Rolling in bearings on a 6v92

[David Anderson]

I've read many posts in the past about "rolling in bearings" in a Detroit after 100k miles.  Best I can tell I've got about 92k on my engine.  No problems, only uses a quart every 1000 miles.  I'm just wondering if I should put this on my calender in the near future and start planning the the $$$ set aside now.  It is beyond my skills and don't have the facilities, so it will have to be a shop for me.

Any thoughts?

David
1985 Houston Metro 10

[papatony]

Most Detroit's should not need bearings in less than 300,000 then do a bottom end job you should be o k .  I'm sure someone will tell you something differant but that is what long time mot-er men tell me.

[lostagain]

You could go farther before new bearings. I just did mine at 130k miles and they weren't bad. They could've stayed longer. Although changing them makes me feel better. It is not hard to do. Put the bus up on blocks so you can crawl under. Take the pan off. Take the oil filter pick up w/ screen off. Take the oil pressure regulator and press. relief valve off, and you're there. The service manual describes the procedure quite clearly. You'll need a big wrench with a pipe extention to remove the crank bearing cap bolts. And a torque wrench to put them back on at 240 ft/lbs IIRC. The rod caps are easier. Bearings and gaskets cost me less than $300 IIRC. It took me a couple of days (I only work about 4 hrs/day ). A professional shop would do it in less time, but labor is still going to be the biggest part of the bill.

JC

[luvrbus]

David, if your oil pressure has started dropping a little in the past year then it is time DD does recommend 100,000 miles,that said I been into a 6v92 with 200,000 miles very little wear believe it or not the guy never used anything but 15/40 oil 


good luck

[JohnEd]

David,

The hardest thing I have ever done with a bearing was to not replace it when I had the chance.  But I have replaced very few that actually needed to be replaced.

Now here is the "skinny".   Go to your DD book and look up what is considered acceptable wear for a bearing.  In many cars I worked on the change out point was 4 thousandths of wear....just an example and FYI.  I never did the "check a couple rods and mains and button it up if you are under 4 thou.  I checked all the bearings except the front and rear mains.  They should all have the same general appearance.  Your oil analysis should not show high amts of lead and or copper.  If that is the case you really really need to find out where that is coming from.

The way you measure wear is with a good caliper or micrometer.  You measure a one thousandth feelers gauge with a caliper and the caliper says "one thousandths...use that caliper and save the time you would spend with a mic.  The book AND your parts dealer will be able to tell you what the thickness of your bearing should be when it is new.  You get the picture.  If you want to go all the way separate a rod bearing and wipe it dry on top and bottom....the bearings and crank journal.  Put a piece of 1 to 4 thousandths "plastigauge" in the bottom of the rod bearing.  Tap the rod down to seat it on the journal firmly.  Put the lower cap back on and torque the nuts/bolts.  Then remove the cap and match up the plastigauge with the lines on the package to "read" the clearance.  That number should be less than the "allowable oil clearance" in the book.  If the bearing thickness is acceptable and the clearance is within spec also then button it up and check it in 50K miles or every couple years.

Now remember, I have never peered into the guts of a DD.  Read your book and read the response to my advice.  I mean to encourage you with this.  Enjoy the engine work.

Blower drive gear.  Generator drive gear,  Cam drive gear.  Find out how to eval this clearance and play and do those tests for absolutely sure.  A bearing will rattle or knock and can be dealt with.  You loose a gear and the engine is scrap.  Lots of tragedy with the "just inframed" engine lunching a badly worn cam drive gear.  I am gun shy on the topic.

My best wishes and envy,

John

[Brassman]

A standard rule is a thousandth of an inch per inch of journal thickness for the bearing clearance, but that was on steam ships.

[TomC]

When I was driving my 8V-92TA, the suggested maintenance intervals were- every 100,000 miles run the rack, adjust the valves and governor; every 200,000 miles roll in new bearings; every 300,000 miles rebuild the turbo, blower, and new injector tips.  Unless you're seeing a drop in oil pressure, I would leave the bearings alone.  Good Luck, TomC

[TomC]

The kicker now is the maintenance intervals on the new Detroit DD engines.  Adjust the valves at 60,000 miles, then every 500,000 miles after that; oil change every 50,000 miles; fuel filter changes every 100,000 miles with the use of the Davco 482 water separator; no bearing replacement unless oil pressure drops; overhaul at 1.2 million miles.  Quite a bit different then the old 2 strokers.  Good Luck, TomC

[lostagain]

When I replaced the lower end bearings in my 6V92 a couple month ago, I put a washer under the oil pressure regulator spring to stiffen it up. As per the DD service manual. I can't remember the thickness of it off the top of my head, it is in the book though. My oil pressure was around 40 psi once warmed up at full rpm. That is supposed to increase it by 5 psi. I will see the results in March when we go to Laughlin.

JC

[David Anderson]

Thanks for the replies.

I'm running 60psi at any rpm above 1200, 22psi at idle (180 degree temps).  I change my oil and filter every 6000 miles, so I've changed it about 10 times in the 10 years I've owned the bus.  Straight 40wt oil.  Only a small cloud of smoke on startup, none otherwise. 

I'll keep watching things, but it is in the back of my mind.

David

[RickB]

David,

Considering your low oil pressure shutoff is at somewhere under 5lbs it sounds to me like you are a bit premature on the bearings. And if you need bearings with 60 psi at cruising speed that means basically all of us do. I would be tickled with 60 lbs. I'm more on the 50-55 lbs side of the fence.

Good luck and consider thinking of this maybe in a couple of years again.

Just my thoughts

Rick