88 XT-4 MPFI.

 

I swapped pistons into another block, and now that I have better light I see an arrow that I assume is indicating front-of block. Unfortunately (maybe), the arrows are pointing to the rear. (Apparently, I put "left-bank pistons" into right-bank case, and vice-versa.)

 

Another set of MPFI pistons has no front/back arrow, and neither do turbo pistons. FSM does not mention a left-side/right-side difference.

 

Any of the Gurus know if there is any difference, or if I can avoid the hassle of pulling the pistons back out and swapping them to the other side?

Edited October 17, 201015 yr by NorthWet
Remove incorrect information

The marked pistons are an offset wristpin type. IF they are backwards the offset is to the wrong side of the rotation, not sure what that will do....possibly nothing.....possibly slap? possibly hammer the rod bearing or wristpin bushing.

 

I think you will want to switch them around, or use the Symetrical pistons (other 2 sets you mentioned)

That would imply the one of the engines used different connecting rods then the other engines. Although this is possible, I don't remember reading anything about different rods in any of the EA82s. If they are truly offset at the wristpins, then these pistons would not work in this block (as it sits) anyway, since I didn't swap the rods along with the pistons.

After a couple of hours of trying to remember, looking at FSMs, and using SEARCH, I think that these must be SPFI pistons.

 

*Edt - Not necessarily SPFI pistons after all. Finally found a drawing in my FSM that indicates XT having pistons with L/R markings. endedit*

 

In all of my searching, I could not find how they are different. (I could only find 2 posts that mentioned L/R markings.) But, all sorts of posts about how they are interchangeable without mentioning sided-ness of the pistons.

Edited October 17, 201015 yr by NorthWet
New info

That would imply the one of the engines used different connecting rods then the other engines. Although this is possible, I don't remember reading anything about different rods in any of the EA82s. If they are truly offset at the wristpins, then these pistons would not work in this block (as it sits) anyway, since I didn't swap the rods along with the pistons.

 

It's a .5mm offset from the centerline of the piston. There is no difference in the rods...but the pistons ARE offset and there is a reason they stamped them with the arrows. This places them "loaded" to one side a tad to prevent piston slap and tilting back and forth within the cylinder.

 

There is LOTS of info about this in the FSMs. Started in 87 or 88 I believe. The offset wristpin hole is something Subaru still does on the new engines.

 

Don't believe me, fine. But you asked a question and that IS the answer.

That explains why they list Left and Right side pistons when you look them up for SPFI after a certain year.

 

Were any of the EA71 or EA81 pistons offset too?

Were any of the EA71 or EA81 pistons offset too?

 

No - none that I've seen. EA71/81 pistons have no such markings nor is it discussed in their respective FSM's. I would go with what Gloyale is saying that it started in the later '80s with the SPFI engines. I have a set of unmarked SPFI pistons in my shed for a (someday) EA81 hi-po build so they must be from an earlier engine. IIRC it was an '87 FWD GL Coupe that I scrapped.....

 

I was not aware that Subaru did this with any of the EA's - but then I don't mess with the turbo's at all and the later SPFI engines aren't really worth the trouble to tear down - if they have an internal issue I've always just sourced a cheap used engine. Such is the nature of the EA82 around my shop. I've had heads off but markings are usually obscured by carbon....

 

GD

Edited October 17, 201015 yr by GeneralDisorder

It's a .5mm offset from the centerline of the piston. There is no difference in the rods...but the pistons ARE offset and there is a reason they stamped them with the arrows. This places them "loaded" to one side a tad to prevent piston slap and tilting back and forth within the cylinder.

 

There is LOTS of info about this in the FSMs. Started in 87 or 88 I believe. The offset wristpin hole is something Subaru still does on the new engines.

 

Don't believe me, fine. But you asked a question and that IS the answer.

It is not that I don't believe you, it is just that any other time that I have heard of offset wristpins the rods have also been offset in some way.

 

Your explanation cleared things up. My 88 FSM has one drawing that shows a side indicator, and several that do not bother to show any markings, and there is no text that I have as yet found that refers to sided-ness or why.

 

Thanks, guys.