Cylinder liner supports

I was at a Porsche event at the weekend and got to talking to another owner, they had there engine in for a rebuild not long back and he was telling me he didn't change liners etc but got some kind of support ring fitted. This is on a 3.4 M96 engine.

Anyone heard of this and is this instead of new liners ?

Im sure Hartech will be along shortly, so heres one of theirs:



This has a 'ring' fitted. From my understanding, when you do a closed-deck conversion you get this ring to give extra support.

This is the other liner availble (from Westwood for this example):


These dont have the 'ring' support.

Not sure you can uild in any supporting bits if you dont change the liners - there would be nothing to support the ring itself.

Yes
Hartech can sometimes hone the bore and fit a ring to support the liner.

Have a look on their website, there is some great information.

There was a topic in hear recently where Baz did a really good explanation of the process, pro's & cons.

Page 4 of this thread. http://911uk.com/viewtopic.php?t=128330&start=60&postdays=0&postorder=asc&highlight=baz

yep, the hartech support ring makes the engine a closed deck vs the standard open deck so the bores won't oval and crack. If the cylinders are OK then this is a good solution if going for a preventative rebuild before something goes bang or as a cost saving measure for undamaged cylinders when one has scored or cracked.

I remember a similar thread

http://911uk.com/viewtopic.php?t=125583&postdays=0&postorder=asc&start=20

I contributed to this thread on page 2 with a photo of a cross sectional view of a cylinder support system for sock liners.

To make the cylinder block casting possible under pressure in metal moulds the standard cylinders are like tubes free at the top and bottom and only connected to the outer casting via a ring in the centre half way down - so they are free to distort under the pressure of the piston in the thrust direction and will slowly go oval.


The cylinders for the early and smaller diameter piston examples were strong enough to resist this but the 3.4's and upwards didn't increase the outside diameter to match the bigger pistons (to allow enough coolant space) and they are not strong enough not to distort.


If you bore out a tube and fit another one iside so the dimensions are the same from the bore and the outer diamter of the bigger tube - the resulting 2 tubes are not as stiff to resit movement and bending as the original solid tube of the same overall dimesnions - so boring out and fitting a sleeve inside results in a weaker construction than was there originally.


Some engines in which we have had to replace a ferrous liner with our system had gone wrong because the thin iron liner pushed under thrust loads against the now even thinner and weaker alloy outer sleeve and gradually distorted it until the top of the iron liner was no longer a tight interference fit and this allowed it to rotate, slip down or even crack the outer sleeve.


Luckily Porsche designed the cylinder block shape so it was possible to machine out a diameter to fit a "top hat" shoulder into and this enabled us to completely machine away the original cylinder and replace it with a whole solid new cylinder with better bore finish (Nikasil) and supported at the top and centre (see above photo).


Our solution is also the same as that used by Porsche in their GT3 and turbo models that have no cylinder issues (despite more extreme general use and power delivery) - so is a doubly proven solution while using an alloy cylinder enables better clearance control between the piston and the bore during warm up and different running conditions and temperatures.


Our oversized engine versions (with larger pistons) are also working well and when fitted to crankcases that have smaller original bores we also fit a ring into the bottom of the cylinder block to support our one piece cylinder at the top, the centre and the bottom - once again providing a perfect solution.


In most examples you cannot machine a circle in the top of the block to fit a top hat into with a rotating tool because you would machine away parts of the outer block - so you need an expensive and very accurate CNC machine to circular machine the mating hole in sections - which most engine rebuild machine shops do not have. Ours is a brand new top quality machine capable of machining to incredible accuracy.


The older engines with ferrous coated pistons are the worst for cylinder cracking and yet the pistons are hard enough to resist bore scoring for a very long time so we can fit a ring into the top of the cylinders to prevent further distortion but this is not a perfect solution as we cannot get the bores pefectly round again (because they have been wearing and running while gradually going oval) - we can only improve the shape and stop the tops cracking - for those who absolutely cannot afford the much better option of new cylinders.


To encourage everyone to try and afford the best option we have discounted the price of a full 6 cylinder replacment to the bone and and developed oversized alternatives to give back something better.


Baz