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Blazer 6.2 Diesel Rod Knock

H

howardjnl

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My son and I have run out of ideas on how to stop his 6.2 from wearing out con rod bearings in a matter of hours. We've been through two new crankshafts, several sets of bearings, new con rod bolts, a new high volume oil pump and no improvement. Oil pressure is steady at 45 PSI, temp at 195, no blockages in oil channels, no oil leaks, check clearances with Plastigauge when assembling, torque according to specs, no rushing repairs. Switched up to 10W-40 Mobil 1. Sounds great, runs great, lasts a few hours before hear bearings knocking. Damdest thing I've every encountered.
We're obviously missing something, but damnedfino what it is. Any thoughts?
John :confused:
 
okieraptor said:
Are the two closest main caps sized right?

Is the block align bored correctly?

Are all oil passages clean and free of blockage?
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Oil passages are clear, haven't measured block alignment other than to spin the crankshaft by hand with new main bearings installed (spins freely). Not sure what you mean by "Are the two closest main caps sized right?". Would you please explain this a bit?
John
 
If the two closest are over bored then on the compression and combustion strokes the crank could be flex. It will cause the bearings to ride uneven on the crank causing premature failure and eventually a broken crank.
 
Do the bearings look bad when you restrip? did ya try plastigauging the failed bearings after knocking to recheck clearance?

You should also either acurately measure the rod bores yourself or take them to a engine reconditioner, sounds like the rod bores could be out of round mate, they only need to run the bearings once in a petrol engine and the rod bores get outa round and need resizing, good luck mate
 
Does ALL the rod bearings fail,or just one or two??...

I recently had a glow plug fail and it broke in two,and the loose peice was smashed between the piston and head (and valves maybe)..my engine still runs OK,but has a loud ticking from the rockers on that cylinder--so it may have a bent pushrod or wounded lifter..it goes away as it warms up fully though...

I am hoping the peice of glow plug was eventually blown out of the exhaust,and didn't end up lodged in the top of the piston..THAT would put a nasty dent in the rod bearings life span I would think!..:eek:..
 
Blazenkiwi said:
Do the bearings look bad when you restrip? did ya try plastigauging the failed bearings after knocking to recheck clearance?

You should also either acurately measure the rod bores yourself or take them to a engine reconditioner, sounds like the rod bores could be out of round mate, they only need to run the bearings once in a petrol engine and the rod bores get outa round and need resizing, good luck mate
Click to expand...
This whole thing started when my son had the truck for a few months and one of the con rod bolt nuts apparently unscrewed and came off. Weird, huh? No stripped threads, one bolt bent. Haven't gotten it right since. When the bearings fail, they have the wear pattern of lack of lubrication we see on various place on the Internet. Too bad no one has pictures of one out of round, so that I could see any difference :-). That's a good point, though, possibly being out of round. We've not been able to measure out of round with measuring tools, or with plastigauge with new bearings. The damaged bearings are for cylinders 1 and 2, which are 1) the con rod bearings furthest away from the oil pump and 2) are consistently the ones that fail, #2 bearing the one consistently most damaged, the one that originally came unbolted. I think we'll pull the engine again and take it to a proper shop for checking and possible repair. Thanks, "mate"!
John
 
Hi John, if those are the bearings that keep failing and were the same ones that originally failed, I'd definately take it somewhere that can acurately measure for you, get them to re measure the crank for you as well, good luck mate lol
 
hey, this may sound stupid but a friend of mine has a 6.2 and it got a bad knock. he parked it for 3 years and finaly got the money for a new motor, he took it to a GM mechanic to have him install a new one. he called back the next day and told him, "it's good to go" it ended up only having a bad injector.
 
howardjnl said:
This whole thing started when my son had the truck for a few months and one of the con rod bolt nuts apparently unscrewed and came off. Weird, huh? No stripped threads, one bolt bent. Haven't gotten it right since. When the bearings fail, they have the wear pattern of lack of lubrication we see on various place on the Internet. Too bad no one has pictures of one out of round, so that I could see any difference :-). That's a good point, though, possibly being out of round. We've not been able to measure out of round with measuring tools, or with plastigauge with new bearings. The damaged bearings are for cylinders 1 and 2, which are 1) the con rod bearings furthest away from the oil pump and 2) are consistently the ones that fail, #2 bearing the one consistently most damaged, the one that originally came unbolted. I think we'll pull the engine again and take it to a proper shop for checking and possible repair. Thanks, "mate"!
John
Click to expand...

sound like that rod is out of round now, possibly bent as well.
 
Don't mean to hijack, but what does rod knock sound like? My 6.2 occasionally has a loud klack-klack-klak that can not be heard from above (open hood) but is very loud from underneath. It changes or goes away in different gears and goes away once it warms up. I've had it off and on for about a year. Same thing or different?
 
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