Main Bearings

I discovered this forum a while ago and I'm impressed with the depth of knowledge being displayed. Now, after lurking on the sidelines for a while, I figured it's time to join in. I'm back on my '72 Combat Roadster restoration after an embarassingly long time. Like a lot of Combat Commando afficianados, one of my main bearings gave out after a particularly spirited ride. Cracked the case too. And while I am committed to a full, as original as possible restoration, I'm starting with freshening up the "Power Unit". When my motor first went south, I wasn't aware of the deficiency in the stock bearings or the reccommended fix of going with "Superblends". I did buy some main bearings way back when from a Norton dealer (remember them ?!) and I want to make sure that I'm not installing some inferior product. These bearing are still in new condition and bear the manufacturer name "Beck Arnley" and are numbered "MRJA 30". Also on the race are the letters "RHP" and they are roller, not ball, bearings. So my question is, should I install these bearings, or is there something better? Also, sticking with the bottom end, can anyone comment on the difference between Combat cam "2S" & "SS" ? My original is an "SS" but is not in good enough condition to reuse. A brief search for Norton cams online yielded no "SS" cams or remanufactured to original specs. but I did locate a "2S" Combat cam. Thanks in advance for your help !!

Peruse this thread. It's mostly all there. crankcase-superblends-revisited-t6039.html?hilit=superblend

If you are an easy rider, don't need the roller on the timing side, use the ball and you won't have to shim the cases. I used C3, but might use C2 next time.

RGM and Norvil have real good bottom end rebuild kits for a real good price, even with delivery to the US, I got mine from Norvil and specified the C3 which Les didn't like, but he supplied them. I'm sure RGM will do the same but you will have to ask.

Can't speak to the cam.

Dave
69S

Check out what Megacycle has in cam selection. 560nr is a good one.

DanD, my kind of motorcycle and usage.
What cracked in cases?
i had to have Combat cases repaired then reenforced, a booger to get sealing again but did with help of Hylomar and thread embedded.

Might think about a lighter steel flywheel for faster response and less crank whip lash. TS ball is better for hi rpm as allows more crank flex before damage. Only wears a bit faster than a roller version and lot less shimming tear down hassle.

When cases in hand, worth while to correct the oil sump location or suffer the wet sumps just when a Combat starts kicking its heels up on a 2S cam or more. Old Brit's site has the photo instructions.

Valve gear can be spiffed up to tolerate an on cam Combat.

Then it you'll easy get into hinged handling in the hot sweepers.

Steve 'hobot' Shiver
N.W. Arkansas Ozarks,
4 cycles, nothing road worthy, again.

DanD said:

"MRJA 30"

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Two "MRJA 30" (alternatively, NJ 306, NF 306, NJ 306E) were the standard 1972 pre-Superblend roller bearings.

The "Superblend" bearings were 6/MRJA 30 (with the "6" etched on) introduced in late '72, however they were soon replaced by the higher capacity FAG NJ306E.C3 bearings (Norton part 064118)-which are still the recommended replacement main bearings for all Commandos.

http://www.nortonmotors.de/ANIL/Norton% ... s-list.php

I've had good results with a 4S cam, better mid range than 2S but similar top end. RGM can re-grind your existing cam to any spec you like, so if it is only the lobes that are damaged this is a much cheaper option than buying a new one.

DogT, mkane77g, Hobot, L.A.B. Dave M, Thanks very much for your replies. I see from the thread mentioned that this topic has been discussed plenty. Interesting reading. My bearings do not have a # 6 anywhere. So they're pre-superblend.........Don't use? My case cracked on the counterbore face holding the outer race. Forget which side. Visible hairline crack. Probably was "weeping" oil. Also, RGM for cam regrinds? Do you have any contact info?

http://www.rgmmotors.co.uk/main.htm

Dave
69S

The pure flat pre-s-blend-#6 rollers can work fine for a fast long time, as long as not lugged nor over rev'd. Which brings up subject of electric ignition with a rev limiter. Gear up to 20T and maybe the 850 ratio 2nd gear, so you can still zing up to the speeds you like to in each gear or higher w/o brushing so close to over 7K. Both my Combat when opened for other reasons were found to have essentially pristine flat and ball bearings installed. These babies were not pampered bit still ran strong when I got them home.

2S cam sure don't need no more top end and plenty grunt for my lower gear
spins and leaps, so the 4S testimony it adds some mid range is cool. Combat hi CR head seems the main reason some say Combat don't pull so good as standard 750, but kicks in extra piston of power approaching crank whip -valve float - piston parting - case cracking red line. I tried a standard small port head with the 2S cam and had to serious brace 1st before throttle snaps in lower gears.
Lost that nice power response when CHO 32 mm head installed, then only came on same 2S cam torque nearing red line. 4S and bigger cam may work better with CHO head. Can also learn to degree cam to get more out of them.

I know what can be done for the crack case, usually on DS that eventually works to back of case to pop it in half. Just don't know what your up for in the options.
Getting it welded is the easy part, getting bores re-aligned can be an issue.

I'm not sure where the cracked case ever got to. I scored a new set decades ago. Maybe I'll use the bearings I've got. There will be many more opportunities to spend $$ on other stuff. Thanks !!

Not sure it was clarified SS=2S cam.

Russ

I put back stock Combat Trixie's original flat roller and ball bearing on her 3rd bottom end rebuild that had nothing to due with over rev or the bearings.
I'll just not ever run over 6800 but also not lug in pure torque mode where ya feel each piston hit jerking on everything. I think Norton made more '72s than any other so we are in good company of very pleased owners of cream of the Cdo crop.
Even a poor tuned Combat is still a 13 sec 1/4 ET cycle w/o blowing its bearings up.

I've another money draining Commando i'm building for abuse. Trixie is close to recovered, just finish top of engine and accessories surrounding engine.
No end in sight for the my other weirdo addiction, my 1st Combat love affair.

Hi DanD
Welcome to the forum. Once you sort out the Superblend bearings the combat will be reliable. Check out Jim Noll’s website. http://britishbikeconnection.com/
He is in your neck of the woods and might supply some of the parts you may need. Mega Cycle cams are good. Use "New" or resurface the pushrod followers on new or changed out cam. What ever you decide. Once engine is running, keep it above 2500-3000 RPM to maintain oil splash on cam. A good mod is to install an oil filter, as 72 combats never came with them. The International Norton Owners Association is good to be part of with Tech Digest Manual to help you along on other modifications, or here in this forum you will have others to help you spend your money. :mrgreen:
CNN

I did not abuse my brand new Combat at all and the main bearings went at 4700 miles. I think it is false economy to use anything but superblends. These have gone 30K miles since then no problem in my combat.

Who knows why your sane run Combat blew while sales test bike still famous to local hooligans like my pre-Peel - lasted the 30 yr fine till I go her. Hell I drag racer here the first week against wheelie bar bikes getting the jump on em going over red line. Maybe yours way a Monday made bike during a pre-strike Union mood of assembly or sabotage. Both my Combats had over 30K miles, likely more knowing how long intervals of tack failures run. 2nd Combat was from New Orleans owned by a young soldier. Think it got babied? I just lucked out is all with proven good original bearings so no worry to me as long as aware which Commando I'm on, stock factory or very modified.

Have read many reports of Combat bearing failure and find that slow lugging on bearings comes up as having something to do with them fracturing at hi rpm. Combat lug just fine on their innate Norton torque. There is some feed back that two flat roller are more fracture prone than DS flat with TS ball. For my hi rev Peel I put a superblend on DS and 11 ball on TS instead of 9 ball stock version.

Ditto on the Superblends, they must be fitted.

Also while you are in there you need to do this mod if the crankcases are orginal.

http://www.oldbritts.com/n_c_case.html

Hobot - No I didn't lug it either. Would say I rode it like a 21 year old whose bike before that was a Ducati 160 Monza Jr ridden on dirt trails. I didn't over-rev or beat the hell out of it but I did enjoy full throttle acceleration to redline thru the gears at times just like any Norton 750 asks to be ridden. I think it is nearly impossible to resist a handful of throttle on these things even now as a doddering old coot. Isn't that part of the appeal?

Maybe just my preference but as long as the bike is apart I would rather try to make it as right as possible so I don't have to do-over. It is not OK to say that "well, I won't rev it above xxxx RPM" because the next owner -- who maybe could be your son or daughter -- may not feel that way or even know that. I really believe that we are only temporary caretakers. The next guy may have lusted for a Norton 750 after reading the 12.9 sec road tests and want to experience that as he should be able to do. Nothing like it that I have found so far.

Mine did not blow up in a spectacular way -- just made a low pitched growling noise from the bearings. The drive side races looked like the face of the moon. My local dealer was very busy that winter of 72-73 replacing bearings in combats.

Russ

Ok Russ, I love to hear red blooded hoogian use of Combats. What the heck its just dead collection of parts while us soft bodied short lived creatures might as well use up everything around us before we expire. Does sound like classic over rev Combat glee to me. Think you'd feel better or me better remembered for how easy you toured around maturely conservatively or getting the very most out of it? Just more than flat roller crank flex and case fatque could take.

I built 1st Ms Peel to take as high rpm as possible with parts available and lesions learned by desert and drag racers and vendors offered. Combat cases re-enforced at bolt mount faces and dual plates between top of case and rear bolt with 11th clamp bolt added, superblend on DS, 11 ball TS [MAP Cycle] 5 lb lighter steel flywheel and 2:1 ratio belt drive, small port head and bigger single carb. All cryogenic tempered and dry friction coated. It really surprised me and others on the responsive acceleration and essentially relieved me of tach watching concerns. But even above her power was the Insane Handling Hook UP with the rear and front linkage, I did not have to slow up for hardly any turn, just get on tire squeal power going in where everyone else was hard on brakes to flash by them moderns like they were parking lots cones. NO Way will I run an unlinked Commando near what its power allows in fast sweepers, ever AGAIN>
I got bored with normal road racing methods, so I made any turn a fast accelerating decreasing radius one to get the G's I crave. So far have not been able to find limits of sharpness or power like I have on every other bike.

I think the too big Combat head ports are its main down fall, only getting over 100% mixture pack in velocity about when stock crank is starting reach its flex danger zone. Ms Peel stuck throttle showed me the hard way that CHO head + 2S came really came on after 7500 rpm and did not let off till full free rev way over 11,000 the tach could read. I rode it 2000 more miles w/o doing a thing but it ruined her power so had to start over for serious power via torque not rpm to spank the 200 hp bikes at least to 160 mph but likely more in sprints.
I don't expect to ever be able to use WOT till I get a TT tranny.

DogT said:

Peruse this thread. It's mostly all there. crankcase-superblends-revisited-t6039.html?hilit=superblend

If you are an easy rider, don't need the roller on the timing side, use the ball and you won't have to shim the cases. I used C3, but might use C2 next time.

RGM and Norvil have real good bottom end rebuild kits for a real good price, even with delivery to the US, I got mine from Norvil and specified the C3 which Les didn't like, but he supplied them. I'm sure RGM will do the same but you will have to ask.

Can't speak to the cam.

Dave
69S

Click to expand...

I would not use a C2 clearance bearing on a crank shaft. The larger internal clearances (C3, C4) are more tolerant of angular misalignment which Im guessing could be very important in the Norton motor with a relatively flexi crank.... I have seen a crank (KX500) snap because the wrong clearance bearings were used, 6000 series balls that should have been C4 but standard clearance units were used