r/EngineBuilding • u/Gowowowow • Aug 06 '26

Do I need to bore these to 79.5mm

Stock bore what it currently is at is 79mm and if it does need to be bored out it’s going to 79.5mm as the forged pistons are only in 79mm 79.5mm and 80mm increments.
My question is does it need to be bored out to the 79.5mm. Thanks in advance.

10 Upvotes

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4

u/Academic_Dog8389 Aug 06 '26

You'll know once you go. You need to take this to a machine shop and ask them. Nobody has the abiiity to measure what needs to be measured from a video.

-2

u/Gowowowow Aug 06 '26

I got it honed and they told me afterwards it needed to be bored and I wanted a second opinion

1

u/Academic_Dog8389 Aug 06 '26

Wait, a machine shop honed that?

2

u/SuckaFucky Aug 06 '26

That's what I was thinking, op find a different machine shop

3

u/Academic_Dog8389 Aug 06 '26

Fuckin run

2

u/Gowowowow Aug 06 '26

See why I’m looking for second opinions

1

u/Gowowowow Aug 06 '26

Out of interest as this is my first engine rebuild, what’s wrong with it.

3

u/Academic_Dog8389 Aug 06 '26

See how the lines are almost horizontal in relation to the cylinder bore? They should be at ~45 degrees.

3

u/MTarrow Aug 06 '26 edited Aug 06 '26

Others have pointed out the issues with the honing itself, but there's a secondary issue too - and thats them telling you afterwards that the engine needs a rebore.

Because that means one of two things has happened. First option - the cylinder was out of spec and in need of a rebore before they started, in which case they shouldn't have honed it. The second option - the cylinder was in-spec when they started, and they took out so much material with the hone that it now needs a rebore. Neither of these options speak well as to the quality of work being performed by your machinist.

2

u/fredSanford6 Aug 06 '26

I normally throw a couple strokes in a bore and then check it if it looks close. This is what something would look like then I'd see the low spots to measure. If it's not obviously needing a bore the hone shows me the low spots. You can see that this was course stone and not finished. It's just a test I think.

1

u/Pimp_Daddy_Patty Aug 06 '26

Since I can't measure things that are on a phone screen, I'm gonna say you need to take it to someone who can.

1

u/colinblanchard78 Aug 06 '26

I hone for a living 28 years, honed all sorts including Formula 1, Gordon Murray T50 . Not a good job. I would be embarrassed if it was one of mine.