Hi Graham how are things going???

Here is some fortage be it a little rough and old of Keith Duckworth and his high speed engineer talking about the Cosworth DFV and what goes into building a hi speed engine and associated forces and so on.... Very interesting.

http://www.youtube.com/watch?v=M7-YgfLHKNo Part 1
http://www.youtube.com/watch?v=L-lQ1R7BoX4 Part 2

Hi Wobbles
Things are going good made some more cams, got some new springs just need some time to test all of these things but the mini will be quicker this year will do some more tyre testing soon, and if we can get on top of that it will be very interesting.
Thats a great story on the cosworth engine, Keith Duckworth was a very smart man a genius i don't think there will be another man as cleaver as him again there may be a group of men as cleaver but no one will replace him read the cosworth book and you'l see what i mean, he did all of the design work at home at night by him self then would go in next morning and say this is what we have to build make it, and any problems he sorted them out the same way, a big loss to the world.
Graham Russell

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"It's better to be not informed than ill-informed"

This artical from metaldyne [formally holset] explains the function of a cam damper better than I can.
Have a look at the companys info on cam dampers. They have quite a range of types for various engine applications.
As I was trying to point out this could be a simpler solution to your particular problem with cam design.

The intake and exhaust valves of an internal combustion engine are operated by camshafts extending the length of the engine. The camshafts are driven by a sprocket attached to the end of the camshaft and a flexible tension-transmitting member
such as a belt or chain meshes with the sprocket for driving the camshaft from the engine crankshaft to synchronize the camshaft and crankshaft rotation.

Due to the length of the camshaft and the cyclic resistance to camshaft rotation that occurs as the engine's valves are operated, and due to the vibrations occurring in the belt or chain, an engine camshaft is subjected to many torsional
vibrations. One end of the camshaft may be torsionally vibrating about the camshaft axis with respect to the other end of the camshaft or the camshaft may be vibrating as a rigid body causing the chain or belt to stretch and relax, and thereby act as a
spring. Either or both such torsional vibrations cause wear in the belt or chain and also produce excessive wear at the cam surfaces. Further, if the engine ignition distributor is driven by the camshaft, as is common, the torsional vibrations within
the camshaft will produce excessive distributor gear wear.

The degree of torsional vibration existing in an internal combustion engine camshaft is directly related to the natural frequency of the camshaft and the frequencies being imposed upon the camshaft during the operation of the engine and, usually,
these frequencies are above the normal engine operating range. However, should the rotational speed of the engine match the natural frequency of vibration of the combination of the camshaft and belt or chain, torsional camshaft vibration can become very
serious and effective apparatus for controlling such camshaft vibration have not been heretofore available.

It is an object of the invention to provide vibration damping means for camshafts of internal combustion engines wherein torsional vibrations may be damped without significantly adding to the cost of the camshaft-related apparatus, nor
significantly adding to the size and configuration of the camshaft-related apparatus.

Another object of the invention is to provide a method for damping torsional vibrations occurring within internal combustion engine crankshafts wherein such vibrations may be absorbed by an elastomeric material associated with the camshaft drive
sprocket.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
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A question from a n00b.....If a damper is fitted to the camshaft, woudn't the cam have a tendency to change its timing during rev changes?

The damper is fitted to the end of the shaft same as the damper on the crank shaft. The drive is positive but most modern types of dampers use a high compressed silicon filled damper.
When you look at a roller chain drive to the cam like a mini and with out a effective chain tensioner then as the chain vibrates and the cam load is fluctuating the timing relationship between the cam and crank also fluctuates. You can have the best made accurate cam in the world ,but if the drive fluctuates even a few degrees then the cam accuracy means zip.

Next time you have your engine running look at the fan belt and you will see it vibrating. This is the transmission of the crank shaft torsional vibration to the belt. A "V" type wedge belt is never going to be able to create a torsional vibration.
Then for a interesting exersise leave the timing cover off and run the engine to see what the timing chain is doing.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

This is all very interesting. Most Minis with a timing chain show a lot of timing scatter when tested with a timing light.
Mine has a timing belt, and a Nissan Pulsar dizzy. Timing scatter visible under the strobe is practically zero.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thats right and bear in mind that the strobe is only acting for a fraction of a second and twice every crank revolution and at that point the torsional problem is at is minimum. Imagine what is happening after the firing position as the crank is accelerating then de-cellerating.
It's a wonder that engines even work

_________________
Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

Duckworth came up with a very fancy harmonic damper in the gear-train of the DFV motor. They were suffering a lot of failures in the valve gear in the early motors.
According to John Judd this is why the 4 cam Repco motor kept breaking cam followers in the 3 litre F1 motor.

With the HQ Holden racing motors there was a sudden rush of camshaft breakages when we were allowed to run Avgas. The better fuel meant we could run more compression and more power meant different harmonics.
Holden motors in road use used to always break number 5 piston. According to Repco there was a harmonic vibration problem built in from new!

Hi David
Your not listning to what your saying, you keep mentioning the vibrations from the crank sending torsional vibrations up to the cam and v belt,this is what i'm saying the crank is the problem not the cam so if you fix the sorce of the problem you don't need any more problem bits bolted on and thats what iv'e all most done.
now if you have a look at all the cosworths 4 cly motors BDA etc the nissan motors l series and most good 4cly motors you will notice none of them run a torsonal damper on the crank don't have any twisting in the length of the crank because they have so much over lap on the big ends to the main and they are much bigger dia and this is what i have done to the mini crank to help stop some of the problems the mini motor has the 970 motor does'nt really a damper because of the good over lap it has.
Now no matter how many dampers you bolt to the camshaft it is not going to stop the shock wave of the valve being wacked open by the cam lobe this has to come down to cam design and valve springs.
The closest motor to our DINOSAUR engine is the nascar engine, they still run a cam stuck down in the block with cam followers pushrods and rockers but none of these run any kind of damper apart from what is on the crank, they do run a belt drive on 99% of the engines and there is more r and d done on these engines than any other pushrod motor in the world so what ever these guys do i would tend to go with.
Another way to help vibration is to mount rubber blocks blocks on the engine or melt it on the thicker the better but a little messy,like puting a rubber band round big brake drums when machining them to stop them ringing but it does work.
Graham Russell

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"It's better to be not informed than ill-informed"

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nah now common Gt, that`s only a little one

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Hi Graham
OK just a couple of questions to make sure we are talking about the same things here. Now I am NOT talking about a vibration from a "out of balance' centripical force[ not to be confused with a centrifugal force]

1 What Is torsional vibration and how is it created.
2 what componets in a internal combustion engine create a torsional vibration.
3 What factors do you work out to find out how much vibration there is.
4 what effect does it have on a engine.
5 what is "hookes law" and what does it deal with in relation to a I.C. engine componet.

Now I can list 100's of engines that are similar but their construction is different but they all have a common fault [including rotarys] when they are running.

Now I know we are talking about mini engines [and a few more that you have brought up] but basically all reciprocating piston engine are build around a common design.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

Hi David
I just spent 2 hours typing your answer pressed preview and lost the lot may be some one can tell where it has gone.
Graham Russell

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"It's better to be not informed than ill-informed"

Hi Graham, sorry but I didn't really mean to put you thru all that.

OK now everyone else I just want to make things VERY clear. I am not about bagging or belittling anyone, that just not me and those who do know me will agree.

Now to set the record straight I do have a degree in marine engineering and as part of out job is to study every single componet of a diesel marine engine to know exactly what's going on with it. The ship owner would be really pissed off if I stuffed up his $5 mil engine .

Now I am only going on what I have been taught and learnt for my stuff ups over 40 years working and designing engines. All the info I give I have the text books with all the calcs and how it all works to post on here. I know there are some very smart people here and just maybe some of this info will be benificial. It was to me.

Now I AGREE with GR that a mini crank is the most diabolical crank ever designed for balance, and there are many engines that are much better, but irrespective of the engine there are basic laws of physics with every componet's operation.

Now crankshaft. There are 3 basic forces that a crank shaft is influenced by.
1 centrifical force. as it is rotating this force is trying to throw it apart. So we make the crank out of a suitable material[not chinese steel ] and constuct it so this will not happen.

2 centripetal force. This is when a irregular mass is rotated IE crank. cam. Because the bits that stick out this causes a "out of balance force" and this creates a vibration. Now GR has addressed this problem by re-designing the crank shaft so it is in balance more. When we do the calcs for this we also have to add in the mass of the piston, conrod and also calculate the frictional force of the piston. Very complicated.
So we have a crank just spinning around but the engine is not firing. The crank is all in balance[ well almost a perfect balance is impossible]

3 Torsional force. Now say you have the crank in a lathe and is is spinning around all nicely balanced, then asit is turning you give a bigend a whack with a big hammer. What happens.
This is what torsional force is about. The whack on the big end is the explosion created in the cylinder.
So the big bang therory. The force of the explosion hits the piston[ refer to the video that was posted and the forces measured in tons when this happens]. Now come the tricky bit as the next to things react against and also with each other as the process continues.
The piston is technically statonary TDC. so it is then accelerated down the bore. This action is a "linear to reciprocating " action and as the crank is moving in a circular path the acceleration is calculated from the length of the conrod to the crank pin and thru the radians of the crank. The bigend is moving thru a "chord" of a circle.
Now Sir Issac Newton's 3rd law of motion comes in. "For every action there is a equal and opposite reaction" The reaction is the whole crank shaft twists. Now the amount of twist will depend on the resistance in the crank. so it will twist at different amounts in different places.
Next part is also Mr Newton, because the action of twisting there is a action to un-twist once the magnitude of the force is reached and the position of the crank.
This is then occuring everytime the engine fires and to top it off once the piston has accelerated to approximately 90 Deg it then starts to decelerate and stops it's movement at BDC. That the tons of force refered to in the video.

This action is occuring exactly the same with a cam shaft[ yes I know GR does not agree] but as the cam lobe pushes the push rod up and the rocker arm pushes the valve down it has to create a force to do so.
This is where "hookes law" comes into it. Example to compress a FIXED pitch coil spring 3mm a load of say 10kgs is used. Then to move it another 3mm the load is also 10kgs. and so on.
So the valve is at it's maximum travel IE ontop of the lobe and as the cam turns the valve starts to close, but hang on we have this coil spring under tension . It has now taken the kenetic energy to squash it and is not turning it into potential engery , so the springs pushes the cam lobe around quicker then the cam is turning or tries to.
This action is exactly the same as the forces on the crank so a torsional force is created. Number of times per second is the frequency. same as crank.

Agree or dis-agree we can discuss it rationally but I am only a old useless pig iron polisher so I will do my best before the dimentia kicks in

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

Hi David
I'm not going to type out all the stuff on torsonal vibrations as it takes me far to long but what i was saying is the mini crank is not stiff enough and has serious problems with twisting [torsional vibrations] and flexing and as the hp is transfered down the crank number 4 cyl having to transfer more hp to the end of the crank than the others it's no wonder no 4 is the one to brake most of the time plus you have this large dia flywheel mounted 5 ins from the main bearing flexing creating a skipping rope effect on the crank, we just to make the crank as stiff as possible which BMC did by getting the nitrideing in as deep as they did .060 to stiffen the crank, try telling these heat treatment people today how deep it is and listen to there answer they just tell you your all BS.
David i don't use any maths to work out the vibrations and twisting in the motor 1 because my maths is not up to that standard and secondly i do things by trial and error it either works or it doesn't.
I did have acces to the magic box that measured the vibrations and harmonics from the engine but that had it's limitations because it was hooked to the dyno and the water helped to dampen the vibrations.
But i do have FRED, fred is a series of paino wires some short some long some fat some skinny that vibrate at different frequencythis can be measured and looked at with a strobe light.
The big problem being that the crank can not be balanced over the entire rev range so you have to balance it for the rev range you work in,
as for the cam shaft the shock wave set up by the lobe wacking that valve open can only be cured by better cam design and valve springs,with the help of better harmonics coming through the engine,
It also amazes me the amount of people that think heavy valve springs rob power from the engine because of the force taken to open them,you must remember that for the one being opened there is another one being PUSHED CLOSE which cancels this out been there tried it many times
Graham Russell

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"It's better to be not informed than ill-informed"