P11 gets the JSM treatment

I'm just getting started. Very slow compared to the last time I had the motor out of the frame. Getting older makes me overthink everything. Plus, I forget where I put tools down once in a while and spend 15 minutes looking for a socket. If lucky I find it before I forget I'm looking for a socket.

This JSM stuff is all old, repeated news to most of you guys that have been on this site for years. It's new to me, because I'd never heard of JS Motorsport before signing up as a member.

What I am doing is taking a P11 engine previously modified on the timing side for a 2S cam. Motor also sports a Fred Barlow ported head and a slightly lighter crank that was rebalanced when the 2S cam was installed. Motor has somewhere over 10K miles on it since the 2S was put in there. I'll be putting the following JSM parts in it.

JS2 cam, lifters, pushrods, valves, valve springs, rods, and high CR pistons.

I hope I don't miss that 2S cam.

I'm a shade tree mechanic. Only thing I'm anal about is keeping the parts clean and making sure they spin freely and don't wobble funny.

A few teardown pics so far. Nothing technical will be discussed in this thread. Hence it may not appeal to very many members here.


The messy space where I'm doing the work.



Need a pinion puller. If it isn't one thing it's another.
More to follow.

Hi Schwany, which pistons did you order? I fear the high CR pistons giving 9.5:1 will produce a lot of vibration in the light P11 frame. I tested a P11A once which had standard flat Commando pistons (CR 8.7:1). Granted, it may not have dynamically balanced, but it shook worse than any twostroke I have ever tested. Not fun at all. I hope you fare better.

- Knut

Guess I'll be finding out. +.040 high CR pistons is what I got. (Edit: Pistons came and they are Wiseco for a 74mm bore.) I'm going to use a .021 base gasket and .040 copper head gasket, and can get thicker if I need it. I can't remember why I talked myself into the high CR pistons. Might have had something to do with the JS2 cam liking more compression. (Edit: The Wiseco pistons are very light weight compared to the stock pistons or any full skirt high compression piston. Definitely going to be fun. I don't think I'm going to miss the 2S cam.)

The motor had +.020 Commando flat top pistons in it up until last week. The crank was re-balanced (possibly dynamically balanced) when I put the 2S cam in it and got the head work done in the early 1990's. I can ride it for 6 hours before my hands start to get numb. I did 380 miles in one day toward the end of summer last year. The last 30 miles were not my favorite. I just keep telling myself I'm a wimp need to buck up and get er done. I'm still in relatively good shape and I'll push myself to get home if the situation calls for it.

If it sucks, I'll pop the lid and put Jim's flat top pistons in it.

Oh and unbeknownst to me until I looked at the crank, I've been wrong about the crank balance factor. It's either 62% or 52% according to the scribble scribe on the drive side crank cheek in the out of focus pic I took. I thought it was higher. Could be a different number on the timing side though. Still haven't got the crank out of the timing side. I'm going to wait on the pinion puller and save my big hammer antics for later.

Just be prepared to do a lot of dry assembly, measuring, tearing down, and re assembly and you’ll get to where you want I think. With Jim’s fabulous selection of different thickness head and base gaskets you can really adjust to suit.
Do an initial assembly and measure the Combustion Chamber Volume and start from there. It might not be as high as you think.

Often the CR will be lower and than stated as the valves may be cut lower, material may have been removed to blend in new seats, etc, etc. A lot can happen to a head in 50-60 years!

I juggled around a lot with my 920 build, but I was juggling getting a tight squish and a ‘reasonable’ CR. Jim’s gaskets were a life saver.

FWIW I ended up at under 0.040” squish and 11:1 CR. This was a higher CR than I wanted but it runs perfectly fine on the Super Unleaded we get here in the U.K.

Schwany said:

I'm just getting started. Very slow compared to the last time I had the motor out of the frame. Getting older makes me overthink everything. Plus, I forget where I put tools down once in a while and spend 15 minutes looking for a socket. If lucky I find it before I forget I'm looking for a socket.

This JSM stuff is all old, repeated news to most of you guys that have been on this site for years. It's new to me, because I'd never heard of JS Motorsport before signing up as a member.

What I am doing is taking a P11 engine previously modified on the timing side for a 2S cam. Motor also sports a Fred Barlow ported head and a slightly lighter crank that was rebalanced when the 2S cam was installed. Motor has somewhere over 10K miles on it since the 2S was put in there. I'll be putting the following JSM parts in it.

JS2 cam, lifters, pushrods, valves, valve springs, rods, and high CR pistons.

I hope I don't miss that 2S cam.

I'm a shade tree mechanic. Only thing I'm anal about is keeping the parts clean and making sure they spin freely and don't wobble funny.

A few teardown pics so far. Nothing technical will be discussed in this thread. Hence it may not appeal to very many members here.

The messy space where I'm doing the work.

Need a pinion puller. If it isn't one thing it's another.
More to follow.

Click to expand...

Easy to make a puller if you have a piece of 42 or 48mm steel tube a and a welder
Weld a washer on the end of a piece of tube that's a about 3" long
Then split it length ways with a hacksaw
Then drill and cut a slot in both halves to pass a piece of flat bar through
Tap the centre for a 1/2" bolt
Hook each half behind the pinion
Hold the two halves together with a jubilee clip
Then wind the bolt onto the crankshaft (grind a taper on the bolt so it indexers in the oil feed hole)
I made one of these up over 40 years ago , expecting it to work maybe once but it's turned out to be stronger than the factory puller!
I lent it to a mate of mine after the factory one he had hired from roebuck motorcycles broke
But my one pulled the pinion off

Schwany said:

Oh and unbeknownst to me until I looked at the crank, I've been wrong about the crank balance factor. It's either 62% or 52% according to the scribble scribe on the drive side crank cheek in the out of focus pic I took. I thought it was higher. Could be a different number on the timing side though.

Click to expand...

Some good balancing info

baz said:

Easy to make a puller if you have a piece of 42 or 48mm steel tube a and a welder
Weld a washer on the end of a piece of tube that's a about 3" long
Then split it length ways with a hacksaw
Then drill and cut a slot in both halves to pass a piece of flat bar through
Tap the centre for a 1/2" bolt
Hook each half behind the pinion
Hold the two halves together with a jubilee clip
Then wind the bolt onto the crankshaft (grind a taper on the bolt so it indexers in the oil feed hole)
I made one of these up over 40 years ago , expecting it to work maybe once but it's turned out to be stronger than the factory puller!
I lent it to a mate of mine after the factory one he had hired from roebuck motorcycles broke
But my one pulled the pinion off

Click to expand...

That would get the job done, but I have so many other things to do I'm taking the lazy route and using one from Andover. I doubt the pinion will be difficult to pull. My motor is clean and slippery on the inside.

Fast Eddie said:

Just be prepared to do a lot of dry assembly, measuring, tearing down, and re assembly and you’ll get to where you want I think. With Jim’s fabulous selection of different thickness head and base gaskets you can really adjust to suit.
Do an initial assembly and measure the Combustion Chamber Volume and start from there. It might not be as high as you think.

Often the CR will be lower and than stated as the valves may be cut lower, material may have been removed to blend in new seats, etc, etc. A lot can happen to a head in 50-60 years!

I juggled around a lot with my 920 build, but I was juggling getting a tight squish and a ‘reasonable’ CR. Jim’s gaskets were a life saver.

FWIW I ended up at under 0.040” squish and 11:1 CR. This was a higher CR than I wanted but it runs perfectly fine on the Super Unleaded we get here in the U.K.

Click to expand...

Yeah, the "drop in" concept is a lot of work.

In theory it should all fit together with the base gasket and head gasket I'm going to use, and the depth measurement at the squish band, but I did plan on some mockup. It'll be tight. Compression may end up in the high 9's. I could have a lot of work ahead. I could second guess my decision all day long on the high CR pistons. Would have been like assembling a motor with Velcro fasteners if I'd used the standard flat tops.

Jim has been very supportive. He supplies plenty of information to get the job done, and answers my goofy questions. Really a great man for putting up with my BS.

Schwany said:

Yeah, the "drop in" concept is a lot of work.

In theory it should all fit together with the base gasket and head gasket I'm going to use, and the depth measurement at the squish band, but I did plan on some mockup. It'll be tight. Compression may end up in the high 9's. I could have a lot of work ahead. I could second guess my decision all day long on the high CR pistons. Would have been like assembling a motor with Velcro fasteners if I'd used the standard flat tops.

Jim has been very supportive. He supplies plenty of information to get the job done, and answers my goofy questions. Really a great man for putting up with my BS.

Click to expand...

My guess would be that if you run a tight squish you’ll be around 10:1. With the hot cam I’d say you’ll be fine with that, provided you have access to decent octane fuel.

Fast Eddie said:

My guess would be that if you run a tight squish you’ll be around 10:1. With the hot cam I’d say you’ll be fine with that, provided you have access to decent octane fuel.

Click to expand...

Hope I don't have to run 50% race gas. That stuff is pricey.

Pump fuel here is 92 octane. BS starts here: The Trispark runs a non-aggressive timing curve, so I could get lucky and be good with pump gas. If I install the cam straight up it might be pump gas friendly as well. I could also use a completely stock Commando head I have if required. It has a stock squish band. My head is a little thinner at the squish, but the flat top Commando pistons stood close to .040 proud of the barrels and worked. Jim says the high CRs are .050 above. I will be using a .040 copper head gasket, and a .021 copper base gasket. Both of those gasket were thinner with the Commando flat tops and the head I'm going to reuse. Gonna be interesting for sure.

Barrels are in machinist jail. The machinist I was referred to by a member here makes me nervous. Fingers crossed.

I think that your 92 is equivalent to between our 96 and 97.

Super unleaded here varies from 97 to 99.

’Standard’ fuel here is 95.

So you’re on the bottom end of what we would recognise as Super.

The JS2 cam is a fair bit of cam, but it sounds like you have done the research. Building a performance commando engine is like being married, lots of frustration combined with moments of pure joy. Like Fast Eddie said, be prepared to assemble and disassemble a few times. I had a laugh at the memory thing, i have just pulled my head back off because i couldn't remember if i torqued the through bolts down HAHA.

One of the best things I did was get my mate with a lathe to turn some slightly undersized and longer dummy rocker spindles. They‘re a nice sliding fit, and have knurled ends, it makes inserting and removing a breeze. Worth their weight in gold when pissing around with squish / compression / valve to pistons clearance / striking angles / etc, etc…

outawack said:

The JS2 cam is a fair bit of cam, but it sounds like you have done the research. Building a performance commando engine is like being married, lots of frustration combined with moments of pure joy. Like Fast Eddie said, be prepared to assemble and disassemble a few times. I had a laugh at the memory thing, i have just pulled my head back off because i couldn't remember if i torqued the through bolts down HAHA.

Click to expand...

I've done some really poor things resulting in expense to motorcycle engines due to memory brain farts. I'm moving so slow on this one I don't think I'll miss anything. I'm also digging into the old AMC gearbox past the outer cover for the first time. That should slow me to a crawl.

My motor and brain should get along with the JS2 cam. Jim compares the JS2 to the PW3 and 2S. I think I'll get a little more grunt I can make use of with JS2 than what I had with the 2S. Hope to know in a couple of months or sooner if I can get my mojo working.

Searched for discussion related specifically to the JS2 cam performance in a small displacement Norton motor and did not find anything other than the somewhat exaggerated praise in the Sunburst revival threads. It can make people very happy apparently.

Schwany said:

I'm also digging into the old AMC gearbox past the outer cover for the first time. That should slow me to a crawl.

Click to expand...

The next best thing to getting Mick Hemming's video (which helped me enormously) is reading the cheat sheet


The video

Minor progress.

Holier than though or lighter than stock. I'm leaving some patina. Not sending anything to the blasters or doing any blasting of my own.



Rods


P11 Atlas case timing side modified for a Commando timing cover.

Schwany said:

P11 Atlas case timing side modified for a Commando timing cover.

Click to expand...

Interesting. Which Commando timing cover are you fitting, and which modifications are involved?

Cheers, Knut

The cases were modified 30 years ago to provide clearance for the 2S cam lift, and I also wanted to put the Lucas K2 magneto in a box and run dual point ignition. The P11 timing cover had a little hole in it for a tach drive off the end of the cam in the timing cover. No housing space for AAU and points plate. Only way to use Commando dual points at the time was with a Commando timing cover. Not sure what year Commando the timing cover came off of. An Early model most likely. Could have been a 72 Combat. Believe me what was done all works.

Without an Atlas timing side case I can't be sure exactly what was done to the timing side other than add the support for wiring through the case and into the points housing. I think the intermediate shaft boss was cut down closer to the case. I also think a small hole for a tab off of a cam thrust washer shown below was added so the cam could be shimmed on the timing chain case side since there is no timed breather spring at the other end pushing the cam against the bush on the inside of the case. Yes, the top layer is cracked on the tab. It's not cracked in the lower two layers. I tried to bend it a little more and that is when it cracked. Did not go get another one. I was young and in a big hurry. Hasn't busted yet.



I added a hole above and left of the intermediate gear shaft to get more pressure out of the crank case. The 2S cam does not provide support for a timed breather. My cNw breather is attached to a cover plate over the magneto hole in the timing case. I could move the breather to the location used on Combat cases, but probably won't. It works well enough where it is. Edit: The JS2 cam does support a timed breather setup. I'm not going to install the piece and plumb it. Apparently does not provide any benefit if the cNw breather is already in use.

I may have drilled this hole as well. I know I cleaned up the radius a little with a Dremel yesterday.



By the way, anyone else nuts enough to ruin a perfectly good P11 motor would need to clearance the cases for the JS2 cam as well. It actually has a taller set of lobs than the 2S. Although the JS2 uses radiused lifters, so it may not have more lift.

I did not proofread the above. It may not make any sense.

Nice upgrade. What will you be running for a clutch? Planning for any improvement in that area?

Fast Eddie said:

And why ?

Click to expand...

This explains the breathing issue for the 2S. https://andover-norton.co.uk/en/sicombatcrankcase/

I actually built the P11 back then (1990's) to chase modern motorcycles from Alice's Restaurant on Skyline out to the coast in California. You have to know where that is. It was a popular gathering spot. I thought I could save some money by making the P11 sort of quick for the twisties. Didn't turn out that way. I ended up with 5 modern bikes in the garage and the P11 parked in the corner. Now of course it's kind of cool, cuz I don't have the testosterone level I had back then and hauling ass on the street is not that intelligent.