Combat build - first steps

I'm finally making some inroads into a Combat Interstate I acquired in rather lamentable condition last year.

Maybe a contender for 'most improved? We'll see....



It came with an 850 engine installed, but is a '72, so I've tracked down the correct stuff to put it back to how it came out of the factory.

Much as I like the spanglyness of early Commando paintjobs, they don't look right on Interstates, and this one was originally black.
At least it made a refreshing change from the psychedelic trip I was having with the other stuff :shock:

I've made a start on the engine, and the crankcases I found had already had the breather relocated, but the pickup and baffle still needed to be done - The OldBritts article was a great help here, and explained it all
http://www.oldbritts.com/n_c_case.html

Before (note the pencilled in area to be removed):




After (I fettled the casting with the Dremel to get rid of any sharp corners as my milling cutters aren't radiused and I didn't want to introduce any stress raisers):



Note that the original design had the rear scavenge hole blanked with that sodding great big lump of alloy, so milling off the baffle opens up the hole, so to speak
I just need to plug the front oil scavenge hole (Araldite was mentioned, but I think I'll tap it and fit a grub screw), and make a blanking plate for the original breather hole.


So here's the tank - just like a Velocette



After painting this I felt all cheap and dirty, so I did these as well...









The green is the best looking IMHO, but they're all rather captivating... except the black :?

Actually it does look pretty good and suits the big tank very well.

Onwards...

If you can get it done, I would call it a shoe in. I would be an honor to watch this one come to truition.

The green reminds me of the wizard of oz. The Red is awesome.

Yes indeed ...
The green reminds me of the wizard of oz. The Red is awesome.

Fix the black yellow [instead of black gold] tank with a deep mid night purple base so dark its hard tell its purple, toss in some rainbow diffraction flakes and dust in the clear layer with powered gold and I'll take it off your hands. Would pay extra for shadowy hints of magic mushrooms if the light strikes just right.

WOW ... just gorgeous B+ I luv the sparkly tanks looks, but yer green one is super 8) 8) 8)

Thanks for sharing !

Was it not that all the combat engined bikes were 750s?

Yes, but as he mentioned in his post, that's why he's replacing the 850 that a previous owner installed with a proper Combat spec 750.

Ken

About that hot rod Combat engine, its main power poopper is the large sharp bend port CHO head that don't really work until close to red line but smaller port faster velocity head pull hard off idle to beyond red zone with 2S cam even w/o milling head for 10CR. if that matters to ya keeping it true to factory issue. I run around on pure factory Combat and its just fine and fun slow to 120+ if ya hard hearted enough to hold on till it spins that harshly.

What will become of the 850 engine as would make me a nice chopper lugger chugger.

hobot said:

About that hot rod Combat engine, its main power poopper is the large sharp bend port CHO head that don't really work until close to red line but smaller port faster velocity head pull hard off idle to beyond red zone with 2S cam even w/o milling head for 10CR. if that matters to ya keeping it true to factory issue. I run around on pure factory Combat and its just fine and fun slow to 120+ if ya hard hearted enough to hold on till it spins that harshly.

What will become of the 850 engine as would make me a nice chopper lugger chugger.

Click to expand...

My old combat head is basically a paper weight with bad geometry, a broke fin, seat that are cut too wide and guide that will wear out in a couple thousand mile due to the poor geometry.

The RH1 I got over the winter has been modified and only the intake port have been opened up to match the manifold and only about 1/2 to 3/4" in from the surface. There were some RH5's and 6's available but this RH1 was a fraction of the cost and with a little work and some good parts, beehive springs and Comnoz's golden tough, it has became a high performer.
It runs very very well.

My bottom end and midrange is fantastic up to 90mph in 4th and although it keep climbing, I am hunching that the 1 1/2" big bore exhaust may be holding me up a little. My thought are that the Maney exhaust, or the like, would bring it all together. We would then go give Ms Peel a run for her money.

I suspect your lagging after 90 is not d/t too big tubes in head of exhaust as that's when they become more effective but maybe the carb feeding or cam degreeing or ignition timing. Both Combats I tried with CHO heads were as good as other Cdo up to 90 then they come on good cam and pull even hard to 115 before pulls lessens but till pulling when I chicken out d/t engine destruction - not bad handling. I actually don't like the upper power band any more on a un-tammed Cdo as its so easy to zoom in beyond Hinge recovering. I do not give much throttle while leaning some going slow like entering roads or hwy or rear just slides out and a number of times in 60's -80's mph have given it higher throttle to feel rear step out a tire width before I cut back but it did not Hinge in these special places but does program in better safety limits. There's not many areas as over all twisty as here so leaning and powering takes up a good part of any ride to stay below fear induction. My factory Combats were spunky enough to keep up to 125 mph elite sporks bike fun but only did that once last fall to see if it could but its really wearing on engine drive train and pilot nerves, so never intend to again on un-tamed factory insides Commando. In early fall I went ever harsher solo for 20 miles by holding WOT longer and faster than it took to hang with elite joy rides, so really don't consider Combats all that fast or handy, just quiant touring corner cripples that are a delight if not trying to blow them up.

I mainly worry about police tickets as I don't qualify for a driver license so tend to get taken to jail and bike or car impounded, but did get last No DL ticket dismissed May 15th, because I had STATE by the short and curley's so they dropped the ball w/o a witness to proceed. I set judge back in seat telling him I was not pleased with a dismissal and wanted the opportunity to resolve my issues of being compelled to a legal impossibility. Most folks would consider a dismissal a win, but not me, so there's going to be more action on this but me bringing the suite case in my own court like any King of the Road is allowed by international law and treaty. So my outings have a bit more faith factors than most. Leave your DL home on a ride and see how scary fine it feels to be a freeman on the land. Off to leave sound tracks behind, chow.

B+Bogus said:

I'm finally making some inroads into a Combat Interstate I acquired in rather lamentable condition last year.

Maybe a contender for 'most improved? We'll see....

It came with an 850 engine installed, but is a '72, so I've tracked down the correct stuff to put it back to how it came out of the factory.

Click to expand...

I just took a closer look at the picture you posted, and that doesn't look like an 850 engine to me. Picture's not too clear at the base of the cylinder, but it looks to me like a 750 with cylinders painted black.

Ken

lcrken said:

B+Bogus said:

I just took a closer look at the picture you posted, and that doesn't look like an 850 engine to me. Picture's not too clear at the base of the cylinder, but it looks to me like a 750 with cylinders painted black.

Ken

Click to expand...

Click to expand...

Ken,

Definitely an 850 - 3XX series engine number, long outer barrel bolts, big pistons, breather from top of timing case... all the key features
It was so rusty you would be hard pressed to tell the difference.
I'm pondering what to do with the motor - much as Steve would have me slap it in a long hardtail with candy-pearl-flip-flop-shimmer job, I may not bother.
It was actually in OK condition internally, just a -.010" crank grind and +.020 bore and piston job.

I take it as proof that it must originally have been a Combat as it needed a engine change :mrgreen:

I'll get more photos up later - including the IOM TT ferry 'tank pumped out' stickers from the late '70s.

Andy, Keep them picture's comming, you know we all like proggress in HD.

much as Steve would have me slap it in a long hardtail with candy-pearl-flip-flop-shimmer job,...

Aw Andy you know how to make me melt into a puddle of colorful chopper lust. I've come across the thermal color change paints so will apply to Peel's OIF to see the temps reveal stuff under the top color. Lavender on top and electric blue under?

[quote="B+Bogus]
Ken,

Definitely an 850 - 3XX series engine number, long outer barrel bolts, big pistons, breather from top of timing case... all the key features
It was so rusty you would be hard pressed to tell the difference.
[/quote]

Thanks B+. I thought I saw nuts on studs at the base, but must have been wrong. Will be interesting to see the final product. We all like to see one saved from the scrap heap.

Ken

Great paint , like the underlying mushroom in the right light idea Steve. Steve,tell us (perhaps a new thread ?) about the court case re: formal permission from a constituted authority to do a specific thing , as to drive a motorbike. Every new barn find seems to be a bit more rusty, no ?

The removal of the weir at the bottom of the crankcase (old Britts mod) is not considered a good idea by some because it allows large chunks to be sucked up by the pump. (More than normal!) A series of small holes as done by DynoDave and Windy among others is an alternate method. Maybe a stainless screen JB-Welded over the trough would be a good way to provide some coarse filtering now that you've gone and hogged it out.

batrider said:

The removal of the weir at the bottom of the crankcase (old Britts mod) is not considered a good idea by some because it allows large chunks to be sucked up by the pump. (More than normal!) A series of small holes as done by DynoDave and Windy among others is an alternate method. Maybe a stainless screen JB-Welded over the trough would be a good way to provide some coarse filtering now that you've gone and hogged it out.

Click to expand...

Even better would be to make sure you don't have any large chunks of stuff in the crankcase to start with :lol:

Ken

The sharp edges will wipe oil better

It's certainly food for thought, but to be honest, the original setup was fit for purpose (apart from the location), and all the usual debris will get collected by the spin-on filter in the return line, so the only component arguably at risk is the oil pump.
Agree with the sentiment about keeping the large chunks at bay... 'the pump failed because it sucked in a big-end bolt and half a piston' kind of scenario :lol:
I'll be sticking a magnetic sump plug in, just to show willing

Thinking about it, running a series of holes (I'm assuming along the length of the gallery?) may still result in cavitation and potential loss of scavenge, so now I've over-thought it I'm going to have a lie down :roll:

I did this mod on my '72 combat in 1998 during it's restoration - started at 20,470 miles, now over 52,000 miles. In retrospect I would not do it as it really didn't have any noticable gain. Still no bad affects either.