Mechanical Dilemma need Help

[NewUser]

ever since i got my 77 K5 it had a rattle like a rod or main bearing...well i didnt think that was it because it held great oil pressure...but after replacing the timing chain and gears last night i pulled the oilpan off just for a cursory inspection and found that one of the rods had some slack in it...after pulling the cap off i determined that the bearings needed replaced on that rod....my dilemma is...the rest of the rods are good and tight and have no slop in them at all...should i replace them all while i have the pan off or just replace the one bearing and let it go?.....also if i do replace allt he rod bearings should i replace the main bearings at the same time?....im hoping to have this thing done by sunday i hope



Keith

 

[4X4HIGH]

GM used selective fit bearings in many engines. If your engine utilizes the GM selective fit bearings then you cannot just throw another bearing in there because you would end up with worse clearances than you already have. Secondly, once a bearing goes south there is damage done to the rod and usually the crank as well. The crank journal usually becomes out of round and the rod big end bore also becomes out of round. The third thing to consider is that all the bearing material has went threw the rest of the engine including the oil pump. Do as you wish but take this from a PROFESSIONAL engine builder (me) slapping a new bearing without fixing everything else is just leading to another quick failure.

 

[diesel4me]

I must agree...

I have seen many Chevy motors with a loose front main bearing,and the first connecting rod bearing,nearest the timing chain..engines with A/C often show more wear on those two bearings that ones without it,due to the strain of the A/C compressor,and the belts..

I agree that just putting a new set of "shells" in won't last long..in most cases the crank gets scored some,or wears out of round as already noted,or the journals wear "tapered",and the new bearing will ride only on one side of the journal mostly,leading to rapid failure..I've seen only a few engines live for very long after putting just new bearings in,even if you measured the journals, and used the appropriate size bearings..

But your motor might run for years like this,with a slight knock ..I've had many engines that were "wounded" by running them too low on oil ,or overheating them,that lost some oil pressure and were noisy,but they held together as long as I used 20W-50 oil and some Lucas or STP type "thickener" in the oil..most of them sounded like a woodpecker when you started them,until oil pressure built up..just don't rev you motor over 3500 or 4000 RPMs,if you want it to last,especially when its cold-that is when you'll "spin" a bearing the easiest..

 

[NewUser]

let me add that there wasnt an enormous amount of movement in the rod bearing just a very slight wiggle...the rod bearings look like they have worn evenly as does the one main cap i pulled off...the crank journals all look fine and have no scoring or any imperfections that i can see or feel(nothing catches my fingernail)

even with the noise it was making the engine held 60psi oil pressure cold and 35 psi hot at idle in gear so im thinking the timing chain was the cause of most if not all of the noise due to the large amount of slack it had in it ....i guess im just asking if i should freshen up the bottom end while i have it apart or not


Keith

 

[Leper]

I belong to the slap-and-go tribe.