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Main bearings and rod bearings
- Thread starter old88xj
- Start date
- Location
- Torrance, CA
Make sure they use plactigauge to make sure they put the right size bearings in!
Judd W. VA
NAXJA Forum User
- Location
- new Hope, Va
Rule of thumb you can easily go .001" undersized on any crank journal with some miles on it, and maybe .002". I'd test a .001" with plastigauge and see. If can go .002" then most certanly do.
A package of precise plastic 'wires' of fine diameter. About $8 at any autoparts store.old88xj said:
Insert one into the space between bearing and journal and tighten the bearing cap to spec.
Do this for each bearing.
Tightening the bearing bolts will flatten the plastigauge. How much it is flattened identifies the space between journal and bearing.
Remove cap and compare the width of the flattened pastigauge to the chart on the package.
Thanks Rix anything that i should watch out for or is this a "fool proof" install.....what happens if they put in the wrong size bearings? How would i be able to tell/
If they put in to small of a bearing do i get weak oil pressure?
or if they put in a tad to big, do i get off the chart pressure??
If they put in to small of a bearing do i get weak oil pressure?
or if they put in a tad to big, do i get off the chart pressure??
- Location
- Terra Firma
old88xj said:
It is not fool proof, and that's why any engine builder worth his (or her) salt uses Plastigauge to confirm the fit. However, you have it backwards. If the bearing is too big, you get a loose fit and low oil pressure. If the bearing is too small, you get a tight fit, scored crank journals, and possibly a spun bearing.
- Location
- Terra Firma
It may be a bit counter-intuitive, because the numbers refer to the crank journal diameter, not the bearing shell. Thus, a .001 bearing is larger than a .002 bearing, because it's for a crank journal that is .001" under standard diameter, whereas a .002 is for a crank that's .002" under standard diameter (and .010 is for a crank that has been ground to .010" less than standard diameter).
RTownsend
NAXJA Forum User
- Location
- Gainesville, GA
I need to replace my rod bearings in my 215K mile 4.0 to solve a low oil pressure problem. I had intended on just putting in the same size that I removed. From what you guys are saying it sounds like I need to check each one.
RTownsend
NAXJA Forum User
- Location
- Gainesville, GA
I'm not trying to steal your thread but to you more experienced guys I have a question.
My oil pressure seems to be running a little low lately. Sometimes I'm at about 30 PSI at 2250 RPM and around 20 at 1500 RPM. I need a new rear main seal and wanted to replace the bearings and maybe oil pump while I'm in there.
What are the chances that my mains are in good shape? Do you think that new rod inserts would solve the low pressure? Is my pump almost shot?
My oil pressure seems to be running a little low lately. Sometimes I'm at about 30 PSI at 2250 RPM and around 20 at 1500 RPM. I need a new rear main seal and wanted to replace the bearings and maybe oil pump while I'm in there.
What are the chances that my mains are in good shape? Do you think that new rod inserts would solve the low pressure? Is my pump almost shot?
RT...Steal away..i got most info that i need. I had same problem as you...needed new Rear Main seal...had it done along with front crank seal and oil pump and harmonic balancer. Well My Heep went in with a oil leak and came out with an engine Knock. Hence the purpose of this thread.....Ask away there are quite a few brains on this forum and like i said i picked em for what i needed
By the way i appreciate everyones input and advice.....now its decision time...the #1 rod bearing is spun and i have a scarred crankshaft so should what do you guys suggest i do? Replace it? How long will it last? will replacing it affect the top half of the motor? HELP PLEASE
AZ Jeff
NAXJA Forum User
- Location
- Gilbert, Arizona
If the rod bearing is spun, you will need to replace the bearing, AND RESURFACE that journal of the crankshaft. Just replacing the bearing will not result in a durable repair, as the lack of a smooth and round journal on the crank will trash the new bearing in short order.
Back years ago, there used to be guys who could resurface a crank IN THE VEHICLE, but I don't know if that practice is still done.
If not, the only solution is to remove the crank, and take it to a machine shop for refinishing, and use new bearings as necessary.
Back years ago, there used to be guys who could resurface a crank IN THE VEHICLE, but I don't know if that practice is still done.
If not, the only solution is to remove the crank, and take it to a machine shop for refinishing, and use new bearings as necessary.
yea well the shop is gonna charge me $1300 to do all that but i have some blow by on the top half. will replacing the bearings and crank hurt the top half anymore? also for around $1400 i can get a remanufactured motor from advanced and have a good friend/backyard mechanic take the old one out and put the new one in or i can buy the parts myself and try to replace it myself with the help of said friend if this will solve my problem and get my jeep back on the road for a good while before anything else goes bad...i love my heep and since i got another car lined up i don't have to rush to get this back so the way i see it is its build up time after i get the motor taken care of first that is
- Location
- Terra Firma
old88xj --
Why don't you just buy a crank kit from one of the parts chains? It should include a remanufactured crank and a full set of bearings. Somehow, I have it in my head that I saw a price of around 250 clams for that. Won't have any effect on the top end -- rings will be undisturbed, as will valves.
RTownsend --
Check every one. Rod bearings seem to go before mains. If changing the rear main seal you'll have the rear main cap off, so you can plast-gauge that one. If it looks good visually and gauges close to specs, leave the mains alone and just replace the rod bearings.
Oil pump is probably fine.
Why don't you just buy a crank kit from one of the parts chains? It should include a remanufactured crank and a full set of bearings. Somehow, I have it in my head that I saw a price of around 250 clams for that. Won't have any effect on the top end -- rings will be undisturbed, as will valves.
RTownsend --
Check every one. Rod bearings seem to go before mains. If changing the rear main seal you'll have the rear main cap off, so you can plast-gauge that one. If it looks good visually and gauges close to specs, leave the mains alone and just replace the rod bearings.
Oil pump is probably fine.
Eagle....Advanced Auto has the kit for I wanna say $125 or so. Do you recommend changing out the timing chain and gearing since it has to be taken out or moved to get the crank out? from the parts that the shop suggested needing replacing he is charging me $500 for the parts and $850 for labor to put them in. I can get all his recommended parts my self for $185 from Advanced and that is after a 10% discount because my brother works there. So with the cracnk kit do i still need to plastigauge the bearings?
HossHoffer
NAXJA Forum User
- Location
- Aurora, CO
Crank kits
NAPA has the kits for $179.00 so you price is right in there. You will still have to use the plastigauges as they are just part of the assembly process to assure the right fit for proper oil passage. They're easy to use and once you've done one you'll be a pro.
NAPA has the kits for $179.00 so you price is right in there. You will still have to use the plastigauges as they are just part of the assembly process to assure the right fit for proper oil passage. They're easy to use and once you've done one you'll be a pro.
