so lets say i just buy standered bearings and replace the old ones, would it work or do i have to mesure the clearance and all that? cause i dont know if the bearings are for sure even the problem.

 

Im so confussed right now it rediculous, so if i do use the plastigage where and what am i doin with it? like i get im supossed to see how worn the rods are to see if i need over sized bearings right? and if i dont use it what do i do? jus get the standered bearings and slap em in?

 

I would check it anyway, just put your new bearings in place. take about 1/4 to 1/2 inch of plastiguage lay it across the bearing in the cap. Pot your rod cap in place and torque it down, remove rod cap and measure how much the plastiguage mashes down and compare to the measurements on the paper. wipe down the journal really good so it will be nice and clean. When your ready for the caps final instal coat it down really good with some oil or a touch of gearlube.
Your old bearings will be worn, your crank may be worn some, yours prolly wont be worn so bad you need oversize bearings for what you are doing, unless the moter has been rebuilt in the past and the crank was turned and you need them. The plastiguage should mash down from ,001 - .003.....003 is alowable but alot......I had to do mine I went up to .006 mine still rattles at startup but it a trail jeep so i dont care it was a $300 jeep

 

Sorry, I contributed to running away with your thread. If you opt for the Plastigage, what dbcox says is the correct method.

If you haven't already, open up the Plastigage package. There will be a strip of paper in there with lines of varying widths printed on it. This is what you compare the width of the smooshed Plastigage to in order to get the clearance reading.

 

this is the part i dont get, i buy new bearings and use the plastigage and if the clearance is too much i need the over sized bearings right? i thought the whole point of the plastigage is to figure out what bearings i need so i might wined up buying two sets of bearings?

 

You may even have to buy more than two sets of bearings. When I was building engines I usually had a case of over 100 bearings shell halves at the ready in order to get the clearances right.



The rod oil clearance is on the order of .0015” to .002” so you’re literally splitting hairs. A sheet of standard copier paper is .004” thick.

In your situation, replacing the rod bearings only, the Plastigage is only used to verify the clearance is between .001” and .002”. (This is an extremely rough tolerance, but it’s about the best you can do with Plastigage, and only if you’re very careful with it at that.) If it’s larger or smaller than that there’s not much you can do.

Sometimes you can get away with swapping bearing halves until everything fits. Even though all standard bearings are supposedly the same thickness, they have some manufacturing variance. And, you don’t have to swap the bearings in pairs, it’s okay to use two bearing shells with different thicknesses. You can even swap between the old used ones and new ones. (Not preferred, but better than an out-of-tolerance oil clearance.)

 

If you've damaged the engine to the point that you think you may need to go with "oversized" (actually smaller diameter) bearings, you need to get the crank ground before you bother doing anything.

If all you're doing is replacing the bearings with new ones the same size as the existing ones, why bother with the measurement? What are you going to do with that information regardless of how it comes out? Unless you intend to have the crank ground if the clearances are out of spec, slap the new bearings in with some good assembly lube and put it back together.

 

bouts to not even worrie about it, im just going to put the oil pump in and call it good, george said that probably my problem anyways.

 

I would do it anyway, do just a couple at randon it only takes a few minutes while your in there anyway. bearings are only like $30
Or atleast drop a bearing cap and see what the bearings look like, if they look new and smooth dont worry about it.

 

i just came across this thread , but can you change out the bearings without removing the entire motor??? I mean i have low oil pressure when my jeep warms up and i have a constant tick/rattle and i have been told that its could be either the main and rod bearings, or the cam and cam bearings/lifters.... But i went the cheap route and just replaced the oil pump and it is still doing this so i am faced with this same decision but i am unsure of wat it is exactly, and if i can do it without removing the engine from the vehicle...

 

You can do it with out removing the motor but what I did was just put a new oil pump in (high volume) and ran thicker oil and called it good