Combat fixes

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Hey Worntorn,
When I rebiult my Combat, after an internal failure, I did the 'common modifications', plus as the
Cam was damaged, I replaced it with the Norton 4s which is a great old cam.
Because of the added compression due to the rebore, I removed .020" from the top of the pistons, as
recommended by a well respected member here, just for my own peace of mind.
I run a 22th front sprocket, which is still OK with high bars and the wife on the back.
A good cruising speed of 60mph @ about 3,400 revs or 70mph @ about 4,000.
Because a Combat is ' under ' the Cam, it doesn't mean it has no power or torque.
Mine pulls two people easily at 2,500 revs with the high gearing.
However... I would dearly like to have an 850 for my wife pleasing rides, so I could turn the
Combat into a 'selfish, self pleaseing Cafe racer' to nail our country roads for as long as
my old lower back could take it.
AC.
 
Since my bike is a 72 Combat that had sat since 1977 I felt I needed to go into the case to confirm the bearings were superblends.
Actually the barrel shape of the rollers is very subtle so you can't trust your eyes to confirm but I did find that the number of rollers on my bearings was different from the bad bearing so they checked out ok.

I didn't intend to ride the bike to it's Combat potential so I opted to tame her a bit.
With case open I got a new standard cam on E-Bay for $75 and installed. Had cam followers ground.
Under barrel I installed spacer (Old Britts) to bring down compression.
Took off twin Amals and installed new single 34 MM VM Mikuni with manifold that I got new on E-Bay for less than what I got for the set of Amals and manifolds.
Installed Pazon Sure Fire electronic ignition for easy start and to avoid hassle of keeping point system in good fettle.

Bike runs great on gasoline available with no pinging (pinking). Can't imagine needing the Combat power that comes on at higher rpms with its 2S ca.
Starts within three kicks in winter 1-2 summer. 1 kick when hot.
Smooth idle at 1,000 and could go to 600 but want to keep oil flow up and quick reponse on cracking throttle.
 
Leave the big ole stag to live and kill the active dangerous does, that are typical women that can't go to the bathroom w/o company.

Amend to Combats = solo rides, but that's because it can more than hold it on against any made today if ya got balls enough and hard heart enough to keep er in the red zone.

I carry as much cargo as a good woman and though the springs sags its no bother to Combat 2S 10:1 on cheap no lead pump gas. Worse thing for any Norton is short shifting lugging under load, keep the rev's up is best. But quite fine to short shift lug like I do but its on easy lazy throttle "increase" only done for the Harley like sound waves projected behind me, not to speed, then soon as around a bend in 4th/2500 rpm soft putters fading away, I snick down 2 cogs to 2nd and come back on like 5000+ rpm and climbing. Of course there's a hand full of bends, so then handling practice or wits to behave come in. Real lugging is slow rpm that don't respond much to more throttle in current gear.

On pre-Peel Combat on new years eve on eve of Y2K, after 1/2 a yr learning it and counting 14 oil weeps, decided I'd learn to renew the innards and to try and break it. Entered first down hill LH bend bowel laid to peg and held on to get 3rd piston kick in @ 6800 then front lifted till I let go mid red zone to look where going to lay over oppostie in up hill bend in 2nd and didn't have to wait for 3rd piston kick and front lifted again til mid red zone. mid 50's in 1st upper 70's in 2nd on 19T in like two heart beats. Lub Dub Lub Dub. Wow what an antique!
 
rx7171 said:
Since my bike is a 72 Combat that had sat since 1977 I felt I needed to go into the case to confirm the bearings were superblends.
Actually the barrel shape of the rollers is very subtle so you can't trust your eyes to confirm but I did find that the number of rollers on my bearings was different from the bad bearing so they checked out ok.

I didn't intend to ride the bike to it's Combat potential so I opted to tame her a bit.
With case open I got a new standard cam on E-Bay for $75 and installed. Had cam followers ground.
Under barrel I installed spacer (Old Britts) to bring down compression.
Took off twin Amals and installed new single 34 MM VM Mikuni with manifold that I got new on E-Bay for less than what I got for the set of Amals and manifolds.
Installed Pazon Sure Fire electronic ignition for easy start and to avoid hassle of keeping point system in good fettle.

Bike runs great on gasoline available with no pinging (pinking). Can't imagine needing the Combat power that comes on at higher rpms with its 2S ca.
Starts within three kicks in winter 1-2 summer. 1 kick when hot.
Smooth idle at 1,000 and could go to 600 but want to keep oil flow up and quick reponse on cracking throttle.
Click to expand...

Forgot I went to a 21 tooth gearbox sprocket for better cruising use. 52mph at 3,000 rpm in fourth.
Since the oil pickup problem that OldBritts suggest maching the case for is for sustained running of the engine at rpms above 4,500 and I never intend to do so and my motor was in good shape after being treated rougher by previous owner than I ever will I opted to leave it alone. I've done 6,000 mile since I went through engine and no problem.
MikesSX breather for sure or equal. Mike's works great and is cheap.
Clutch rod seal.
Other mods that aren't specific to Combats can be found by looking through lots of threads on this site.
 
Torontonian said:
Hey RennieK ,Hobot not be the only wildlife hitting fishermanny backwoods exploring Nortoneer here. Have Destination Highways Motorcycle Enthusiast's guide to the Best 185 Roads in Southern B.C. in my hand now with notes. Used it for 5 1/2 weeks this summer , never rained on us once too. (not in the book).Salmon river fishing ,Uclulet,Vancouver island etc. Now this is the way to travel.Lunch in Atlanta Ga.in a few hrs. Having sena in Mexico city tomorrow aft. Then hunting down big ones on the pacific coast. Swordfish n' tunas. Yum. Update - Crazy Combat in pieces ,stanchion tubes shot, Paint shot, primary apart to fit R.G.M. kit on spring return .Enjoy.
Click to expand...

Sounds like a blast! It's a great way to enjoy life whether you catch any fish or not. So many roads, so little time...


DogT said:
RennieK said:
The thing I envied about Harley riders was their ability to pack a big mama on the back...
Click to expand...
The thing I like about the Norton is the harder you twist the throttle, the tighter the babe sticks to your back.

Dave (dirty old man)
69S
Click to expand...
They make nice sissy bars don't they : )
Auh, those were the days, such fond mamories
 
rx7171 said:
rx7171 said:
Since my bike is a 72 Combat that had sat since 1977 I felt I needed to go into the case to confirm the bearings were superblends.
Since the oil pickup problem that OldBritts suggest maching the case for is for sustained running of the engine at rpms above 4,500 and I never intend to do so
Click to expand...
Click to expand...

Gooday rx7171

I have a semi-stock 73 750 with combat breather. Running 10:1 with 98 Octane it snorts. I have Combat breather and added 850 breather with larger holes in the timing case, all to a bottle. Have done extended cruising (1600 miles) at 5500 rpm (100miles at 6500rpm) with no ill effect and no oil pickup issues. Bottle is always dry. I wonder what the issue is ?
 
from what the OP asked I would still recommend a slight drop in compression by machining the pistons. if you are traveling around SOME places will not have 92+ octane fuel and IT WILL PING on lesser fuel's. Once again I will say it I DON'T LIKE THE PLATE as it is already a weak joint so why double the chance for trouble!!! Once again the OP wanted to do long distance riding NOT A LOCAL POSER riding around the neighborhood or never going more than50 miles from home. how many on here have done 600+ mile days??? my guess is NOT MANY so I stand by what I recommend from experience at long distance riding!!!!
 
Sheet man, I don't do 600 miles a day in car!

So my question is this...Is a detuned Combat an improvement over a well set up 850?

Russ
 
rvich said:
Sheet man, I don't do 600 miles a day in car!

So my question is this...Is a detuned Combat an improvement over a well set up 850?

Russ
Click to expand...

hobot seems to think so, others may disagree. I have one of each and I would say there is no significant difference. It's all in how you set them up and how good a job you do building them.

It's funny, not long ago you couldn't give a Combat away. Time bombs with short fuses, and a powerband totally unsuited for street use. That was what people thought. Non-Combat 750s were considered ok, but the sought-after model was the kick start 850. The very pinnacle of Commando development. People seemed to think the 1974 850 was better somehow than the 1973 model because it was a year later and presumably better developed. You saw a lot of posters proudly referring to "my Mk2a", meaning their 1974 850. Now, not so much. It's all "72 Combat"! :roll:

Debby, flame suit on! :mrgreen:
 
Windy (bill) - Have to say you are right... I'm more of a local bar to bar rider than a 600 mile/day tourer. I don't like to sit on mine longer than about 150 miles but has more to do with the seat than the Combat engine. I don't like 600 miles in a car either!

Russ
 
batrider said:
I don't like 600 miles in a car either!
Russ
Click to expand...

I agree with that! Too far for me, even in the car. On the motorcycle, maybe 250-300 miles is my limit these days. I prefer my Ducati for the long rides though. Faster, more comfortable, parts don't fall off...

Windy, you must be a tough old bird! I'll probably be dead when I'm your age. :wink:

Debby
 
worntorn said:
Thanks for all the replies

As someone said above, if you detune it enough the 850 is probably a better choice. Sounds like the Combats can be made reliable and left at 10 to one tho, which is encouraging.
I guess for twoup with gear riding, which is close to a 500 pound load with my 160 lb wife, 230 lb me, two sets heavy armoured leathers and luggage, the low and midrange torque of the 850 is better suited to the job. The 850 Mk3 I have now works quite well for this type of riding.
If I find a good deal on a Combat, as sometimes happens here, Ill plan on keeping it as a hooligan bike or for mostly solo riding.

Glen
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That's some good common sense.
I do not believe for a second that my bike was an original Combat, but it sure is now. The cases I had when I bought it were 200155, well before combat. It is the fact that it came with a combat head that got me started, along with the front disk. My unit is as a bitsa as they come but all the bits come together quite well. It is now very fast and very dependable. I take a couple trips to the Leelanau peninsula in the summer. Smooth as silk at 80mph. 160mi. one way but that's enough for me.

I guess the point is that you can make a Combat out of what is not, and you can take the Combat out of what is. To this extent you can tweak and balance these units to your particular needs and wants and never be locked in to one particular aspect. ENJOY!

"It's my bike, I do what I want!"
 
it all depends on what you call an improvement. the 850 with it lower compression will run on most anything they call gasoline and is a litter easier on itself. on my bike it is ONLY detuned with a slight drop in compression and the 21 tooth countershaft sprocket and I still need to watch out for premium fuel, I have mixed 87 octane with a tank and was OK but NOT on the second tank in a row when there was a fuel shortage one summer. I do like the little extra performance when I am in my local haunts ( 489 turns in a 12 mile radius of me ) but if you were to start from scratch I think a well setup 850 would be the better bike only because of today's fuel.

rvich said:
Sheet man, I don't do 600 miles a day in car!

So my question is this...Is a detuned Combat an improvement over a well set up 850?

Russ
Click to expand...
 
AWW come on now I aint that old YET. It is getting harder to go those distances on an old klunker but I still think a 150-200 mile day is just a fun morning's outing. :lol:


debby said:
batrider said:
I don't like 600 miles in a car either!
Russ
Click to expand...

I agree with that! Too far for me, even in the car. On the motorcycle, maybe 250-300 miles is my limit these days. I prefer my Ducati for the long rides though. Faster, more comfortable, parts don't fall off...

Windy, you must be a tough old bird! I'll probably be dead when I'm your age. :wink:

Debby
Click to expand...
 
Wes and I did 450 mile a day to Texas and back, him on low bar '71 and me a factor low bar Combat just fine in upper 30's starting out early. I was pleased I still felt like riding more when we got home. On Ms Peel Combat with tall bars and big tank I could rest on I never wanted to get off and break the bodiless trance of being the bike itself. You can run 87 octane just fine as long as ya remember what ya put in and don't do hard throttle launches and hi gear WOT loaded down climbs is all till refilling for the hooligan stuff.
 
Oh my yes, and you'll still responding to me after Ms Peel's affairs?
DynoD+ here has about worst eye sight of anyone still allowed out w/o a stick or a dog. My college room mate had same condition and made a great caver to pair up with. Dyno has set me back on my seat hard on what it takes and means and reveals in super close examination to see crack in case that haven't really fully made it to surface. My mentor Dr. George Goodheart had a motto - See with eyes that really See. David has alterted my brain wiring to accomadate deeper visual processing. Don't think I never told David this, but changed me for the better like other masters just by his very being. Just try and find someone that can line bore a Combat back to take beyond redline testing and noting bad happened to cam or bushes. Hope you can handle the machining requests now. After the mid night rear bearing swap I'd want you as field combat surgeon on me.

Put the dang Drouin stuff up on site please or I'll pay to send back as need the Lake Injector needle details in an article and scribbled notes. I remember me twitching a bit back at the whirl as you tagged your electric commensor button.
 
bill said:
it all depends on what you call an improvement. the 850 with it lower compression will run on most anything they call gasoline and is a litter easier on itself. on my bike it is ONLY detuned with a slight drop in compression and the 21 tooth countershaft sprocket and I still need to watch out for premium fuel, I have mixed 87 octane with a tank and was OK but NOT on the second tank in a row when there was a fuel shortage one summer. I do like the little extra performance when I am in my local haunts ( 489 turns in a 12 mile radius of me ) but if you were to start from scratch I think a well setup 850 would be the better bike only because of today's fuel.

rvich said:
Sheet man, I don't do 600 miles a day in car!

So my question is this...Is a detuned Combat an improvement over a well set up 850?

Russ
Click to expand...
Click to expand...
The 850 does work well for this kind of riding, especially when fitted with the big tank.

I noticed a difference in my 850 just in changing from a thick copper headgasket to a thinner fire ring gasket. As I recall the thickness dif was. 015 or.020, so the same effect on cr. as shaving the head by that amount. Combined with the. 020 overbore, I calculated this would add about .5 to the cr, so up from 8.5 somewhere close to 9 to one, similar to the earlier 750s, but with some extra oomph from the bigger displacement, good on long Mountain grades.

It still runs on regular without pinging, tho To be safe I use midgrade if available. Regular actually has slightlymore energy in it than the higher grades, something that often gets forgotten in the power equation.
But the more important issue is availability of premium in the boonies, as Bill pointed out.
 
I remind thee the IS tank first came out on a poster that said "Further Faster" or visa versa in '72.

I've bone stock Trixie Combat with fast rise points AAU and often forget I'm a hick in the woods with 87 oct in tank and nail her to about redline as so easy to do on a real Combat but no ping or knock nor evidence on plugs or piston tops of anything but more efficient low octane fuel use. Trix still has 19T sprocket but nullified by the steeps I do in top gear 30-40 mph no sweat just care not to give throttle faster than its eager to take. If I was pressing it on purpose on 87 oct I'd just make sure to keep the rev's >5000 so dang pistons out run the detonation enough to use it up. 2S cam needs 10'ish CR to function as designed d/t its over lap dropping CR below its power band. I didn't find low end response a bother, but a pleasure of torque ease, just not seat pressing power, for that i just snick down a cog or 2 and hang on. But i don't want to rebuild Trixie too soon so don't really press her much like my made for it Ms Peel - long dead by my own hand now.
 
My combat roadster is the only motorcycle I own and ride. The comments about holigan, self centered purpose, etc ...I agree. For "touring" I would choose an 850 with interstate setup and single carb such as VM Mikuni. That said every year I do a 500 mile Sunday covering three mountain passes in the California Sierras (in August). The combat roadster has no problems with this. At elevations above 5000 feet there isn't enough oxygen for the engine to ping and it runs on anything. Sonora Pass is around 9500 ft, Tioga Pass is over 10,000 ft.
 
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