P11 engine build
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Schwany
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Yes it can all work if the barrels and cylinder head are both for a Commando 750. A Commando 750 head will fit on P11 barrels, but the P11 barrels need to be drilled and tapped for 3/8-26 bolts in 5 locations. Rods, pistons, and ect are or can be the same. Although the Commando pistons will be flat top and slightly higher compression than the dished pistons P11 used originally. The cam has to be for a pre-commando in P11 cases, unless some additional modifications are made to the timing side case to support a Commando cam and ignition in a Commando timing cover. I might be wrong about the thread count on the 3/8" head bolts, but a stock P11 had 5/16" bolts in the 5 locations.
Shorter answer is... Yes I've done it. Go for it.
EstuaryBoy
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In addition to the above, might be prudent to point out the rocker oil feed positions are different, but obviously not insurmountable, but would check that the P11 head steady can be fitted to the Commando head?
Again, I defer to yer man above to elaborate
Again, I defer to yer man above to elaborate
Schwany
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Adding more to my steaming pile of info:
I had one of Raber's machinists do the drill and tap stuff for the 3/8" bolts in the P11 barrels, and used a Commando head for a short period while my P11 head was getting ported by Fred Barlow. Once I got the P11 head back I put it on the P11 barrels with the 3/8" bolt support after drilling out the 5/16" holes to 3/8" or whatever it took to get the larger diameter bolts through the P11 head. I used braided PTFE oil lines for the Commando head, and the P11 head. The cross over line ends up being a bit long on the top fed P11 head, but it works. Fairly certain I used the same head brace I made from aluminum bar stock for both heads as well. I still have the Commando head, which is basically like new but really old. I'm slowly, when I fee like it, improving the ports on both intake and exhaust as well as using it to hold and modify Commando intake manifolds so they can be used for CR and FCR Keihin carburetors. Improving the ports is not hogging them out. It is cleaning up the crappy work Norton did and increasing the entrances to 31.5 mm and blending them in to a 29.5mm neck with a minimally raised roof before the valve guide. Not quite Narly, but Narly enough. All done with emery cloth and my fingers. Slow and steady wins the race. Also adding some epoxy to the floor and reshaping it a little. I'm basically sort of copying what Fred Barlow did because it works really well without any loss of bottom end torque with an SS cam and properly seat of the pants dyno tuned FCRs.
I had one of Raber's machinists do the drill and tap stuff for the 3/8" bolts in the P11 barrels, and used a Commando head for a short period while my P11 head was getting ported by Fred Barlow. Once I got the P11 head back I put it on the P11 barrels with the 3/8" bolt support after drilling out the 5/16" holes to 3/8" or whatever it took to get the larger diameter bolts through the P11 head. I used braided PTFE oil lines for the Commando head, and the P11 head. The cross over line ends up being a bit long on the top fed P11 head, but it works. Fairly certain I used the same head brace I made from aluminum bar stock for both heads as well. I still have the Commando head, which is basically like new but really old. I'm slowly, when I fee like it, improving the ports on both intake and exhaust as well as using it to hold and modify Commando intake manifolds so they can be used for CR and FCR Keihin carburetors. Improving the ports is not hogging them out. It is cleaning up the crappy work Norton did and increasing the entrances to 31.5 mm and blending them in to a 29.5mm neck with a minimally raised roof before the valve guide. Not quite Narly, but Narly enough. All done with emery cloth and my fingers. Slow and steady wins the race. Also adding some epoxy to the floor and reshaping it a little. I'm basically sort of copying what Fred Barlow did because it works really well without any loss of bottom end torque with an SS cam and properly seat of the pants dyno tuned FCRs.
Schwany
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One thing that can't be swapped with a Commando part is the timing chain adjuster foot regardless of which way you go with cam selection. You can't use the one for Commandos with ignition in the timing cover. The P11 case has the mounting boss in a different location and the Commando adjuster foot ends up in the wrong place. I'm not sure about the earliest Commandos, but stick with the adjuster for pre-Commandos to be on the safe side.
Also want to add that all my P11 engine internals are Commando as well as the current set of barrels I am using. Roller bearings on both ends of the crank which in my case is a stronger lighter weight after market Commando crank.
Hope your barrel stud threads in the cases are in good shape, cuz if not you should install thread inserts. If you have the equipment to do that you have a leg up. Otherwise doing it with a hand drill would be a big mistake. I was very lucky in that regard because I'm probably the only person that ever opened up the engine I got with a basket case P11 in '72. It has never sat outdoors or in a garage for decades apart.
Also want to add that all my P11 engine internals are Commando as well as the current set of barrels I am using. Roller bearings on both ends of the crank which in my case is a stronger lighter weight after market Commando crank.
Hope your barrel stud threads in the cases are in good shape, cuz if not you should install thread inserts. If you have the equipment to do that you have a leg up. Otherwise doing it with a hand drill would be a big mistake. I was very lucky in that regard because I'm probably the only person that ever opened up the engine I got with a basket case P11 in '72. It has never sat outdoors or in a garage for decades apart.
hybridracer
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That is a strange thread (3/8"x22tpi) to find in a pre-commando head as 3/8" bsf is the standard size.
If your budget allows it, I suggest you buy a new 750 barrel of the through-stud type. The old type of barrel is notoriously weak at the mounting flange, especially if the barrel has been sleeved, which is the case with many s/hand barrels.
You will have to drill, tap and fit helicoil inserts in some of the crankcase fixation points for this. Incidentally, it's the only type of 750 barrel that AN sell at this time.
- Knut
You will have to drill, tap and fit helicoil inserts in some of the crankcase fixation points for this. Incidentally, it's the only type of 750 barrel that AN sell at this time.
- Knut
Richard, you need to have your (presumably s/h) crankshaft checked thoroughly. Old Norton crankshafts are ticking bombs altogether .....
Same goes for conrods. These are the most fragile parts of a Norton engine.
If your crank and rod breaks at higher revs, most of your engine will be smashed to pieces. Investing in new parts gives peace of mind and a protection of investment.
- Knut
I have a set of original P11 exhaust pipes, if your interested.
Junglebiker
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I think I remember you went with JSM Carillo rods a few years ago (as I also did) but did not bother to rebalance the crank which was already stamped with "62" as I recall unless I am getting your engine mixed up with somebody else's--was that the original P11 crank or was that your aftermarket Commando crank? It took me a fair amount of effort to get my balance factor to 62% with the JSM rods and pistons, but I don't remember what the crank I started with was out of. Atlas, maybe? I am pretty sure it wasn't Commando.
Schwany
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Interesting you bring that up. The first version of the 750 P11 engine with Carrillo long rods and pistons had the original P11 crank lightened a little with the 62% BF and in it. It had the P11 iron barrels and +.040 pistons. Also had the JSM JS02 cam and accompanying valve train components. I did not get that crank rebalanced. It ran really well but did shake a little more than it did with the stock rods and +.020 pistons at slower cruise like 47-57 mph. The second version got the Molnar alloy barrels with iron liners and a Molnar crank for 750 Norton engines, but I tried the standard bore MAP long rods and pistons because I had purchased them before I got the JSM long rods and pistons and wanted to compare. Molnar supposedly balanced the crank for the JSM rod and piston weights. I have no idea if he actually did, but he uses or used at the time 75% BF for solid mounted Norton engines. Anyway, engine was a different beast. The Molnar crank is 3 lbs lighter and the Molnar barrels a bunch lighter. I could pick the engine up fully assembled and move it around. At 75 years of age not too smart, but I could do it. Was a harder to pick up with the stock crank and barrels. Actually only maybe a 12lb difference, but it felt like more.
Anywho, I rebuilt it again and put the JSM Carrillo long rods in with standard 73mm bore JSM (Wiseco) long rod pistons. Reason for the rebuild is I finally got up the balls to push the engine with the RGM belt clutch and the engine hit the wall and would not go past 93mph. The MAP pistons were starting to seize up due to a lean condition and excessive heat because the fuel bowls were not staying topped up, but I caught it in time, backed off, and was able to ride home maintaining normal speeds. The RGM belt clutch always worried me. Fortunately no issues with the clutch. I had pinched the float bowl tube to atmosphere and my fuel filters were too small and not flowing worth a hoot with the throttle wide open or an extended time. Fixed all that and now with the JSM rod and pistons the bike is nice to ride. Also reinstalled the Norton SS cam and stock lifters, which I prefer over the JS02 cam and lifters. The SS cam has a nice power hit where the JS02 cam in linear in power delivery. I'm still 18 years old between my ears, and like the violence of the Norton SS cam.
Enough of my off topic rambling BS.
Anywho, I rebuilt it again and put the JSM Carrillo long rods in with standard 73mm bore JSM (Wiseco) long rod pistons. Reason for the rebuild is I finally got up the balls to push the engine with the RGM belt clutch and the engine hit the wall and would not go past 93mph. The MAP pistons were starting to seize up due to a lean condition and excessive heat because the fuel bowls were not staying topped up, but I caught it in time, backed off, and was able to ride home maintaining normal speeds. The RGM belt clutch always worried me. Fortunately no issues with the clutch. I had pinched the float bowl tube to atmosphere and my fuel filters were too small and not flowing worth a hoot with the throttle wide open or an extended time. Fixed all that and now with the JSM rod and pistons the bike is nice to ride. Also reinstalled the Norton SS cam and stock lifters, which I prefer over the JS02 cam and lifters. The SS cam has a nice power hit where the JS02 cam in linear in power delivery. I'm still 18 years old between my ears, and like the violence of the Norton SS cam.
Enough of my off topic rambling BS.
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