m20b25 rod bearing help

[ekurty]

in the last year i have been trying very hard to get all bad noises out of my engine as i want my car to be reliable. head is rebuilt and i replaced block after months of chasing down the culprit. much to my dismay, shorty after replacing block im gettin a knock from the bottom end. its not terrible but it is slowly gettin worse in time. my question is, is it a legitamite fix to replace rod bearings with going any further into the engine? i would much like to get rid of the noise and room for possilbe failure in the future, but if its just a bandage fix that i shudnt b expecting to last long i wont wast my time or money and just try n rebuild the old block i got sitting. any thoughts or suggestions are much appreciated!

[jlevie]

If a rod bearing is bad, there is an excellent chance that the main bearings also need to be replaced, which means pulling the engine so you can remove the crank shaft. If the journals aren't worn that might be all that is needed. If the engine has significant mileage on it, replace the oil ump at the same time.

[ekurty]

i guess my question is, would this be a legitimate fix or sumthin i shudnt expect to last much more than 10k? i would like to get rid of this knock if possible without going that far. at the time u decide ur goin further than rod bearings, does that include new rings, resurfaced crank, bores cleaned, resurfaced/replaced rods? seems like if u go further than the rod bearings the cost become exponential. i replaced a block with one from a reputable e30 guy here in spartanburg, and now a year later ive got close to the same problem. im not so keen on another "junkyard" block" seein as how they are all 20+ years old. i guess the answer is gonna be, which i guess i just dont wanna hear, suck the cost up and do it right. im just lookin for advice from people with much experience before i go spending alot of money.

[jlevie]

What to do and cost of doing so depends entirely on the condition of the block. If the cylinder bores are within their wear limit cross hatch honing of the cylinders and new rings might all that's needed. But if worn past the wear limit an overbore and new pistons/rings would be necessary. Pistons are expensive (~$600). If the crank shaft is good, new bearings will fix that. While apart, the head should be rebuilt.

If an overbore isn't needed the parts for a rebuild will be a few hundred. It is the labor the that sets the price.

How may miles on the engine?

[ekurty]

est. 150k on replacement block and head was rebuilt when i put it back together last time , bout 12k-10 monthes ago

[ekurty]

im obviously newer to this level of mechanic work. i had sourced about 5 people to get me an idea of what was makin my noise at first. many people said it was a valve issue so after being certain they were adjusted correctly i decided to get the head rebuilt. on removin it i saw galvanic corrosion that had about eatin thru the coolant sleeve to exhaust port. i got the head rebuilt and welded for 400. ended up the head wasnt bad short of a few valve guides with some wear and the obvious corrosion. when i got it back together it had the same noises which pointed me to bottom end. i found a block for 400 and put it in. while its not the same noise i had before, it has definate got a lil more prominent as time goes on. mayn people tell me not to worry about it and "drive it till it blows", but i just want my e30 to b reliable and last for a while. i dont plan on racing and just enjoy it as my DD. fortunately i have the old block i took out that i can work on so i dont have to take my car out of commission. the old block and the one i have in now both had compression within 5% of the cylinders, if that helps in the determination of the condition of the bottom end. i hope i can have an m20 without that knocking and it not take thousands of dollars to get me there.

http://www.iemotorsport.com/bmw/E30-engine/m20rodbcoated.html

thats what i was loooking into

[jlevie]

If you can do work yourself, the cost to rebuilt a block isn't that bad. But you don't just throw parts at it. After tearing down the block the cylinders must be checked for wear. If within the wear limit the cylinders must be cross hatch honed so new rings will seat. If the crank looks okay (no grooves, etc). It can be polished. Then the journals have to be measured to pick the bearings that provide the correct clearance. Since the measuring work requires instruments that read to a tenth and since those are expensive, have that done by the machine shop.

Make a new oil pump and pressure relief valve a part of the rebuild.

But before embarking on this, have pro diagnose the noise.

[ekurty]

i tried to go to what i thought were "professionals" and they were the ones that pointed me towards the head making the noise. i guess thats just a sign i need to find other people with experience to do the diagnosing. it ended up being my backyard mechanic buddy that was right on the noise was in the bottom end. everyone else pretty much said it was a hanging valve or something from the head. ive done quality control for spartanburg steel and a few other suppliers to bmw and got decent using a caliper, but ive never done any measuring of engine internals. off what ive said so far, would u say this work is beyond my capacity? i would really like to learn bottom end work. i try and do a lot of research but also know experience matters more than references.