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Oil changes on my now 35000-mile rebuilt AH 3000 BJ 7 engine (with 0.010 / 0.010 crank grind) are showing some aluminum-colored glitter. Not too much, but enough to drop the oil sump and inspect rod (big-end) and main bearings (Vandervells were installed). If the crank journal clearances are within tolerance and not marred /damaged, is it possible to replace main bearings with the engine in chassis? I read that removal of front and rear main bearings will damage crank seals etc., so bearing replacement is limited to the two in the middle. Replacing the rod bearings should not be a problem, depending on journal condition, but some pointers would be appreciated. And why is it that the Haynes workshop manuals state "replace main and big-end bearings as a matter of practice every 30K to 50K miles to extend crankshaft life and avoid costly problems in future". Thanks all, Gonzo.
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Time to check Rod and Main Bearings
- Thread starter gonzo
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red57
Jedi Knight
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You can replace rod inserts and the two middle main inserts but the end plates have to come off the block to change the front and rear mains so engine removal and complete tear down is needed to do all mains. The aluminum-colored metal bits could be cam bearing too, and they also require a complete tear down to change.
Is your oil pressure unchanged? If so, I would dop the pan and check rod inserts visually and plastigage to check clearances. IMO these engines should be good for 100k or more.
Not sure but I think the comment in the Haines manual is based on the fact that there is always some wear on the inserts - there is a brief period of running 'dry' on start-up before oil pressure comes up and that is when the wear/damage occurs. Eventually the clearances get big enough that oil pressure suffers as the aluminum layer wears away and the copper layer of the inserts gets exposed. The copper is a bit harder and more likely to damage the crank. So changing the inserts restores the correct clearances and extends the life of the crankshaft. Once oil pressure is up, there is no metal to metal contact, therefore no wear.
Is your oil pressure unchanged? If so, I would dop the pan and check rod inserts visually and plastigage to check clearances. IMO these engines should be good for 100k or more.
Not sure but I think the comment in the Haines manual is based on the fact that there is always some wear on the inserts - there is a brief period of running 'dry' on start-up before oil pressure comes up and that is when the wear/damage occurs. Eventually the clearances get big enough that oil pressure suffers as the aluminum layer wears away and the copper layer of the inserts gets exposed. The copper is a bit harder and more likely to damage the crank. So changing the inserts restores the correct clearances and extends the life of the crankshaft. Once oil pressure is up, there is no metal to metal contact, therefore no wear.
Thanks for responding. Agreed. After a visual inspection, I plan on checking the rod bearings / crank journal clearances with plastigage. Oil pressure when hot is 20# at idle (650 RPM) and 55 - 60 #s at higher RPMs. So pretty healthy pressure. When the engine was converted to the spin on style oil filter adaptor, that was the only time a noticeable drop in oil pressure, about 5#, was observed. Still running the spin on filter with 20W 50. I'll report back with findings soon. Gonzo.
Bob_Spidell
Yoda
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FWIW, I bought my BJ8 when it had about 64K miles. I've always assumed the engine had been rebuilt because the block was painted black, but otherwise don't know much about its history. It was in overall good shape but had been resprayed twice. I did a 'light' overhaul a few years--maybe 20K miles--later because we'd pulled the head and my dad saw a 'suspicious' spot on one of the pistons (the pistons were marked '0.030'). I did a thorough overhaul a few years ago at about 210K miles because compression was uneven. Thinking I'd surely need to grind the crank I'd bought 0.020" under crank bearings, but my mechanic mic'd the crank and found it to be within STD. tolerances. I sold the bearings.