Numbers on wrist pins

What do the numbers on the wrist pins mean?

It means your engine is doomed . . . ?

 

Or someone is seriously messing with you.

 

I don't recall seeing numbers on Subaru wrist pins. Do you have a picture?

depends. part number? or if it was a rebuild, the cylinder it came out of

It looks think I'm the first one going through it. I have one 1 and three 2's.

 

I don't remember any before either. Is hard to see. I'm running one through the parts washer to see if it will make it more visable.

This

that's a factory code for the size. Given they are different, and if you reuse your pistons, you'll want to keep them with the piston they came with. Otherwise you'll have to measure to get the right clearance

The plan was to reuse the pistons but I'm using different rods am I skewed or can I do that?

 

Is that number just for piston fitment or does it include rods too?

Edited December 2, 2020 by RustyRuu

the rod bearing would have matched the piston pin dismeter. You can use the values in the fsm to figure out what size the piston pin should have been, and then the rod bearing size. With those two numbers you can figure out which new bearings to buy for the new rods.

 

you're not screwed but you need a pit more work to make it all work right. You can also use plastiguage if you can find the right tolerance

So only semi screwed since its a short block at this point, but after finding another couple of wrist pins laying around, the difference between a #1 pin and #2 pin is .001 or at max .002 if you measure it a bunch and trick yourself into believing it. Don't know the tolerances yet because I haven't had a chance to look it up.

the rod bearing would have matched the piston pin dismeter. You can use the values in the fsm to figure out what size the piston pin should have been, and then the rod bearing size. With those two numbers you can figure out which new bearings to buy for the new rods.

 

you're not screwed but you need a pit more work to make it all work right. You can also use plastiguage if you can find the right tolerance

 

That would be a nice trick if you can measure a piston pin to rod bore clearance with plastigage

 

From recent teardown of a running (but w 180K miles) motor: piston pins mic to 0.9053. There is no discernible wear from that number anywhere on the pins. Bores in brand new pistons mic to 0.9055 so there is only 0.0002 (note tenths!) clearance from pin to piston boss. I suppose that is where the rule comes from that once well oiled, the pins should slide into the pistons with slight resistance. Oil clearance for the small end bushing in the rod is in the FSM.

 

Interesting data point: I have some brand new pins floating around. They mic to 0.9052, one tenth smaller. Same mic, same temperature. Honestly, if required, those 180K mile pins could go back in an engine. Also the stock pistons still show machine marks on the skirts although all the coating is worn off. But with those parts being so cheap, and pistons a pain to clean, re-use makes no sense.

 

None of the piston pins out of that engine showed numbers after a basic cleanup with solvent. Is this original hardware, or aftermarket perhaps?

To my knowledge its original hardware, doesn't seem like its been messed with before. Previous over ran it out of oil and I was wondering why and just found a dropped exhaust valve guide yesterday when I was going to put the head back on.

 

The markings are only on some wrist pins, I have a bucket at work I was going through, and without putting any through our parts washer I only found a hand full.

 

I need to steep up and buy a better micrometer tenths of a thousand would be rad to be able to see.

a .0001" micrometer worth using is big dollars. Better to get the mm version because of the errors in converting.

 

awfulwaffle made a post recently on the difficulty of getting accurate measurements. something about 500 data points, temperature compensation, and excel spreadsheets.

 

plastiguage is a joke for most of subaru engine stuff. at best is does .001", where the fsm uses .0001 or .00001" tolerances. That said, a considerable number of ppl use hf tools. ymmv.

 

unless there's alot of free play on the crank pin, yer probably ok. There's a recent post by a former IAG engineer. Might be worth it to get them to write some informational posts on the critically or not of measuring

To my knowledge its original hardware, doesn't seem like its been messed with before. Previous over ran it out of oil and I was wondering why and just found a dropped exhaust valve guide yesterday when I was going to put the head back on.

 

The markings are only on some wrist pins, I have a bucket at work I was going through, and without putting any through our parts washer I only found a hand full.

 

I need to steep up and buy a better micrometer tenths of a thousand would be rad to be able to see.

 

The tools you need for a subaru may be less expensive than you think. You need two 0.0001 micrometers: 0-1 inch and 2-3 inch and a general purpose bore gauge. If you lurk on EBay a bit you can definitely pick up excellent quality for these, lightly used: Mitutoyo, Starrett, Standard, Etalon and so-on. You need not pay more than $100 for any one item, sometimes a lot less. You also need a straightedge, which I wouldn't buy used, but they aren't expensive for the accuracy you need.

 

Micrometers are simple tools and good ones last forever unless you drive your Outback over them! A trick for micrometers is to look for ones with carbide faces and ask for clear pictures of same from sellers. Carbide chips (steer clear) but does not wear out so faces remain parallel. Most high-end mics have had carbide faces forever. Inch or metric is fine although constantly converting can be a pain. Maybe stick to one or the other. Bore gauges are comparator instruments so, combined with a reliable micrometer, they don't need to be calibrated themselves.

 

I don't recommend big capacity mics or bore gauges for the cylinders, though I have them. Cylinders are impossible to measure with these engine apart, in my experience, so just find a way to measure the piston grade point (nothing fancy needed there) and call it a day.

 

However, and this is a big however, using these tools is quite another thing. Once you measure in tenths, temperature, orientation, position of the moon (just kidding) seems to come into play. Not to mention that it takes a lot of practice to get the right feel. If you do this day-in, day-out, fine. If you pull out the big boys once every two years, expect to have a frustrating few hours while you relearn the feel and double - triple check everything.

 

That being said, I haven't figured out how anyone could reliably build one of these blocks without doing the measurements to tenths and checking your list twice. Or paying someone else to do it. Otherwise, it is a crap shoot. Not that it can't work, but it may not work, spectacularly, as we have seen.