90mm conversion to 93

[HKZ Bob]

Hello Rebuilders. I like to find a reasonable solution to rebuild worn out 90 mm cylinders and replace the piston by a Alfa Romeo mass production 93 mm version.

Here the id. Increase the liner diameter from 90mm to 93 mm.

Where is the borderline of the cylinder wall thickness.

Attached the current 2.7 Carrera RS piston
and the two potentials

Thank you for feedback.

[cnavarro]

With a cast (OE or otherwise) cylinder, I would say no way - 92 is as far as Mahle went. You'll just break the skirts of the cylinders. I've been doing 93 mm bores in 2.7 registers (and various other very, very thin wall slip fits) with Nickies and it's not a problem with our cylinders because of the way our alloy is extruded and its other characteristics.

My question would be whether or not the rings would work with Nikasil, but more than likely there is something out there that could be made to work? The oil ring seems to be an odd size at 3.5mm. Also, what piston to cylinder clearance would you run, not being familiar with how the piston is cammed and how is expands (i.e. a mahle piston in a mahle cylinder is different than a je in a mahle cylinder).

[HKZ Bob]

Thank´s for the quik response.
The attached sketch are from a Mahle CATALOG. I still have to find out if the pistons is coated. You think die/sandcast linern won´t make it to 93mm.

The idee is to rebuild worn cast cylinders, use new coated pistons, and not buying
all new. The other piont is a new Aftermarket set is 1300 US,
A set of pistons for ex. Alfa Romeo are easy to get for 250 US & rework the liners.

Any other ID on this point.

[HKZ Bob]

Here I found a 92 mm Motor Guzzi piston out of Daytona 1100, which looks familiar to the 911 piston. Height 64.5 mm

any comments

[cnavarro]

I see a directional indicator, are those offset? There are varying amounts of offsets built into pistons and be quite honest, I don't use any offset with JEs and Nickies.

The dome volume also looks mightly low on those pistons. I like the slipper skirts though.

I'm not sure if you are factoring in the cost of replating the cylinders as well, the difference between doing everything with a proven set of JEs and pistons sourced from another application, although resourceful, might not be all that much more economical with many variables that would have to be careful considered.

Another consideration is whether or not your cylinders have a CE ring cut in them - if they do, even 92mm is not possible, without decking the cylinder to remove the groove, cutting the top fin to restore the proper depth, and having some custom base shims made up to correct the head to deck length.

Not to discourage you, but like I said, it took me three tries to properly set up clearances of a vw type 1 cima/mahle piston in a set of Nickies, since those pistons are designed to expand very little - you literally have to set them up so tight you can barely put the piston through the bore, or they slap so bad when hot it sounds like the engine is knocking from detonation bad. Good thing the Nickies expand quickly, never had them sieze!

[HKZ Bob]

Here one other choice:
2 new Orginal Moto Guzzi piston with rings and pin
The piston height is 72 mm , Diameter is 92 mm.
Diameter pin 22mm.

1) I see a directional indicator, are those offset?
I don´t know what you are pointing out. Do you mean the arrow on trhe top of the piston.

There are varying amounts of offsets built into pistons and be quite honest, I don't use any offset with JEs and Nickies.

2) (Do you mean JE pistons & Nikasil liners)

The dome volume also looks mightly low on those pistons.

3) If you compare the volume of an Mahle Carrera 2.7 they
might have the same displacement. I added anothe motorbike piston to it which I saw first. see picture.

I like the slipper skirts though.
4)Me too

I'm not sure if you are factoring in the cost of replating the cylinders as well,
5) Nobody in the automotive industry are plating cylinders.
I like the piston to be coated.

of JEs and pistons sourced from another application, although resourceful, might not be all that much more economical with many variables that would have to be careful considered.

6)What is the wholesale rate for JE with Liners for a 2.7.

Another consideration is whether or not your cylinders have a CE ring cut in them
(what is CE Compression ring cut)

- if they do, even 92mm is not possible, without decking the cylinder to remove the groove, cutting the top fin to restore the proper depth, and having some custom base shims made up to correct the head to deck length.

7) That would be painfull to do
This is a good point to consider !!! I´ll chack with my liner where the grove starts.

Not to discourage you, but like I said, it took me three tries to properly set up clearances of a vw type 1 cima/mahle piston in a set of Nickies, since those pistons are designed to expand very little.
8)That really depends what you choose.
What is CIMA.
Have you set the clearance according Porsche Spec.

[cnavarro]

Those last pistons you show look like they have enough dome volume to have a decent street compression ratio.

You mention having the pistons coated - I am referring to the bores when I mentioned the nikasil plating. With all the available cylinders for the 911, they have to be nikasil plated, at least with the aircooled engines. The factory only used alusil on some 2.7s and the 3.0SC. Alusil does not like to be run hot. There are modern variants - Lokasil, etc, but all the high end Porsche engines still get Nikasil - although superior, it is expensive.

If you have an alusil cylinder, I would most definately bore and replate to the size for the new piston - whether the piston is coated or not is inconsequential. If you are wanting to do this with alusil cylinders, I would highly suggest not. There are enough variables to contend with when it comes to properly reconditioning an alusil cylinder. Do a search for alusil on the forum. If I think you are trying to do this with an alusil cylinder, you have alot of research to do first before making any decisions.

My comments as far as offsets and not using any with JE's and Nickies are in reference to the Nickies cylinder we manufacture, not any of the Mahle, KS, or other manufacturers cast cylinders.

[HKZ Bob]

charles I tried to call you on 815-472-2939 ,like to talk on the phone.
but I got linked to an answer machine.
when is the best time to call.

Robert

[cnavarro]

Sorry I missed your call, I was on the phone, but did see an international call coming in. I'm usually available all day, unless out for lunch or on the phone, since it's just me handling all the calls.

[HKZ Bob]

Charles I just came back from downstairs.
Yes I do have a cylinderhead groove in my liners.
the bottom out diameter is 96,750 mm & the inner is 90.00 mm
The cylinder wall thickness is now 3.375 mm.
If I would implement an 92,00 mm piston the wall thickness would be reduced to 2,375 mm. charles is that still acceptable??

The upper part has an grove. the inner grove is 2.5 mm thick.
That portion will be reduced to 1.5 mm.

I have also a source for coating the cylinders. When I spoke about current technology, we are using laser honing in our plant for strait four diesel application. We are having no eperience in boxer motors & air cooled applications. Not our core buisness. We are not coating the cylinders only the pistons. Is that different to air cooled applications.

I saw your webside. Quit impressing. But I know what we are paying for a piston mass production. Approximate 5 million units a year. Now you may understand why I mislike current market pices.

Greeting to Illinois. I have just been to Freeport.

[cnavarro]

Bob,

So you have access to the required materials to re-etch an alusil cylinder then, right? Even with a coated piston, a normal aluminum bore is not a good wear surface. The what I would consider un-plated alusil cylinders have a high silicon etching just at the surface that makes for it's wear surface in lieu of a liner or plating like Nikasil.

5 million units a year, damn.

It has been my experience (and that of others too if you guys want to chime in) that the cylinder material around the ce ring closest to the bore is too thin at the top of the cylinder when the bore is opened to 92mm from 90mm, it will want to crack, just like the skirts will want to, with a cast cylinder.

Sorry I missed your call yet again, I was on the phone and I just don't have enough time to switch over.

[HKZ Bob]

charles when my piston is at TDC I have 18.4 mm clearance between top of the head. Orgininal Mahle has an 5.5 mm overheight. They are having a compression ratio of 8.5 to 1. Your JE pistons are having what overheight and produceing 10.5 to 1 compression ratio.
May you post a drw. of the piston for comparison.

robert

[cnavarro]

Usually we set up the JE's with a .040 - .060 deck height and take the customer's chamber size and specify a dome volume needed to get the compression ratio desired - nothing is off the shelf for me since I prefer to dial in everything as closely as possible. If I do use an off the shelf piston, I get them from EBS Racing on short notice.

[Jim Housman]

Pelican Parts lists a 93 mm Mahle Motorsport P/C set. Am I missing something? Why mess with anything else?

[Steve@Rennsport]

Originally posted by Jim Housman
Pelican Parts lists a 93 mm Mahle Motorsport P/C set. Am I missing something? Why mess with anything else?

Jim:

Although I'm a big fan of Mahle P/C's, the 93mm ones were not their best effort.

These have VERY thin walls and do not stay round when hot resulting in loss of compression, increased blowby, and a shorter lifespan than the thicker walled ones such as 90mm or 92mm ones.

Given the stud spacing on these engines and thus limited room for big bore P/C's, I'd suggest nothing larger than 92mm ones at best.

[cnavarro]

Jim,

Our 93mm Nickies cylinders are superior to the mahles because of the properties of our alloy and method of manufacturing, allowing for thinner walls without giving up longevity or reliability because of their strength, greater cooling, and higher ductility over the inherent problem of the thin-walled Mahle 93s that Steve mentioned. Even thinner, i've done 89mm slip-fits for a 2.2/2.4 without any problems, although 87.5s are much more common among other vary popular thin walled cylinders for other applications, like 88s and 90s (and larger custom private label cylinders for some well known engine builders) for the 356 and 912, where before all that was offered were 86s. That's one of many reasons why someone would use our cylinders over Mahle. The whole JE piston debate of Mahles has been discussed until we tured blue in the face - I'll just regurgitate that Mahle pistons work best in Mahle cylinders and JE Pistons work best in Nickies cylinders, because of expansion rate differences.