56 G11 so putting this engine in should make it all 56 G11.
looking through the parts catalogue the crank is the only real remaining part that seems to have a different part number obviously because of balance issues.
I may be able to get a crank but not sure if there is any way of identifying it to make sure it is a 600 crank and not a 500 crank?
Any identifiers that are on the crank that could be used to ensure it is a 600 crank, it probably is but the seller is unsure and I don't want to spend money to get another 500 crank, already got one of them!
This is just the usual gathering up of the known missing parts before starting to pull it out of boxes and starting to rebuild.........
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
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Duncan
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Re: Converting 500 Twin to 600.

Post by Duncan »

Have you considered getting your existing crankshaft dynamically balanced to match your pistons etc, this would resolve the balance issue and hopefully give you a smoother engine.
BruceB
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Location: INVERNESS-SHIRE UK

Re: Converting 500 Twin to 600.

Post by BruceB »

It has crossed my mind but there is a real dearth of folk that would or could do that, specially when you know I live in the north of scotland and most of the engineering specialist are in the midlands.
It is the back up plan if I can't find one.
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
BruceB
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Posts: 95
Joined: Mon Dec 19, 2016 11:42 pm
Location: INVERNESS-SHIRE UK

Re: Converting 500 Twin to 600.

Post by BruceB »

Having searched around it looks like it may be the best option to get the whole thing dynamically balanced and be done with it, so this means I have a crank :)
The next question is about converting the bike from dynamo to alternator, mainly to be able to use the alloy cover rather than the banded one.
However not sure of the implications of this never had a non alternator non points bike before, even my G12 was alternator/points and so have all my other bikes.
What do I need to modify and what needs to be changed? I have seen alternator convertors, how are these fitted and any mods to the engine or can you just bolt the conversion parts on?
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
BruceB
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Posts: 95
Joined: Mon Dec 19, 2016 11:42 pm
Location: INVERNESS-SHIRE UK

Re: Converting 500 Twin to 600.

Post by BruceB »

Got the barrels and pistons today, barrels are nigh on perfect and pistons are in good condition and good fit to bores, doesn't look like any more than a clan and hone is required.
However there are no piston rings and looking on the club spares site there are none suitable available.
I have emailed Thorntons as they advertise new piston and ring sets but awaiting a reply re rings only.
They are +40 AE pistons, anybody any idea were I may get a set of rings for these pistons, an internet search only brought up Thorntons and I am not too hopeful they would have them.
66 BSA Spitfire MK11
77 Yamaha XS750 Triple
98 Suzuki Bandit GSF600S
78 Honda Superdream (rebuilding)
51 Cyclemaster (in queue)
56 G11 bitsa (in boxes awaiting courage)
78 Series Landrover (rebuilding)
72 MG Midget (in queue)
06 Honda XL1000
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dave16mct
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Location: LANCASHIRE UK

Re: Converting 500 Twin to 600.

Post by dave16mct »

I would keep the tin chaincases. With the new improved seal it's easy to make them oil tight. Cox & Turner will provide the rings.
Dave.
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