Engine bearing wear analysis

[dirtygalant]

Hey guys, am a newbie here, sorry if this is posted in the wrong section.

My name's Phil and I'm from New Zealand I have a 1993 Mitsubishi Galant with a 6A12 'MIVEC' 2.0L V6 engine which is rated at 200hp in N/A form.

Long story short the engine suffered catastrophic rod failure so I stripped down the engine and replaced the rods, crank, pistons and had the heads looked over. I had the local engine rebuilder hone the bores and measure (ended up being standard size) and polish the replacement crank. I had assembled the engine with Penrite engine and camshaft assembly grease and the crank did spin freely in the block with no binding or tight spots with the pistons and rods attached before the cylinder heads were bolted down. Once the engine was back into the car it was cranked for a few moments with no spark in order to gain oil pressure, and then proceeded to be started. I ran it in on Penrite running in oil for the first 100km, then switched to a full mineral 20W40 for the next 500kms when switched to another full mineral 15W40 for the next 5000kms then changed to semi-synthetic 10W40 and have been running that ever since.

The bearings I used were ACL 'Dura-Glide' bearings, as new genuine bearings from Mitsubishi themselves were going to cost three times as much and would have been a two week delay from Japan.

Fast forward 20,000kms and it turns out I had not tightened up the crank pulley bolt enough (oops!) and as a result the keyway in the crank had worn out. I decided I didn't want to fluff around with reparing the crank in place with some kind of epoxy, so a spare crank was sourced and new ACL bearings purchased. When I pulled the old crank out I was shocked by the amount of wear on the old bearings, especially the main bearings. Remember this engine only had 20,000kms (12,000 miles) on it.

Surely that amount of wear does not correspond with only 20,000kms of use?

I'm no expert on bearings, but does that wear signal that perhaps there was contamination in the oil on initial startup? I had thought I had cleared out all the oil galleries, oil pump, sump, heads etc of any left over engine bearing material when the engine initially threw a rod.

Just a note on the bearings, the ones I had got are 'one size fits all' type bearings for the 6A11 SOHC 1.8L V6 (140hp), the 6A12 SOHC 2.0L V6 (155hp) and the 6A12 DOHC 2.0L V6 (170hp), there was no specific listing for my MIVEC 6A12 which is rated at 200hp. While speaking to ACL they specifically said the bearings are not suitable for the 240hp twin turbo variant of the 6A12 engine, but did not specifically say they weren't suitable for the MIVEC engine. Could it also be the case that perhaps these bearings weren't up to the task?

Now I've purchased some ACL bearings to put in with the new crank, but I'm a little hesitant to do so if this is going to happen again after another 20,000kms. I should probably mention that in that 20,000kms I did not hear any bearing noise of any kind.

Any thoughts on this matter would be greatly appreciated!

 

[vxcalais]

Try something like a Filtergram test.

http://mainlube.com/cms/index.php?page=Filtergrams_For_Performance_Vehicles

Seems can reveal more than a used oil analysis.

 

[dirtygalant]

unfortunately I've long dumped the oil which was in the crank case, more specifically I've dumped the oil into a waste drum mixed with other used oil.

 

[bullwinkle]

If they have Plastigage in New Zealand-use it to make sure your oil clearances are OK. You might want to use oil analysis this time to make sure the new bearings aren't getting chewed up again.

 

[PROJECTCAR]

Did you have an oil pressure gauge to monitor that there was actually oil pressure initially?

 

[dirtygalant]

yeah we have plastigage which I unfortunately did not use when I first put the motor together, but the engine builder did have ahold of the block, crank, cradle and bearings all at the same time and I'm pretty sure he checked for clearances before giving it the OK to leave him.

and nope I didn't use an oil pressure gauge, am guilty of relying on the oil pressure light (more so the idiot light..) I did wind the motor over a good few times with the starter though before the oil pressure light disappeared, and I smeared the oil pump with engine assembly grease and packed it with engine oil, and filled the filter to the brim with oil before spinning it on to reduce the initial oil pressure loss.

I have an aftermarket electric oil pressure gauge here but it has a broken sensor, will have to track down another sensor and a T-piece and fit it before starting the motor again this time.

 

[BuickGN]

Did you remeasure things when you pulled it apart? The wear doesn't look that bad. The uppers look a little better than the lowers but they usually do. Maybe it's the picture quality but I don't see the problem. What did the crank look like?

 

[dirtygalant]

Nah I don't have plastigage on hand at the moment and don't have a decent enough set of vernier calipers to check either. The crank journals had light scoring but I'm confident they will mostly polish out, however the crank is toast anyway as the keyway slot is well worn out (a good tooth on the cambelt of play)

I was just initially alarmed as I tore down a Mitsu 4G37 with over 400,000kms (250,000 miles) on the clock and the bearings had less wear than that.. having said that the 4G37 bearings being a 4cyl were much wider, had five main bearings and the engine didn't produce even half of the 200hp and didn't spin up to 8000rpm+ like the 6A12 does.

The more I think about it the more it does seem like my error in putting it together in the first place, perhaps the bearing and crank journal surfaces weren't totally clean apon assembly and perhaps the oil pressure wasn't high enough on initial start of the engine. I guess the debris from the piston rings wearing into the bores could have had some part to play as well, but I would have thought my frequent oil changes for the first few thousand kms would have reduced that somewhat.

The donor crank this time around came from an automatic 6A12 twin turbo engine, which it too had been rebuilt previously at some stage (unsure why it was later torn down again, I received the motor in bits) and the lower main bearings looked pristine with no scoring, and more so there were the beginnings of a channel either end of the bearing which quickly tapered up to meet the ungrooved section of the bearing. I'll pull that bearing out of the cradle, take some pics and see what brand they are. I dunno if it's warranted, but I'm just a little bit dubious of the ACL bearings now.

 

[dirtygalant]

if anyone wants a laugh, this is what happened:

lucky those pathetic excuses for rods were so weak they couldn't even puncture through the side of the engine block

These engines are a bit better than the 6G72 in the way that all of them are four bolt mains

and have a fully closed off valley and a deeper block for rigidity