My Norton, and "why do mufflers crack?"...

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delagem

delagem

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Hello,

35 years ago one of my college professors had a Norton Commando; I remember it well. I've wanted one ever since. After many years of looking, and raising my price target each time, I finally found one I liked.

It's a 1972 750 Combat, with 38,000 miles! Not the best day for a ride, but any day that you can ride in February in upstate NY can't be too bad...

My Norton, and "why do mufflers crack?"...
IMG_0977 by michael delage, on Flickr

My Norton, and "why do mufflers crack?"...
IMG_1048 by michael delage, on Flickr

Now the bad news. 60 miles after I got the bike, the right hand muffler cracked. The seller thought these were NOS mufflers, but from my reading the OEM mufflers didn't crack, did they? He did state that these were the 2nd set of mufflers to crack on this bike in the last 1,000 miles.

What's the best fix for this? I really like the peashooter look. The bike did come with another set of "loud" peashooters of unknown manufacture.

My Norton, and "why do mufflers crack?"...
IMG_1050 by michael delage, on Flickr

Michael
 
it is not an uncommon issue. 1 is cheap mufflers as that is a thin area and the cheap ones are thinner there although i had a viking crack there also. 2 is to stiff of rubber mounts at the muffler and or having them in a bind. i also see you have a no no with the anti sump valve in the oil feed line. i would highly recommend getting rid of it before it is to late and cost's you an engine.
 
I also had that problem. I've gone with only one bolt into the muffler and I don't completely tighten the muffler clamp. I think this gives it a chance to shift as needed.
 
Look how the crack has opened up. This most likely means that the muffler was fitted under stress and has been ‘pulled apart’ by a combination of that stress and vibration.

Stress + vibration = fractures!

With old Brit bikes, it pays to try and ensure things are stress free when fitted and tightened up, even if it means doing the job again and juggling things around a bit.

Also, (as Bill said) looking at your picture... I notice what looks like a none return valve on your oil feed pipe. There is huge, almost religious opinion about these, some ‘for’ and some ‘against’!

Yes, they stop or reduce wet sumping, which is nice and convenient. But if they fail, they can (and do) destroy whole engines!

Personally, I would remove it. Even if you are ‘for’ such things, unless you know it’s source and can vouch for it, it could be one of the ‘bad uns’.
 
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There is a specific assembly sequence recommended by the factory engineers after this type of problem surfaced years ago. I have a copy of the bulletin somewhere, but I'm sure someone else around here has it, too. If you follow the procedure and still get cracks, it's the components at fault.
 
no750 said:
i also had cracked mufflers (Wassel,Emgo?) together with frequent loosening of pipe nuts. i welded the mufflers and did this

https://www.accessnorton.com/NortonCommando/exhaust-header-supports.18049/#post-268167

together with a "loose" muffler clamp and high temp silicone like suggested here in the forum.

works!

perhaps making sure the muffler/pipe connection isnt too rigid will do the job alone.
Click to expand...

The lack of rigidity IS the problem! Make sure it's a damn good clamp done up tight and you will not have an issue. It's when you allow things to move around that you have problems.
 
When you want a permanent fix, fabricate some muffler mounts that bolt up to the transmission cradle, so that the entire assembly moves as one unit. No rubber buffers needed after that.
 
That sounds like a great idea. I'd like to see a patent on that that would support long mufflers hanging in the breeze.
 
I was driven to distraction by this problem. The first set of peashooters from Mick Hemmings lasted ten years before cracking. These were the ones with the perforated tube baffle & the Norton logo on the end. The replacements were made by Brituro & looked well made & best of all, had the correct fluted baffle, which sounds fabulous. These lasted for a few thousand miles at best, until they also cracked. The next set I got Brituro to make with thicker walled tube. These also cracked.
Finally some one on this forum suggested leaving the clamps slightly loose. These are still on the bike after quite a few thousand miles, & to date have not cracked.

Martyn.
 
Thank you all for the replies. I fitted the purported "louder" straight-thru pipe that came with the bike. No stress in fitting that one, it slipped straight into place. No issues yet, but not even 100 miles since fitting this. It really isn't that much louder, either. EDIT: I will say that I did like the sound of the quieter pipes better. Can't even describe it, but the closed-throttle deceleration just sounded better.

I spoke with Windy, thank you for answering my many newbie questions! I appreciate any and all advice on this bike. I will pull the anti-sumping valve.

Danno's mention of a bulletin on mounting the mufflers got me to searching. I didn't find the bulletin itself, but Trinorton had retyped it back in 2009. Here it is again for anyone searching, and for my ease of finding it again!

Michael

trinorman said:
This tightening sequence service bulletin might help. Keep in mind it was for the 850's with crossover pipe, but I suppose it may be applicable and help prevent fractures. I'd ignore the part about the lockring tab washers as these are generally not used.

SERVICE RELEASE

CATEGORY OF RELEASE: NATURE OF RELEASE:

Recommended assembly sequence - exhaust system

MODELS AFFECTED: 1973 850c.c. Commando

DISTRIBUTION: Worldwide (General Distribution)

EXPLANATION: Below is an extract of publication NV1300 "Fitting Exhaust System - Assembly Sequence" which is now included with the instructional literature in each new motorcycle case.

In order to eliminate possible stresses introduced into the exhaust system during assembly and fitting, follow the procedure outlined below:-

ACTION:

1. Fit L.H. exhaust pipe complete with lockring, sealing and tab washers. Run up lockring but do not tighten at this stage.

2. Fit L.H. muffler to exhaust pipe, align the mounting pommels and assemble loosely to the L.H. muffler bracket mounting rubbers.

3. Fit R.R. exhaust pipe complete with lockring sealing and tab washers. Run up lockring but do not tighten.

4. Fit R.H. muffler to exhaust pipe, align the mounting pommels and assemble loosely to the R.H. muffler bracket mounting rubbers.

5. Slide both connector sleeves to the centre of the cross tube. Place cross tube in position and slide both connector sleeves outwards to engage with the C~~5t pipe stubs.

6. Slacken off all footpeg support and muffler bracket bolts in the left and right hand aluminium support plate castings - to allow the bracket6 to swivel and adjust to the exhaust pipe/muffler alignment.

7. Tighten up the total exhaust system, commencing at the cylinder head lockrings and cross tube connector sleeves. Do not forget to bend up the lockring tab washers.

8. Finally retighten the muffler bracket/support plate bolts.

NORTON VILLERS CANADA LIMITED
May 1973
Click to expand...
 
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A bit more noodling around. NGK, lol... Anyone recommend a better plug cap?

My Norton, and "why do mufflers crack?"...
IMG_3216 by michael delage, on Flickr

Left (Port? Garboard? Dunno, never had a sideways twin before) plug:

My Norton, and "why do mufflers crack?"...
IMG_3217 by michael delage, on Flickr

Starboard:

My Norton, and "why do mufflers crack?"...
IMG_3218 by michael delage, on Flickr

A bit of good news:

My Norton, and "why do mufflers crack?"...
IMG_3221 by michael delage, on Flickr

And more good news:

My Norton, and "why do mufflers crack?"...
IMG_3222 by michael delage, on Flickr

So, plugs look lean to me, but not terribly so. Wasn't a proper plug chop anyway, just driving down Main Street at 1/4 throttle, into the driveway and then switched off.

Compression seems decent for unknown mileage. 38,000 indicated but must have been rebuilt at some point.

Can anyone suggest how to hold the piston at TDC for a leakdown test? My other bikes (KTM) have a bolt to lock the crank at TDC, or on my Ducatis I can leave them in gear and stand on the brake lever. This didn't work on the Norton.

Michael
 
what main jets are you running? Just a thought, I wonder whether fractured silencer are after market stainless steel?
 
Yoose guys can't stay on thread subject so lets hobot nose in. If not smoking then highly suggest not doing a leak down test but if ya really want to be a fully initiated Nortoneer- to wear badge of proper leak down success, ie: well off TDC under 80-100 PSI, I put a hammer handle in spokes and 5-6 ft lever on rear brake peddle and sill almost broke spoke soon as .3333' off TDC, but still had to open engine completely so though test was a success did not help issue or my mood attall.
 
Plugs don’t look too lean to me.

Personally, I use NGK iridium plugs, others have own preferences.

Nothing wrong with NGK plug caps. They are probably resistor caps, so, are fine with non resistor plugs. If you fit resistor plugs, you need non resistor caps.
 
hobot habits learned the hard way, is loose/slip tight fitting of silencers on header for endurance reasons only, not respectable tensioned fastened rigidly. If using as daily ride then headers/mufflers last about 4-5 rear tire and couple of chain changes. If not daily user or off road rider then firm respectable attachment might last a life time, except for Lords mounts, so next owner can deal with it again.

Ludwig's smug capacity is beyond most of us desires, but still clever straight forward path to create cradle hangers, if smart enough to triangulate/fasten for long term. Just extra complexity/mass to me.

In between life's distractions, and Mz Peel priorities, might fab up a hobot hassle-less hangers to bolt on for factory Commandos forgetaboutit once does it upgrades. Its been done before me but unknown how generally.

Until then reverse cones are a consumable item like chain and brake pads or use Harley logic - make it big, expensive heavy enough to last a good while- ugh.
 
delagem said:
Left (Port? Garboard? Dunno, never had a sideways twin before)
Click to expand...

Left-hand side: Drive side (look where drive chains are), usually abbreviated D/S,
Right-hand side: Timing Side (cam drive and ignition points/pickup), abbreviated (you guessed it) T/S.

...and, don't EVER refer to our sweethearts as a "sideways twin" ever again! They're properly Parallel Twins. That's one of the reasons they sound so great, versus a hyped-up John Deere Model B tractor. You all know what I'm talking about... (run the video up to about 1:29)



Welcome to the gang! There's a phenomenal amount of great knowledge and experience to be found in these pages, and, as you probably already noticed, the simplest query will explode about eight ways from Sunday. 'Makes for great late-night reading.

Nathan
 
Aw man Nater/tatar that is cleaned up version my Uncle Boots had but with a compression release to drop after it made bang combustion. His had the fenders installed so me and late younger brother Dale watched in awe as he controlled the jerky tri-cycle front in deep/soft Florida sand ruts steering with knee while whipping out tobacco Prince Edwards porch rolling a joint like cigarette, licking it sealed then one handed work out a wood match stick to lite it and carry on no problemo feeling each combustion hit on slow rpm HI tongue twin. These tractors were used as much for portable power drives for saw mills and pumps as much as pulling plows or planters, so the wide belt pulleys on the other side used for 20 ft long 6" wide belts too. Very dangerous and heard tales how local chewed up killed in fields. Almost happened to me too on em.

Its equivalent to racer motor sports to stab one brake to pivot on it barely missing fence with the plow or brush hog swinging around in G force need to put hand on fender to stay in seat. Then drop three point hydraulics settling implement back to work to carry on next long boring row till next spike of pilot mania.

Hehe as teen ran Ford 2000 brush hog,some chicken farmers would hand me sub nosed .38 with rat shot to kill Buffo toads on the fly. Alas toads hung out in chicken shit over flows crusted over with grass the tires would break thu to spin coating in slim, no problemo til returning to base at hwy speed the shit would sling out tires landing all over tractor and me, loving the sense of life flavors.
 
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Nater_Potater said:
don't EVER refer to our sweethearts as a "sideways twin" ever again!
Nathan
Click to expand...

Ha! Funny, I suspected that "sideways twin" would be construed as an insult. No insult intended, however.

Interestingly, my Norton sounds a bit like that JD Model B when first started, too; for maybe 30 seconds. The port (D/S?) carburetor tickles very quickly. Guessing it's got a leaky needle, and the bike single-cylinders until the bowl is down to a reasonable level.

I don't know the jetting as of yet, haven't gotten that far into it yet. And while I have done the hammer-thru-the-spokes trick on a magnesium rim, I wouldn't try it on a spoked one. Any other suggestions on holding the engine still for a leakdown?
 
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