SPFSkyline

One of my friends is a tech for Subaru and I had him over last night and we looked breifly at the block and Intake Manifold. Looking at the manifold in the light shows a substantial amount of blow-by. From what we dicussed, he felt like rings is a high possiblility due to the massive blow-by that appears in the manifold and the fact that the head checked out (took .007 off). Now that the top end is off, it really isn't much more work to drop the pan and pop out the pistons. However, he talked about the honing of the sleeves. They are smooth, no cross-hatching left, or so it looked last night in bad light. He seemed concerned about that, however, the s2k service manual states that smooth is fine as long as there is no scoring and bore is within specified limits. How true is that? I figure best course of action is to get a new head gasket, torqur down the head, leak-down test and see if rings leak before I open up the bottom end. Tech friend also said I should get new pistons once they are out. I figured I could measure, clean and re-use if they are ok? Service manual makes it seem that way, but it makes it seem like you can re-use all parts if they are within specified limits. My main concern is honing, as I can do the rest in my garage and can borrow almost any tool needed, I do not want to pull the block to re-hone the sleeves and completley disassemble the bottom end.

marcucci

I would normally say the bottom end is OK as you note in the manual, but your oil light issue has me concerned. You should never see that light as long as the engine is full. It should never be run lower than H on the track, in fact I generally run it a half quart over. If you ran low enough for the light to come on (I think 2psi at the sensor, or basically air being pumped) for any length of time, I would not trust that bottom end at all.

As noted by another posted it could be glazed walls and dead rings causing higher blowby than normal, and oil consumption, which may have gotten away from you and caused a low oil condition?

SPFSkyline

Well since the head came back all well and good, I desided to take a look at the pistons. I dropped the oil pan and took out #3. Everything looked ok on first glance. Took the rings off and none of them are cracked or broken. I still need to remove the others, but since 2 and 3 were the offenders in the leak-down I was hoping I would have an answer by removing it . What else could be some causes of blow-by? I guess after I remove the other 3 pistons I will need to measure bore and pistons to make sure they are still within spec.

marcucci

Well, you are committed now to a rebuild. You can't (better: shouldn't) reuse rings. If you hone to restore the bore surface then you will undoubtedly exceed the OE spec for piston-to-wall clearance.

Note that the FRM honing procedure is unique, and whoever does it should have experience with it. They must follow the OE spec and use the proper stones.

I'd say at this point just rebuild the bottom end and hope that the vac test was OK.

SPFSkyline

Well to my benefit, one of the people I work with's father is the service director for a Honda dealer and offered to bring his master tech over to help me out. Hopefully they can help me out, plus they have tools for me to use ...

I assume I need to pull the other pistons, measure EVERYTHING per service manual, clean up pistons/rods, new rod bearings/rings/gaskets, put back together. I pushed the pistons up through the top, so I figure I do not need to mess with the crank since it was not touched?

bpaspi

You can do a check for yourself. It's a DIY within a few minutes:

Pull the Top Ring from one of the pistons. Be careful not to bend or even break it!
Buy a feeler gauge -the type of measuring tool when valves are adjusted.

Then place the ring into the cylinders, look for equal distances to the deck.



Then measure the gap with a valve feeler gauge. You can do this for several positions in he cylinder. They aren't equal any more



The gap should be:

new: 0.25mm - 0.35mm
wear: 0.60mm

Write down the values for every cylinder and every position (Top, Middle, Bottom).

If possible I wouldn't hone the block. That means new pistons, a.s.o.... It could be that only new rings will do the job. It depends on the measured values.

marcucci

If you don't hone the block, don't expect new rings to seal any better than the old ones. Also don't expect the bottom end to last very long before you end up with more blowby.

bpaspi

The Hone-Process takes min. 0.02mm of Material away. And this should help? You get even more Blow-By! And Piston-Slapping!
As long as there are no marks, scratches or other impacts in the cylinder wall, there's no need for hone.
Let's wait for the testing and measure. Then decide what to do.

chris_barry

I find that in a conventional engine rings bed in much quicker on a bore that has been lightly honed. I use a dunny brush hone ( flex hone brand) that removes a minuscule amount of material. The freshly cross hatched surface provides some texture to seat new rings, and holds some oil on the bore walls.

I'm not sure how the flex-hone would work on FRM bores. They use a soft stone and leave a grey slurry on the surface which would take a lot of work to clean up if you were doing this with the crank still in the engine.

If this was my engine I would stuff rags over the crank and run the flex hone around 10 strokes in each cylinder, then clean up with lots of avgas and rags till the bores wiped clean.

New rings on a glazed bore will just flutter around and take an eternity to wear enough for a full seal.

marcucci

Have you ever looked at the Honda piston-to-wall clearance spec, or honing procedure? I would not recommend ever reusing Honda pistons, you generally can't hone and get them to still fit properly. I'm not recommending that, I'm recommending a proper rebuild with .25mm OS pistons and a proper bore and hone to fit those.

I recommend that because re-ringing OE pistons and not honing is not much better than just reusing your old rings. Re-ring and you're going to end up not much better than before, and probably get another 50k out of the motor, max, before you end up with so much blowby you start to get misfiring.

This isn't a Ford or Chevy small block that's only running at 9:1 CR and making 150psi of compression on a good day. Doing anything to increase blowby on this motor will result in an extremely short lifespan.

Maybe the original poster doesn't care about longetivity or performance. In that case, by all means, re-ring and reassemble.

WRT to Chris' post, I would not want to even lightly hone (may not be possible, FRM is HARD stuff) as Honda bores, especially with oiling issues, usually egg or "un" taper badly with age. This might improve ring seal some but the blowby is driven by more than just the ring/bore interface.

I've had the opportunity to play with piston-wall clearance some, as well as taper, and deviating from Honda's spec usually ends in poor results.