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Piston to wall clearance 2618 alloy pistons

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On the way to built a 4g63 7bolt engine with wiseco 2618 pistons (9.0:1 - 85,5 mm with skirt coating). The turbo is a td05-18g, so will be around 400hp @crank. Pump gas 98octane, time attack race car.

The suggested clearance (ptw) by wiseco is at .0025. I said to the machine shop to make the clearance at .0030 but after i got the short block back and got some measurements, i found that its been done with .0060+ !!

Should i replace the pistons with 86mm and sent the block again for honing? If i build it like this, will having blow by or compression issues? And lastly what about the piston rings. With a bore now at 3.3700, according to wiseco the top must be around .017 and the second at .019..

Id be making that machine shop fix their screw up. it shouldnt be on you to deal with it. Somebody obviously doesnt know how circles work.

I can see you having piston slap issues for sure.

Again, they are accountable. Tell them they need to fix it, weather it is by a. finding you a new block or b. by doing the honing for free and getting you new pistons. I cant stand it when people dont take responsibility for their shitty work.

Hope it works out for you.

I can see this being a long drawn out affair.

Unless you gave the machine shop the machining instructions in writing they will just say you told them .0060 and it will be your word against theirs. What's the legal system like in Cyprus? Do you have the time, energy, and funds to fight this through the courts if it goes that way?

Unfortunately there is no such a thing with our legal system, its a long story. But how would you proceed in a case like this? Except from piston slap, what you do think about compression or blow by? Can i keep it and make it work? I am thinking to try the Totalseal rings. Anyone familiar with this product?

Also can i tune it with a leaner AFR to get a more expantion on the pistons?


Not same as yours, but same idea. Guys mention piston slap until good and warm, with .0045. yours is more. I dont have

good hopes for it. That really sucks man. I would be spreading so much bad word about a machine shop if they screwed me like that.

I guess bore it out and go bigger pistons? Can probably sell the old ones.

0.006" is very loose for a 85.5 mm bore and a 2618 piston. In saying that though, 0.0025 is tighter than I'd be comfortable with on a high power engine setup unless there's something unusual about the alloy that Wiesco use. PTW clearance varies with the specific piston alloy but typically on the JE pistons I use, I'm somewhere around 0.004".

My opinion is that 0.006" is going to result in a very noisy engine and potentially increased blow by and oil consumption. I'd certainly be going to an 86 mm bore and starting over. Preferably with a machinist who can work to tighter tolerances by the sounds of it.

Thank you all for your answers and the support, but Andre, or anyone, is it possible a noisy engine, to make the tuner's life harder? Does piston slap sounds like knock? And finally can piston slap couse in a fatal failure? With these facts, whats the worst case scenario?

First off, do not run this engine with these pistons at that clearance. It simply will not have a happy life. And it may be a short life. What you currently have will not work well.

IMO in this situation, your best bet may be to have a custom set of pistons made to suit the current bore, as long as the bores are properly machined, straight, round, finished, etc. Yes custom pistons do cost more than off the shelf sizes, but could be workable.

The cost of 4 properly sized pistons and perhaps another set of rings if required will likely be the simplest path. Many piston manufacturers can make custom sizes down to half a thousandth of an inch. Cup engines are usually finished to half a thousandth when re-built.

If the bores are all good and the custom pistons arrive on spec no further machine work will be required, saving a step and cost.

The result of excessive piston to bore clearance will be an engine that is mechanically noisy. This can make it difficult to distinguish knock, so yes it can make the tuner's life more difficult. On top of this the engine will generally exhibit more blow by and higher oil consumption than an engine with correct PTW clearance.

6 thou is unlikely to cause a piston to fail, however piston life may be shorter as the piston will tend to rock more in the bores than if the PTW clearance was correct. I would be inclined to correct this clearance rather than running it as it is.

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