birkhoff

Can you still feel those fire ring depressions? Earlier you said you thought they were maximum 0.002 deep. I'd be at least a teeny bit concerned about them -- there seems to be a special religion around getting the sealing surface right with Subaru. Example. My heads were as clean or cleaner than yours when I took them in for decking. They measured dead flat. I asked the machinist to take off the minimum and the response was, I'd be surprised how much needed to come off to clean them up to spec. No marks of any kind left when they came back. I think I lost 5 thou thickness. Would have to check. I'm no expert, particularly on the Subaru front. Could someone experienced with preparing Subaru heads chime in here?? Is it ok to leave those rings? Is there is a similar issue with the case halves?

As with everything in Canada, we speak both languages and flip from one to the other without a thought. Want it in gallons? Imperial or US? Litres? whatever. We don't even spell consistently! Centre, centred, centring, centering . . . All that aside, 95% of my measuring tools are imperial so I really appreciate that Subaru USA has already done the conversions in the FSM.

I wouldn't worry about o'all height just yet. The important measurement is from the contact point at the seat, to the stem tip. Or, to put it another way, it is unlikely the face of the valve (which is one point in your measurement) will sit in the valve pocket to exactly the same depth as your old valves, even if you remove all the carbon on the latter. It depends on how the valves are ground, and where the contact takes place. And they still have to be lapped in. Does that make sense?

That's why I asked. I've never seen anything definitive. This questions gets asked all the time. We should construct a sticky on how to read the codes stamped on the top of the block -- what they mean and what it means to the guy/gal about to launch into a rebuild. I've only seen 22222 blocks myself. If you have a 22323 we are in luck. When you split the case, mic the 2 shells vs the 3 shells. that will tell us a lot. Do you have a ball mic?

Fair enough, but beware about purchasing bearings based on this before you actually measure crank and mainline. Most of us seem to be finding cranks down near the lower end of spec at rebuild time, so a standard factory bearing becomes an undersize or at least a half shell if you want to run stock clearance. Where did you find a translation for the number codes? Link? When I built my block, the only company I could find that supplied undersize mains was ACL. They make a +0.025 mm bearing that translates to a 0.0004 thicker shell.

This ^^^^^^^ makes my day! Ask the forum for a set of AAAB and ye shall receive. Don't try to change any bore size unless you are getting a professional hone. Even then, I would be wary of not getting a round bore back unless the shop has a torque plate. Bottle brush hone? Forget it.

From my build records, crankshaft journal ovals (#1 - #5, in tenths) were 1, 2, 2, 0, 0 Smallest min diameter was 2.3619 on #4 which exactly hits min spec. Largest max diameter was 2.3622. These measurements were taken after the crank had been cleaned and polished at the machine shop. On assembly, calculated main oil clearance was (#1 - #5, in tenths) 12, 13, 14, 16, 14 Minimum stock is 12, but that is the best I could do even with mixed shells. Crankpins were all below minimum. Again, I used mixed shells to get oil clearance back into the stock range. You seem to be finding much the same so plan on two sets of shells to make things right. No big deal in the grand scheme.

All this measuring and discussion of errors got me curious. I have a few new and used pistons here after tidying up. Two brand new A-grade pistons measure 3.9178 at the grade point. Both of them, and the measurement is repeatable. Then I grabbed one of the used A-grade pistons from the 180K motor I just pulled and tore down. 3.9175 at the grade point. Skirt wear was not too bad; I can see the machine marks on almost all of the skirt, except for a couple of polished areas just above the grade point. There are some pictures of these pistons in my rebuild thread. Impossible to know how much diameter was lost since there can be variation in the A-grades when new (I guess) but that gives you a sense of the scale of things. Tolerance on machined parts for these motors seems to be very high. Cranks, pistons, rods etc. I assume tolerance on the case bores is very high too, but then everything distorts once the case is out of the clamps. FWIW, I think you should aim for more consistent measurements on machined parts. You have made great progress and just a little more practice will get you there. One more point. The measurements I made above were at some temp, somewhere below 20C since that is ambient daytime temp up here these days anyway but my basement is quite a bit cooler. I didn't take any special care with handling the mic, but I worked fairly quickly. It took me a couple of tries to get back into the rhythm mind you. It's all about practice and feel.

Correct on your edit. One might think you could work back from those numbers and the known bearing thickness and oil clearance, but you still won't know the base bore because the designed crush is an unknown. What you can do is measure the big end bore parallel to the parting line and assume that that is the designed base bore since rods elongate mostly in the other direction. Now measure the other direction for oval. You probably know this already, but base bores are supposed to be perfectly round. Running bores are not -- the shells taper out near the parting line. Not much, but enough to measure. That slight opening up is for the oil wedge. That is why you always measure running clearance perp to the parting line of an insert bearing.

There is no spec in the FSM for the base bore in the rods. You can only check for oval. Same as the main bores in the block. How long before you have your new bearing shells in hand?

Interesting. Is your mic warming up? Check it against your gauge blocks. You have a 3 inch one, right? Intuition would suggest that your measurements should drift lower if you are expanding the body of the mic with heat, but maybe it distorts the `G' shape and closes up the anvils. Who knows. Thats a lot of error to attribute to temp drift, however. A couple tenths I would believe. FWIW, I find getting the mic on diameter to be pretty easy; as you nicely put it, you can see when the contact point is centred on the moving anvil. It is a little trickier making sure you are right in the other direction. One way is to do a few test points and look for the minimum measurement. With practice, you can actually feel when it is right. That's why I described it as a two step centring process.

It's, like, what keeps your bearings from spinning around, eh? The outer diameter of in insert bearing is always larger than the bore in the block. The extra is the 'crush'. In an iron block, with iron caps, hot rod magazines will tell you that the crush works entirely to reduce the diameter of the running bore. Machinists will tell you otherwise, that in fact the bearing pushes out against the block and cap enough to slightly enlarge the base bore. How much? Experience. I just reviewed my notes from the build and I was getting a full 0.001 enlargement in aluminum. I'll edit my previous post. So where it says 'add 0.0005' it should say, add 0.001. That was my experience anyway. The effect on the rods (steel) will be much less. Just torque 'em up and measure the running diameter. Swap shells as required. That's quite a range. To be clear, you are reporting four consecutive measurements at the grade point? Perp to the piston pins? In making this measurement, as you sneak the mic onto the piston, move it back and forth a bit to find the diameter, and then up and down to find square. It is a little wiggling exercise that, as you say, you get more consistent with as you practice. Your mic has a friction thimble, right? Use it. Personally I would trust the lower numbers more than the upper ones. If you mic something and get xxx, than you can generally conclude diameter is <= xxx. Unless you are measuring way off the diameter, cranking down too much on the mic or misreading the barrel. It kinda looks like you have a set of 4 B pistons, which can't be right.

STD/undersize bearings are designed with the same size shell back. Use undersize if your crank journal is down just a bit. STD and 0.025 mm undersize are available from some suppliers (ACL in particular) Oversize bearings are (almost) unobtainable for our engines. You only use that if you have honed the mainline to correct something. Which means machine shop. Which means, not related to this thread. I'm told king can supply 0.025 OS. There are some marks on the top of the block; 22222 for example. My understanding is that those tell you the factory shell thicknesses on the 5 bores in order, used to fine tune the oil clearance. I've never had this confirmed by the 'experts' so if someone knows. . . It is pretty common to see 22222. If you have a block that says 22122 then maybe something different was fit for bore #3. You could mic the shell thickness to confirm. Here is how it worked out on my block. Measured all the bores and took the smallest diameter on each. Subtracted twice the bearing thickness (you can find this information on the manufacturers website). Add 0.0005 for bearing crush in aluminum. That is your estimated final bore diameter, minimum. Subtract your measured crank journal max diameter and that gives estimated running clearance. I had zero luck using plastigage at such small dimensions, and with all parts out of round. Once you fit the bearings you can do a final bore gauge check on the inside of the shells to confirm everything worked out. It will put light scratches on the bearings. You can polish that out with a piece of newspaper if it bothers you. If something ends up too big, you can swap out for a thicker shell. It is unlikely anything will be too small. Finally, it is a good idea to do one final test fit with plastigage just to check your math. As long as it shows approximate clearance, you are good to go. If you repeat with plastigage, you will get different approximate numbers. That's the problem with plastigage. Final assembly with lube, new washers and torque to spec. Except for pistons, there's your new short block! EDIT: Since I built my block over a year ago, I thought I better check my notes. It looks like the crush allowance (aluminum) should be more like 0.001 (10 tenths) not 5 tenths as reported above. If you have a machinist friend, they might be able to give you a more reliable estimate to work from. This was a one-time thing for me.

Oh, the other pistons are used too. I see. I had a link ready to point you to some pictures of new pistons, but I see you are already beyond that. Post 4 in the link you shared; there is a good shot of the skirts. Don't they look nice? If I recall, that long thread went back and forth about whether there really was a difference or not. What I know is, I've never seen a set of the double dot pistons for sale, or in a motor, so apparently we are all using the EJ257 pistons anyway, and that is what you can find lots of these days

Are you really planning on re-using those pistons? That is an unusual step. There is no skirt coating, unknown ring land wear (maybe you checked that already, but you need a new set of rings to do it) and something else I can't really think of at the moment. You can see I'm not a fan of this part of the plan. There is a set of BBBB fresh pulls on Outfront site right now for $150 which is $50 more than you really need to spend, but they are trustworthy and won't send you borked pistons. Pistons can be damaged in handling, apparently. If you are confident in your measurements then there's your pistons. You could check some of the site vendors (could = should) as they may have something similar on the shelf just waiting for such an occasion, especially if you want to go AAAB, which might be the best bet. Considering all invested in gaskets, hard parts and time spent, saving a couple hundred re-using pistons . . . I'm trying to get my head around this.

Oh, well, you know me. Mr. Stock. I can't bring myself to paint anything that wasn't already painted. If 'don't paint anything' was an option in the poll, I would have voted long ago.

Measuring mainline. Your bore gauge will need to be set up to measure about 2.520 inches. There is no spec I could find for std bore diameter, without shells. You are looking for oval and differences between bores. Torque case halves together following the spec pattern and values. The latter is really important -- I did some experiments with partial torqued case and found things moving all over the place. I didn't bother with the small case bolts off the mainline. You main want to. Run your straightedge in and look for any rocking in various direction. None? Good. Check the flatness of the fire decks again. That may change when you clamp the case halves together. With bore gauge, check perp to parting line, and then along parting line (not exactly along, since that won't give a good measurement, but angled just off) That will tell you oval. Do this for each bore and write things down. You should find that the bores are slightly wider perp, than parallel due to the crankshaft pressures. The small web bores are likely to be worse than numbers 1, 3 and 5. How much is too much? I really don't know, but if it is approaching the target oil clearance, you may want to rethink things. It is a good idea to set up a micrometer with some standard value in the right ballpark and frequently check back with it to eliminate drift in your bore gauge. Just like you did with the cylinders, right? I looked over your tables for evidence of drift and nothing really stood out. So either you are really good at this, or you reset your bore gauge a few times during measuring. I have to do the latter. Hot hands I guess.

That is a perfect description and would be the end of discussion if engines ran at a steady 20 deg C. The lash is mostly to compensate for the fact that the overall valve length is longer in a running engine than in a cold one. Plus a little something for wear and margin of error. In older engine designs, lash was also linked to valve open and close time, and overlap, but with independent cams and variable timing, I doubt that has much to do with it anymore.

Exactly, which means the valves are not transferring heat properly through the seats, hence running hotter than they should and, if bad enough, allowing hot combustion gasses during ignition to contact the sealing surfaces. The extra valve lift is inconsequential, I would think.

That is an impressive amount of measuring you have there. For the record, it looks much more consistent than what I found, but I have bore gauges measuring to tenths, with interpolation to 0.000025, one more significant digit. Not necessarily a good thing. In your position, what I would do is try to get a measurement just above, and just below the ring travel low in the bore perp to the piston skirts. That will give you an idea of how much the bores have been opened up. Forget the H1 - H4 stuff. If the difference is less than 0.00025, then you are probably safe to re-hone and put like back into like. If it is more than that, you may want to get your new pistons first, then mix and match to keep the PTW numbers under control. That means more measuring, unfortunately in the latter scenario. The next step is to torque the halves together and check your mainline. Not quite out of the woods yet, but well on your way

Is it possible that your #2 exhaust valves (they were the tight ones, right?) were out of spec long enough to carbon up the seats? Then, even though you corrected the valve lash, the valves could not fully seat properly after that, pounding the carbon into the `lands' we see on the valves and seats. That would be interesting, as in, if you find way-out-of spec-lash, with symptoms, and the symptoms don't respond to correcting valve lash in a reasonable amount of time, then, basically, you may just need a simple valve job. Or a host of other scary things, but best not to jump to conclusions. Can you remind us: what was your leak down result, cylinder 2 vs the others? If I recall, it was inconclusive.

You are shooting for 0 PTW clearance. From ME-77/78: Cylinder: Standard diameter: A: 99.505 — 99.515 mm (3.9175 — 3.9179 in) B: 99.495 — 99.505 mm (3.9171 — 3.9175 in) Piston: Standard A: 99.505 — 99.515 mm (3.9175 — 3.9179 in) B: 99.495 — 99.505 mm (3.9171 — 3.9175 in) Cylinder to piston clearance at 20°C (68°F): Standard −0.010 — 0.010 mm (−0.00039 — 0.00039 in) Realistically, with new A pistons in reconditioned A-Bores, you are going to be at the upper limit for PTW: +0.0004 Just checking StkmltS, but you plan to measure and record everything to tenths, right?

In the mercedes world these are termed `optical streaks' if you can still see the remnants of the cross hatching under them. They are considered benign. As in, if you see them when you have the head off for rebuild, it is standard practice to leave the short block alone and run it for another 500K If you still had the pistons as they came out of the bores, you may have been able to index those streaks with corresponding marks on the piston skirts. So yes, it is the skirts doing this although there are debates about exactly what causes it. If the streaks are indeed optical, they will come out with the hone.

Good pictures! Thanks. The lower end of ring travel -- that line down near the bottom of the bore -- I would try to get a measurement just above and below to figure out how much the bores have worn. Are you going to enter all the measurements into your spreadsheet? I'd be super interested in what you get for oval and taper. With PTW clearances at +- 4 tenths there isn't much room for any of that.

New rings in old (as in not freshly honed) bores is a well-known recipe for building an oil burner. If you don't take the rods off the crank, how will you clean everything up?