944T Engine Rebuild
- Thread starter barks944
- Start date
Just for interest sake - when I had the parts made for our mark 2 3 litre turbo (pistons, valves, cylinder studs to boly 16 valve head to 2.5 linered block etc, cast liners etc) I made extra so when it is finished there will be spare parts available if others want some to build something similar.
They are 104mm and capable of running with 8 or 16 valve heads (but you need to mod the combustion piston top to suit your chosen C/R).
Photos and specs will follow completion of the engine in a couple of months.
Baz
They are 104mm and capable of running with 8 or 16 valve heads (but you need to mod the combustion piston top to suit your chosen C/R).
Photos and specs will follow completion of the engine in a couple of months.
Baz
This is only what I was told by more than one engine builder when I was looking at options for mine. They said that its very hard to get the finish on the bores right with final finishing process and they often end up being very hard to run in i.e. to get the rings to seal. When mine was put together I was fully expecting the same problem but the engine was perfect from zero miles using no oil. We put this down to the fact that it was an original block and not a refinished one. Not very scientific but my guess is that its down to the lapping of the bores with the felt pads and paste to bring out the silicon in the Alusil, which when done in the aftermarket is probably not as accurate or repeatable as when done by Porsche.
sawood12
New member
I read in an article charting the development of the 928 that the process for 'bringing out the silicon' is an etching process and not a lapping one. Back in the 80's practically all German alloy blocked cars used Alusil (MB, BMW) - at that time it was the only way to get an alloy block without sleeving, hence saving weight, production complexity and cost while improving reliability, and, I believe, was a process developed by Porsche and licensed to the others. Apparently it was also used with moped engines. I think that as alloy engine development has moved on the capability and technique required to carry out this post machining etching process has long gone and there are probably only a handful of small specialists that will be hard to find who can still do it - It is probably the case that the capability within Porsche is long gone.
The specialist I used with my old 944T, rebuilt an S2 engine which required a re-bore greater than the limits in the manual therefore re-etch was needed, and he scoured the whole of the UK to find someone who could do it. He struggled but eventually found someone who did it with moped engines out of his back garden shed (probably not literally a shed, but was how he described it to me). As far as I know it was a successful job. but in theory there is no reason why a re-bore with a re-etch shouldn't be as good as new if you can find someone who can do the re-etch.
The specialist I used with my old 944T, rebuilt an S2 engine which required a re-bore greater than the limits in the manual therefore re-etch was needed, and he scoured the whole of the UK to find someone who could do it. He struggled but eventually found someone who did it with moped engines out of his back garden shed (probably not literally a shed, but was how he described it to me). As far as I know it was a successful job. but in theory there is no reason why a re-bore with a re-etch shouldn't be as good as new if you can find someone who can do the re-etch.
Here in Finland is only one company (luckily in my small home town) who can do re conditioning to these blocks. They have done this for local Porsche importer over 20 years, so they have good experience of this.
These blocks are quite interesting what comes to modifying them. For example aluminium used was very speacial and if for example you would like to have deckplate installed it is very risky business to use anything else than original block aluminium, mainly because different grade of aluminium expand differently under heat.
A friend of mine fabricates special deck plates for these blocks. He uses aluminium which is made from melted 944 blocks. Aluminium is also having full forging process. These aluminium sheets looks really interesting.He then fabricates deckplates with very high tech CNC machines.
First versions of these deck plates went for a 928 block. I am going to have one made for my 3.0L turbo build up based on S2 block.
These blocks are quite interesting what comes to modifying them. For example aluminium used was very speacial and if for example you would like to have deckplate installed it is very risky business to use anything else than original block aluminium, mainly because different grade of aluminium expand differently under heat.
A friend of mine fabricates special deck plates for these blocks. He uses aluminium which is made from melted 944 blocks. Aluminium is also having full forging process. These aluminium sheets looks really interesting.He then fabricates deckplates with very high tech CNC machines.
First versions of these deck plates went for a 928 block. I am going to have one made for my 3.0L turbo build up based on S2 block.
TTM
Well-known member
When searching for workshops here in France who were able to rebore Alusil blocks we got in touch with people who said similar things - to later find out that they either lacked the tooling or the experience, or both. Luckily we found one who had the tooling, the knowledge and the experience. His main experience on Alusil blocks consisted of rebuilding Lamborghini Diablo V12 which he told us were made within the exact same Alusil process. He also had experience with 928 and 944 blocks before we met him (without even mentioning his general expertise/experience in piston engines in general, ranging from Porsche 935, 7-piston aircraft engine and Velocette KTT. When I picked up my 968 bottom end he was in the middle of a Ferrari flat 12 rebuild).
As we replaced the headgasket a couple of months ago this gave us the opportunity to check the bores and were pleased to see no scores (12k miles). The bores had the same "mirror" finish as on Sly's 2.5 (the new bottom end which he bought from SimonP), the only difference being the deepness of the bores, Sly's engine having done back then 36k miles.
So yes, starting from a new block will save one the hassle of finding competent workshop who know how to work on Alusil blocks, which in our experience are not so easy to find. The downside of the UK having many more workshops and a generally far more active "sports car scene" than in France is that it's perhaps less easy to spot people who know from people who don't.
sawood12
New member
Yes, in the simplest terms, but it is a very complex process requiring the accurate control of many parameters. The right acid needs to be used at the right concentration, the right exposure and right pre and post treatments. Chemical machining (which is what etching essentially is) is one of the most difficult of manufacturing processes to control and achieve consistency in. So don't think you can just swab some locally sourced acid over the bores for an hour or so before wiping off!!
DivineE
New member
In prictice it is usually done with a tube of paste 'like tooth paste but smaller' applied during final honing (or so I've seen). I think its a very easy thing to get wrong as some people claim a re-built engine wont run for more than a few thousand miles whilst others such as Serdi in London seem to be able to produce bores to the same quality as the factory originals.
sawood12
New member
Honing is a completely different process aiming to achieve different ends and is carried out on all engines irrespective of the material of the block or liner. Honing uses spring-loaded pads that reciprocate and rotate within the bore and use an abrasive paste. The purpose here is to ensure modify the surface finish of the bore to polish off any high spots and to introduce very small and shallow scores in the cylinder walls. These are there to ensure you don't get a too perfect seal between the piston rings and the cylinder walls - they allow air and oil to get between to lubricate and reduce friction. Without these scores the piston rings would effectively stick to the cylinder walls massively increasing friction, heat and wear rate. These scores wear out once the engine has been run in and the piston rings have worn into the cylinder walls and 'free up' slightly.
The etching process is not carried out on all block/liner material types, but is applied to AluSil blocks (Aluminium Silicon Alloy).
The etching process is not carried out on all block/liner material types, but is applied to AluSil blocks (Aluminium Silicon Alloy).
sawood12
New member
You could be right, from this it looks like Audi has developed a mechanical way of exposing the silicon particulates to streamline manufacturing flow:
http://www.kspg-ag.de/pdfdoc/kspg_produktbroschueren/a_audi_zkg_e.pdf
On our cars though Porsche definitely chemically etched the bores.
http://www.kspg-ag.de/pdfdoc/kspg_produktbroschueren/a_audi_zkg_e.pdf
On our cars though Porsche definitely chemically etched the bores.
http://picasaweb.google.com/tombarker1804/944TurboEngineStripdown#
Clutch was on the way out, crank and cylinders are barely worn. Bearings were ok except for the thrust bearing which was fairly worn. Overall its in great condition. Some scoring to the inside of the block, looks like the crank play has caused the crank to wear the front and rear inner faces of the block a bit, shown in pics 19 and 20. 21 and 22 show some machining to the oil ways, was this done from the factory to correct a casting defect?
Clutch was on the way out, crank and cylinders are barely worn. Bearings were ok except for the thrust bearing which was fairly worn. Overall its in great condition. Some scoring to the inside of the block, looks like the crank play has caused the crank to wear the front and rear inner faces of the block a bit, shown in pics 19 and 20. 21 and 22 show some machining to the oil ways, was this done from the factory to correct a casting defect?
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