well....crap. please help

[xt2005bonbon]

yeah but you got misfires on #2 and #4 no? Can't remember now. How can you get two blown ringlands? That's just nuts.

 

btw, I believe there is an 'easy' procedure to remove the piston without splitting the block halves. Can't remember if it is 'easy' to put them back though.

[ehsnils]

The first stage is to inspect the cylinders when the heads are off. If they look good then it's at least not a major issue with the rings/pistons that has caused wide-spread damage.

[SBT]

You can pull the pistons without splitting the block... it's designed to be done that way.

 

Easy in and out, especially if you've already got it on the engine stand and the heads are already off...

 

That's why there's block access holes... cycle the crank, line up the wrist pin with the access hole, bump the wrist pin out, pull the piston, done.

[xt2005bonbon]

That's it.

[ehsnils]

I did know that the EA81 engine had it, but never considered that they kept that feature for the EJ.

 

 

Just make sure that the clip isn't lost and properly mounted when re-assembling the engine. I messed up a 2-stroke once due to that.

[1-3-2-4]

That’s how I did it when I removed the pistons from my block pretty easy

[JazzAvi8r]

yeah, i know how to get the pistons out without splitting the case. if i was only going to replace rings, i would go that route, but if i have to replace pistons, then i{ll want to do a hone on the bore before installing new pistons and rings. i know it can be done, but i refuse to hone the bores while the engine is assembled because thats just asking for debris and shit to get in places they ought not be.

 

visually, the cylinder walls look great. i{ll post pics in just a sec

[JazzAvi8r]

here's the pics of the cylinder walls as they sit right now and the pics i took after yanking the engine last friday.

[Max Capacity]

That first cylinder picture looks like there are some scratches going up/down the bore ?

[ehsnils]

yeah, i know how to get the pistons out without splitting the case. if i was only going to replace rings, i would go that route, but if i have to replace pistons, then i{ll want to do a hone on the bore before installing new pistons and rings. i know it can be done, but i refuse to hone the bores while the engine is assembled because thats just asking for debris and shit to get in places they ought not be.

 

visually, the cylinder walls look great. i{ll post pics in just a sec

 

 

It's actually the rings that benefits from honing the cylinders, the pistons wouldn't matter.

 

 

The cylinders looks fine. At worst the rings have once become overheated and lost their hardening and won't seal as well as they should since they are weaker than intended. This wouldn't easily show up on a plain compression and leakdown test.

 

 

Since you are already at this level of disassembly pulling the pistons would just be one more piece of the puzzle added to figure out what's wrong.

[1-3-2-4]

Is it possible the rings are upside down? I can’t remember if orientation matters

[JazzAvi8r]

so would you just recommend i replace the rings all the way around and run with it? without honing the bores?

[aj_mariner]

Wouldn’t think to be concerned with rings since your leakdown numbers were solid

[JazzAvi8r]

so, i just inspected the bottom end from a visual standpoint. i cycled the pistons and checked for play, looked for scoring on the walls, etc. everything appears to be normal -- better than normal in fact. one of the cleanest engines i have ever seen. but i have a theory...

 

there's three rings on each piston. the top ring, the compression ring, and the oil ring. if the top ring or the oil ring were hosed, it would certainly create some scoring on the cylinder walls. but if the compression ring was bad, it wouldnt, right? essentially, if the compression ring were to lost it's flexible properties, it would just sit in the ringland and not expand against the cylinder wall, right? this would, in theory, explain the good leakdown numbers as well as the low compression.

 

or am i full of shit and dont know what i'm talking about?

 

edit: I think that's what ehsnils was talking about, right?

[JazzAvi8r]

That first cylinder picture looks like there are some scratches going up/down the bore ?

 

good eye, max. i saw that as well. both cyl2&4 have those vertical marks on it, but they are exceptionally smooth. not grooved at all.

[JazzAvi8r]

one more question: looks like I can get new piston ring set from heuberger for $105. since I have 2 'A' pistons and 2 'B' pistons on this block, does that mean i have to get two different sets? or will the standard set work for both size pistons?

[ehsnils]

so would you just recommend i replace the rings all the way around and run with it? without honing the bores?

 

 

Yes, the rings themselves aren't a big cost at this stage, it's the job that you have already done that's the expensive part.

 

 

Wouldn’t think to be concerned with rings since your leakdown numbers were solid

 

 

And what I highlighted before - if the rings have become weakened so that they have lost much of their tension, then they may cope well with the leakdown test but still not seal well when engine is running.

 

 

It's also a great time to inspect the pistons and check that the gaps between ring and piston is up to spec as well since the ring space tend to grow a bit over time. Also checking for if there's soot deposits in the ring lands.

 

 

 

And replace all rings if you do a replacement, not just a single. Pay attention to where the gap goes as well. Personally I'd place the oil ring gap at 12'o clock, the other rings at 4 and 8. No gap at 6 since that would increase the risk of oil passing through into the cylinder when you have parked the car. But that depends on what the piston allows as some pistons have stops preventing the rings from ending up in the wrong location. But that depends on engine/piston manufacturer.

 

 

Comparing old and new rings could also be interesting - take the opportunity to keep us up to date on that since we all can learn something here. Unloaded diameter as well as force to compress them to cylinder diameter.

 

 

Overall - giving up on trying to find what the problem is will just mean that we don't learn anything at all. And if we find out things here then others doing a rebuild will also know what to look for and what to do.

[ehsnils]

one more question: looks like I can get new piston ring set from heuberger for $105. since I have 2 'A' pistons and 2 'B' pistons on this block, does that mean i have to get two different sets? or will the standard set work for both size pistons?

 

 

The "A" and "B" markings are slight tolerance differences between the pistons, and you should check if there's even a difference in the ring size there.

 

 

You have some more information here: http://www.iwsti.com/forums/2-5-liter-litre-factory-motor/157394-piston-markings-vs-b-what-do-these-mean.html

 

 

Just make sure you have the right piston size in the right cylinder.

 

 

One list of differences I found:

STI sizes are below. As you can see "A" is bigger. Not by much but bigger.

A 99.505 — 99.515 mm (3.9175 — 3.9179 in)

B 99.495 — 99.505 mm (3.9171 — 3.9175 in)

Source: http://www.rs25.com/forums/f105/t137449-piston-sizes-b-why.html

 

 

 

Notice that other manufacturers have the other way around - A is smallest and then going up in size over the alphabet.

 

 

So if you plan on new pistons - measure the diameter of the cylinders since they can have changed over time, not necessarily through wear but also since the metal itself has stretched a tiny bit over the years. The metal flexing in the cylinder walls is what causes head gasket failures. Smaller cylinder diameter allows for more goods and less flex - which is why the amount of head gasket failures are lower on the 2.0 and 2.2 engines and worst on the 2.5 turbo engines.

[ehsnils]

Further reading here: http://www.ultimatesubaru.org/forum/topic/551-ej25-a-b-pistons/

 

 

from the shop manual:

 

"1) The cylinder bore size is stamped on the cylinder block’s front upper surface.

NOTE:

Standard sized pistons are classified into two grades, “A” and “B”. These grades should be used as a guide line in selecting a standard piston.

Standard diameter:

A: 99.505 — 99.515 mm (3.9175 — 3.9179 in)

B: 99.495 — 99.505 mm (3.9171 — 3.9175 in)"

2) How to measure the inner diameter of each cylinder Measure the inner diameter of each cylinder in both the thrust and piston pin directions at the heights shown in the Figure, using a cylinder bore gauge.

 

CAUTION:

Measurement should be performed at a temperature 20°C (68°).

Taper:

Standard

0.015 mm (0.0006 in)

Limit

0.050 mm (0.0020 in)

Out-of-roundness:

Standard

0.010 mm (0.0004 in)

Limit

0.050 mm (0.0020 in)

 

3) When piston is to be replaced due to general or cylinder wear, determine a suitable sized piston by measuring the piston clearance.

 

4) How to measure the outer diameter of each piston

Measure the outer diameter of each piston at the height shown in the Figure. (Thrust direction)

CAUTION:

Measurement should be performed at a temperature of 20°C (68°F).

Piston grade point H:

37.0 mm (1.457 in)

Piston outer diameter:

Standard

A: 99.485 — 99.495 mm (3.9167 — 3.9171 in)

B: 99.475 — 99.485 mm (3.9163 — 3.9167 in)

0.25 mm (0.0098 in) oversize

99.725 — 99.735 mm (3.9262 — 3.9266 in)

0.50 mm (0.0197 in) oversize

99.975 — 99.985 mm (3.9360 — 3.9364 in)

 

5) Calculate the clearance between cylinder and piston.

CAUTION:

Measurement should be performed at a temperature of 20°C (68°F).

Cylinder to piston clearance at 20°C (68°F):

Standard

0.010 — 0.030 mm (0.0004 — 0.0012 in)

Limit

0.050 mm (0.0020 in)

 

6) Boring and honing

(1) If the value of taper, out-of-roundness, or cylinder to-piston clearance measured exceeds the specified limit or if there is any damage on the cylinder wall, rebore it to use an oversize piston.

CAUTION:

When any of the cylinders needs reboring, all other cylinders must be bored at the same time, and use oversize pistons. Do not perform boring on one cylinder only, nor use an oversize piston for one cylinder only.

(2) If the cylinder inner diameter exceeds the limit after boring and honing, replace the crankcase.

CAUTION:

Immediately after reboring, the cylinder diameter may differ from its real diameter due to temperature rise. Thus, pay attention to this when measuring the cylinder diameter.

Limit of cylinder enlarging (boring):

0.5 mm (0.020 in)"

 

you can find what the block was originally bored for from the stamp on the top of the block...

[RustyRuu]

look into your compression ring gap (top ring) and file it down if necessary. I think it's a larger gap for an STI (ej257) and some believe to adjust to that spec if you plan on any engine/ turbo supporting mods.

 

also no bake oven cleaner works really well on cleaning pistons at home. it will get everything off.

[aj_mariner]

So back to the honing question...are the cyl steel sleeved or aluminum? If steel, then honing is a good idea. If aluminum, then the cyl walls will be coated with “something” and it would be safer to not hone. But there is much debate on this subject. Couldn’t hurt to remove the pistons and check at this point with the engine at parade rest. Plus then you could check the bore with a dial bore gage and see if the pistons should all be the larger size

[JazzAvi8r]

Thanks all. Gonna take the pistols out next weekend with intent on just replacing the rings all around. Ill do a thorough inspection of course amd see if the pistons or ringlands are shot. Will report back then

[ehsnils]

Don't forget to check the ring gap too so it's not too wide. That issue isn't as obvious without checking the permitted values and using a feeler gauge combined with the new rings.

 

 

With new rings - drive carefully the first 1000 miles so that they break in correctly.

[JazzAvi8r]

Well, pulled #2 piston. Cracked ringland. Gonna pull the rest after I take the motor off the stand

[JazzAvi8r]

Ill post pics later when i get to my computer. My phone wont let me upload it