Mahle cylinders & Omega pistons?

[Spenny_b]

Folks,

Would like some advice please, concerning inter-operability of cylinders and pistons.

There's a long story about how I'm now in the position I'm in, but until it's fully resolved, I need to do the right thing.

Question....I have some 97mm Mahle 3.3 barrels (from a 1992 965, fully finned) that need re-Nikasil coating. Dimensionally, they were in great condition after 84k miles.

The 98mm Capricorn barrels I recently bought (2nd hand) are scrap....beyond repair for a number of reasons. These are going to be refunded.

I understand that the Mahle's can be stripped, re-bored from 97->98mm and re-coated.

BUT....I've read/heard a few times, that due to the aluminium used by Mahle, you should only ever use Mahle pistons inside Mahle barrels...expansion rates, etc.

I have some brand new Omega 98mm pistons....gorgeous examples of fantastic machining. Bought yesterday.

Is the above statement really true about Mahle + Mahle, or more an urban myth?

Could I use my new Omega's inside re-worked Mahle barrels?

As another alternative, could my 97mm Mahles be re-worked to accommodate a 98mm cast liner, instead of Nikasil coating? Am aware that Porsche did something similar many years ago (casting ally around an iron sleeve)....

Or am I into a new set of Nikkies?....lovely though they are, its yet another £2,500+, by the time they're in the UK.

I'm so over budget with this latest set-back, all I'm trying to do is limit my exposure, re-using what I have, so long as it's good practise....I'm not into taking risks with this engine project.

Thanks for any guidance folks,

S.

[Steve@Rennsport]

Spenny,

You can use your Omega pistons (2618) in Mahle cylinders provided you maintain proper piston-to-cylinder wall clearances. Mahle pistons do not expand as much as 2618 ones do so they run tighter.

You simply have the cylinders honed & re-nikasil plated to whatever you need.

Done this several times without issue.

[Spenny_b]

Thanks Steve,

Does that mean, therefore, that because Mahle pistons don't expand that much, the cylinders also don't expand too much and are thermally (fairly) stable?

If so, then I would need to know how big the Omega pistons expand out to, when hot, to ensure that they don't become pinched/tight?

But wouldn't that also mean that whilst the Omega's are cold and getting up to temperature, they'll run loose?

...Or...

Are we saying that the cylinders do expand a fair bit, due to there being less material than a piston?

Cheers
Spencer.

[Flieger]

The MAHLE cylinders expand less than the equivalent in 2618 alloy. Yes, the 2618 pistons will run looser than the MAHLEs until warm. The Nickies are made of 2618 and so can run tighter tolerances across the warm up regime when matched with 2618 pistons.

[Spenny_b]

Thanks Flieger....am taking myself off to count the pennies left in the piggybank....better search down the back of the sofa whilst at it.

I really do like the idea of Nickies, with increased cooling ability as well....just seems like the "proper" thing to do at this stage of the project. Have tried the "get by, they'll be fine" avenue on somebody's advice, and it's (almost) bitten me in the ass...time to trust my gut instinct and do it right.

Will speak with Fred @ Omega in the morning to get their specs for expansion rates; I'm pretty sure they'll be inline with JE and compatible with Nickies, but want to be double-sure.

Cheers
S

[Steve@Rennsport]

Originally Posted by Spenny_b

Are we saying that the cylinders do expand a fair bit, due to there being less material than a piston?

Cheers
Spencer.

Hi Spencer,

Pistons & cylinders expand at different rates, depending on the alloy and temperature so allowances are made at ambient temps to ensure proper fitment at operating temperatures. Pistons run much hotter than cylinders so this must be compensated for when determining proper running clearances.

Charles @ L&N Engineering has a cylinder that closely matches the 2618 alloy, but there are other factors to consider such as piston design.

The unique and proprietary Mahle piston alloy offers the lowest growth forging in the industry, albeit at higher weights, for maximum longevity and durability.

[PhilDY6]

Originally Posted by Spenny_b

Will speak with Fred @ Omega in the morning to get their specs for expansion rates; I'm pretty sure they'll be inline with JE and compatible with Nickies, but want to be double-sure.

Cheers
S

Hello Spencer,

Ok, the expansion rate of 2618A is .000022mm per mm (diameter or length) per degree Celcius increase.

When you speak to Fred ask him if he will pass on your telephone number to Mark the Porsche guru. We won't give Marks mobile out unless he agrees to it but we can pass on your number to him. He will tell you anything you want to know about Porsche. I mentioned him to you the other day

Very best regards

Phil

[Spenny_b]

Originally Posted by PhilDY6

Hello Spencer,

Ok, the expansion rate of 2618A is .000022mm per mm (diameter or length) per degree Celcius increase.

When you speak to Fred ask him if he will pass on your telephone number to Mark the Porsche guru. We won't give Marks mobile out unless he agrees to it but we can pass on your number to him. He will tell you anything you want to know about Porsche. I mentioned him to you the other day

Very best regards

Phil

Hi Phil,

Ah yes, Fred did mention somebody this morning, sure it was Mark - he's the chap who knows every single Porsche part number ever made, isn't he? Used to work for Fred?

Thanks for the expansion rate...so, just under 2.2um/degC increase for a 98mm piston then. This morning Fred gave me the tolerances he would want a bore to be.

Thanks again
S

[Spenny_b]

Originally Posted by Steve@Rennsport

Hi Spencer,

Pistons & cylinders expand at different rates, depending on the alloy and temperature so allowances are made at ambient temps to ensure proper fitment at operating temperatures. Pistons run much hotter than cylinders so this must be compensated for when determining proper running clearances.

Charles @ L&N Engineering has a cylinder that closely matches the 2618 alloy, but there are other factors to consider such as piston design.

The unique and proprietary Mahle piston alloy offers the lowest growth forging in the industry, albeit at higher weights, for maximum longevity and durability.

Thanks Steve

Chris Carroll @ TK is liaising with Charles for me, as we speak, to ensure that the recipe is going to be good....it's those "other factors" that are scaring the cr4p outta me at the moment, lol!!

I think I've more-or-less talked myself into going the whole-hog and getting the Nickies (assuming there aren't any show-stoppers, of course)

Cheers
S