Boring Mahle Cylinders
 

I have a set of worn 90mm Mahle cylinders. Is it practicable to bore these to 92mm and have them re-nickasilled?

TIA

Mark

It's possible but not a good idea. The margin between bore and CE ring inner groove becomes too small to seal properly. People have done this over the years but I would pass.
Run a 9.5: 1 compression piston and a standard 90mm bore and you pretty must stress the mag case to it's performance/reliability limits.

Thanks Henry.

Case is a fully prep'd 901/14 al case. Was thinking of building a 2.8L, 10.5:1, twin plug etc. engine and getting a set of 92mm JEs. Just trying to save the cost of a new set of jugs...

Mark

http://www.summitracing.com/parts/sce-31542


I know experiments are frowned upon around here but you could weld fill the CE groove and then deck flat before the hone. You could re-machine the groove further out in the diameter of the same surface to maintain or increase the cylinder wall thickness relative to OEM and use aftermarket o-ring wire that is more commonly available. Or you could try without any ring groove the same as the later engines/ P&C kits.

What heads are you planning on running?

My pictures kinda stink but you can get an idea of how thin the remaining cyl wall is after boring.

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/724260-core-mahle-nikasil-cyls-98mm-sc-style.html

My cyls above were 95mm SC cyls bored out to 98mm. I know the 2.7 head stud spacing and cylinder spigot is different. But I just wanted to show what it looks like when you bore a cylinder that has an original ring groove

The factory started the same way because the early 2.8 cylinders had the CE groove. It was found at the slightest whiff of detonation that that thin bit cracks. So the later 2.8 pieces got rid of the CE groove.

I just had cylinders plated at Milinium. It was $1.2k. I'd think it would be another 600-800 to weld and blanchard grind. A savings maybe by the time pistons are tossed in and you wait.

t

The 2.8 is cool but what do you really get? The reason for building the 2.8 RSR was to maximize the racing rules. The 2.8 is just a .080” overbore from stock. Replate your 90mm or if you must go ahead and make a 91mm with 10.5:1 pistons and you will not notice a performance difference.

They ( 91mm) are indeed a better combination because the cylinder walls ends up being thicker, CE ring has a reasonable margin and the cylinder still slips into a stock 2.7 case.

The twin plug in this soft window 67S I built has a set of 91mm pistons and cylinders. Note the 935 CD boxes. Jerry let me build some pretty cool stuff.

http://forums.pelicanparts.com/uploa...1368024958.jpg
http://forums.pelicanparts.com/uploa...1368024990.jpg

All marginal benefits... slight displacement increase is slight performance increase. Less material in cylinder means lighter cylinder. Cheaper to skip a meal to get the weight savings however... depends on the level of competition and if you want that tiny advantage. Or if the 2mm over bore is required for repair.

Thanks for the replys. The short answer is 'no'. That's why guys like you are here - to keep guys like me from doing silly things SmileWavy.

To make a short story long, the engine was assembled from parts prepared and supplied by John (Otto) Williamson in the mid '90s. It was first run in 2003 and did maybe 12 track days, a few tarmac rallys and sundry journeys totalling about 10000 miles before being put in storage in 2006 and replaced by a 2L engine. It was limited to 7300rpm and never ran over 180deg.

I already had the cylinders and knew they were a bit worn, but talking with JE, they said the piston expansion rate was a bit higher than Mahle's so should be OK.

Now, I want to use the bottom end as the platform on which to build a much stronger engine for a car to be used in a range of activities from track days to touring. It will need a 50000 mile service life. I want to go new tech (I've sold the cams and carbs and will sell the existing 9.5:1 JE pistons) with EFI, crank fire ign etc. 98 gas (93 US??) is available most places so 10.5:1 twin plug is not silly. Heads will need to be re-worked obviously. I already have a set of 171i 149e Web cams. The big (read expensive) bit will be whatever induction/ignition is chosen...

Henry's 91mm suggestion sounds like a good option (nice looking engine BTW) as ultimate power is not the goal here. The Nickasil costs here are about line-ball with Tadd's. If I was trying to optimize it for competition, Andrew's suggestion of re-positioning the CE groove may be worth a look, but I suspect new cylinders would be the better option for an optimized comp engine anyway.

Many thanks.

Mark

According to Millennium Technologies, Mahle cylinders are not weldable.
My thinking is that even if they were, the intense heat would change the molecular structure making the cylinders less reliable.

Have any junk cylinders to test your weld theory? I'm up for myth busting as usual. I'll pay shipping and use my own vendor for testing. Molecular change... care to elaborate?

Heat in excess changes the Rockwell and distorts the shape requiring additional machining.
That's funny: which myth have you busted?

You can weld these with proper tooling just fine. It's aluminum not wood. Don't forget your nikasil coating is your strength on these.

Proper tooling is not the issue.
When you apply heat to the aluminum that Mahle uses to make their cylinders, the silicone and magnesium in the material creates nitrogen bubbles on the surface of the weld. These bubbles or pockets can be as large as 1/6" rendering the surface useless for most applications.
Of course a kluge might try to fill the pockets but no professional would accept this kind of defect.

Interesting. Tell me more. Which welding method is this experienced with?

The problem is not the welding technique. The problem is the cast aluminum. Much like trying to weld pot metal.

I know you give little weight to expert opinion but if you really want to know, call Millennium Technologies. They repair and plate 150 cylinders a day. My information comes from them.

I know what you're saying. It is very difficult to weld cast aluminum that has been in an engine environment... it absorbs oil and can be sloppy or impossible to weld to. No denying that fact. It doesn't make a lot of sense to fight it when there are other options. However, it can be done if you're technique is correct and your prep is meticulous. I've welded much thinner cast aluminum on an engine... much thinner than these cylinders and know the pot metal effect you describe... it can be managed and I'd love to try if you have a single junk cylinder. Fun experiment?

One more question: How can you tell if the cylinders have suffered unacceptable heat stress in an earlier life?

Usually warped or out of round. If you're welding before you hone and re-plate then going to be real hard to tell the difference all done... unless you take a map gas torch to them and melt them causing damage to the substrate... which I think is what Henry is describing. You should be able to avoid that as an experienced welder with temperature control.

Thanks - the reason I ask is that the guy at the plating shop said he'd seen several that had been overheated and were 'too soft' and had to be tossed out.