[wdco42]

First, let me wish you a very happy Christmas ! And please forgive me not to have answered earlier (cold weather+ xmas gifts = homework)
Tom, I have looked at my cams, they effectively go on 5/8" shaft, but have 40 teeths.. the width of the lobs is 14.2mm. So it should mean the S cams won't fit.
I have in stock (certainly an old Bullet one, as it has too 40 teeths, and the lob the same width as the J2) an inlet cam that has 20° more opening than the J2 one, but no "S" logo.
Some datas :
The inlet port has a 1"1/8 mm diameter
The inlet valve head is 1.625" (effective diameter : 38.2mm), the exhaust one is 1.5" (effective diameter 35mm)
The exhaust port (at the pipe) is 35mm x 2
I have looked at the head, and the biggest diameter for both valves would be 1mm more.
The crankshaft is a brand new one, with 25mm shafts. The bearings I have got are, for the drive side : 1 x NJ205 (25x52x15)crank side, 1 x 6205 (25x52x15), separated by a circlip.
For the timing side a NJ2205 (25x52x18), and the bronze bush
All are FAG, C3 and have a bronze cage.
The compression ratio isn't determined for the moment, but the top engine is all cast iron.
I have some interrogations about the way to go :
- the possible compression ratio
- the use of the Bullet inlet cam (I don't have the exhaust one, and don't know if the Bullet has the same caracteristics).
- Should I open a bit the inlet port, and fit bigger valves, or is it ok like that (Bullet cam or original one)
- As the bearings are 10mm smaller than Bullet ones, will it be a weak point ?
To resume : will my J2 allways be a good old purring cat, or a roaring tiger
Anyway, BW, I'm in for a set of S cams that will go in my Machismo.

[ace.cafe]

First, let me wish you a very happy Christmas ! And please forgive me not to have answered earlier (cold weather+ xmas gifts = homework)
Tom, I have looked at my cams, they effectively go on 5/8" shaft, but have 40 teeths.. the width of the lobs is 14.2mm. So it should mean the S cams won't fit.
I have in stock (certainly an old Bullet one, as it has too 40 teeths, and the lob the same width as the J2) an inlet cam that has 20° more opening than the J2 one, but no "S" logo.
Some datas :
The inlet port has a 1"1/8 mm diameter
The inlet valve head is 1.625" (effective diameter : 38.2mm), the exhaust one is 1.5" (effective diameter 35mm)
The exhaust port (at the pipe) is 35mm x 2
I have looked at the head, and the biggest diameter for both valves would be 1mm more.
The crankshaft is a brand new one, with 25mm shafts. The bearings I have got are, for the drive side : 1 x NJ205 (25x52x15)crank side, 1 x 6205 (25x52x15), separated by a circlip.
For the timing side a NJ2205 (25x52x18), and the bronze bush
All are FAG, C3 and have a bronze cage.
The compression ratio isn't determined for the moment, but the top engine is all cast iron.
I have some interrogations about the way to go :
- the possible compression ratio
- the use of the Bullet inlet cam (I don't have the exhaust one, and don't know if the Bullet has the same caracteristics).
- Should I open a bit the inlet port, and fit bigger valves, or is it ok like that (Bullet cam or original one)
- As the bearings are 10mm smaller than Bullet ones, will it be a weak point ?
To resume : will my J2 allways be a good old purring cat, or a roaring tiger
Anyway, BW, I'm in for a set of S cams that will go in my Machismo.

Claude,
I was mistaken about the teeth number. It is 40 teeth.
I think that they should fit.

Actually, this is a diversion of this AVL thread which is not related to the main topic. You should start a thread about this in the Vintage section, and that would be the proper place for it.

However, we need to back up a little bit, and start from the beginning. These "S Cams" were used in an effort to overcome an issue in the AVL engine with valve bounce. This is an issue that your engine does not have. So, you have an open road to decide what cams you might want. It appears that the Iron Barrel type cams should fit in your engine, and there are some to choose from.

Your head is restricted in flow, and has cast iron construction which is much more laborious and time consuming to port than aluminum alloy. Also, it has that troublesome dual exhaust port, which is a bad design. We can talk about that.

You should decide what you want this engine to do. The smaller main bearing shouldn't be too restrictive to your desires for output.

The compression ratio would be about the same as we use with the other Bullets. Setting the compression to go with the cams you use will be needed. You set the compression with the type of piston you get, and also with gaskets or spacers under the barrel.

With your current situation, you have flow limits which will make your maximum hp occur at somewhere around 4300 rpm. Things will need to be done to raise that up higher, so more hp can be made. Your port is small, and your valves are small, and your cam is small. You need to increase these things for the engine to be able to operate with more flow at higher rpms. I would suggest following the same basic methods as we use with the later Bullets. Port the inlet port up to about 32mm, use a 32mm carb, put the larger intake valve in it, and port the bowl to make it flow well with that valve, put a higher lift Bullet cam set into it, improve the valve springs with competition springs, get a higher compression and lightweight piston.

With the cast iron head and barrel, cooling will be limited, so I would suggest keeping it below 30 hp.

[wdco42]

Thank you Tom for your expertise.
I'll open a new topic in the good section (as I posted the message, I realised how it was at the far borders of the AVL section...).
there are some good news in your message, the more important ones are that the cams can fit (will have some interesting testings with the J2 and the Machismo, and maybe the CO if they fit..), that the engine will be able to cope with some more power (around 30 bhp will be a good goal for a 65 years old rigid bike), and that I'll have your all good advises to get that...
Lot of fun for the future