Big End Bearing Wear

jacckk · Post by **jacckk** » Mon May 19, 2014 8:41 pm

Some of the big end bearings in my engine seem to have quite a lot of wear on the sides. Not all of them have the wear on them and some are worse than the others. The bearings had only been in for 300-500 miles. There's no wear in the main bearings. I didn't measure the clearances at the time. The crankshaft doesn't have any obvious marks on it that could be causing it.

Here are the pictures:
http://imgur.com/a/o2Iji

Any idea what it could be so I can prevent it happening when I reassemble the engine? I'll make sure I check the clearances this time.

paul c · Post by **paul c** » Tue May 20, 2014 3:22 am

are you sure the rods and pistons were installed correctly, looks like the offsets may be the wrong way around.

jacckk · Post by **jacckk** » Tue May 20, 2014 7:53 am

What are the offsets?

Does that mean the pistons could be installed onto the rods incorrectly? I didn't remove them from the rods/install them to the rods, I was given them assembled. I'll check later.

jacckk · Post by **jacckk** » Tue May 20, 2014 10:38 am

Just to make sure I've got them right which way around should the bearing caps be?

Should they be like this https://imgur.com/a/Yz3P3 with the locating clips next to each other and the other holes next to each other? Or should it be the other way around?

DaveEFI · Post by **DaveEFI** » Tue May 20, 2014 12:29 pm

There is a rib on both which faces the front of the engine on the RH bank, and the rear on the LH.

ChrisJC · Post by **ChrisJC** » Tue May 20, 2014 5:07 pm

On the pistons there should be arrows. All eight should point forwards. (This might not be true for non-offset little end pistons, i.e. pre P38 engines)
On the con rods, there is a pip. The pips on each pair of rods should face each other, i.e. one bank has all the pips facing backwards, the other bank facing forwards.

Chris.

jacckk · Post by **jacckk** » Wed May 21, 2014 1:39 am

Ok I think I must have assembled it wrong somehow. Looking at the outside of the connecting rods they look like they've been rubbing against each other. Some other connecting rods I looked from another engine didn't have any wear like this.

I didn't remove the pistons from the connecting rods and the marks on the top of the pistons were aligned properly. I did follow the procedure and made sure the marks on the connecting rods were aligned the correct way but perhaps I got it wrong.

Is the circled mark in the picture below the rib on the big-end bearing cap that should face the front of the engine on the RH bank and the rear on the LH bank?

What I don't understand is what it means by the rib should face the front of the engine on the RH bank and rear on the LH bank. In the diagram in the overhaul manual neither of them are facing the front or the rear they're in the middle. Here is the page showing that

bigaldart · Post by **bigaldart** » Wed May 21, 2014 6:48 am

Hi,

On the rods you have shown laid on their side you can see a big chamfer, this should face the crank counterweight in all cases. ie big chamfer face away from each other on each pair. It certainly seems you had them the wrong way round.

Alan

Pocket rocket · Post by **Pocket rocket** » Wed May 21, 2014 7:05 am

Those aren't the "ribs" referred to in the manual, hence your problem.

There are bosses cast into the con-rods but unfortunately i can't seem to upload any images etc atm

Pocket rocket · Post by **Pocket rocket** » Wed May 21, 2014 7:39 am

Hopefully this image will show the "rib" or boss that is cast into the con-rod

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DaveEFI · Post by **DaveEFI** » Wed May 21, 2014 8:33 am

jacckk · Post by **jacckk** » Wed May 21, 2014 2:56 pm

Just to clarify I know about the mark on the connecting rods and they were aligned correctly. What I'm trying to find is the mark on the big-end bearing caps since it says "ensure reference marks on bearing caps are aligned" and "rib on edge of bearing cap must face towards front of engine on RH bank, rear of engine LH bank"

DaveEFI, I don't have the mark that's indicated in your bottom picture.

Here's some pictures of just the bearing cap

Sorry if I'm being dense!

DaveEFI · Post by **DaveEFI** » Wed May 21, 2014 4:08 pm

Ah - I've not seen con-rods of that design before. What is the actual engine?

Pocket rocket · Post by **Pocket rocket** » Wed May 21, 2014 5:05 pm

I've had a look through my workshop manuals (not Haynes) for both the early and later engines and the bearing caps are all supposed to have the same markings (even for the American market).

I've also had a look at my pictures from various builds over the years and can't find any difference

As per Dave - I haven't seen that type of cap before.

Sorry - not much help

DaveEFI · Post by **DaveEFI** » Wed May 21, 2014 5:10 pm

They appear to have bolts which screw into the conrod - rather than nuts and bolts? Looks a bit like a main bearing cap to me.