Welcome to the Austin Seven Friends web site and forum
As announced earlier, this forum with it's respective web address will go offline within the next days!
Please follow the link to our new forum
http://www.austinsevenfriends.co.uk/forum
and make sure, you readjust your link button to the new address!
What should I expect to pay for a set with the bearings in good condition?
Given that they've not made any for the best part of 80 yrs, Frank, I would say whatever the seller asks!! If you can find one.
Ian Mc.
Location: Shropshire
Bought a crank and rods on ebay 3 years ago for less than the cost of one phoenix rod. Crank is ok, flywheel has been loose but fixable. Rods have had the little ends bushed but are not too thin I have picked up a couple of other rods that are much thinner round the little end. The white metal looks like its breaking up so will be redone.
I will reduce the flywheel taper to clean it up then make a floppy flywheel for it with the hub machined from billet. Outer part will be from standard flywheel.
I would be interested to hear from anyone with a Nippy crank that has enlarged / modified the oil scoops. I understand that they where opened out to improve the effectiveness. My crank has standard at the moment.
Regards
Rob
Location: The 3D shed,Tewkesbury
Whats a floppy flywheel,Rob.
I always thought the nippy was prone to run big ends due to small oil pick up holes,I would funnel them out as much as possible to pick up more oil mist.
link
Dave, Its a dual mass flywheel. Similar idea to the ones in current fords but those use a flexible bonded joint. They were invented by lanchester in the vintage period as means of reducing vibration. The idea is to separate the mass of the flywheel from the stiff spring that is the crankshaft and in doing so prevent the vibration that causes the crank to break. (the same vibration that makes hands / legs / bum numb in a standard car).
I quite agree the scoops don't look very effective, also the oil holes in the crank are tiny and they go diagonally through the crank to the journal rather than having the larger hole through the crank pin to act as an oil reservoir. I was hoping to hear about / see pictures of modifications that have worked to fix this. I was thinking of drilling out the oil holes a bit as well as enlarging the scoops.
Regards
Rob
Location: The 3D shed,Tewkesbury
I will reduce the flywheel taper to clean it up then make a floppy flywheel for it with the hub machined from billet. Outer part will be from standard flywheel.
I would be interested to hear from anyone with a Nippy crank that has enlarged / modified the oil scoops. I understand that they where opened out to improve the effectiveness. My crank has standard at the moment.
Regards
Rob
I have a nippy crank and rods. i think the oil scoops have been opened out a bit i will look later. The ones i have got have over size little ends i thought about bushing but either the rods would be thin or the bushes would be non existent what size are you little ends and bushes how thin is the left over rod
Thanks
David
Dave, Its a dual mass flywheel. Similar idea to the ones in current fords but those use a flexible bonded joint. They were invented by lanchester in the vintage period as means of reducing vibration. The idea is to separate the mass of the flywheel from the stiff spring that is the crankshaft and in doing so prevent the vibration that causes the crank to break. (the same vibration that makes hands / legs / bum numb in a standard car).
I quite agree the scoops don't look very effective, also the oil holes in the crank are tiny and they go diagonally through the crank to the journal rather than having the larger hole through the crank pin to act as an oil reservoir. I was hoping to hear about / see pictures of modifications that have worked to fix this. I was thinking of drilling out the oil holes a bit as well as enlarging the scoops.
Regards
Rob
Rob,on the Nippy we used we deepened the machined slot and then radius the centre of the slot into the oil hole with a small tungsten ballnose. I think the width of the catchment area is sufficient but I would imagine that alot of it simply flies over the shallow lip. Increasing the bore sounds an improvement. We never did so. I am writing from memory, has anyone got a pic?
Our take as to why cranks break is different. We believe that the bending of the crank is due to the dynamically unbalanced mass of 2&3 journals and conrod bigends. The bending causes the flywheel to run at an angle and at every revolution you get a gyroscopic load at right angles to that bend. It's that cyclic loading which causes fatigue cracks either at the rear main or the further away, but thinner, no.4 journal.That is why fitting a lighter flywheel helps as it reduces the gyroscopic reaction. The flywheel you mentioned sounds very interesting and depending on the way it is designed to flex might also solve the problem. My understanding is that the early dual mass flywheels were designed to cope with torsional vibrations, especially on long cranks where they also fitted damping flywheels on the front. Of course I could be talking ********* Someone please correct me. What model Ford is it fitted to?
David ,you don't say how much oversize your little ends are,is it possible to bore out to 13mm and use Honda piston?
Did someone write an article in the quarterly mag about making a dual mass flywheel?
My thoughts on breaking cranks is that pressing the clutch,along with centrifugal force etc goes a big way towards the inevitable.Who has fixed the rear bearing instead to take the thrust,and what was your result?
Dualmass flywheels are fitted to Transits amongst other vehicles. If you tow lots of heavy trailers like I do they fall apart. Clutch and flywheel problems on Transits can be expensive! But still at least the crank shouldn't break!
I think from memory the 750 green book has info on using the rear main to take the thrust load. I guess the front bearings would then have to float because of the difference in expansion rate of ally crankase versus steel crank?
I remember seeing some info in one of the mags re Robs flywheel and since my memory has been jogged I am more seriously considering it now.
Steve
I've been told that opening out the oil holes in Nippy cranks didn't always solve the problem of run big ends. When I had to replace a broken crankshaft in my Speedy, the only crank I could locate was a Nippy one. So we filled up the oil holes and bored the shaft up the middle a la modern crankshafts to suit the pressure-fed arrangement. Pressure-feeding overcomes potential Nippy shaft problems, so there's another alternative to think on. Good Luck & Cheers, Bill in Oz
Location: Mount Eliza, Melbourne, Australia
I think from memory the 750 green book has info on using the rear main to take the thrust load. I guess the front bearings would then have to float because of the difference in expansion rate of ally crankase versus steel crank?
I remember seeing some info in one of the mags re Robs flywheel and since my memory has been jogged I am more seriously considering it now.
Steve
Re the mains bearing. we stopped using twin ACs and rear rollers 30yrs ago. We fit single rollers front and rear with the location at the rear. Full stop. We have 4 engines with this set up and have never had to change a bearing or anything associated to one.
Frank,
The dual mass flywheels are on most fords, they are for torsional vibration as well.
I quite agree with you about how the crank flexes and forces the flywheel from running true. This is my take on it... If you take the flywheel cover off a standard engine with 1 5/16 crank and standard flywheel (realise this doesn't apply to your cars) If you rev the engine and watch the flywheel the rim of the flywheel disappears into a blur at then settles and runs true at higher speed. The vibration occurs at around terminal velocity in a standard car. This is the source of vibration that makes hands and bums numb and the vibration puts the high cyclic bending load on the crank. The high stress cannot be on every revolution of the crank because you would get to 10^7 cycles very quickly and the crank would either break very early in the car's life or not at all.
The floppy flywheel has enough flex to let the rim run true irrespective of what the crank is doing. The vibration is eliminated. (anybody who drives my dads cars comments on this)
If you have a lighter flywheel or stiffer crank the vibration occurs at higher speed, it is possible that with a 1 1/2 crank and light flywheel that you wouldn't rev the engine fast enough.
The 1 1/8 cranks go through the vibration at lower speed so tend not to be in the vibration phase at terminal velocity however the crank is weaker and therefore probably takes fewer cycles to failure.
Dave,
The flywheel was my dads (Nick) idea after breaking two cranks in quick succession ~20 years ago. He wrote an article for the grey mag on the subject while he has A7CA chairman. His two cars (box and opal) have done in excess of 45000 miles between them since. The early versions of flywheels fell apart but no crank problems so far.
Nick has made 6 flywheels one is on his spare engine, one is matched to a crank awaiting re grinding (previously in the opal), one is in his ruby which is still to be finished, and one is on a friends car also not currently on the road. I have made 1 which is in my ulster waiting for the rest of the car to be done. Nick made the first few using a lathe and a pillar drill, we now have a milling machine and a rotary table so the job is much quicker and more accurate.
Regards
Rob
Location: The 3D shed,Tewkesbury
The dual mass flywheels are on most fords, they are for torsional vibration as well.
I quite agree with you about how the crank flexes and forces the flywheel from running true. This is my take on it... If you take the flywheel cover off a standard engine with 1 5/16 crank and standard flywheel (realise this doesn't apply to your cars) If you rev the engine and watch the flywheel the rim of the flywheel disappears into a blur at then settles and runs true at higher speed. The vibration occurs at around terminal velocity in a standard car. This is the source of vibration that makes hands and bums numb and the vibration puts the high cyclic bending load on the crank. The high stress cannot be on every revolution of the crank because you would get to 10^7 cycles very quickly and the crank would either break very early in the car's life or not at all.
The floppy flywheel has enough flex to let the rim run true irrespective of what the crank is doing. The vibration is eliminated. (anybody who drives my dads cars comments on this)
If you have a lighter flywheel or stiffer crank the vibration occurs at higher speed, it is possible that with a 1 1/2 crank and light flywheel that you wouldn't rev the engine fast enough.
The 1 1/8 cranks go through the vibration at lower speed so tend not to be in the vibration phase at terminal velocity however the crank is weaker and therefore probably takes fewer cycles to failure.
Dave,
The flywheel was my dads (Nick) idea after breaking two cranks in quick succession ~20 years ago. He wrote an article for the grey mag on the subject while he has A7CA chairman. His two cars (box and opal) have done in excess of 45000 miles between them since. The early versions of flywheels fell apart but no crank problems so far.
Nick has made 6 flywheels one is on his spare engine, one is matched to a crank awaiting re grinding (previously in the opal), one is in his ruby which is still to be finished, and one is on a friends car also not currently on the road. I have made 1 which is in my ulster waiting for the rest of the car to be done. Nick made the first few using a lathe and a pillar drill, we now have a milling machine and a rotary table so the job is much quicker and more accurate.
Regards
Rob
Your take, I agree to a point, we also saw the blur when we ran on 1 5/16. I think that at the lower rpm, say below 5000 the gyroscopic reaction is not enough to reach the point where fatigue sets in ( the threshold limit). Above 5000 it does. Our cranks never lasted more than 30mins. 5000 is a guess.
So my question to you is ; what do YOU mean by crankshaft vibration? My take does not involve the crank vibrating, it assumes that the crank simply bends more as the rpm increases.
The shaft goes round like a skipping rope because all things are elastic, the higher the rpm the more it bends but the bending stress would then be constant at a given rpm rather than cyclic.
As the rpm increases the gyroscopic effect of the flywheel increases to a point where the forces making the crank bend and the forces making the flywheel run true get more or less equal and the vibration sets in. This causes the crank to whip and creates a changing bending state in the crank, this causes the high cyclic stress that causes fatigue. Think of it as the crank trying to go round like a skipping rope and the flywheel wanting it to run straight, the vibration is it going between the two modes but probably results in it going further in both directions ie with 2 and 3 oscillating between hitting cylinder head and bending the other way.
The key point is, doesn't really matter which of us is right, the floppy flywheel works for both arguments. With the flexible straps the flywheel rim cannot put a bending moment on the end of the crank.
Regards
Rob
Location: The 3D shed,Tewkesbury
Re the mains bearing. we stopped using twin ACs and rear rollers 30yrs ago. We fit single rollers front and rear with the location at the rear. Full stop. We have 4 engines with this set up and have never had to change a bearing or anything associated to one.
Am I being very stupid or missing something (either a reasonable possibility)
If you have rollers front and rear how do you manage "location at the rear"?
Charles
Re the mains bearing. we stopped using twin ACs and rear rollers 30yrs ago. We fit single rollers front and rear with the location at the rear. Full stop. We have 4 engines with this set up and have never had to change a bearing or anything associated to one.
Am I being very stupid or missing something (either a reasonable possibility)
If you have rollers front and rear how do you manage "location at the rear"?
Charles
No, you are neither it was me being stupid whilst editing out a line.
I meant balls! Sorry,I think it was getting late.
We gave up on rollers as they were expensive and not really suitable for our purpose.
While we are talking about crankshafts can anyone post a picture of the Hadley crank and rods?
As the rpm increases the gyroscopic effect of the flywheel increases to a point where the forces making the crank bend and the forces making the flywheel run true get more or less equal and the vibration sets in. This causes the crank to whip and creates a changing bending state in the crank, this causes the high cyclic stress that causes fatigue. Think of it as the crank trying to go round like a skipping rope and the flywheel wanting it to run straight, the vibration is it going between the two modes but probably results in it going further in both directions ie with 2 and 3 oscillating between hitting cylinder head and bending the other way.
The key point is, doesn't really matter which of us is right, the floppy flywheel works for both arguments. With the flexible straps the flywheel rim cannot put a bending moment on the end of the crank.
Regards
Rob
Let me have a think over the next few days. It's a fascinating topic and I'm very glad to have your take and your critism of mine. I agree the flywheel does solve the issues you raised.Did you ever take a pic of it so I can see how the flexible straps are arranged?
I have posted a link to pictures further up the page.
There are drawings of the parts on the A7CA website but I am intending to update those to the latest version which is tweaked to make it easy to make on a rotary table. Nick has also written some updated notes this week to go in the grey mag.
Regards
Rob
Location: The 3D shed,Tewkesbury
There are drawings of the parts on the A7CA website but I am intending to update those to the latest version which is tweaked to make it easy to make on a rotary table. Nick has also written some updated notes this week to go in the grey mag.
Regards
Rob
I just had a look. Excellent. What a wonderful solution. Congratulations.
Rob
Having just stripped my 65 engine following a valve insert detaching itself on the L2B run, all the big ends show signs of being underlubricated. All oilways/orifices were clear so can only think it is due to the oddly small oil holes on the crank. Has anyone had any success with modifying these?
Location: Farnham
Rob
Having just stripped my 65 engine following a valve insert detaching itself on the L2B run, all the big ends show signs of being underlubricated. All oilways/orifices were clear so can only think it is due to the oddly small oil holes on the crank. Has anyone had any success with modifying these?
When we raced with one we used a small ball nosed cutter to blend the scoop,which to me seems wide enough but a bit shallow, into the oil hole. In effect this deepened the scoop. There are also two countersunk holes at the base of the rod H section which I have assumed are there to collect oil. They usually lead to a groove across the bearing which I also assume is there to spread the oil across the bearing surface. This has led me to think that things are a bit iffy. Surely there is an expert out there on this?
. There are also two countersunk holes at the base of the rod H section which I have assumed are there to collect oil.
I had assumed they provided lubrication to the little ends, spraying the oil upwards??
. There are also two countersunk holes at the base of the rod H section which I have assumed are there to collect oil.
I had assumed they provided lubrication to the little ends, spraying the oil upwards??
Well to be honest that was my first reaction. Then I had second thoughts. Why on earth would they go to all the trouble to fit those bloody awful oil baffles and then chuck even more oil up there? Secondly, why would you put a dirty great gouge across the most loaded part of a bearing if you weren't in deep **** already? Thirdly, why countersink the hole? I think that the pressurised cranks don't have this on their rods.
On the other hand the dirty great gouge could act as a scraper removing oil from the bearing so more oil can enter in order to increase flow and cooling. But in that case you would have put the scraper at the bottom or side to reduce the oil going up the bore. Have I lost the plot here?
I have taken engines apart that also had two grooves at sides of the bearing where the cap joins the rod.
these did not extend fully across the bearing and were probably about 5/8" wide. Never knew quite why they were there though. Prehaps the counter sink th the top holes are no more than the machine shop using a centre drill to make the hole during the manufacturing process.
Frank and Rob,
I hesitate to get involved in a discussion with people who have had much experience with Austin 7 engines at high speed, but isn't the crankshaft large movement when it goes through 'whirling'.
When the always out of balance shaft spins it bends then goes through a critical frequency at a certain speed depending on the shaft stiffness, where the deflection increases until this speed is exceeded when the deflection decreases.
Of course all this is obviously affected by the piston forces etc. The 'blurring' of the flywheel indicates the shaft deflection and will be greater at the critical speed.
I would have thought that the flywheel gyroscopic effect would contribute only a small force compared to the bending caused by whirling, not giving rise to crankshaft breakage. The stress is in the crankshaft flexure which is constant through to the flywheel at any given speed, increasing to a maximum at whirling speed then reducing, but not oscillating. Or am I completely wrong.
Tony.
Location: Melbourne, Australia
Tony,
What you are opening here is a science that I am not qualified to deliberate on; however, you are not completely wrong just a little.
What you are talking about is resonant frequency and standing waves. All rotating bodies have a critical resonance known as nodes and anti nodes and are variable due to the structure of material oscillating. If the oscillation is not controlled by a gamete of remedies miniscule cracks in the material will form eventually growing until they reach the critical fracture point.
The above is my crude explanation as this subject would bore the tripe out of most readers.
Regards,
Doug Baker
Location: Scarborough Western Australia
Tony,
As you say crank whirl is a static load that varies with rpm and therefore does not contribute to fatigue. Since the crank is steel the number of cycles to failure must be less than 10^7 so the crank is not loaded every engine cycle above a certain speed (if it were it would break very quickly). The rear main bearing is incapable of applying a bending load to the crank of any significance. The only way a load significant to the section of the shaft can be generated is by a highly dynamic situation where the mass of the rim of the flywheel exerts a bending load on the crank.
The piston forces / driving torque is insignificant, if you look at a broken crank you will see that the section left before final failure is tiny compared to the size of the crank.
As I said above, the actual mechanism for the dynamic loading of the crank is irrelevant if the mass of the flywheel rim is uncoupled by the floppy flywheel.
Regards
Rob
Location: The 3D shed, Tewkesbury
Rob,
Maybe I am being dense, but I would think the front bearing pair should tend to hold the crankshaft nose and resist bending during whirling, more than the spinning angled disc of the flywheel trying to 'straighten' out at the rear of the crankshaft would hold this end. Aren't most breakages at the rear of the shaft.
Tony.
Location: Melbourne, Australia
As you say crank whirl is a static load that varies with rpm and therefore does not contribute to fatigue. Since the crank is steel the number of cycles to failure must be less than 10^7 so the crank is not loaded every engine cycle above a certain speed (if it were it would break very quickly). The rear main bearing is incapable of applying a bending load to the crank of any significance. The only way a load significant to the section of the shaft can be generated is by a highly dynamic situation where the mass of the rim of the flywheel exerts a bending load on the crank.
The piston forces / driving torque is insignificant, if you look at a broken crank you will see that the section left before final failure is tiny compared to the size of the crank.
As I said above, the actual mechanism for the dynamic loading of the crank is irrelevant if the mass of the flywheel rim is uncoupled by the floppy flywheel.
Regards
Rob
Rob, having reread some of this I realise that I was not to clear explaining my view. I'll try again.
1) The crank bends as the speed increases due to the
unbalanced mass at journals 2 & 3. The flywheel is now
not running true. My thought has been that the flywheel wants to run true and is placing a steady load on the crank.
2) The reciprocating loads are also increasing with rpm and I recall a figure of 3000lbs at the top of the stroke and 2000lbs at the bottom for 2 & 3 @ 7000rpm but this is from memory. I take it that this is the vibrating load you mentioned. In a normal 3 bearing engine the 3 or 5 mains would stop the crank from bending and the crank would simply accelerate and decelerate (which is why some racing bikes have a 3D crank to get around this as it causes the tyre to break away earlier under acceleration). Again the flywheel reacts against this. But I guess that with a 2 bearing crank there is a mix of cyclical bending and torsional loading.
3) The engine firing adds a load but I agree with you that this is minor in comparison.
Your flywheel is a good solution.
Tony, the front bearings still allow enough bending movement and when the limit is reached I would expect the crankcase to flex. The flywheel is reacting all the time to the bending and once the cyclical loads become large enough fatigue will set in.
Frank,
One of my dads floppy flywheels has fallen to bits - brilliantly its the one in his mondeo!
R
Location: The 3D shed, Tewkesbury
Rob, which model year Mondeo is it (I am trying not to sound worried about mine!)
Location: Farnham
Its a 52 plate turbo diesel, cant remember which engine but its one of the first with their "dual mass" flywheel.
Location: The 3D shed, Tewkesbury
