jesse jay

So i got an oil pump and all that to replace it, and i got plasigage, but i dont know how to use it, i guess im supossed to use it to check what size bearings i need? cause im gona change the bearings. my motor has a rattle to it when it warms up when there isnt a load on the engine, but if im exelerating the rattle isnt there. i figured out that the oil presure drops really low like down to 5 at idal when the jeeps warmed up, and thats when the rattle come about.

dbcox

you need to see wha\t bearings you have prolly standard. do them ONE at the time so you dont mix them up.
1.take rod cap off
2.remove both bearing halves
3.place new bearings halves in
4.place a small piece of plastigueage on new bearing in rod cap
5. Tighten down to torque specs
6.remove rod cap and measure plastiguage. with paper it comes in
7. replace cap
8. retourqe
9. do another
Just do one at a time and you will be ok

thorguy57

Your block should be marked to show if you have oversized bearings in it.

dbcox

The bearings should have a mark. Mine had an X for standard

thorguy57

They also usually mark the block if it came from the factory with oversize bearings. Coming right out of my manual it says " If any letter codes are stamped on the boss between the ignition coil and distributor, different size bearings were used" You need to read the markings and see if any were used. Keep in mind though this was from the factory so if anyone has went through that motor before this may no longer apply.

dbcox

And all bearings are marked one way or the other

jesse jay

isnt the whole point of plasigage to find out what size bearings i need?

thorguy57

no, its to measure clearances after you install new bearings.

blasto9000

Are you changing the bearings with the engine in the vehicle or out of the vehicle?

If in the vehicle, using Plastigage will be a major pain in the butt. You’ll have to clean all the oil off of the journal otherwise the Plastigage will dissolve (and it will probably give an erroneous reading to boot). Plus, it’s just not a very precise measurement – you tighten down the bearing cap so it squeezes the Plastigage, remove the bearing cap then compare the width of the crushed Plastigage strip to a printed line on a sheet of paper. It totally sucks.

Anyway, if the engine is in the vehicle, and you can determine if it’s rebuilt or not, using Plastigage for a simple bearing replacement is sort of a moot point because changing the bearing will close up the oil clearance anyway. It still might not be within OE spec, but it should be better than what you started with at the beginning of the job.

wildspear

So, your saying just skip over the "Plastigage" part?

dbcox

1. Its not that hard
2. your new bearings will be clean, just wipe the journalm good you will be fine
3.Plastiguage sucks? Wow what do you use? That is part of a blueprinted engine when you build one , thats all it is.

dbcox

No you dont skip this part. it is im portant to know what you got.
Granted putting in new bearing isnt the 100% best way but it will buy you some or al ong time. your journals dont wear round, they wear oblong or not fully round. Ive done it before and people all over have done it before and never looked back.
I guess if plastiguage suck thats why they use it in high dollar racing applications also

wildspear

Ok, Just checking. I'm in the process of dropping my oil pan to take a look at things ( I may have a busted rod) saw this thread and decided to ask.

blasto9000

Actually, I misstated. Using Plastigage will suck when the engine is still in the vehicle because the oil will keep dripping down and dissolving it. Then you will have an erroneous reading showing too large an oil clearance.

Anyway, it’s easy when the engine is clear of oil and sitting upside-down on a stand in the shop. When the oil is still dripping down you could check the clearance 20 times with Plastigage and you’ll get a vastly different reading every time. Also, Plastigage does not work properly when the piston rings are installed because it relies on a free-sliding piston to get a correct crush.

I have rebuilt 30+ engines and what I use is a dial bore gauge, standard micrometer for the journals and a bearing shell micrometer for the bearings. I have regularly gotten oil clearances to 0.0001”, and in fact did not ship an engine unless the clearances were within this tolerance.

Plastigage still has its uses to verify the assembled clearance on a build. On an engine that’s already been assembled and running I would verify the shell thickness of the new bearing and if within range, yes I would skip the Plastigage.

dbcox

alot of people dont have those tools not even a micrometer, So yeah go ahead and skip the plastiguage its like $3, and no idea of what you have is better than a really close measurement. That much oil doesnt interfere with it if any