Well I finally got this oil pan dropped and managed to check out the cylinder bore markings on the bottom of the block. I have managed to source a set of brand new type II pistons I could use but I think I'm out of luck as I think it's type III that I need. Basically, the markings on the underside are as you can see here (if I am looking up from below):



Am I right in thinking those markings would refer to the piston type required for each cylinder as I am looking from the bottom (i.e. cylinder 4 needs type II and cylinder 3 needs type III)? Am hoping this is not the case and that it refers to the cylinder type going in ascending order from the right to left or down the length of the block, but kind of expect that it is. Any thoughts would be appreciated

 

Um no. There is no such thing as piston type.

It's interesting that you found a part that doesn't exist.

The markings refer to bearings used for the MAINs and RODs.

 

Well according to Mitsubishi Japan, there is. Pistons for the Evo I and others have 3 types for standard (A, B, and C), as well as offering various types of overbore pistons.

It also hints at it in this post:

https://www.evolutionm.net/forums/3769493-post5.html

 

 

Its cylinder BEARING BORE, not cylinder bore having anything to do with pistons.

 

Still doesn't explain the difference between the 3 types of standard pistons available for the Evo I (and other models). And the roman numerals refer to the cylinder inside diameter size.

 

I can't see your picture, but do you have any corresponding part numbers? What do the dealers in Japan say?

 

Part numbers give a Standard A, B and C type which have part numbers MD313285, MD313286 and MD313287 respectively. Tuning shop I tried in Japan today said there were different types but I haven't been able to speak to anyone since I dropped the oil pan this evening and checked out these inside diameter marks.

My mistake on the cylinder bore marking comment initially - I meant cylinder inside diameter.

 

Well, I hope you can get to the bottom of it, as I would like to know the answer. I had always thought it was because they sold standard pistons in ten, twenty and thirty overbore.

 

+.20, +.40 and +.60

85, 85.5, 86, 86.5mm

 

Err, yeah, that's what I meant.

 

Yes, the pistons are also available in oversize by 0.25, 0.5, 0.75 and 1.0 according to the Mitsubishi parts system, and these parts have part numbers MD300040, MD313291, MD300042 and MD313292 respectively.

 

They have nothing to do with your original post requesting what the numerals on the bottom of the block meant.

 

Correct. I was adding comment to the post which was above mine about overize pistons. As the user asked for the part numbers of the standard pistons, I also thought it might be useful for him to have the part numbers for the oversize ones from Mitsubishi.

But back to topic, you've no idea about the Roman numerals and which exact cylinder is represented by which number?

 

None of the numbers have anything to do with cylinder bores as we already stated.

They are referring to the bores of the mains and bearing sizes.