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Cylinder Wall Scoring

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Hi all,

I'm hoping for some advice from someone with more experience than myself in performance engines.

A friend of mine purchased a freshly built, "forged" 1.8L 4cyl turbo engine for his '90 MX5 from Facebook marketplace. After driving for approximately 5000km, multiple oil changes in between, his oil is still coming out very metallic.

The metal led us to do some testing on the engine, results as follows

Leak down test;

1 - 6%

2 - 8%

3 - 9%

4 - 4%

Compression test;

1 - 125psi

2 - 127psi

3 - 124psi

4 - 123psi

We then decided to put a bore scope down each cylinder, which is the point of concern I'd really appreciate advice on. All cylinders had scoring, which on camera looks quite significant. The heaviest scoring being on the major thrust side of each cylinder wall, and some not as heavy on the minor thrust side. Front and rear of the cylinder had very minimal scoring if at all.

The build was undocumented so we have no knowledge of compression ratio, p2b clearances, ring gaps, nor does he know the quality of the build or environment it was assembled in. It's currently running 20psi boost. It was purchased on marketplace with no receipt or invoice so returning to the builder seems out of the question.

I'd like to know, in your experience, if the pictures I've taken & will attach in order below of the major thrust side scoring would justify tearing down the engine for a proper inspection. I'm torn between not wanting to advise my friend spend unnecessary money, having already spent a heavy sum on the purchase, if the concern isn't as bad as it looks on camera - Or whether it would be best to advise to inspect & repair now before the damage gets any worse.

All advice is greatly appreciated,

Blair

Attached Files

I would suspect two different things.

Those markings are very similar to what I would expect if the engine was being used without an air cleaner - was one being used? They could also be the result of the short block being stored in the open, with dbris in the air being allowed to accumulate before the head was fitted. It is possible it's pick-up from ring gaps closing up, but that's usually very quickly a terminal condition.

The second part is that while it's certainly possible the "very metallic" appearing oil is down to bore and/or piston wear particles, you don't know and even oil analysis may not be able to eliminate possible sources.

Hate to say it, but the ONLY ways to find out are either stripping it down to do a thorough check, or keep using it until something definitely fails. The former is by far the cheaper option.

Your friend, and you, can consider it an expensive mistake on their part to buy something they have no real idea what it is, dropping it in, and driving quite hard - 20lbs - on what might be a stock, worn engine is pushing it, rather.

Cheers Gord,

I should add that it was sold to him as a turbo-engine package, fitted by the (private) seller.

To the best of my knowledge an air filter has always been fitted, though I can't speak for any use prior to him initially receiving the car of course.

I appreciate response. And unfortunately you have confirmed my initial thought that stripping it down will be the only way to find the cause and extent of the damage. Though being still fairly inexperienced in the industry (5 years) compared to others who have been doing it far longer and seen far more, I still find it's always good to seek opinions & advice when second guessing myself. Especially when they can suggest likely causes as you have done.

An expensive lesson for sure!

I just want to add, where was it leaking when you did the leakdown test? That really helps narrow down where worn parts lie, and some are much easier to further inspect than others. For example, if there was leakage past intake or exhaust valves, are they covered in gunk and maybe would seal up better if they were just cleaned up?

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