Crankcase crack.
- Thread starter Al-otment
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Al-otment said:
The lightweight pistons (reciprocating weight) comes out 34% lighter than on a stock 850. Thats a huge difference. Plus the longer rod takes a lot of stress off the motor because the "snap" when the pistons reverse direction is given more time to do so with the longer rods. This is especially important on the exhaust stroke when there is no compression to inhibit the pistons from throwing themselves through the cylinder head. With two identical motors (except for lightweight pistons & longer rods). The short rod/heavy piston motor is going to crack its crank and cases when the lightweight pistons motor is going to keep on running. How long? My guess is at least 34% longer but I'll bet its a lot more than that begause there is a point where things break and then there is a point where the metal is not stressed enough to get to the point of breaking. Or think of it another way - Imagine adding 34% more reciprocating weight and how much sooner your crank and cases would fail - I suspect its exponential stresswise.
stock 850 reciprocating weight = 972 grams (edited corrected specs)
lightweight 850/long rod reciprocating weight = 772 grams (edited corrected specs)
It makes all the difference in the world.
Also note that your stock/replacement rod bolt broke. The high quality (and expensive) CARR rod bolts on the JS - Carrillo bushless rods will last the life of the rod as long as you don't overtorque and stretch them. They don't need replacing.
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Peel's flywheel was last of the racer specials that Ron Fratturelli http://nortoncommando.com/ had left. I ran it in past Peel with just its 2 locating pins and three 3/8" allen bolts. Peel idled fine to 600 and never a hint of stall on let offs as I was warned might happen going that light and tight. Ron knows his Commandos. Its ~4.5 lb lighter and 1/2" smaller OD so emphasis on hi rev response that allowed Peel to out bench race 600's to 1300's inline fours to redline spotting their sluggish inertia an initial 4000 rpm to Peel 2000, they run to 9000-10,000 while holding WOT, Peel would hit almost 8000 before I could get to WOT. You betcha that gave me a big head and gunslinger attitude at any sneering impoliteness toward my obsolete rubber baby buggy. I have the spec numbered graphic sheet as seen in photo but also the CNC 'putor code file that your local water jetter could spit out. I sent this to one builder already but no feedback since. VarrroOOMMMMM, Ah sucks, so so sorry to hear > BLATTT!
Peel's cases were found cracked by Coke bottom glasses Dyno-David Commeau so racers [before accessnorton available] advised me thoroughly on its various models innate weakness, most especially Combats and re enforcements, but left out most of what it might take to make cases seal again, ugh* but cases survived to become a similar engine again. Not much else survived but head and flywheel to become next Ms Peel barn stormer.
Peel's cases were found cracked by Coke bottom glasses Dyno-David Commeau so racers [before accessnorton available] advised me thoroughly on its various models innate weakness, most especially Combats and re enforcements, but left out most of what it might take to make cases seal again, ugh* but cases survived to become a similar engine again. Not much else survived but head and flywheel to become next Ms Peel barn stormer.
B+Bogus
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hobot said:
I had a good long discussion with Steve Maney regarding lighter flywheels, and his take was that it offers advantages throughout, and no real negatives.
He was of the opinion that some mainshaft failures may be due to the flywheel effect loading the crank - as much on deceleration as acceleration.
The whole concept of a flywheel is to store energy, hence any attempt to accelerate/decelerate will be resisted, so it seems pretty intuitive that shedding mass will improve acceleration - less provides more, so to speak. Good to know that it doesn't compromise a decent idle.
A racer friend runs standard a flywheel in his Thunderbird outfit, but as a sidecar racer he feels the heavier flywheel is beneficial. He races, I don't :roll: , and more importantly, he wins races, so rather difficult to argue :wink:
I run a Thruxton flywheel (standard fit in '68 I believe) in my '76 Bonnie, and it made a significant difference to the snappiness under acceleration - it likes being revved now, and is also much smoother than originally. This may be due to the crank being better balanced than originally, but it can only be good for the longevity of the crankcases on any motor.
Unfortunately Steve Maney will only sell complete cranks these days, so manufacturing a bespoke one appears to be the only option.
Feedback guaranteed. PM sent :wink:
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jseng1 said:
I weighed a pair of AE pistons, +0.020" complete assembly at approx. 800 grams. Replacement Carrillo rods reciprocating weight per rod approx. 134grams I'm assuming this is in the region of standard Norton rods. Total standard reciprocating weight is approx. 1064 grams.
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Al-otment said:
I accidentally doubled the reciprocating weight (thinking it was one side). Correct specs are:
stock 850 reciprocating weight with Hepolite pistons = 972 grams
lightweight 850/long rod reciprocating weight = 772 grams
It makes all the difference in the world.
Your heavier pair of AE piston & bushed Carrillo rod setup, is approx 38% heavier than the JS lightweight setup.
Bare lightweight JS 850 piston is approx 205 grams
bushless small end of JS design Carrillo rod is 105 grams
Bare Stock 850 Hepolite piston is approx 317 grams (some aftermarket pistons are heavier).
All the JS balance specs are here:
http://www.jsmotorsport.com/technical_balance.asp
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How long do MK3 cases last. It seems to be a crap shoot. I have seen plenty of failures over the years.
The engine I blew up last fall was running old Venolia 880 kit pistons from TC and standard Carrillo rods. The reciprocating weight was 1350 grams. I rode the hell out of it for over 75,000 miles and although I often wondered when the cases would split -they never did. They were just stock cases with a crank that was about 4 lbs heavier than stock. Jim
The engine I blew up last fall was running old Venolia 880 kit pistons from TC and standard Carrillo rods. The reciprocating weight was 1350 grams. I rode the hell out of it for over 75,000 miles and although I often wondered when the cases would split -they never did. They were just stock cases with a crank that was about 4 lbs heavier than stock. Jim
I have a friend who has just stopped riding his MK 3 at 112,000 miles. He bought the bike new, cases have never been apart.
He stopped riding it because the motor is now (understandably) tired , starting to use oil and needs a top end redo.
At this mileage it makes no sense to only do the top end , so he is currently saving up to do a complete rebuild.
It will be interesting to see if the cases are OK still. Externally they appear fine, but closer inspection will occur on rebuild.
Glen
He stopped riding it because the motor is now (understandably) tired , starting to use oil and needs a top end redo.
At this mileage it makes no sense to only do the top end , so he is currently saving up to do a complete rebuild.
It will be interesting to see if the cases are OK still. Externally they appear fine, but closer inspection will occur on rebuild.
Glen
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Al....
I was in Norman White's on Saturday collecting barrels, I chatted a bit with him about cracked cases. He said he has never used anything other than Norton/Andover Norton cases.....and generally no problems....
But he also said that in his highly stressed racer, racing to win, they were getting through two sets of cases a season until they significantly reduced reciprocating weight, and by more than Jims pistons and rods alone would achieve....but if I undersstood...at a cost beyond most that of us can bear...the outcome was no more cracked cases...
But he also said...take care not to take too much weight off the flywheel as is spoils the rideability....and....in a road bike...something else is wrong if you crack cases!
I have Maney cases and crank and Jims rods and pistons...so I am hopeful we can avoid cracks!
I was in Norman White's on Saturday collecting barrels, I chatted a bit with him about cracked cases. He said he has never used anything other than Norton/Andover Norton cases.....and generally no problems....
But he also said that in his highly stressed racer, racing to win, they were getting through two sets of cases a season until they significantly reduced reciprocating weight, and by more than Jims pistons and rods alone would achieve....but if I undersstood...at a cost beyond most that of us can bear...the outcome was no more cracked cases...
But he also said...take care not to take too much weight off the flywheel as is spoils the rideability....and....in a road bike...something else is wrong if you crack cases!
I have Maney cases and crank and Jims rods and pistons...so I am hopeful we can avoid cracks!
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SteveA said:
Norman is using Titanium rods I believe and they are very expensive. I also offer an ultralight setup with underdome milling etc and a lighter rod thats good up to 80 hp (endurance racing). But I don't get many (or any) takers.
There doesn't have to be anything wrong with a street bike to crack cases and cranks. It just depends on how much your revv it. I think Comstock was lucky with his motor (until it blew - and what happened I don't know).
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jseng1 said:
Chatted to Steve Maney today and his cases will be arriving this week and I'm collecting a low mileage Maney modified crank at the week-end, balanced for Carrillo rods. As I'm not planning on slowing down (the engine does get revved), and as it's only money I'll be getting a pair of Carrillo rods to go with the crank. Anybody would think this was an obsession - but you know it makes sense. If I'd known before that the cases were going to crack I may well have invested in the JS longer rods and lightweight piston setup - as it is I'm confident the Maney cases will cope with the internal forces. Anybody wishing to make a donation can send money to http://www.ispendallmymoneyonnortons.co.uk.
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After stripping down of primary drive and spraying penetrant dye and developer over the suspected area of the drive side crank case, the crack can be clearly seen and runs horizontally, 1/4" above and to the left of the top stator stud (Mk3), and runs left for 2.5". I was expecting to find a crack starting from the main bearing housing. This one has appeared in what I assume is a relatively low stress area and I reckon has been caused by a faulty casting.
Fast Eddie
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jseng1 said:
Jim, maybe one reason you don't get any takers is that no-one knows about them! Maybe I've missed them somehow, but this is the first I've heard of them, and I would definitely have been a taker.
Maybe a good idea to make them a higher profile on your web site.
PS: I'll be back home soon Jim, and will be able to return the not required pushrods.
lcrken
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SteveA said:
lnteresting statement. What does Norman think is the minimum squish with titanium rods in a Commando engine? My experience is that an 872 cc race engine using Mk3 cases, Nourish crank, titanium rods, and Omega forged pistons, and set to .020" squish (not by me), will hammer the pistons into the head pretty hard. The same engine rebuilt with new cases after the blowup and set to .040" squish will have no problems, and run well enough to finish well at Daytona. I assume the minimum is somewhere in between. .040" is the same squish I use with both stock rods and Carrillos. I've run it down to .035" successfully, but I like to keep a little margin for over-rev.
Ken
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I spent last few years fretting over squish and quench for jets and sucks of honey thick mixture near TDC from Ricardo to Singh and Comstock, Schmidt, Canaga, ken Augustine, Ron Frattenellii, then famous V8 hemi chamber dragsters to come to conclusion its wasted area of worry with little to no effect on Nortons power so don't spend to press your clearance luck for nothing to gain. I am relieved to learn this as mean if Ms Peel detonates too easy I can just stuff in spacers till it just don't. Comnoz path is heavier flywheel to protect cases but with Maney's and JSM kit I think a lighter flywheel will be more for my jerky style of fun. Go out and blow some moderns minds eh. How will you determine red line and how can you prevent exceeding it with missed gear or stuck throttle out of gear? Luck of the draw on part till spending big bux.
Fast Eddie
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Steve A ay correct me here, but I think that Norman went down to .032".lcrken said:
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hobot said:
I suggest that you already know that revving a commando over 7,000 RPM is hazardous. Also that forces increase as the square of the accelerations. So unless you drastically increase the strength of that the reciprocating bits and their containers, and power increases must come without raising the top of the rev range. A light flywheel can be very disadvantageous. If you spin a heavy flywheel up then climb using more gears, it is often a better thing than spinning a lighter flywheel which doesn't have as much inertia (stored energy ). If you ride a commando engined bike with the heavy flywheel and it only drops a few hundred revs on every gear change, and stays near maximum torque - that is good. Initially it won't accelerate fast, unless you have a low first gear to get it going off the start, however once it is rolling and the motor is up in it's operating rev range and pulling a lot of gearing .... ?
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