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MaxDiesel

Time for a top end rebuild... part 2

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Six years after originally rebuilding my engine (http://www.impactbumpers.com/forum/index.php?/topic/8055-time-for-a-top-end-rebuild/), I've decided it's time for some more tinkering and an upgrade to 3.4litres... :rolleyes:

 

The engine's done ~8,000 miles since the rebuild and been faultless barring a few annoying issues with things like crank position sensors that I probably should have just replaced when I did the rebuild.

 

Before taking the car off the road, I did a hot leak-down check to see how the cylinders have fared since the rebuild:

 

leakdownupdate.jpg

 

Leakages all still very low apart from cylinder 5 which is leaking past the rings - could hear this by removing the oil filler cap.

 

Next thing was to get the engine out - the wheel stands and engine cradle I made last time meant this was quite straight forward; still took the best part of a day working single handed though. Engine is still pretty clean considering six years have past:

 

IMG_8772.jpg

 

IMG_8773.jpg

 

Wasn't long before it looked like this...

 

IMG_8900.jpg

 

Cylinders look OK - the bores are more glazed than I was expecting though:

 

IMG_8895.jpg

 

Pistons have got more carbon than I'd have expected for 8,000miles - I suspect this is linked to the shiny bores...

 

IMG_8896.jpg

 

Measured the bore on cylinder 5 to see if there was any reason for the higher leakage than the others; it was fine at the gauge point Porsche specify to measure at, but out of spec at the top ring reversal line, which explains the higher TDC leakage. I'm pretty certain this was the cylinder that had a carbon locked top ring when I originally stripped the engine.

 

Decided to do a check and light refurb of the heads while it's all apart again:

 

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Heads stripped and bead blasted - put bungs in both ends of the guides to protect their bores while blasting:

 

IMG_8959.jpg

 

Giving the valves and seats a check over and light lapping:

 

IMG_8971.jpg

 

Quick check on seal with brake cleaner - might do a vac check too just to be belt and braces...

 

IMG_8973.jpg

 

A little while later all done Just need to give the heads a final clean before re-assembling springs etc.

 

IMG_8975.jpg

 

Had a closer look at the Mahle 3.4litre kit - it's 98mm bore, 10.3 compression ratio, it's a 'drop in' kit, so no machining of heads or block required.

 

Externally the cylinders look like they've come from the same pattern as the original Mahle 95mm cylinders - exactly same markings and features as the originals, but with the new size and part number laser etched on at the base of the cylinder:

 

IMG_8944.jpg

 

The pistons are quite different though with much flatter crowns:

 

IMG_8945.jpg

 

IMG_8946.jpg

 

IMG_8947.jpg

 

Quality of the Mahle bits all looks great, came very well packaged in some nice 'Mahle Motorsport' boxes :) Pistons rings are pre-installed on the pistons ready to go. I'll weigh the pistons and see how they compare with the original 95mm ones before putting it all together.

 

Hopefully get back onto it again next weekend and get the pistons and cylinders onto the engine.

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Nice, hopefully you stick more miles on this build :)

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Good luck with the new rebuild Matt, thanks for sharing with the thread and look forward to subsequent pictures and comments.

Regards,

David.

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Thanks Shirish and David.

 

Just nipped back down the garage and weighed the old and new bits...

 

Original 95mm piston with rings, pin, clips and a bit of carbon = 632g:

 

IMG_8981.jpg

 

Mahle 98mm piston with rings, pin and clips = 656g. Only 24g increase is impressive considering its 3mm bigger diameter:

 

IMG_8979.jpg

 

For what its worth I compared the cylinders too, original 95mm are 1136g:

 

IMG_8983.jpg

 

New 98mm cylinders are 964g:

 

IMG_8985.jpg

 

So the engine's going to be nearly 1kg lighter :rolleyes:

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Great stuff Matt. That's some admirable dedication to finding power to rebuild after 8k miles. Do you have any other plans for it while it's all apart?

 

Love the operating theatre workshop too, very jealous.

 

Did you have a good look at the rings on #5 to see why it was leaking?

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Great stuff Matt. That's some admirable dedication to finding power to rebuild after 8k miles. Do you have any other plans for it while it's all apart?

 

Love the operating theatre workshop too, very jealous.

 

Did you have a good look at the rings on #5 to see why it was leaking?

 

Cheers. I did check the rings on #5 and they're fine and very similar to all the others - the top rings have bedded in almost completely, 2nd rings about 50%.

 

I'm pretty certain the leakage on #5 was just down to the wear at the very top of the bore - you can feel it if you run your nail up the bore. Doubt it was causing any real performance loss as 20mm down the bore it was all in spec - I reckon if I locked the engine a few degrees off TDC and repeated the leak check on #5 it would have been as low as the others.

 

At the moment I'm just planning to change to pistons and cylinders - going to stick with standard cams for now, I quote like the torquey low end they give... maybe I've been driving diesels for too long !!

Edited by MaxDiesel

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Wow nice work Matt. Shame you're doing this so soon after your first rebuild. Remember seeing your immaculate operating theatre of a workshop first had a few years ago. And your clean as a pin 3.2.

 

I'd be so tempted to do some head work and fruitier cams. Go on you know you want to! ?

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Always beautiful quality. Don't ever sell that car: I would miss your projects too much.

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Good luck Matt - looking slick!

 

cheers

 

Nathan

Edited by R2D2

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:signs72:
Matt, looking forward to your updates. It is nice to see a hands on rebuild thread for a change!

:signs85:


The pistons are quite different though with much flatter crowns:
IMG_8946.jpg


Is the flatter profile of the piston crown to negate the need for going to twin plug as they allow the flame front to spread better?

Mark

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Yes, these look like the Max Moritz shape Mahle pistons, which are relatively low compression and designed for single plug. You can also do a low compression JE piston but its slightly lower compression again and looks like a less optimal design for single plug meaning you might have to pull a little timing for safety thereby giving up some of the gains you expect from going up in displacement.

 

Matt - this looks like a great project. Now just drop a 964 intake on it as well...

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Is the flatter profile of the piston crown to negate the need for going to twin plug as they allow the flame front to spread better?

 

Mark

 

 

Yes, these look like the Max Moritz shape Mahle pistons, which are relatively low compression and designed for single plug. You can also do a low compression JE piston but its slightly lower compression again and looks like a less optimal design for single plug meaning you might have to pull a little timing for safety thereby giving up some of the gains you expect from going up in displacement.

 

 

 

Agreed - I spent some time looking at 98mm options and what would need single or twin plugs:

 

I considered the Nickies cylinders with JE pistons, these come at either 9.5 or 10.5 compression ratio; the 9.5CR JE piston would probably have been OK with single plug, but the 10.5CR would require twin plugs due to combination of the piston shape and higher CR.

 

My understanding is also that the Mahle kit was specifically designed to match the original European 10.3CR and run single plug - its the relatively flat piston crown that achieves this. Some of the other high CR pistons options have more steeply angled crowns which effectively divide the combustion chamber in two at TDC and necessitate twin plugs.

 

I'm trying to keep my car and engine looking as original as possible.. so didn't want to go down the twin plug route - for this reason the Mahle kit seemed the best option, plus I like the fact they come from the OE manufacturer.

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FWIW, mine was cc'd at 10.45:1 after the first rebuild with the same kit, no detonation issues experienced to date .

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FWIW no detonation issues experienced to date .

How would you know?

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Provocative...

I only arsked- can one always hear or feel detonation?

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fair question - I couldn't tell, Wayne schofield confirmed its not.

 

Don't know what the visual clues would be to detonation -ill google it sometime.

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Yes, these look like the Max Moritz shape Mahle pistons

 

They don't look like Max Moritz to me...

 

Moritz pistons have a wedge shaped crown.

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Six years after originally rebuilding my engine (http://www.impactbumpers.com/forum/index.php?/topic/8055-time-for-a-top-end-rebuild/), I've decided it's time for some more tinkering and an upgrade to 3.4litres... :rolleyes:

 

 

OMG 6 years! Feels mike like a few at most.

 

Looking forward to the rest of the rebuild, please keep the pics coming :)

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post-3-0-07850600-1421313248_thumb.jpg

 

Tea is right. This ^^^ is a Max Moritz piston. Clearly there is now another Mahle single plug option. The MM pistons were always very expensive, so this is probably a good thing.

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You could save money with those Wossner's as you could have your 95mm cylinders bored out to 98mm, but those pistons would need twin plug i think which negates the cost save?

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Why do you think the Wossner's need twin plug?
maybe I've been 'Pelican-ised' but they look v similar to JE which on Pelican at least normally need twin plug, partially down to piston shape as well as Ron/mon availability.

Am I wrong?

 

 

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maybe I've been 'Pelican-ised' but they look v similar to JE which on Pelican at least normally need twin plug, partially down to piston shape as well as Ron/mon availability. Am I wrong?

 

No, you are absolutely right.

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