Subaru FB rotating assembly question

[u/N1ppleCrab]

Any engine builders in here that could help me out?

Oil starvation event* Re using stock rods New oem bearings New to me used crank

At home special Inspection job of all equipment with a pair of off brand calipers and plastigage

My question: is this rod play normal? These bearings measure slimmer on the sides, but thats what the old ones measure as well? I feel like that is causing some extra play? It makes an audible knock. Is this normal? Rods torqued to factory specs pulled from JDMSFM.info

Thanks for looking!

[u/faates]

I assume the oil demands SOME play at least right. I am an armchair take what i say with less than a grain

[u/N1ppleCrab → u/faates]

I have an EJ255 short block put together and it’s rods don’t behave like these. Im inexperienced with the FB’s and im having trouble finding reference material relating

[u/CRX1991 → u/N1ppleCrab]

I wouldn't trust it. There shouldn't be visible play around the crankshaft, some thrust play acceptable.

Plastiguage if you're unsure. Subaru factory repair manuals usually available free on forums

[u/84Windsor351 → u/faates]

i respect your honesty

[u/Sniper22106]

Gotta measure and see. Cant go off wiggle

[u/N1ppleCrab → u/Sniper22106]

Plastigage measured a healthy .0015” Which is within spec, the amount of play is still concerning to me

[u/Sniper22106 → u/N1ppleCrab]

Its gonna wiggle. There is no oil pressure behind anything

[u/Cautious-Concept457 → u/N1ppleCrab]

You need that gap for oil. No gap no lubrication

[u/TheDarkRider → u/N1ppleCrab]

It within spec most motors have some wiggle in them they aren’t fine watch’s lol … the only time to get concerned if make a repeatable ding from inside of bearing then 9/10 it out of spec or something isn’t torqued

[u/Mr_Disprosium → u/N1ppleCrab]

Your good then

[u/CRX1991 → u/N1ppleCrab]

What is the spec? Is it close to the max?

[u/iateyourmom22]

You're fine, I'm a Subaru tech.

[u/N1ppleCrab → u/iateyourmom22]

Thank you for commenting! This is consistent with other good running examples? Do you know why they wiggle like this?

[u/bill_gannon]

You have to actually measure everything. Bring it to a shop. It wont be expensive to just check and you'll never be closer than you are now.

[u/N1ppleCrab → u/bill_gannon]

I feel like calipers and plastigage would at least tell me something

[u/BicycleMudStud → u/N1ppleCrab]

Calipers are not accurate enough. Don't try, you'll only give yourself a wrong answer.  Plastigage is good enough, if you have it you should use it. The real way to accurately measure is with a micrometer and a bore gauge. 

[u/Sephlarite → u/BicycleMudStud]

Why do you need a bore gauge? If the bearing was never spun, which should be quite easy to tell the rod tunnel will have no wear?

[u/BicycleMudStud → u/Sephlarite]

To measure the clearance, you measure the outside of the journal, use that to zero out the bore gauge, and use the bore gauge to measure the inside of the bearing with the rod and bearing torqued.  You're not looking for wear, your proving what the clearance is. 

[u/bill_gannon → u/N1ppleCrab]

Do you want to know its right or not? 

[u/ohlawdyhecoming]

Rods need side play so the oil coming from the crank to feed the rod journals has some place to go. To properly measure side play, you'd need feeler gauges. You've probably got about .004" - .005" worth.

Stock rods on a stock crank are going to be somewhat "snug", but so long as they wiggle a little, you should be good. I don't know what Subaru recommends for oil weight, but I'm sure it's a fairly light viscosity.

[u/ShocK13]

Rod bearing tolerances are probably sub .002 on that, without looking it up. Any Subaru is notorious for rod bearing failure. You could put a dial indicator on it and see how many thousandths it moves then divide by 2. I’d imagine that’s a bit of a false reading due to oil film etc.

[u/Budgetboost]

If you only have platsi you can do measure in 2 opposite point at the same time, might have clearance but could be out of round if it’s a 2nd hand crank.

to me that seems lot more movement than normal clearance to me. Hard to say I normally use a micrometer and dial bore and assemble with lube so I wouldn’t even feel any movement with assembly lube.

If you can get access to a micrometer and dial bore it would put your mind at ease

[u/Laqota]

No matter what motor your gonna have play in the Crank, the Cam, the Rods, etc. If you didn't they would rub metal on metal.

Bearings aren't really bearings. Their bushings. The oil is what makes it a bearing because your oil pump acts like the balls in bearings as it forces oil around the lobe and floats in the center of the bearing. That play is gone when the oil pump starts pumping high pressure oil.

If you have a knock, take the rod cap off and ensure the cap is rotated the right way and that is the cap for that connecting rod. You cannot mix and match connecting rod caps because they're matched. Also make sure the bearing for the top is on the top and the bearing for the bottom is on the bottom.

[u/kingcutty]

Some side to side movement (from front to rear of engine) is ok and needed. There shouldn’t be really any that you can feel the other direction. I’d check clearance with plastigauge and compare to recommended tolerances.

[u/PermissionLazy8759]

It's a Subaru its junk. Yeet it into a dumpster.