AndrewVanis

How to determine cylinder ring size for a re-ring?

I am looking to re-ring two 2.5 short blocks. Both have been rebuilt previously so I am not sure what was used for rings or if they were bored.

How can I determine what size and type of rings to get?

I’m re-ringing to eliminate (reduce) oil consumption.

I’ve assembled the EJ engines when getting them back from the machine shop with the parts/rings provided but I’ve never had to do this type of assessment/measuring.

Thanks in advance.

Andy

stockcar

the rings have to match the piston size, i.e you can't use larger / smaller rings than the specific piston used.......

BUT EJ25 / EJ257 blocks are notorious for ovality so first job would be to check the cylinders are actually true, round and within piston size tolerance otherwise your looking at a hone o re-bore to suit

AndrewVanis

Thank you for that reply. Cylinder oveling is something else to look at.

I'm still interested to know how to do what's in my original question - How to determine the rings needed for a re-ring?

Danjo

If bores are good and it’s standard sized Subaru pistons you’d just order a standard Subaru ring pack and check gaps.

AndrewVanis

​​​​​​How does one determine this?

And what dimension should the cylinders be for a standard piston? - I wish to be certain that the bore and cylinder are what they should be and compatible as I don't know what decisions were made on the prior rebuild.

If this is documented in some resource I should be looking at please let me know where to find/get it.

Don Clark

As per Stockcar, rings are a matched set to whatever size piston is fitted, be it standard or an oversize piston.
And as he says if the bores are oval then it may need a rebore to suit an oversized piston from that already fitted
For example: Info for US MY06 2.5L wrxsti


Ring Packs


Further info in attachment.

AndrewVanis

Don, that is a very helpful response. Thank you.

1) I was under the impression that all the 2.5 short blocks were the same - are they? and if not, how are they different with respect to cilynder rings?

2) I know there are different pistons based on variable timing or what ever. How can one determine what pistons one has?

3) the info you attached is model year specific. How can I identify what block I have so I know what specs to look at since I do no know the history on these? Are some of the numbers of the block model numbers or some kind of code that van be deciphered?

Don Clark

@stockcar may be of assistance with this as he builds engines

Don Clark

I believe the EJ255 block is also semi-closed, it's the n/a engines that had the open deck blocks in the US
https://forums.nasioc.com/forums/sho....php?t=1480737

https://www.possumbournemotorsport.c...n-deck-blocks/

Equivalent info for MY02 2.5L SOHC EJ251 engine attached:-

AndrewVanis

So possibly the EJ25 cylinder spec are the same for all model years?