mitsuturbo
(Banthony )
09/08/10 01:53 PM
ATTN: Mahle PTW clearance

I wanted it in writing, so i got it. Here is my exchange with Mahle regarding their 4032 forgings for a 4g63.

Quoting mitsuturbo:


I'm looking for some help with Piston To cylinder Wall clearance on a set of pistons i purchased. The machine shop i took my block to decided to put it at .006" because the bright green spec sheet included with the pistons says to set PTW clearance at .0025 to .0030" and add .001 to .003" for applications such as forced induction, filled block, nitrous. Since this is going into a turbocharged car, they put it at max. PER YOUR SPEC CARD Everything i've known in the past, am hearing and reading now, says that this is WAAAAY too big. This engine is going to be running in a (primarily) STREET CAR that will peak at about 24psi of boost most of the time. It "might" see 30 or a shade over PSI if i ever decide to run some leaded fuel and take it to the track.

The pistons are model MIT367385i13 (4g63 turbo, with 13cc dish for 3.386 bore) I've already pulled another block in order to get this right, as .006 seems way too sloppy. Please advise.




Quoting Tony Ford @ Mahle:


Talked to you last week on the phone about this. 0.006" is too much clearance for those pistons. You need to finish the bores on the new block to 3.3855".




Quoting mitsuturbo:


I relayed this information to the machinist, and he's since expressed concern, stating this only allows for .0018" clearance. He's asked if this is acceptable, stated that the included documentation with the pistons states otherwise, and is wondering if the coating is somehow a factor in the bore size vs PTW clearance. He's asked if maybe he's measured the piston skirt in the wrong area. I expressed that these are very low expansion pistons and factory spec is .002" on the extreme loose end. Still he seems to think that's not enough clearance" if you're going to be running 20+ pounds of boost. I think I'm comfortable with .002" but any clarification you can offer would be helpful.




Quoting Tony Ford @ Mahle:


The actual clearance is goinn to be 0.0035", but you can't measure that, because they're coated. We count our clearance to the aluminum.
That should be plenty of clearance.
I designed these pistons, and have prescribed the specifications to hundreds of people. No complaints.


Kind Regards,

Tony Ford
MAHLE Engine Components USA, Inc.
MAHLE Motorsports (IMO7)

270 Rutledge Road, Unit C

Fletcher, North Carolina 28732 USA
Phone: 1 (828) 650-0814, Fax: 1 (828) 650-0819
[email protected], click





Edit: noticed some characters weren't showing up right, such as the and some quotation marks


cheekychimp
(Director of Housing and Urban Development, and carbon/kevlar balls)
09/08/10 02:11 PM
Re: ATTN: Mahle PTW clearance

That seems very clear but if he is so damn sure that clearance should be 0.0035 why does he provide a spec card that can only meet those specs at the minimum end of all the scales used i.e. 0.0025 PTW clearance plus 0.001 for use in a forced induction engine?

I don't think your machine shop can be held accountable for you essentially ruining a block by over boring it, BUT I think he should be held somewhat responsible for what has happened when his recommendation hardly matches what is written on the spec card. He obviously has some sort of scale based upon boost pressure and whether only forced induction or forced induction plus nitrous is going to be used etc and that spec card ought to reflect that.

It would be better to supply no information at all (rather than misleading information). At least then you would probably have asked at the start.


mitsuturbo
(Banthony )
09/08/10 02:57 PM
Re: ATTN: Mahle PTW clearance

Right, but this is here to reflect how these pistons SHOULD actually be set up, not to illustrate that it was done wrong on my end first.

Machinist and i agree that the spec card seems generic and should probably not have been included, or should be FAR more specific. It'll be taken care of properly now, regardless.


cheekychimp
(Director of Housing and Urban Development, and carbon/kevlar balls)
09/08/10 03:28 PM
Re: ATTN: Mahle PTW clearance

Yeah I appreciate that and for the record I just looked back over my post and I didn't mean it to come across the way it did. I don't think you did anything wrong either really and I think it sucks that you've been left in this situation. Like you have said however, at least it is being taken care of now and better that than to have put the motor back together with the wrong clearance.

Props to you also mate for being unselfish enough to post this up for the benefit of others so that they don't need to go through what you did.


mitsuturbo
(Banthony )
09/11/10 02:25 PM
Re: ATTN: Mahle PTW clearance

One last thing, which I found out during my endeavors on the phone with them.

Pronunciation:

Mahle is pronounced just like the female name "Molly" (it gets mispronounced a lot)



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