Are these scratches and clearance between the piston and cilinderwall normal?
 

Hi guys,

Ik had some gasket failure with my build engine with forged Wiseco pistons, i drove about 1000km with it. It was only smoking when i let of the throttle after WOT. It didnt smoke when i let off the throttle/80%

I brought the car to the shop because i didnt have time to fix it, and now when they took the head of the send me this.


Dont look at the oil, that was because of the head gasket failure, i think the scratches are pretty normal

https://www.miataturbo.net/attachmen...ine=1447103361



They also send me this video. i know this is not a very good way to measure look at the clearance of the pistons. And remember.. those are forged pistons

You can't measure piston to cylinder clearance with a video. If you want to know the clearance, ask the machinist/builder who assembled it. Or tear down and measure it yourself.

From the pic, there's a bit of vertical scoring, but not too bad.

First, I am wary of your mechanic, because he's sending you pictures and expecting you to diagnose a potential problem on your own car. That's what you're paying him to do.

Second, since you can still see the crosshatching underneath that scoring, it's not too severe. If you can't catch your fingernail on it, I would not be concerned.

What is the tolerance of a human fingernail. Are some people more adept at feeling scratches than others? I chew my fingernails so I assume they would be duller than others? Am I more likely to miss an important gouge because my fingernails are too dull?

Agreed that the crosshatch marks mean good things.

I'm a little weirded out by what appears to be pitting near the top of the bore, along with whatever this mark is:


https://www.miataturbo.net/attachmen...ine=1447122392

When I saw you replied Joe I was expecting a nice long response about finger nail thickness.

your mechanic is retard

u shoulda leakdown

iirc the last time i did leakdowntest dry. They were all between 5-10%. And compression around 180-180-178-180

180 even is good, solid numbers. I assume you're running 9:1? My 8.6:1 motor was low 170s across the board last I checked.

Unless the vertical mark was deep enough to cut a channel through the cross-hatching, I wouldn't worry.

pitting=dirt/debris
mark=2nd or oil ring TDC

the fuking guys couldn't even wipe the bore clean before asking you to diagnose it for them.

There are Wiseco low comp yeah. So something around 8.8-9:1

Wiseco makes 8.6:1 and 9:1 low compression pistons. I think FMs are all 9:1.

You can feel, with the pad of your finger, something crazy like 20nm difference in height on a flat surface. The finest piece of measuring equipment I've ever been so lucky to use would measure down to a couple microns, had temperature sensors in twenty places for temperature compensation. I can't even tune WUE, lol

http://www.sciencedaily.com/releases...0916110853.htm

I can't type all eloquent and smart, so this post is DIY from here out.

Get your car out of that shop. Now.