Crankcase crack.

Drive side crankcase crack, discovered this yesterday. Having done a search it turns out this is a common problem. The crack runs from 10 o'clock on the drive side inner chain and crankcase joint for about an inch in the direction of the cam shaft. Explains why I thought the drive side crank seal had failed. The bike (Mk3 Commando) is used on the road, apart from a recent track day at Cadwell, and does get revved a bit, I'd noticed the oil mist prior to Cadwell. Crankcases are Andover Norton bought brand new 6 years ago and now with 34,000 miles on them - crap or what. Ordered some proper ones from Mr Maney.

Uhg Al-, sorry to read your set back but glad to read your enjoying it to destruction. Do note the thicker Maney ds case needs the primary chain/belt case milled open to fit back on and a special adapter to mount alternator stator. I've a spare Maney Alternator mount I'll never use so offer it for mailing, though could leave case off for exposed belt drive and handful of lbs lighter rawness.

Al-otment said:

Drive side crankcase crack, discovered this yesterday. Having done a search it turns out this is a common problem. The crack runs from 10 o'clock on the drive side inner chain and crankcase joint for about an inch in the direction of the cam shaft. Explains why I thought the drive side crank seal had failed. The bike (Mk3 Commando) is used on the road, apart from a recent track day at Cadwell, and does get revved a bit, I'd noticed the oil mist prior to Cadwell. Crankcases are Andover Norton bought brand new 6 years ago and now with 34,000 miles on them - crap or what. Ordered some proper ones from Mr Maney.

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Maney cases are surely stronger than either original cases or Andover Norton ones, I have a pair, but I am pretty sure the Andover Norton ones are not crap, the cracking you describe was more typical of MKIIa cases back in nthe day......the basic MKIII was stronger than those (I ran a set in a race bike for 4 seasons no problem) and the Andover Norton ones should be better again.....if not quite up to the Maney cases...which are really a little over engineered for road use...though you will need to have some of the inherent drive side 'strength' machined away to fit your primary cases.....I am sure Steve has been through your options on that with you.....I am not criticising your choice as a replacement.....but........plenty of road engines are built in Andover Norton cases.

Two of the most respected Norton people in the UK (Norman White and Mick Hemmings) build race bikes and don't use Maney cases, so maybe you need to look a little deeper than a weakness in the cases themselves for the reasons yours developed a crack....what crank, pistons, rods and balance factor you have in them will have an impact for sure...but the biggest destructive forces are not necessarily caused by 'revving it a bit'.....more like using lots of roll on from low to mid range revs, which creates more destructive crank whip than high revs, by which I am assuming you mean up to 7000....it was this crankshaft whip that led to Combat and 850 main bearings failures and the 'superblend' saga.....

This means that how you ride may indeed have an effect on the longevity, but maybe not due to what you think.....the 34000 miles of loaded up touring and daily use could have inflicted more damage than the track day.

You will have invested a decent amount of cash in your Maney cases, making sure everything else you put in the engine is set up properly will help your cause in avoiding future expense.

T'wertn't the crank whip or plain rollers per say that did in Combat cases as much as poor manufacturing errors and mis firing ignition stability that got corrected. Maney cases weigh a handful of lbs more that others too. Hi rpm crank sling is more stressing on cases than clutch drop dragster launches which can develop cracks in the sharp corners of the mounting bolt flat bosses, which can be ground out, filled back in then ground with radius and cases beaten back to seal again. Cyrogenic tempering is said to help compact Al alloy denser though can't have any other non Al parts left in to treat or thermal distortion may damage stuff. NZ offers a billet set of cases too.

Thanks for the advice/offers Hobot and Steve A. I'll double check with Steve Maney that the Mk3 chaincase will go straight on - I don't really want to get involved in anything other than a 'standard' rebuild as I've got holidays booked, and limited cash, but will do what is required and will definitely investigate the cause of the failure. These cases (Mk3's) were a replacement for the originals (115,000 milers) when a 15,000 mile old conrod bolt let go at about 5,000rpm in 2008 - genuine Andover Norton purchased 2006 with conrods. That caused loads of damage. Now wish I'd spent the extra and got the Maney cases. What's the life expectancy of standard cranks on a road bike? Engines in standard tune except PW3 camshaft, Thunder engineering 7075 T6 alloy rods, standard balance factor.
Thanks for your help, hopefully there's no internal damage (me and the bike!).

This is exactly what happened to my Mk 2a D.S case (9 o'clock crack) I've also bought a set of Mr Maneys finest. For extra strength I got the race style D.S. case & will modify the primary to suit. There is no way these monsters will break.
Martyn.

My crank case cracked at the main seal area, the weakest part, but when I was young and silly in the head I was doing a lot of burnouts on my Norton, a expensive lesson indeed, but now older and wiser, I still ride my Norton hard but no stress from burnouts, but my motor has been balanced to 72% for the Featherbed frame which helped run smoother.

Ashley

StevA,

"...but the biggest destructive forces are not necessarily caused by 'revving it a bit'.....more like using lots of roll on from low to mid range revs, which creates more destructive crank whip than high revs, by which I am assuming you mean up to 7000....it was this crankshaft whip that led to Combat and 850 main bearings failures and the 'superblend' saga.....

This means that how you ride may indeed have an effect on the longevity, but maybe not due to what you think.....the 34000 miles of loaded up touring and daily use could have inflicted more damage than the track day."


Help me understand here... you're statement above suggest you believe that the forces exerted on the crankshaft, enough to cause it to deflect appreciably, are GREATER at low revs by virtue of combustion chamber pressures generated by aggressive throttle usage.... greater than the centrifugal forces at high revs? :idea:

when a 15,000 mile old conrod bolt let go at about 5,000rpm in 2008 - genuine Andover Norton purchased 2006 with conrods. That caused loads of damage

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Got me worried now, not the same annual mileage as you but 30,000 on those same reproduction Andover rods and bolts from Dec 2002, and bought from Les E. Perhaps HIS bolts are the ones to go for now they werent back in 98 when one of his plain wrappered bolts was fitted and went 3000 miles later resulting in major damage as yours.

Keith1069 said:

when a 15,000 mile old conrod bolt let go at about 5,000rpm in 2008 - genuine Andover Norton purchased 2006 with conrods. That caused loads of damage

Click to expand...

Got me worried now, not the same annual mileage as you but 30,000 on those same reproduction Andover rods and bolts from Dec 2002, and bought from Les E. Perhaps HIS bolts are the ones to go for now they werent back in 98 when one of his plain wrappered bolts was fitted and went 3000 miles later resulting in major damage as yours.

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According to their website AN are aware of problems with con-rod bolts, but claim that the problem ones are pattern. Mine were definitely genuine from a reliable source but looked more like the pattern parts on the AN web site. This was 8 years ago and I think it may have been before Joe Seifert took over so hopefully the current parts give no problems.
I wouldn't even think about buying anything, let alone stressed engine parts from Emery.

The best way to avoid this is to use lightweight pistons - they were designed to reduce vibration and take stress off the cases and crank. If you're running stock heavy pistons and you just bought replacement cases - then the next thing to worry about is the crank. The cranks crack just as often as the cases if not more. Get rid of all that extra stress and have peace of mind.

That's certainly been my experience. Apart from cracked cases I've also broken two cranks. One on my old 650ss broke through the big end journal, only the rod keeping it from destroying the rest of the motor. The other on my 850 when the drive side mainshaft broke off. Steve Maney told me he thought they sometimes had cracks from new, due to the casting technique.
Martyn.

concours said:

StevA,

"...but the biggest destructive forces are not necessarily caused by 'revving it a bit'.....more like using lots of roll on from low to mid range revs, which creates more destructive crank whip than high revs, by which I am assuming you mean up to 7000....it was this crankshaft whip that led to Combat and 850 main bearings failures and the 'superblend' saga.....

This means that how you ride may indeed have an effect on the longevity, but maybe not due to what you think.....the 34000 miles of loaded up touring and daily use could have inflicted more damage than the track day."


Help me understand here... you're statement above suggest you believe that the forces exerted on the crankshaft, enough to cause it to deflect appreciably, are GREATER at low revs by virtue of combustion chamber pressures generated by aggressive throttle usage.... greater than the centrifugal forces at high revs? :idea:

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Not exactly, what I am saying is that occasional use of 7000rpm is less likely to have the accumulative stress effect of habitual roll on from low revs with heavy loads.....you get plenty of vibes at low revs, sure there is interaction with isolastics going on here...but you bet it stresses something...

A lot of cracked cases are road bikes...you simply can't use 7000 all day on a road bike...not least your body will complain...a race bike will spend pretty much all of its life over 4000, very few road bikes are used like that.....

I am saying that I don't think everything was fine and then one track day caused all the damage.....

This is what happens when you straighten the frame on a Commando - you over-stress the crankcases :twisted:

jseng1 said:

The best way to avoid this is to use lightweight pistons - they were designed to reduce vibration and take stress off the cases and crank. If you're running stock heavy pistons and you just bought replacement cases - then the next thing to worry about is the crank. The cranks crack just as often as the cases if not more. Get rid of all that extra stress and have peace of mind.

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A modified Steve Maney crank will be going in - standard timing and drive side cheeks fitted to steel flywheel, big end journals have been aligned to ensure the pistons go up and down together. Apparently the standard cast iron flywheel can crack and fall to bits as well as cracks forming on the journal radii if not ground properly........shit!

$$$$$$ :shock:

worntorn said:

$$$$$$ :shock:

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What's cheaper - cases and a crank - or lightweight pistons & longer rods?

I agree reducing reciprocating weight will help to reduce loads on the crank and cases but by how much on what is effectively an 828cc single? Original cases lasted 115,000 miles before a replacement rod bolt broke, replacement cases failed at 34,000 miles. I think these cases would have failed no matter what rod/piston combination was fitted. Actually forget the 828cc single analogy - as it's a 360 deg. twin the reciprocating forces are surely still considerable even with reduction of reciprocating weight.

Al-otment said:

A modified Steve Maney crank will be going in - standard timing and drive side cheeks fitted to steel flywheel, big end journals have been aligned to ensure the pistons go up and down together. Apparently the standard cast iron flywheel can crack and fall to bits as well as cracks forming on the journal radii if not ground properly........shit!

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Does Steve sell the flywheels separately?
I have a pair of freshly ground and magnafluxed 850 cheeks waiting for just such a thing

I don't know, give him a call.