Advice on common sense engine modifications

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Hi All,

I have read thread after thread until my eyes have bled... The Big Valve Head thread, for instance, was very good, but I think it would be helpful if we could to get everyone's opinion in one thread, if possible. I would like to respectfully ask that people don't respond to each other's post. I am trying to make this a thread that has opinion's from those with experience and knowledge without getting into arguments, debate, etc. So, as an example, if Comnoz states that he thinks opening up the intake valve is one of the first things he would do, I would appreciate it if someone didn't criticize or add their own opinion to his choice. Just state your own opinions. Short and sweet!

I am looking for each person's idea on what would be common sense, best bang for the buck, modifications. Not trying to wring every last horsepower out of the engine. Just want to have more of what the Commando engine already gives us...

The type of riding I do is a combination, like most of us. Lots of country roads, twisties, mountains roads, some city street riding, etc. I like to ride fast and hard sometimes, but other times, just like to cruise along at moderate speed. But, boy how I love to feel the Commando come out of a corner and feel that wonderful torque!

I am hoping to keep the power band pretty much where it is, but adding more low and mid range torque. However, it would also be nice to have a bit more top end, and not have to worry about hurting the engine. Reliability is extremely important! Again, this is not about building a top of the line, high strung, screamer. It's about using common sense to get the most bang for the buck. I think there are a lot of us who would never be able to get all the potential out of a highly tuned commando engine. I know that is subjective, but that's what I hope to find out. For budget, let's just say a couple of thousand dollars. $2k - $5k tops.

So, given the above parameters, what are your suggestions?

First off, what year/engine would you use as a base? Head work? If so, what? New head? Pistons? Rods? Cams? What carburetors? Do you think it's possible to get by with a single carb? Increase compression ration? If so, how? Milling or gaskets, or combinations? Anything you want to add would be greatly appreciated.

Again, this is just each person's opinions. Please try to refrain from critiquing each other's choices. That just derails the thread. Feel free to post more than once if you come up with additional ideas.

Finally thanks so much to those of you who contribute your knowledge and experience to make this such a great forum!

Chris

P.S. I am just a dumb farmer from Ohio, so if you could keep that in mind when you respond, it would be much appreciated! :roll:
 
Well this one should run and run!

It might help if you clarify your starting point, meaning, which version of Commando: 750, Combat, 850 etc.

He's my starter (but I am new to these bikes):

First thing is to ensure you're not running with the restrictive black caps etc.

If you want to keep the power band pretty much as it is, then, unless your cam and followers are US, I would keep them standard.

If its an 850, I would suggest checking and raising the CR (to what, depends on where you live and what kind of fuel you can easily get).

Ensuring the ignition is good is also important (Tri-spark, Pazon, etc).

If you've got the head off, and it needs new valves etc, then as Mr Comstock has already demonstrated, bigger valves will help keep the power band where it is, but give a little more everywhere.

So, my order of attack would be: exhausts, compression, ignition, head job.
 
I'll not get into specifics...others are more qualified than I am. In general and in order:

1) more cc's....bore as far out as you are comfortable

2) up the compression without getting into fuel octane augmentation

3) a hotter cam without getting too extreme and losing tractability. Head work to include larger valves. Of course you will need adequate carburation to match.

4) very important.....a hot ignition system

5) port, polish, match comb chamber volume, balance.

6) if your budget is not yet broken, high rev mods such as light weight valve train.

Slick
 
Just want to have more of what the Commando engine already gives us...

I am hoping to keep the power band pretty much where it is, but adding more low and mid range torque.

More cubes, higher compression.

Not hot cams or bigger valves, this adds power to the top end and you lose at the bottom.
 
Here's mine:

1.) Crankcase breather
2.) Electronic ignition with idle stabilization
3.) Coil to match the ignition
4.) Updated Charging and regulation system
5.) Rock Solid wiring harness
6.) Good Tires!
7.) Good brakes!
8.) If my budget allowed I would be looking at a Fullauto head or talking to Comnoz about air flow on my existing head. I'd be looking for an RH10 if I had an 850.
9.) Amal Premier Carbs (yeah OK so I am a bit of a traditionalist!)

A lot of what makes a bike feel good to ride isn't about engine mods. It stuff like making sure your joints all seal properly so it isn't leaking oil. Or that the fork tubes and wheels are all properly aligned. Are the shocks matched to the weight of the rider and the kind of riding. I would place as much or more emphasis on technique as I would which parts to select.

Russ
 
1. What ever power the engine generates you want to make sure it's getting to the back wheel with minimum resistance. So alignment of frame inc. wheels, output shafts (crank and gearbox), primary drive sprockets, final drive sprockets. Sprockets and chain in good condition. Brake calipers mounted square and equal to disc. (no dragging)

2. PW3 camshaft. Pushrods correct length to get the rockers hitting the valves central. Ditto shimming of rockers on shafts.

3. Top quality rebore and rings. i.e no more than 0.0002" ovality on bore after plateau honing.

4. Valve seats with 3 angle cut and in good condition. No pocketing. 100% contact between valves and seats.

5. KibbleWhite valves and guides.

6. Twin Amals, K&N air filter. Preferably with velocity stacks.

7. Electronic ignition.

8. Inlet and exhaust crankcase breather.

9. No leaks between head and barrel. Or anywhere for that matter.

10. Peashooter exhausts. Single pipes.

11. 21t gearbox sprocket. Gives 80 - 90mph cruising and good acceleration on 850Mk3.

12. 19" WM4 rims (2.5") Avon RoadRiders 100/90 front and rear.

13. Koni's rear. Compression and rebound bump stop mods to Roadholders. 5w fork oil.

14. Rearsets, European/low 'bars.

That's about it I think. Makes me smile :D .
 
1 A good RH 10 head job as per Comstock recommendation, no need to go to bigger valves if the budget doesn't allow, and even then for a road bike, only the inlet valve.
2 If rings and bore and all crank and rod bearings are good, fill in the timing side crank case oil path holes, drill relief hole under oil pump,
then fit a reed valve style crank case breather. If you need rings and pistons and a rebore, I have JS Motorsport bits in my race motor, very smooth due to the ligt weight gear and longer rods.
3 Pazon or similar ignition.
4 Check geometry of valve gear and align all.
5 If using Amal Premier carbs and standard manifolds, blend and align all the way to the head, lengthen inlet tract if able to.
If using flat slide PWK or similar, blend and align cast manifold as above. Dont polish, the inlet tract.
6 JS Motorsport Stage 1 or PW3 cam or equivalent ( my Roadster has a standard cam)

7 Run on the dyno to tune, if running peashooters and have several sets , do the dyno tests with the different mufflers as I found I had a hug midrange loss / gain depending on what mufflers I used
8 Standard Commando headers.
Also note you can kill the power using the wrong air filters as I just found on my Roadster, I had a 5 HP gain by going to larger filters

Base motor, I like my 850's Race bike produces 65 BHP with 2 x 32 mm Amal Premiers (inlet tract not yet extended) with a K&N airfilter
Road bike is stock std motor although I run 2 x 32 mm JS PWK flatslides and have 45 BHP with UNI filters
The rest is up to you, electrical upgrades, headsteadies etc, my list is for the motor only Norton 850's have stacks of midrange, just enhance it
Regards Mike
 
There are a lot more guys on this forum better experienced than myself to advise you. However if I was building a bike for the street, I'd use the 850 engine and I'd never enlarge the inlet ports or valves. I'd make sure the valve seats were cut and throated, and the valves seated correctly by using the three cutters. I'd use a two into one pipe with a nonrestrictive final section, then find a good mid-range cam and adjust the timings to suit the pipe. Your local noise regulations need to be kept in mind. A two into one pipe is usually quieter unless you start seeking more go by adjusting the cam timing. I'd use Mk2 Amal carbs, and a range of Mikuni needles to suit and then concentrate on getting the tuning correct right over the whole range of throttle openings. I'd also buy a decent ignition system. I would not raise the compression ratio unless you have a high grade of fuel readily available.
The problem with the two into one pipe is appearance and convenience. If you run it down the side of the bike, it will burn you. If you run it under, it will probably foul the stand. On a classic bike, they obviously look wrong. However they work well - getting the system to be quiet and still deliver the max torque is a problem, however there should be enough for your purposes without advancing the cam too much.
The question which needs to be asked of this forum is which standard cam gives the best mid-range with non-restrictive two into one exhaust pipe.
 
Thanks for the responses guys, keep 'em coming.

I appreciate the input about wheel alignment, suspension, brakes, tires, sprockets, etc. For our purposes here, let's assume all of those items have been addressed. Only concerned about the engine at this point.

And yes, for better or worse, I want more of a good thing...
 
Why not keep the Norton for what it is and love it. Take the 5k and look for a used, large engine Ducati. They're dirt cheap. Just a thought.
 
Norton engines except for the early Combats *before the manufacture faults found and corrected* were wining endurance races so there ain't much to do to them but make sure parts are correct items and fit and assembled well. All the rest of the suggestions are for extra performance or slightly lower threshold of isolation onset, which is nice but rather low on list of things to do spend on a Commando. Could trim cast iron flywheel down for better response and less chance of fracture, which has happened to a small hand full of owners that were ***not racing*** them wildly prior or at the time of failure. Worth while to grind the very ends of rockers off to allow push rod to slip in/out w/ a hassle but does little to easy vale train loads or rpm limits. A touch up on ports and the valve seats as Alan mentioned would add a bit of peep for cheap. Bigger valves are said to add more spunk from idle upward and not that costly to do. Removing base gasket crush down and loss of clamp force and leaks is common and bumps CR up some, then diddle the push rods to center rocker on valve stems, which is cheap but time expensive. Polish chamber and piston crowns for better heat reflection and less carbon collection. Could drill out pistons some like Jim Schimdt does for bit better response and sooner isolation rpm.
I'd sure think about cryogenic tempering on know wear areas cam/liters and rings and barrel. Tiddy up oil pump wear is no cost way to maybe get less wet sump w/o anti-sump valve but even crappy pumps flow enough to go as long as any non-Raced C'do. Diddle pressure bypass valve to get decent oil pressure on the fly but not so much it blows seals on cold starts. Might open cam oil feed holes and scroll or dual bush cam bushes for a bit of piece or mind there. Crankshaft dynamic balanced is long known pleasing procedure to spend a few $100 on. Points systems AAU's are not made any more and wear out so w/o rebuidling or finding a few good AAU, must shop for electronic ign. kit for another couple $100. Could paint barrel in GunKote or similar for better heat flow if that matters in non-Racer. There are fuel flow mods to Amals if ya find can't hold WOT w/o running bowls down.
 
Lots of good responses here. Your self deprecating comment referring to "I'm just a dumb farmer" does not compute for me however, seeing as how my brother-in-law farmer who never went to college has two new airplanes (a Cirrus and a Maule) with fully equipped and heated hanger, well over $1M in John Deere equipment, and has used software for crop management well before I even owned a computer (as an engineer!). It's a noble profession feeding the world and if you inherit a farm, so much the better for you and your family. It's a lot of work and there are a lot of risks as you know, and I salute you for your effort!

I live at close to 5000-ft elevation so I needed more power from my 850 Roadster. I experienced the difference in power at higher altitude from lower altitude when i took a couple trips, from CO to Nebraska and Arizona. I knew I needed to do something to compensate for the less dense air in CO...... riding at lower elevations was very satisfying power wise, but not so much up here. You are closer to sea-level so are lucky in that respect. I've done several mods to my bike and this is my take, others may disagree:

Best mods for power and RELIABILITY at your elevation, including rough cost estimates:

• bump up compression by maybe 0.5 to 1 point, i.e. 9 :1 to 9.5:1, either by new pistons, head shaving or thinner head gasket - anywhere from US$25 to $350 for pistons + $100 for rebore = $450 max. new pistons
• twin carbs, either 32mm or 34 mm; new design Amals or in my case dual 34mm Mikunis...very reliable with multi jet options - $450 for twin Mikunis with adapter manifolds. You can also have your original carbs resleeved (if needed) for a lot less $. But hey, you may not even need new or rebuilt carbs so that would be a big savings.
• 20 tooth countershaft sprocket for rapid acceleration... 19 is too small, 21 too large IMHO :) - $75. See what you have now.
• electronic ignition for sure... no points, reliable spark (I have a Boyer unit, many others out there now) - $300
• mid-range camshaft: see what others recommend. PW3? I have a (supposedly) Axtell grind flat-track profile. The longer duration valve openings reduce the pre-ignition effect of higher compression, thereby allowing the use of gas-pump premium octane with no pinging, even on hot days. Really wakes up the motor at mid-range rpm - $350
• S.S. braid rocker shaft oil supply tubes. The original plastic WILL become brittle with heat and break from vibration over time - $75
• I like the Barnett clutch pak I installed. Eliminated the slipping I was experiencing from oil-splash in the primary chaincase - $250

Total max. estimated cost if you do the teardown / assembly work = approx. $2K for all the above if you do the work (incl. machine shop costs for new pistons if you go that route). That's at the bottom of your allowable expenditure.... not bad. And a LOT less if you don't need new carbs or pistons as mentioned above. You can do this cheaply if you want, especially if your motor is in good shape.

Additional power mods with questionable reliability (IMHO):

• larger inlet valves: expensive, probably requires higher rate valve springs which in turn put more pressure on cam lobes and increase potential cam wear rate
• bigger boost in compression (like I have, 10:1CR or greater). Increased heat at head, every gasket from head gasket to valve cover gaskets tend to leak/seep oil, especially on a hot day and in traffic. You're constantly tightening up every one of those bolts/nuts. I tried an oil cooler, didn't prevent the problem. Not to mention exhaust header pipe threaded collets constantly getting loose and eventually chewing up the exhaust port threads.
• Supercharging: don't even think about it!

Good luck on your choices. These are my comments, and keep in mind I'm not a mechanic or racer, just know what I've done on my bike over 40 years, or have read on these forums.

Bill
 
Here is my two bobbs worth, I have been running this set up for over 33 years now nad is very reliable and the bike performs great, I have just rebuilt the whole bike just over 4 years now so will go from this rebuild, but have been running it this way for most of its life, 850 motor in a Wideline Featherbed frame

Crank sharft balanced at 72%, 40th rebore (Hepilight pistons) with min clearance between the final hone, SS cam grind, still running my orginal valves with new guides, all the ports have been openned up and polished to make the motor breath a lot better, no need for bigger valves in my opinion, shaved head, Jims 32 flatslide carbies (PWKs) and for spark a Joe Hunt maggie.

This motor will criuses around town all day at 40mph in top gear and when you need to screw it on it will get up and go very quickly, the SS cam kicks in just after 4,500 rpms and will run very freely past 7,500 rpm's, but be very carefull you don't over rev it as it will keep going till something lets go, my standard motor only reved to 6,500rpm.

This is the way my motor has been built sinse 1980 when I first converted it to the Featherbed frame and has done well over 130,000 miles with 2 major rebuilds and the 3rd rebuild to replace crack crank cases form doing burnouts in my younger days, this motor is very reliable and has never let me down in 38 years of ownership and 33 years with the hot motor.

I have nothing to prove with this bike but it still surprises a few of the moden bikes on the road with the way it handles and performs, for a old push rod engine it has enough power for my riding style (now 55 years old) but I still push it hard.

Ashley
 
Ashley path sounds great to me, which is bring it up to Combat specs 2S cam and fit a 28.5 port head and configure 10-ish CR to make up for cam and altitude and octane. I too found the 20T sprocket best compromise if wanting to go over 80-90 for a good while on turnpikes yet able to stay longer in lower gears to straff twisties. After a while you get used to blocking out the neck tension and seat pressure so only the nice wrist strain gets noticed. Then ya start shopping ahead for tires. IF up to 5grand on the table get steel flywheel and dyno balance for maybe $7-800, so can run eagerly well into red zone now and then and not risk grenade. In most sane riding bunches a C'do like Ashley's can hold its own and then some rather over the ton when pure hp determines the top speed reached.

To remove mass also costs but the payback forever more is worth it as much or more than engine hop ups. I'm a bad boy example that understands 2S cam exceeds standards after 4500ish but it feels like a 3rd piston kicks in after 6800 as forks extend then front lifts a few inches!! If ya got spare change might install up to 3 stabilizing links so can enjoy smooth red zone lift offs while sideways with all bike/pilot mass on smashed down wide patch out of your mind. Do plan some money for the AMC guts if living it up like that.
 
I'll agree with the $$$, you're not going to get much for that price other than a standard rebuild. Loose some weight somewhere, it will produce more fun and be easier on you and the bike in the long run. See ludwig's 300 pounder.

Dave
 
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