Mahle, JE and others

Fperotti · 06-02-2005, 02:12 PM

I am rebuilding my 2.4T engine and, as far as I know, the noise and partially the wearing -at low working temperatures- from the engine is proportional to the P/C gap. Trying to estimate the behavior of my future engine -wich I think to upgrade with E cams and 9:0 cylinders- I'd like to know the nominal P/C gap in Mahle kits and JE Pistons forged aluminium P/C clearance needed and tolerances of the last ones.

Do you know anything about it?

Thanks,
Fernando.

asphaltgambler · 06-02-2005, 03:57 PM

I'm not sure of your question. Are you asking the clearance difference in Mahle vs JE?

Fperotti · 06-02-2005, 05:16 PM

Yes, exactly but since in mahle you don't have to do anything but purchase it in JE piston you have to hone your cylinders if they are worn out, like mines. So, I'd like to know if the clearance is similiar -in nominal terms at least- in both cases.

Thanks,
Fernando.

Bobboloo · Bobboloo's Garage

If the cylinders are worn out of round (highly likely) then they should be bored out or replaced. They can be bored out for 1st or 2nd oversize Mahles (+.025 or +.05) and matched to their according group piston. Piston to cylinder clearance would be .025 to .045. I would check on availability before boring out for Mahles however before proceeding because I have no idea if they are available at this point in time.

With an aftemarket piston, like JE, you can go even larger like 85mm or so as opposed to 84.5mm. In this scenerio it's best to send out one of the cylinders after they've been bored to get the best fit. This helps prevent any mis-communication problems.

NevenM · 06-03-2005, 03:04 AM

Fernando

I don't think wear is associated with p&c clearance. The reason Porsche and their suppliers minimised this was engine noise ie "piston slap". The 2.4E engines used a cast "autothermic" piston (which had steel plate embedded in them) so that they could start at a closer tolerance when cold. Mahle S pistons were forged from an alloy which had a lower coef of exp to get the same result. JE would probably run at a higher clearance than Mahle but the criteria is different, ie performance not noise. Noise has always been a problem in air cooled engines, but we all love that noise so what s the problem :-)

HTH

Neven

Fperotti · 06-03-2005, 06:34 AM

Thanks for the info.

Neven,

I couldn't agree more. I love the noise but the proper one :-).

I think I am going to JE pistons "2.2E profile" in 84.5mm or 85mm. I'd like to know the clearance for this ones since I will buy the pistons before going to the machine shop in order to reach the correct clearance.

Thanks again,
Fernando.

NevenM · 06-03-2005, 02:44 PM

Fernando

You may be better off sending your cylinders to someone like EBS and getting them to supply the package (they have done it many times)

HTH Neven

snowman · 06-03-2005, 08:46 PM

JE pistons come with the exact size bore that is recommended. Have it bored and honed to the exact size , within the tolerance recommended by JE. For the final honing operation I strongly reccommend that it be 5 to 10 passes with a flex or grape style hone. This operation does not affect size, just the finish. I also recoommend that you use someone that uses Torque plates for the final honing to size operation.

Fperotti · 06-04-2005, 05:33 PM

Hi Jack,

Do you mean that the specs. came with the pistons?.

Thanks,
Fernando.

snowman · 06-04-2005, 08:30 PM

Should have. If not call JE and find out what they recommend.