Crank desing for k serie, linear velocity piston 2

Hi Again

To see the importance of the length of the con rod crank pin, just give an example.

If you take a toothpick at the ends and apply a continual downward force in the center, will reach the point at which the toothpick is broken, if we do this in a toothpick smaller length and apply the same force, you will see that no breaks and you must apply superior force to break it.

Another question in the design of the crank is the lubrication system.

In this crank 2.0 serie k the lubrication system has been redesigned and improved, connecting every the oil step each other and not are independent as in the original design of the crank rover k series.

Connecting every oil step each other, you get the advantage of increasing the pressure of oil and also if the oil carril is obstructed in any place, the oil moves from one extreme to another, not leaving any crank and con rod bearing without oil.

Finally we can talk of counterweights.

The shape of the counterweights is very important, most of the crank are square with rounded corners.

In my crank 2.0 k series, the counterweights ending in arrow, and because when they come into contact with oil penetrates without hitting, reducing the brake exercised when striking oil in the crank and increasing the speed to take the revs and the oil temperature down at about 10/15 degrees.

The crank with the counterweights made diagonally, are dangerous, because there is an irregular movement in the oil sump, next to that movement of the car, you can leave without oil some point and cause breakage.



Not wishing to start a sh*t fight…

Knife edged cranks have been around a long time and reduce windage, but unfortunately they tend to move the crank away from proper secondary balance. The SOOB forces have a profound affect at higher RPM and will cause the block to move around especially on a stretched engine like the K where even in standard from the crank is under counterweighted I had SOOB calculations done on a number of steel cranks, some with normal counterweighting and some knife edged (wedged), the differences were in the order of 1000KG at 9000RPM.

Most of the steel cranks I use have continuous oiling as you describe, although I have seen these installed without the approriate shells with transfer grooves, ideally each upper main bearing shell should have transfer grooves rather than placing the hurden of oiling the big-ends on just two crank feeds. On standard installs I always improve the oiling to main bearings 2 and 4 since they carry the extra burden of oiling to the big-ends and yet are often undersized due to casting shift. There are various places in the crankcase where the oilways are less than optimal and where drag in the feeds will rob the oil circulation of it’s efficiency. These should be adrressed even with a stock crank with standard oiling.

On a 2 litre with increased stroke I would be less concerned with mean piston speed and more concerned with rod ratio which reduces rapidly when stroke goes up and block height remains the same, this give a very unfavourable rod angle. I think the stock rod ratio is around 1.49:1 against an ideal of around 1.80:1, if you increase stroke by 3mm, then the rod ratio reduces to around 1.42… not too good.

The toothpick analagy only works if the angle of the force applied with repsect to the rods movement remains the same, unfortunately when you shorten a rod, you also increase the angle at which it operates when at full deflection… the forces are then acting less in compression and more in deflection, this will eventually reach a critical point where breakage is certain.

It also moves the beam of the rod closer to the bore wall/piston skirt which means in turn that the rod has to be thinner at this point in order to provide clearance, thus weakening the rod at a critical point.


Hi Dave

I do not wish or you or anyone engaging in any fighting.

Many words and expressions in English I do not understand and I can not answer you correctly.

But if you can say that during more than 10 years, we have made many crank finished arrow to many engines, each a grades of their corresponding arrow and worked infinitely better than if they were them.

You may not agree with this and I respect.

I just spoke from my experience in multiple engine type, not just k series.

With reference to the balanced of the crank, I can tell you that all crank that I have, it have been proven that the imbalanced is less than 1 or 1.5 grams.

I can say that I have my engine 2.0 k serie and I have every disassembled 10,000 km to verify the engine and now has nearly 40,000 km facts in almost two years and I use it almost always in evidence throughout in rally and it is by the moment perfect the bearings,con rods, pistons, rings, etc.

But as you say it’s good to share your experiences, I am happy and I accept your opinion, thank you Dave.



With reference to the balanced of the crank, I can tell you that all crank that I have, it have been proven that the imbalanced is less than 1 or 1.5 grams.

you’re missing the point there…
you can have a perfectly balanced crank with or without counterweights, but the overall engine balance is a completely different matter.
Dave wrote about it mentioning 2nd order imbalance (which depends heavily on the conrod length) but, having 5 journals, the problem is also to minimize 1st order imbalance for each cylinder.

Hi all

At this point in the conversation, I think that I have to make an explanation.

I was talking about the virtues that I think my engine 2.0 k serie.

I know that I do not have much knowledge as Mr D Andrews and Mr S Erland.

But I never designed my crank, the crank was design by a group of engineers designers specialize in this work.

I can tell you that, I dispatched one standart crank of rover 1.8 and request that would make anothe one with more stroke, but that also next to crank, I dispatched one piston, one con rod and one block.

I sent these pieces to the engineers designers so that they could take all necessary data needed to make a crank that will fit with what I needed, after I repeated the same process of the con rod and finally I repeated entire process with the piston.

Let me also say that the piston has the just height between the top and the pin piston, in order to give the maximum length the con rod.

I think that the people who were responsible for designing all the pieces have the wisdom to do so and the results show it.