Main bearings and rod bearings

[old88xj]

So my "shop" (see "getting angry") is gonna replace the main and rod bearings to see if it fixes this mystery noise. I am gonna be there to watch em do it so what do i need to watch out for and any suggestions would be great!

[GSequoia]

Make sure they use plactigauge to make sure they put the right size bearings in!

[old88xj]

So what is Plastigauge?

[old88xj]

and how does it measure bearing size???

[Judd W. 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.

[rixXJphx]

Originally posted by old88xj
So what is Plastigauge?
A package of precise plastic 'wires' of fine diameter. About $8 at any autoparts store.

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.

[old88xj]

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??

[Eagle]

Originally posted by old88xj
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??

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.

[old88xj]

Thanks for setting me straight Eagle. I am not a gear head but like to think i have some mechanical knowledge and abilities so it is nice to be set straight.

[Eagle]

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]

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.

[old88xj]

each one that you replace you need to check is what i gather

[RTownsend]

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?

[old88xj]

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

[old88xj]

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]

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.

[old88xj]

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

[Eagle]

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.

[old88xj]

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]

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.

[Eagle]

I agree with Hoss -- with a kit the bearings should be sized to the crank, but should be checked to be sure. As to the timing chain, you're correct that it has to come off to replace the crank so you might as well put in a new one. The XJ uses all steel gears, so all you really need is the chain -- you shouldn't need new sprockets, so it'll cost you the princely sum of $15 or so. Be sure you replace the front seal, too, but that's probab;y included in the crank shaft kit.

[old88xj]

But seeing as that i have some blow by and rebuilding the bottom half is gonna make it tight, what do you guys think about buying a remanufactured motor and having a mechanic do it on the side?

[HossHoffer]

If you have the money there is nothing like a complete rebuild. It's like starting the clock over. Did you do a compression check to get definitive numbers on how bad your top end is? There are alot of people out there wheelin' on very low compression so if money is the issue or if you don't plan on keeping your XJ much longer then just do the bottom end and relap your valves. If you have time, money and resources (machine shop connections, your own tools, friends with lots of time and like to work on your car) then do everything and put in the best parts you can afford. Remanufactured engines are great and affordable. I'm sure someone on this site can recommend something in your area.

[XJTripp]

I saw a reman long block with a limited 7 yr/70K warranty and the description of the machining and the new parts and brands of parts used all looked pretty good. $1130 and a core charge of $250. I think the address is auto-engines.com. If you want I can get the flyer I printed with the exact address. Said they had performance options too. I have been sort of beginning my plans for a rebuild down the road and the kit is $550-$600 then you'll need machining to do it right. The reman. long block is tempting.

[Eagle]

Originally posted by old88xj
But seeing as that i have some blow by and rebuilding the bottom half is gonna make it tight, what do you guys think about buying a remanufactured motor and having a mechanic do it on the side?

As noted, a lot depends on how bad the blow-by is and how long to plan to keep the vehicle -- as well as whether it's a daily driver or a weekend warrior.

Replacing the crank and bearings is not a lower end rebuild and will not do anything to "tighten up" the blow-by. That's a function of rings, pistons and cylinder walls. It is possible to replace the rings in the vehicle, but to do it you would have to remove the head, and the new rings probably wouldn't seat in because the cylinders would not be bored to correct for out-of-round due to wear.

All the crank kit will do is give you a smooth crank shaft and decent oil pressure. It's a lot less money and a lot less work than replacing the engine, but if the new engine is what you really want or need, then do your homework on where to get one.

[old88xj]

The blow by is not severe as far as i can tell. I wanna keep my heep but i don't wanna keep throwing money at it if it isn't gonna last me at least another year to a year and a half. It doesn't have to be a DD but i want it to be able to make it out of state for functions once i get it done. So if you guys say replacing the crank and bearings and the motor should be good to go seeing as how reliable the 4.0 I6 is then that is what i would probably do. I just like weighing all my options before i do anything.

Reasons for keeping:
Great rust free frame and body!!
30x9.5 BFG AT's have 85% tread left.
just installed home made light bar
been a faithful XJ for the last 2 years

Reasons for not keeping:
Blow by
needs new rear leaf pack
spent $680 and its still broke
wife wants to get rid of it

Decisions decisions decisions

[Judd W. VA]

My views and some clarifications- Forgive me if i repeat much of previous.

If a spun bearing, the crank needs to come outa the block...the engine needs to come out to do that. That connecting rod with the spun bearing needs to most likely be replaced, and all the others should be checked to see if they are okay. Is not possible for the big end of the rod to be in servicable shape if it's bearing spun. To replace/resize that connecting rod, the piston/rod combo needs to come out. To do that the head needs to come off. And while the head is off....

Should replace the timing chain as a set, that is the gears and chain. Is not possible to have 200k miles on the gears without wear pattern on the teeth from the old chain. Chains also vary in design and the gears to accommodate. In addition does not cost that much more to do the 3-pc.

Blow by can be a real problem. How often do you have to replace plugs due to oil fowling? Or how often have to add oil? These are the main two gauging indicators.

Keep us posted-

[old88xj]

The blow by just started prior to taking it to the shop so i am not sure of the oil amnt and i have not had a chance to check the plugs. As to having to remove the head or the engine....You do not have to according to my mechanic....pull the timing gear and slide the transmission back but the motor and head stay put.

It did indeed spin a rod bearing...the one above #1 main bearing. I am gonna buy the crank kit which includes everything that i need to do the job along with a timing set and all the gaskets that i need. BUT what i NEED to know is with the exception of the blow by, will i have anymore problems. Is it worth me spending alot of $$$$$ on an 88 XJ auto 4.0 115K?
Will I be chasing down problem after problem? When i fix one thing another one breaks! Its becoming a money trap!

I know my questions can not really be answered but if this was your Heep what would you guys do? Fix it and go? Sell it? Part it out? Fix it then sell it? the WIFE wants to donate it and be rid of it but i can't bring myself to do that seeing as it has been totally faithful in the 2 years that i have owned it. Just really looking for opinions on this.

[Judd W. VA]

If a rod bearing was spun, the connecting rod to which it corresponds will need to be replaced. That means pulling the head and removing that piston/rod. There is damage to the ROD as well as to that crank journal. That cyl bore will also need to be honed to seat the new rings that will be used with the old piston/new rod. While going in it that far, and the bores are confirmed to be in basically good shape, why not hone/re-ring the other five?

If that shop does not want to at least replace that connecting rod that had the bad bearing, i'd take it somewhere else- they do not know what they're doing.

This is the only way to do this job. Is really rather basic to engine diagnostics/rebuilding. If you are not willing to pay to have all this done, then it would be time to "part" with it i am afraid.

[Eagle]

I'm going to disagree with Judd on this one. I've seen spun bearings that didn't damage the rod. I also checked in with my brother (a dealer service writer) and he said in his experience it's quite rare to see any damage to the rod. It is quite possible to replace the crank with the engine in the vehicle, and that's what I would do if it were mine.

[Judd W. VA]

Whew. I am often amazed at things some will try to get by with. Is rare to find a used rod big end that mics to good specs that HAS NOT EVEN SPUN A BEARING!! Then taking this to the extent of one that had spun!? I would NEVER put a new bearing on a rod that had spun...nor would i trust anyone who has. I stand by my word on this. I have been associated with the most extensive level of engine building and know what i am talking about. The level of compentency in the auto world has really gotten bad.

Eagle, you are not an auto tech, and i bet you have not even built an engine!! Sometimes i think you need to realize that your automotive knowledge does have its limits.

I am not angry with you eagle, but when it comes to the possibility of spending that much $$ on something so major, such drastic corners should never be cut. Perhaps is why i have built such a loyal success-driven cliental!!

[Eagle]

Originally posted by Judd W. VA
Eagle, you are not an auto tech, and i bet you have not even built an engine!! Sometimes i think you need to realize that your automotive knowledge does have its limits.

You're half right -- I am not an auto tech for a living. However, with all modesty I honestly believe I am a better tech than most of the guys out there who do it for a living. Which is why I do as much of my own work as possible.

I have indeed built engines. As I've posted here numerous times, both my brother and I crewed for many years on our friend's modified stock car. We also autocrossed and hill climbed extensively for a number of years. We built all the engines for the stock car, and I built my own engines for my autocrosser and hill climber. I've also rebuilt and repaired engines for my daily drivers.

I would not just toss in a bearing for a race engine, but for a street/trail engine that may not even be a daily driver and only has to live for a year or two ... I'd do it in a heartbeat, and I don't consider that any lowering of standards. I consider it value engineering. I think it would be a waste of money to either replace the engine or yank it out for a complete rebuild unless the intention is to keep the vehicle for at least 5 or 10 more years. Look at the age and value of the vehicle, and the cost of replacing or completely rebuilding the engine. The engine will be worth more than the vehicle, and if he tried to sell it a week after installing the new or rebuilt engine he could never get back his investment. Unless the truck has sentimental value like my original '88 does for me, and is still very straight and solid, it simply doesn't make economic sense to do that. It would make more sense to but another XJ for $2000 or $2500 and sell the one he has, either whole or for parts.

I fully recognize that my automotive knowledge has limits. Where those limits apply, I either don't offer an opinion or I clearly state that I'm guessing. In this case, I am not beyond my expertise nor am I guessing.

[old88xj]

Hmmmmm two very valid and thoughtful points Judd and Eagle!
Replacing the motor is gonna cost me $1500 and a few weekends. The crank and such will cost me $500. Daily driver it doesn't have to be....reliable it does. like i stated above....The body and frame are rust free....interior is excellent, the motor until now was sound. The only problems i had with it were the power windows and locks and an exhaust manifold gasket that keeps blowing. but that is another thread. My mechanic feels it didn't do any damage to the rod itself just the bearing. I have already spent $700 to replace the rear main, oil pan gaskets, front crank seal, and oil pump just to find out that was a waste of money bc 130 miles after that i spun that bearing so if $500 gets me a reliable jeep then thats the way i am leaning.

JUDD
Thank you for you insight and opinions.....just how far are you away from Richmond??

EAGLE
What you says makes sense and thank you for your help also