3.0L Piston to Cylinder Clearances with JE Pistons + Replated Alusil Cylinders

[2jmotorsports]

I am about to send my 3.0L KS Alusil cylinders to be replated with Nikasil. I will be running JE pistons #274048 (9.5:1 compression)

PORSCHE - PORSCHE 911 (Sport Compact Section) - JE Pistons



What kind of piston to cylinder clearances should I be targeting? Below are the clearances listed in the Bentley but since I will have aftermarket pistons with modified OE cylinders I dont know which, if any, should apply.



Thanks in advance.

[Catorce]

Usually what you do in this case is send one piston off to the plater. I assume you are using US Chrome or Millennium; either one will have you fill out a sheet with what you are looking at, turbo or NA, and the bores will come back right.

In probably a dozen rebuilds I have never actually checked with the plater as to what the bore size is; they know what the standard piston to bore clearance is and adjust accordingly based on the piston you send them.

I wouldn't overthink it.

[cgarr]

Mine were .0015 with j&e's


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[2jmotorsports]

Originally Posted by Catorce

Usually what you do in this case is send one piston off to the plater. I assume you are using US Chrome or Millennium; either one will have you fill out a sheet with what you are looking at, turbo or NA, and the bores will come back right.

In probably a dozen rebuilds I have never actually checked with the plater as to what the bore size is; they know what the standard piston to bore clearance is and adjust accordingly based on the piston you send them.

I wouldn't overthink it.

Cylinders are going to EBS. I am not sure what plater they use.

I am sending one of my JE pistons along for the ride, should they need it.

I hope you right about not overthinking it. In a world of "well you didnt specify what they should be" or "you didnt tell us thats what you wanted" I figured I would cross my T's and dot my I's. I do trust the folks at EBS though.

[Catorce]

EBS Sends them to millennium, so they will be done 100% correct if you send your piston along with. Barring some special order or instruction from you, they will do it the way they do the thousands of other cylinders they do. Never had a problem with them.

[2jmotorsports]

This is very reassuring. Thanks so much for the feedback!

[arbita1]

Just did the same thing a few months ago, except they provided the JE pistons as well. They came out great. They know exactly what to do.


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[m42racer]

Originally Posted by cgarr

Mine were .0015 with j&e's


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Were those pistons made from 2618 or 4032?

[cgarr]

Which ever was the older about 2005 the new may be tighter?


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[Mark Henry]

Don't even look at the Porsche Mahle specs, different material and they run a much tighter spec.
In comparison JE's are sloppy till they get a bit of heat into them.

[2jmotorsports]

Originally Posted by Mark Henry

Don't even look at the Porsche Mahle specs, different material and they run a much tighter spec.
In comparison JE's are sloppy till they get a bit of heat into them.

Mark, with that in mind, should I be running JE rings as well?

On their site they claim "The ring grooves are precision CNC machined for OEM style rings". But if the pistons will behave differently than OE then Im thinking I should run the rings that were designed specifically for them.

[m42racer]

Some advice to add to the advice already given. If in doubt, ask!!!!

First, identify the material the pistons are made from. I think 2681. This typically requires you to run + 0.003" clearances. I would think 0.003" would be the minimum and air cooled application probably requires another +.001- 0.002". If this is a race engine you may want more. Call JE and ask. If the piston is guided differently, you can go tighter but error on the safe side until you have some running time on the engine. Expect the piston to make some minor noise on start up. Normal. This can be helped by running an offset pin, but you may have your pistons already. Check to make sure where the pin center line is and if offset, make sure you get then orientated the right way for each side of the engine.

Also make sure you have the correct ring face coatings on the rings. I am not sure if the original Alusil can run a different face coating to Nikasil? The rings if supplied with the pistons would have being supplied based on what you told whomever you bought the pistons from, what cylinder coating you are using. Hopefully. Just remember, no chrome with Nikasil. Also make sure you tell the cylinder repair place what the final surface roughness you want. You should be aiming for around RA4 - RA8 max. Often they come as much as RA 12. This will wear the rings a lot faster and
cause other issues as well.

As for what JE say about the ring grooves machined for OE rings, I would think this is both side and back clearance dimensions for the OE ring sizes. Make sure you fit the rings the correct way (up or down) if they are tapered faced. I suggest you ask or make sure you have a Napier 2nd. This will help additionally with the oil control.

[Trackrash]

According to JE the piston to cylinder clearance should be 0.0015" for 3,0 w/ 9:5 to 1 cr.

[m42racer]

That tight a clearance is typical of 4032 material. If you can run as tight as that with 2618, and have no scuffing issues, that's great.

[prschmn]

I think it's important to keep in mind that although clearance varies with piston alloys
one needs to remember that aluminum cylinders also expand hence tighter than "normal"
is in fact "normal" for air cooled engines.

[2jmotorsports]

Thanks for the feedback everyone. Especially for that JE spec sheet!

[Luke M]

I did this with my brothers 3.0 rebuild using the same part # pistons. The cylinders were sent to EBS and I also sent the JE spec sheet along as well. It all came out perfect and fit well. I've yet to install the heads but should have them back and on by mid summer.