Oversize pistons

[starboard147]

Hi,

It seems that my turbo failure did more damage to my engine that I was previously aware of and I suspect it's heavily scored/scratched. [] Does anyone have any experience of using aftermarket oversize pistons?? I know that the OEM ones are like rocking horse s**t and I see that Lindsey Racing in the US stock Wiseco items at a reasonable price; also, there are a number of machine shops in the UK that can overbore the 944 block and then re-establish the Alusil surface treatment... but I'm unsure of how good the non Porsche items are in the longer term. Does anyone know anything more??

Or, failing that, does anyone have an decent block that they want to get rid of?

Grateful for any advice

Paul

 

[Diver944]

I have oversized aftermarket pistons. 8 mm oversized made by JE [8D] but the block had to be Nikasil coated.

There are only a few of places in the country that can reliably overbore the standard 100mm nikasil coated block, but you are correct in saying that the genuine 0.5mm or 1mm oversize pistons made my Mahle are quite often in short supply. When my original engine was scored we just could not source any from anywhere and at that time Mahle were not planning another production until the next year (which is why I ended up going down the radical road that I did)

Call Jon or SimonP at www.jmgarage.co.uk to talk through your options, they are not high pressure salesman and you will get honest answers to your questions.

If you read the US based forum at Rennlist you will see many problems with all sorts of different aftermarket pistons in our blocks. Far too technical for me, but different expansion rates and different clearances between different suppliers are causing more than a few engine failures []

 

[sawood12]

There are a handful of people around the country that can carry out the Alusil etching process. A couple of contacts you can talk to are Jon Mitchell or Mike at Zentrum.

 

[TTM]

First oversize pistons (100.5 mm) are easily available from Porsche. A friend recently paid about €2k for a set [&:]

 

[starboard147]

Thanks for the info, guys.

Paul, I noticed that there were lots of people on Rennlist suffering failures from MID sleeves but I didn't realise that there were any aftermarket piston incidents - I'll look again... Wouldn't mind following your lead but I'm afraid the budget won't stretch that far. Hell, I was looking to do most of the work myself!! I've been trying to talk to Jon M but he's been elusive of late.

Scott, I've got a recommendation for the etching process, I just need to find the pistons. I hadn't heard of Zentrum, thanks.

TTM, so they're available from Porsche!! I'll make some enquiries - although 2000 euros is certainly a quality price!!

Paul

 

[333pg333]

As one of the abovementioned sufferers of the MID syndrome, I would caution against using the wrong pistons or even the right ones but the incorrect clearances. The main issue with the MID's we believe is that they are of a very thick ductile iron material that doesn't expand like the very expansive JE pistons. This is not to say that the system can't work and we still don't know 100% what the ultimate cause is, but we have given up after many rebuilds failing repeatedly. Very long, expensive, and frustrating waste of 12 months. I am doing another sleeved block but this time it will be dry sleeved.

 

[Guest]

The company to use for the boring work is Perfect Bore in Andover. They are part of the Solent group same as JE Pistons. They can bore your block and provide the pistons to match. Same as Paul I went for a Nikasil plating option and very happy so far

 

[333pg333]

Sounds good Tommo. So long as they're compatible and provide all the spec's needed you should be happy ever after!

 

[starboard147]

Thanks for that, Tommo. Just to clarify, you didn't sleeve? I'm asking because you mention 'same as Paul', who did. How far oversize did you go, and how many miles have you put on the car since the rebuild?

 

[Diver944]

Now that you mention sleeving, you could of course have your cylinder walls machined out and then sleeved back to the standard 100mm bore with alusil coating so you can reuse your existing pistons. I am of course assuming your pistons themselves are fine.

This would remove the sometimes sketchy stock availability of over size pistons, though it sounds from TTM that they are currenty available

 

[333pg333]

Paul, the sleeves are generally made of iron and I'm not sure if you could then have them re-alusilled (wd?). There's no problem with pistons and dry sleeves in terms of matching the compatibility. You can then look at running an oversize motor but you may need new crank and rods.

 

[TTM]

928/944 blocks were made as lumps of Alusil.

Some interesting technical details from MSI here
Scroll down to page 86 and see question 2 with answer.

 

[333pg333]

Thanks for that link TTM. I knew the whole block was Alusil but I didn't realise that you could purchase Alusil sleeves? Interesting. Wonder why engine reconditioners don't use them for our cars?

 

[TTM]

I presume most don't have the abilities (tooling and/or knowledge and/or experience) to perform the work correctly.

 

[Diver944]

I do know that when Helen had her old S2 engine rebuilt at Zentrum they did use one sleeve for one of her cylinders and I am pretty certain that when Willdew on the 968 forum had his 968 rebuilt by EMC, they also used sleeves and the standard pistons.

When mine was being built Jon M did say that I could have the sleeves lined with Alusil but it would restrict my choice of piston. Nikasil is a better process and it would be easier to obtain pistons now and in the future so that's what I was advised to follow

 

[333pg333]

Paul I have to assume that Jon or Simon had some knowledge or experience with JE pistons before your build? You mentioned to me that they have a bit of cold slap on startup and that is due to them being installed with large clearances as they do expand a great deal. We had the same situation and depending on which particular rebuild we were on, the slap would dissipate after 5 or so minutes. Fortunately you have not had any other similarities to our builds. When's your car back?? Must be soon surely?

 

[starboard147]

Good info. So if you're not going for a bigger engine, the choices are overbore,etch and use oversize pistons, alsusil re-sleeve to 100mm and use original pistons, or MIDs. As oversize pistons are available, it seems that the straightforward solution is to go to 100.5mm, particularly given that TTM's link (thanks) suggests that alusil resleeve of all 4 cylinders is not recommended. So I guess the question that I'm left with is, why don't people opt for aftermarket? 100.5mm JEs are $699 (I take it that's each?) and Wisecos $795 (per set), while OEMs are available for 2000 euros. £400 Vs £1400. My conclusion is that people don't believe that Wisecos last! Any thoughts?

 

[Diver944]

ORIGINAL: starboard147

100.5mm JEs are $699 (I take it that's each?) and Wisecos $795 (per set),

Bummer - I wish they had been around (or I was more patient [] ) when my engine got scored.

 

[Diver944]

ORIGINAL: 333pg333

When's your car back?? Must be soon surely?

No news [&o]

The bodyshop have a few things to put right before it goes back to Jon's place for him to check over the mechanicals then do a little work on the engine [8D]. The good news is it's taking so long that I might then have enough spare funds put by to install Big Blacks straight away so she can become trackable again

Also, Santa has already been informed of a company called KW []

 

[starboard147]

Yea, but your car might still be remotely close to standard and you wouldn't have seen the true nature of the dark side... []