944 Turbo S Engine Rebuild Thread

[944Turbo]

Slightly painful update.


Engine is back out of the car and in many pieces again. Did circa 250 miles and used 2 litres of oil. Borescoped it myself and the bores were badly scored, fuel in the oil, tons of oil blow b, plugs fouled, etc. Removed the head and stripped all the accessible bits off the engine during lockdown and then dropped it in the garage for them to drop the engine. Took 8 hours to get the engine out and stripped the rest of the way down - easy second time around []

Pistons are beyond knackered - they’ve shed the coating and it was stuck to the oil strainer in sheets/flakes. Bores are eaten alive and only a sleeving job will save the block. Block and pistons are with the machine shop for them to speak to Wössne but I’ve been in touch with an Australian shop just outside Sydney who have confirmed that after 10 years of 20-30 Wössner Piston/Alusil rebuilds they’ve had the last 2 fail in the same way due to a change in the piston coating.


Looking at Westwood iron dry liners with Wössner pistons again, worst case scenario I can have a viable sleeved block and piston setup for £1500-£2k within a matter of weeks but I’ll prepared to wait a bit longer and see what the outcome is from Wössner first. I have a spare block too, so if this drags on then I can just get that one done in the meantime.


Will update when there’s something to update.

Gutting! sorry to hear that, Tony

 

[924Srr27l]

Oh... so the piston coating came off and ate the bores, Really?
Who measured the bores and ordered the pistons ?

What Running in Oil did you use?



R

 

[Eldavo]

Here we go - figured you‘d raise your unwelcome head.


Yes - the piston coating came off, actually came off in sheets/flakes. The bores have been measured with Mitutoyo equipment by specialists and are 100.502mm nominal with a maximum bore variation of 0.0003mm.


The people that ordered the pistons bored the block and are in contact with Wössner UK about it. Your hero Mike Lindsey told me that Wössner USA withdrew all their pistons from the market due to reports of coating failure and are now having them coated with PC9 by Swaintech in NYC. Buchanan Automotive in Sydney have had two engines eat their bores in the same way and have had Wössner supply uncoated pistons for use in sleeved blocks. Wössner subcontract the coating to Dow Corning who changed their formulation a year or so ago and this had lead to the issues.

But, as we’ve come to expect, you know better than anyone and cant wait to share your misinformed opinions where they’re not wanted. Get the hint, don’t interact with me; go play with your turbofans and spread your nonsense elsewhere.

 

[924Srr27l]

Here we go - figured you‘d raise your unwelcome head.
Yes - the piston coating came off, actually came off in sheets/flakes. The bores have been measured with Mitutoyo equipment by specialists and are 100.502mm nominal with a maximum bore variation of 0.0003mm.
The people that ordered the pistons bored the block and are in contact with Wössner UK about it. Your hero Mike Lindsey told me that Wössner USA withdrew all their pistons from the market due to reports of coating failure and are now having them coated with PC9 by Swaintech in NYC. Buchanan Automotive in Sydney have had two engines eat their bores in the same way and have had Wössner supply uncoated pistons for use in sleeved blocks. Wössner subcontract the coating to Dow Corning who changed their formulation a year or so ago and this had lead to the issues.

But, as we’ve come to expect, you know better than anyone and cant wait to share your misinformed opinions where they’re not wanted. Get the hint, don’t interact with me; go play with your turbofans and spread your nonsense elsewhere.

You see ! I told you my Wossner's were special! ordered and measured by my Hero back in 2014....
Anything after then looks like it was chocolate coated literally !




I think your quote sums it up "I’m not an expert - I know what I am doing and why I am doing it but I don’t always understand the technicalities behind it."

R

 

[Eldavo]

Update: Wössner are offering to replace the pistons (I should bloody hope so) but my machining company are attempting to lean on them for an additional contribution to costs. We’ll also insist on uncoated pistons to run in Westwood steel liners.

I’ve spoken to a lawyer friend who advised that the cost of fixing the engine is probably in a similar ballpark figure to the cost of the case but one will be considerably more drawn out than the other!

Picked up my birthday present early from Goldsmiths though so that’s cheered me up - just need a steering wheel to hold it next to now

 

[blade7]

Unless someone has successfully used IASA pistons recently, it seems like there's no readily available Alusil compatible 944 pistons now?

 

[Eldavo]

Nope - there are options.


JE get their pistons coated with PC9 by Swaintech in New York and they work with Alusil.

Wössner USA pulled all their Alusil pistons from sale and are all being coated in PC9 by Swaintech too. I don’t know about other vendors, but Mike Lindsey confirmed that all the Wössners they now supply are PC9 coated.


I believe that Mahle will do you some as well but only in overbore sizes.

 

[PSH]

Unless someone has successfully used IASA pistons recently, it seems like there's no readily available Alusil compatible 944 pistons now?

Not sure if IASA produce 951 pistons anymore? IIRC from my talk with their tech department at the time, it was a short run for race engines.....Actually I spoke to them a few weeks back, I was asking them about coatings after seeing David's woes.....they replied in Argentinian but if google translate got it right IASA used Molybdenum on their 951 pistons.

 

[blade7]

Not sure I'd take a chance on Mahle Alusil pistons. They have some nice looking Mahle Motorsport 104.5mm pistons for a 968 8v turbo engine. I was tempted, until reports/pictures surfaced of the coating falling off. Same with JE coated pistons a while back. Do you feel lucky? If I didn't want to keep the windage ports uncovered on my 2.7 block, I'd have fitted dry liners to it years ago.

 

[PSH]

I read that too, I also read in a number of these situations no matter which make of pistom, that one consensus is that wrongly sized pistons to bores was the reason...you can't uae Porsche tight tolerances in some of these big power engines... Alusil is a very good surface but it needs working on by shops who know and understand the material fully. IIRC it's 3 to 10 times harder wearing than cast iron, it's chemical makeup is superior to most bore sufaces out there. In fact I beleive that Porsche are still using it in today's 911's, such as the 991's, perhaps later too?..Nikasil and Lockasil both giving some issues in the past. Liners have their own problems.

 

[blade7]

The original Porsche 944 pistons ran around 0.001-2" clearance new I think, and had an expansion rate very similar to the block. It seems to be a mystery exactly what alloy they're made from, as that low expansion rate is more typical in cast than forged pistons AFAIK. The 944 aftermarket forged pistons around now spec around 0.004" clearance, so I don't think clearances are what's causing the issues. Maybe at around $1000 a set it isn't cost effective to coat them correctly, unless they're being made in their 1000's.

 

[Eldavo]

Clearance on the Wössner pistons is 0.08mm - they are manufactured with the clearance built in, so for a 100mm piston you machine, bore and lap to 100mm and unless you’re running massive boost you don’t need to increase the factory clearance.

The machine shop I use are well versed in prepping Alusil blocks for both road and race applications. They also use a lot of Wössner pistons in different builds so know when to increase the gap or not.

Sean Buchanan from Buchanan Automotive told me he’s rebuilt nearly 20 Porsche Alusil blocks with coated Wössner pistons and only the last two have had issues due to the coating change.

It‘a a shame as everyone I’ve spoken to tells me that the pistons are magnificent, uniform and consistent weight, dimensions and finish - they’ve just been let down by their subcontracted coating supplier.

 

[blade7]

0.08mm is just over 0.003". I'm pretty sure Mahle and JE pistons are very good too, and I don't think Mahle subbed out their coating. I wonder what you get if buying brand new 944/28/68 pistons from Porsche now?

 

[PSH]

The original Porsche 944 pistons ran around 0.001-2" clearance new I think, and had an expansion rate very similar to the block.

This is the unknown, what is the expansion rate differences between the block and aftermarket piston? As you say the stock is very good, clearly IASA is too or seem to be along with its coating. The only way to know for sure is a strip down but since the engine burns no oil I won't be doing that anytime soon, hopefully never in my lifetime, the boys can take care of any issues after I'm gone.... The other thing is the ring gap, you need a larger gap when generating higher boost levels, this and the piston expansion rate being greater than the block can cause such issues if too small a tolerance.

 

[blade7]

I just checked the Swaintech website re their PC9 coating, good luck with that and maintaining correct bore clearances. Seems like there's some knee jerk reactions taking place after the Wossner failures.

 

[Eldavo]

I wonder what you get if buying brand new 944/28/68 pistons from Porsche now?

You get told that they’re no longer available!

The original blocks were made by Kolbenschmidt so perhaps they made the pistons too?

 

[blade7]

The original Porsche 944 pistons ran around 0.001-2" clearance new I think, and had an expansion rate very similar to the block.

This is the unknown, what is the expansion rate differences between the block and aftermarket piston? As you say the stock is very good, clearly IASA is too or seem to be along with its coating. The only way to know for sure is a strip down but since the engine burns no oil I won't be doing that anytime soon, hopefully never in my lifetime, the boys can take care of any issues after I'm gone.... The other thing is the ring gap, you need a larger gap when generating higher boost levels, this and the piston expansion rate being greater than the block can cause such issues if too small a tolerance.

Mahle had to ditch their original successful Ferrostan alusil coating for environmental reasons I believe. I did wonder if IASA had no such restrictions in South America, and were free to use whatever they liked. Ring gap is something I'd expect any decent engine builder to be on top of too.

 

[blade7]

I wonder what you get if buying brand new 944/28/68 pistons from Porsche now?

You get told that they’re no longer available!

The original blocks were made by Kolbenschmidt so perhaps they made the pistons too?

I think KS were one of the original piston suppliers. There were some heritage blocks listed in recent years too, seems odd if there aren't any pistons to fit.

 

[Eldavo]

You can buy a new block through Porsche Classic. They’re not *that* badly priced - I did seriously consider it. Couple of grand IIRC.

 

[Waylander]

from what i can see in PET, there are a few dimension group 1 and 2 100,0mm pistons left but no 104.00, and some 104.5 in both groups, and the ones that are left are £350+ each.

that does include Pin, Clips, Rings and Piston