Engine torn down where do I go from here?

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Paddy_SP said:
gripper said:
Wish I knew about that aluminium issue before I racked up 8000hrs in her Majesties helicopters. Phew thank God I'm retired.
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You've misunderstood what was said - aluminium WILL fail given enough stress cycles, albeit that it may be a very high number. This will vary according to various factors, such as component design, material make-up and usage. Your helicopters are very carefully monitored - you must be aware of the need to change certain parts at a given number of hours. That's why.

Dr Paddy_SP, Phd (Materials Engineering)
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In an attempt to un-muddy the waters a bit, Dr Paddy_SP is correct in the strictest sense that aluminum does not have a infinite life fatigue threshold whereas steel does. Steel can be load cycled infinitely below a certain stress/strain threshold; below this threshold (from a practical standpoint) steel will withstand an infinite number of cycles.

Now back to the reality of the Norton Twin: there is a long history on the phenomenal durability of the Commando connecting rods. I have yet to see any credible evidence of a 750 or 828 Commando connecting rod failing due to fatigue. The only ones I have seen and/or heard/read about were associated with bearing/lubrication failure and faulty rod bolt failure. This is not to say it is impossible but faced with the preponderance of evidence, it is not something I would be too concerned with on the rebuild. Many vintage road racers have gone season after season with the stock rods. The closest I have come to hearing about durability of these rods is in the Steve Maney 1,007cc engine where he cautions to go with steel rods as the stock aluminum rods split down the center (only if the 1,007cc is pushing upwards of 90 RWHP). I have read on this forum about some later rods (maybe associated with the E-Start with a D stamping) that may be problematic but I have no first hand experience so others may chime in here. So if the rods clean up well and one has a good idea of the history of the engines use (nitro drag racing, a few decades of road racing, street use etc), one can make a reasonable assessment as to the need to change rods in these unusual instances. Perhaps the OP would like to share his understanding of the history on this motor.

If one were going to make an argument for changing out a Commando component because it is aluminum, a case (no pun intended) could be made for changing out crankcases as there's a rich history of crankcase failures across the drive side main bearing boss as well as rear of the cases where the engine to trans mounts are. I am not suggesting this for the OP but he should do a thorough inspection including die penetration.
 
Matt Spencer said:
SPLIT the CRANK .

fit a Filter .

What model / year is / was it ??

Whats its use going to be ? .
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Completely for to mention it's a '73. Mileage is completely unknown which is why I decided to tear down.
 
pete.v said:
What a bunch o crap. Absolutely, positively, EVERYTHING will fail eventually.

383wss, maybe you better just get rid of that damn before someone gets hurt. :roll:
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:lol: oh man, you're telling me! I work in the aviation industry and there is a reason why aircraft/helicopters need constant maintenance even if parts don't break they need to be replaced way sooner than what the engineers have spec'd them at. Metal fatigue is a fact of life.
 
383wss said:
pete.v said:
What a bunch o crap. Absolutely, positively, EVERYTHING will fail eventually.

383wss, maybe you better just get rid of that damn before someone gets hurt. :roll:
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:lol: oh man, you're telling me! I work in the aviation industry and there is a reason why aircraft/helicopters need constant maintenance even if parts don't break they need to be replaced way sooner than what the engineers have spec'd them at. Metal fatigue is a fact of life.
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Don't get me wrong, there 383, if I seem to have come off a bit conservative. If you read some of my history you will see that my attitude is far from conservative. It is much easier to tell you what is original than it is to tell you what all I have change over the years to get "my" bike the way "I" like it.

This I do believe. "If it ain't broke, don't fix it" could not apply more than it does to the Norton Commando crank as it pertains to the big end journals and shells. Once disturbed, that's it. There is no turning back and the crap shoot begins.

That being said, it's your bike and you can do to it whatever you like (or can afford). I have a lot of JS stuff already. It's all cam, valve train related. This, and the big ass carb, has been the biggest bang for the buck and although it is hot, it is completely street able.

Listen, you have had motors apart before, you have this one opened up now and I am sure you will have a motor apart again sometime, maybe this one. I am sure I will too. If you have a deft touch and as you feel the relationship between the crank and rod is buttery and smooth, then give it a chance. If it fails down the line sometime, then if you are like many of us, you'll have an excuse to take it apart again. This is where you might apply some of Jim Schmidt's fine items and maybe Comnoz's renowned services.

In my opinion, I think you have a good attitude and whatever you decide to do, you'll be pleased with the outcome. I know I am with mine.
Your user name, is that Mopar related?
 
Dances with Shrapnel said:
In an attempt to un-muddy the waters a bit, Dr Paddy_SP is correct in the strictest sense that aluminum does not have a infinite life fatigue threshold whereas steel does. Steel can be load cycled infinitely below a certain stress/strain threshold; below this threshold (from a practical standpoint) steel will withstand an infinite number of cycles.
.
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While I'd largely agree with these comments,
You have heard the story that Slippery Sam etc (race tridents) got reliability by changing the ** crank ** every 2 race meets.
Manxs didn't have an unlimited life to steel rods either...

There is one in every crowd would be my comment on this diversion.
Commando alloy rods have a very good reputation.
Maybe Trident owners like to muddy the waters...
 
pete.v said:
383wss said:
pete.v said:
What a bunch o crap. Absolutely, positively, EVERYTHING will fail eventually.

383wss, maybe you better just get rid of that damn before someone gets hurt. :roll:
Click to expand...
:lol: oh man, you're telling me! I work in the aviation industry and there is a reason why aircraft/helicopters need constant maintenance even if parts don't break they need to be replaced way sooner than what the engineers have spec'd them at. Metal fatigue is a fact of life.
Click to expand...
Don't get me wrong, there 383, if I seem to have come off a bit conservative. If you read some of my history you will see that my attitude is far from conservative. It is much easier to tell you what is original than it is to tell you what all I have change over the years to get "my" bike the way "I" like it.

This I do believe. "If it ain't broke, don't fix it" could not apply more than it does to the Norton Commando crank as it pertains to the big end journals and shells. Once disturbed, that's it. There is no turning back and the crap shoot begins.

That being said, it's your bike and you can do to it whatever you like (or can afford). I have a lot of JS stuff already. It's all cam, valve train related. This, and the big ass carb, has been the biggest bang for the buck and although it is hot, it is completely street able.

Listen, you have had motors apart before, you have this one opened up now and I am sure you will have a motor apart again sometime, maybe this one. I am sure I will too. If you have a deft touch and as you feel the relationship between the crank and rod is buttery and smooth, then give it a chance. If it fails down the line sometime, then if you are like many of us, you'll have an excuse to take it apart again. This is where you might apply some of Jim Schmidt's fine items and maybe Comnoz's renowned services.

In my opinion, I think you have a good attitude and whatever you decide to do, you'll be pleased with the outcome. I know I am with mine.
Your user name, is that Mopar related?
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Pete, I appreciate the words of advise and wisdom. I tore down my Suzuki GT750 for new rings and inspection and not thinking I needed to pay attention to anything else I ended up with leaking main seals a few months later. The GT750 engine opens horizontally and it would have been a piece of cake to pop the top off and pull the crank out. Yet another problem that could have been avoided if I had the "it's apart might as well" attitude.

And yes! one of my projects is a 1970 Challenger Western Sport Special with a 383ci big block.
 
Rohan said:
Manxs didn't have an unlimited life to steel rods either...
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That's because they were intended for performance and not an infinite life. Had the designer wanted to, he could easily have drawn them up to have had the latter - but then they'd have been big and heavy...
 
Rohan said:
Manxs didn't have an unlimited life to steel rods either...
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Paddy_SP said:
That's because they were intended for performance and not an infinite life. Had the designer wanted to, he could easily have drawn them up to have had the latter - but then they'd have been big and heavy...
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So - no infinite life from no metal fatigue in steel then...
A heavier steel rod would have lowered the redline, muchly.

Actually, it was rumoured that the factory race bikes went to a titanium rod to solve this.
When a Ti rod apparently cost more than a whole new manx.
And more than a house did back then .

But we diverge, slightly...
 
My 2 cents...While the crank is out get it magnafluxed for your own piece of mind. If you have the extra $$ to spare, Jim Schmidts Carrillo rods and forged pistons are a really nice addition, I would use them everytime if I could. You will never worry about the bottom end again.
 
Paddy_SP said:
Rohan said:
Manxs didn't have an unlimited life to steel rods either...
Click to expand...

That's because they were intended for performance and not an infinite life. Had the designer wanted to, he could easily have drawn them up to have had the latter - but then they'd have been big and heavy...
Click to expand...

As you say it's what they're designed for assuming that is the designer got it right. Part of that is choosing what material to use and in the case of Commando rods they seem to have got it right. The OP asked for advice on what to do and mentioned rods. I and others said if they are ok spend money elsewhere as the OP said it was a road going engine. The rods were designed for this purpose and if the stress cycles are within the capability of the metals elastic limitations they should if properly checked for defects an properly assembled work as they are ment to. They have a good reputation for reliability unlike other components of the engine and bike as a hole so surely we could expand this discussion onto some of those so the OP may prioritise which other items he may wish to spend his time and money on.
 
one of my projects is a 1970 Challenger Western Sport Special with a 383ci big block.
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Oh Goodie ! . Hope its not a Rustang . :P Those Alloy Rods will fail in a few years , if you use 10.000 regularly . :wink:

Some Turkeys will blow a LOOSE MOTOR , with low oil pressure etc . thrashing it etc. etc. etc .

73 was a good year ! Oil Tanks a bit marginal , if you throw a bleedy great sucker under the seat & throw out the Std. trash under there
youll save weight , and have reserve heat disapation .
Fairly Std. is the Go - but decent carbs , cam & valve springs are mandatory . Stock Ignition CAN be maintained ( 10 CA ) but a decent
pointless Ign saves maintanance .
 
toppy said:
Paddy_SP said:
Rohan said:
Manxs didn't have an unlimited life to steel rods either...
Click to expand...

That's because they were intended for performance and not an infinite life. Had the designer wanted to, he could easily have drawn them up to have had the latter - but then they'd have been big and heavy...
Click to expand...

As you say it's what they're designed for assuming that is the designer got it right. Part of that is choosing what material to use and in the case of Commando rods they seem to have got it right. The OP asked for advice on what to do and mentioned rods. I and others said if they are ok spend money elsewhere as the OP said it was a road going engine. The rods were designed for this purpose and if the stress cycles are within the capability of the metals elastic limitations they should if properly checked for defects an properly assembled work as they are meant to. They have a good reputation for reliability unlike other components of the engine and bike as a hole so surely we could expand this discussion onto some of those so the OP may prioritise which other items he may wish to spend his time and money on.
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Agreed - it's amazing how some people don't read what has been put before them in plain black and white. I'm a great fan of the Commando alloy rods, and yet some seem to think that I don't like them. And I made it clear that a steel component only has an infinite life when it's properly designed...

Anyway - to add fuel to the fire - I did manage to snap a stock Commando rod once. It was my own fault - I'd been sprint-hillclimb racing all weekend, and was riding the bike home late on the Sunday night. With my lithe girlie on the back, I was pulling about 105 mph - on 90 mph gearing, when it felt like the chain broke. Then the pain hit me - the rod had tried to go through the back of my left thigh - at the same time all the engine oil was dumped on the back tyre, and everything locked solid. To make matters much worse, the bike had no battery, so the lights went out - it was dark as hell and we were just entering a series of sweeping bends. I have no idea how I manged to keep the bike a) upright and b) on the black stuff. Luckily, my instinct was to whip the clutch in, and somehow we came to a halt unscathed. Even more forunately, my girlie was drunk, as we had to walk eight miles to get to her place, and she didn't complain once! The engine was so exploded that I took the crank out of the cases - without taking the cases out of the frame...
 
toppy said:
She did not complain about walking that far! You where indeed very luck :D
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Yes, I was - that's why I still remember it after some 34 years - thank the Lord for high strength lager! :mrgreen:
 
toppy said:
Paddy_SP said:
Rohan said:
Manxs didn't have an unlimited life to steel rods either...
Click to expand...

That's because they were intended for performance and not an infinite life. Had the designer wanted to, he could easily have drawn them up to have had the latter - but then they'd have been big and heavy...
Click to expand...

As you say it's what they're designed for assuming that is the designer got it right. Part of that is choosing what material to use and in the case of Commando rods they seem to have got it right. The OP asked for advice on what to do and mentioned rods. I and others said if they are ok spend money elsewhere as the OP said it was a road going engine. The rods were designed for this purpose and if the stress cycles are within the capability of the metals elastic limitations they should if properly checked for defects an properly assembled work as they are ment to. They have a good reputation for reliability unlike other components of the engine and bike as a hole so surely we could expand this discussion onto some of those so the OP may prioritise which other items he may wish to spend his time and money on.
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Thanks Toppy, mainly I don't mind spending the money as long as I can push as much life out of the bottom end as possible. Hence inquiry of reed valve vents, stronger material items etc. etc.
 
Paddy_SP said:
. And I made it clear that a steel component only has an infinite life when it's properly designed...
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We diverge, again, but no it doesn't - so that statement is not strictly entirely correct.
ANY material can only have an 'infinite' life if its only lightly stressed all its life.
Race parts, aircraft parts, rocket parts, helicopter parts etc etc are all routinely replaced, even if they have been 'properly designed'.
Steel rods included....

We'll leave the rest of your comments for the readers to decide on. !
 
Rohan said:
Paddy_SP said:
. And I made it clear that a steel component only has an infinite life when it's properly designed...
Click to expand...

We diverge, again, but no it doesn't - so that statement is not strictly entirely correct.
ANY material can only have an 'infinite' life if its only lightly stressed all its life.
Race parts, aircraft parts, rocket parts, helicopter parts etc etc are all routinely replaced, even if they have been 'properly designed'.
Steel rods included....

We'll leave the rest of your comments for the readers to decide on. !
Click to expand...

No, I'm afraid you just haven't understood this. I will say again: ANY component made of the aforesaid materials - Al, Mg or Ti, which goes through repeated stress reversals has a limited lifespan. It might be a very long lifespan, but nevertheless, the part WILL fail. That is because a few microstructural bonds are lost every time it is subjected to a stress reversal. Sooner or later enough of them will have broken for the item to fall apart. That is not the case with steel, where correct design can ensure a theoretically infinite lifespan simply because no bonds break. It is simply a matter of obeying the laws of molecular physics. I should also make it clear that being a motor racing man I hate the use of steel where Al, Mg or Ti can be used instead!
 
Paddy_SP said:
No, I'm afraid you just haven't understood this.
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We do understand this, you just didn't say it very clearly 1st time.
And we pointed out the error as it was stated....
 
Others have mentioned splitting the crank but were not explicit about cleaning the sludge trap inside it. Once you have done this You will not have to do this again for a long time. If you fit a filter and change oil frequently you may never have to do it again.

Rod bolts can be re-used if they are measured and still within spec, rod nuts must be changed every time, they are deformable one-use only nuts.

Norton rods are robust and reliable according to the experience of our community. They obviously do have some kind of finite life, but in some cases nearly 50 years of operation doesn't seem to have reached it yet. We are all hoping that 51 years is not the tipping point, but when I build my next Norton engine I will reuse the rods if they look good after a detailed inspection. I don't have any facilities for crack testing here in Asia, but if you do then have them checked for extra peace of mind if it is a reasonable price.
 
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