I was tearing down my '94 1.8L block tonight cause it has been burning oil badly. I knew cylinder 4 was the culprit figured it was just the rings. So I take it apart and looks like cyl. 4 piston is missing some pieces, but are no where to be found and no damage anywhere else. But as I look into the block on cyl. 4, there seems to be a big hole and is has some jagged edges but I cannot tell if this is supposed to be there or not. Does anyone have an idea if this is damage to the block or supposed the be like that?

 

Detonation is a bitch.

 

That casting flash you see in the bottom pics are normal.

 

Your tune is terrible, FYI. Not trying to insult you, just calling it as I see it. Massive detonation damage across every piston I can see.

 

LOL, car never got tuned really, I bought it from a friend as he got fed up with the car. So I compression tested it and cyl. 4 was crap, yanked it out, this is what I found. So I am not at all surprised. But I got a whole supercharged miata and tons of parts for cheap. Now time to build it right.

 

Make sure you inspect the cylinder head for damage. The chunks of piston would have been spit out of the exhaust, and it is likely you have bent valves as well as other damage. It is not likely to be too serious, but something you should take care of.

 

That is something I was looking at. I see no visible signs of damage anywhere The far right is cyl 4. What looks to be a mark on the valve, is from me looking at all the buildup on it.

Anyhow, I will possibly be looking at replacing the valves anyway, but I am looking at everything for any damage or needing replacement.

 

I had a similar failure years ago, and I saw no visible damage, but the valves were bent some. If they are not too bad, they can be straightened if you are on a strict budget.

 

That sucks.

On the other hand, you have time to sell the stupidcharger and build the engine and collect some turbo parts.

 

I don't see missing pieces, I see melted pistons.

I also don't really see the massive det sav was talking about; maybe on #3, but the edges and squish area's of the pistons look pretty solid.

 

I am going to build a solid motor, I will keep the supercharger for awhile and build a turbo set-up. That way I can get the Miata back on the road and out of the garage. Ultimate goal is to be build a good track car.

 

What the heck happened to #3? Looks like someone took a die grinder to it.

 

That is just the flash and reflection/angle. The cylinder walls are actually still nice and can see the cross hatching.

 

That hole and flash you see is the oil drain back passage from the head if I'm looking at the pictures right.

 

The holes inside the engine block are normal, I said the same thing when I opened mine a while back.


Certainly check those valves.