sfoti

I have a 2000 XJ with a cracked head, still running good, no overheating, but the oil pressure is barely above 10 psi at hot idle 40 with load behind it. The engine has 132,000 miles on it

My idea, which i stole from another post, is to put a new head on the current engine for now while i rebuild a short block seperately, doing this to hopefully save cost on a remaned engine and to space out the $$ spent also i need it to be driveable for the time being i cant afford it to be out of commision for longer then a weekend, but i have some questions

1.) what possible damage can i do to the new head if the stock short block blows, is it possible to drop or break a valve, or is there anyother possible ways to hurt the new head.

2.) whats an estimated time period for the stock short block before running into serious problems

3.) what machining needs to be done to the new short block, im probably going to a jy to get it, i know it needs to be honed but i truthfully dont know what decking is im assuming its machining where the head sits on the block, it would probably need to be bored, correct? and i dont know what magnaflux is but ive seen it in relation to machining. is there anyother things that would need to be done to the block

4.) i know i would replace the crank, cam, main rod and cam bearings, new oil pump, pistons rings and rods. Am i leaving anything out and will i need the new crank and cam first to assist the machining to make it accurate

does this sound like a horrible idea or a decent one, and what am i leaving out any input will be much appreciated feel free to tell me im an idiot too if you find it necessary, thanks

MVDCXJ

What makes you think the head is cracked?

Also if your stock shortblock gives out it is unlikely it will do so in a way to hurt a new cylinder head. Unless it throws a rod and the piston smacks a valve/head but I doubt that it will do that.

sfoti

and gaskets cant forget gaskets

sfoti

low cooland because coolant in the oil no leaks on the outside of the block or head

Brian71583

Your head is a known bad casting. The block should be fine so why not replace the head and call it done.

The 0331 casting you (and I) have was bad from 00-03. In 03 they strengthened it up so it's still the same head just not defective. I just purchased an '05 head with only 63k on it. I'm gonna put it on as is and call the job done for under $500 including full top end gasket kit, plugs, wires, and oil change too.

Unless your bottom end is bad you have many miles left in that thing.

sfoti

the low oil pressure indecates bearing wear, i need this to run for a long long time, i would feel fantastic knowing i have a basically brand new engine, if i could find a right a head in a jy for the right price with the right miles i would

i dont wanna replace the head just to run into block problems and have the engine die when i need it as transportation if i can just work on the bottom now and replace it later i would feel better then waiting for catastrophe

MVDCXJ

If you want to spend $$ get a Golen stroker . . . . . oh yeah!

I think the last time a had a motor freshened up they wanted the block, the crank, the cam, and a rod (It was a LONG time ago so I'm not 100% sure). If the cylinder walls are in good shape then you will not need to bore them but if they arent then you are looking at new pistons, probably 0.020 over. Have the head and the block planed to ensure they are perfectly flat and you should be all set. Break it in correctly and you will have a brand new motor basically.

sfoti

just one rod? to check the compression ratio? and what do you mean head and block "planed" like tell then what head im putting on or have it mic-ed to double check the size and clearances? and i know it was a long time ago but could you give me an example of price for machine work?

MVDCXJ

No I meant all of them, to ensure the inside area where the crank bearing goes is perfectly round. Also what I meant by planing is they machine the head and block so the mating surfaces of both are perfectly flat. Cost is going to vary since the motor I had done was a 4 cylinder and not a straight 6 and it was over 10 years ago but I do remember it being $5-700 bucks for everything, but that included more then what you would probably need like boring of the cylinders etc. Your best bet is to find a reputable machine shop in your area and call them and ask them what they think. Personally I would take your motor, slap a new head on it and change the cam and crank bearings and maybe the piston rings (maybe) call it a day. With only 130K the rings should be fine, only reason to change the bearings is because of the coolant contaminating the oil.

sfoti

thats a possibility based on the price of machining. but if the bearings are bad then will i have to swap the cam and crank, and if i do that am i gonna have to get new rod/pistons?

my fear was if im gonna spend the money on all that it might be worth while to do the whole rebuild but i guess that depends on preference and on how much machining will be, i just dont want anymore engine problems

Cherockee

I've recently done a complete rebuild of a 4.0L Jeep motor and I can tell you it's not the cheapest way to go. It appears that prices for machine work vary greatly from region to region and town to town. My "kit" included bearing, pistons, rings, oil pump, cam, lifters, timing chain and gears, gasket kit, and a few other odds and ends. These kits go for at least $600 to $900. I used my block, head, crank, and connecting rods. The machine work included hot tanking and cleaning the block, decking the block and head, complete valve job, installed valve seals, machined crank and cam bearing surfaces of the block, polishing the crank and installing the cam bearings. That ran me almost $1000. I also bought a bunch of other things too, like flex plate, harmonic balancer, intake and exhaust manifolds, fuel injectors, cap, rotor, plugs and wires, alternator, starter, and the list goes on. And I assembled it myself. I don't have a grand total but I know my investment is upwards of $3000 or more.

On the other side, you can buy a long block for about $1900 and use all your old parts and do it in a weekend.

fishtaconc

X2, When I built my stroker, machining was $800, $750ish for master kit. Then got it all together, everything running 150ish miles later had 2 injectors stick open and wash down those cylinders.

sfoti

if i can buy a new head and throw it on my current block then why do i have to have it and the new block decked? and if i have a new head then i wouldnt have to do the valve work, a lot of whats on my current block should still be useable like the timing cover its a 2000 with the distributerless ignition so no new distributer or wiring needed

Cherockee

what you can and cant use from your old block wont be known unless you tear it down. you can roll the dice and throw that new head on there and see what happens.

Worst case: your bearing are already going/gone. you put your new head on there but these bearing are wearing fast, and those metal particals are circulating with the oil through your new head. this could cause more loss of oil pressure over time, starving the valve train of oil, there-by causing damage to your new head. party over. again, that's worst case. Other posibility is there's nothing wrong with your engine, you replace the head and get another 100K miles out of it.

the choice is yours, the outcome is decided by the engine.

Oh, and if there is coolant in your oil you'll want to pull your lifters and pump them full of fresh new oil. otherwise they may store some coolant and redistribute it when you begine running your engine again.

sfoti

i didnt think about the lifters thanks for that, but my thought is if the bearing wear is bad would it loosin the crank and couldnt that lead to rough cylinder wear causing bad compression? and could someone tell me if decking is completely necessary cause it sounds to me to be unnecessary, isnt the whole point of the head gasket to ensure its a complete seal, i guess that if there are high or low spots it could potentially lead to weak spots in the gasket but i cant imagine there being a huge variance in the new head or the jy block but idk