Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Novice "Freshening" up a EJ25 - Stock rebuild questions

General Engine Building Discussion

Forum Posts



Tech Articles

Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.

= Resolved threads


Looking at doing a stock rebuild, nothing crazy - just something reliable for a stock car.

Plan on using Enginetech components for rings/bearings - plan to reuse original pistons they do not appear damaged.

Was talking to my machinist who does my cylinder head recondition's and was discussing honing on the EJ25 block.

What is the best method to use?

Are these bores coated with a Nikasil ?

I have only worked with a cast iron block's in the past - so not sure what the best method for a hone is.

Am I able to just hone it myself with your typical 3 stone style hone?

I am also assuming that the Enginetech rings will be a chrome style top ring - meaning a hone should be required for it to bed in correctly?

Upon further reading online, there seems to be a few school's of thought on if a hone is required to seat in new piston rings - depending on the compression ring material. How much truth is there to this? My understanding was if using any style of new piston ring, a hone is required?

The cylinder bore measure out great with my dial bore gauge, the block surface is verified flat with my straight edge - so my thinking is measure everything, document it, ensure everything is within spec, hone the bores, set ring end gaps and reinstall with new standard sized bearings if measurements check out.

Being a novice engine builder, I am just looking for verification that this is the correct way to go about it.

Bump...any advice?

Bores arent coated as far as i know.

Your probably better off getting replacement pistons and honing to 1st oversize. Subaru pistons arent particularily strong, i know you say you want a stockish rebuild, but it might be better to atleast put some stronger pistons in for a bit of future proofing incase you want a little bit of power upgrade down the track.

Normally, upgrade pistons come with some drawbacks like ; rattly when cold, and more blowby due to the looser fit needed to account for the expansion.

You can get pistons made from 2618 and 4030 alloy. I believe the 2618 might be worth considering for a mild upgrade without as many drawbacks as the more common forged material. Worth looking into atleast.

Thanks for the info Bram - I am more concerned about my practical and theoretical approach in ensuring the engine runs correctly and does not burn any oil. Is it ok to hone the cylinders, or should they be left alone? Is it fine to just re ring and assemble?

I will take the forged pistons advice on board - but this engine will not be seeing any modification's.

Exactly which vehicle, model year, and engine is this?

It is a 2009 Subaru Forester XT

2008-2009 EJ255/257 vehicles are notorious for busted ringlands. I would not reuse the pistons. At least get new OEM if you don't want to go aftermarket forged.

Thanks Raymond, I will look into it.

Is the rest of my theoretical process correct in how to assemble/refresh the engine?

Is honing the best method or should the original cross hatch pattern be left?

What do you guys think about not honing the cylinders?

Have a read of the below


I thought honing was done to get the cyclinder size to match the piston size. If you are using old pistons into the same cylinders, then they should already be at size. And in theory shouldnt need any increase in size.

I thought the hatched surface finish is important for oil retention on the bores. You want to keep a fine film of oil on the bores for lubrication. So if you still have good hatch visible, then that should be ok?

Also, OEM piston to cylinder clearances are ALOT tighter than an aftermarket forged piston. So you will have less material to work with if you attempt to hone it before the clearances become too large.

I dont know how important the fresh hone surface is for new rings though?

Hey bram, I think you have the terms hone and bore mixed up.

Bore - "bore out" cylinder to suit next oversize pistons

Hone - to create the Cross hatch pattern, which also removes material but from my understanding it is quite low

No, i didnt mince my words. I definetly mean HONE. I think you will find that most engine reconditioners DO NOT BORE cylinders when going to next oversize pistons. They put it on the hone machine and run the hone up and down until it measures about right. (Some will even say to the customer that they bore it, when they infact hone it.)

This is because to bore it, it takes a very long time to position and indicate the engine straight and true on the mill, and set up the boring head. Where as a hone is alot quicker because the hone will self center so you just put it on and go. And they are only removing a very small amount of material when going up a size. 0.010 bigger piston means you are only taking 0.005 off each side of the cylinder.

I know for a fact the guys over here do it that way. But they have a few tricks to get it to work on Subarus. Because Subaru has webbing right at the base of each cylinder and a short-ish stroke, it means they cant run the hone deep past the bottom on the bore. This has a tendancy to barrel out the cylinders because the hone is always in contact with the middle and top of the bore, but only sometimes in contact with the bottom. So what they do is cut the hone stones down to like half size, so they can then more accuractely control the contact and get a more uniform dimension. They do torque plate them while doing the hone aswell.

Just remember. Engine machining is a fucked industry full of cowboys who dont give a fuck and use ancient machinery.

Thanks Bram - This is the part that really worries me if I was to be building any type of performance motor.

What happened to your EJ block was unacceptable - But what can you do...the damage has been done.

Interesting to know thats how some people do it - Only part I don't like it is that they run the hone up and down "until it measures about right" - When talking precision machining - there is a spec you are asking them to do (or they are doing) and anything else that isn't that - is wrong. Least thats how I would see it.

I dont think there is anything particularily wrong with honing cylinders to size. Aslong as it is done carefully, and the cylinder isnt out of shape to begin with. When I say 'measures about right', I mean within a few tenths. Which is pretty damn good really. The block will grow more than that between morning and night.

Makes sense Bram - When measuring your work after they did the line boring, did you measure it with the bearing's installed or not installed?

I have measured both the main tunnel bore dimensions, and the bearing dimensions/clearances.

After the initial job, (where they forgot to tighten the bolts), I only measured the main tunnel bore, as there was no point seperating the block and putting bearings in, when it was so badly out of spec.

After the 2nd attempt, i measured with bearings installed aswell.

I am assuming that the main tunnel bore measurements directly effect your clearance's.

With the major risk of sounding like a banana - If i measure up my bearing clearance's with the bearings installed - and they check out well, I am sure it would be a moot point in measuring the actual main tunnel bore.

Have you made any more progress on your build Bram?

I have put my build on hold for yet another year. The original plan was to do it last Xmas break. But the CNC shop took 8-9 months longer than anticpated to do the close deck, pinning and 14mm studs. And it came back with damage along the parting face.

So then the new plan was to get it done this Xmas break. But with the drama with the incompetent line hone work, I am cautious to proceed, and I dont really know what I should do with the block now. I am considering buying a new short motor and starting again. But dont really want the hassle of getting the close deck work done again. I fear that I am somehow cursed with shit machinists, and wherever I go, I just get really shit service and incompetent work. I dont usually believe in superstition. But this one keeps proving true.

In the mean time, I have put the motor on hold. I have borrowed a JD2 tube bender, bought a whole bunch of CDS tube and began building the much needed roll cage. I actually bent the main hoop up on saturday. In the last few weeks, I have seam / stitch welded the body inside the cabin and under the floor pan. I will seam weld the forward sections too. But wanted to get the bits where the cage would be done first.

Pedal box, abs/booster delete and fuel cell aswell to be done. Then i will build a bare bone wiring loom as the OEM wiring is friggin heavy, and so much of it is redundant in a race car.

I figure I can get that bowled over in the end of year break. And into the new year. And then focus on the engine next year.

There is a machineshop that I trust - I am happy to forward on there details? The owner is very knowledgeable, and takes the time to explain what he is doing and why he is doing it.

I have learnt alot just from a few phone calls!

Unfortunately for you, he is based in Melbourne, so it might not be practical, but you never know - might work out if you are willing to ship the items to and fro.

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?