Big End Bearing Wear

paul c · Post by **paul c** » Wed May 21, 2014 8:35 pm

in your first pictures on this page you can see the caps are on backwards, the chamfer and the shells are not lining up between the two halves

jacckk · Post by **jacckk** » Wed May 21, 2014 8:45 pm

It's a 4.0 engine from a P38.

paul c wrote:in your first pictures on this page you can see the caps are on backwards, the chamfer and the shells are not lining up between the two halves

Yeah I did have them the opposite way so they lined up but I had been swapping them around to look at them.

I think I probably just installed the pistons with the marks the wrong way around (even though I did follow the manual). That's all that I can think could be wrong.

paul c · Post by **paul c** » Wed May 21, 2014 10:22 pm

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

4.0 - 4.6

mgbv8 · Post by **mgbv8** » Wed May 21, 2014 10:37 pm

jacckk wrote: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.

Are those shells in pairs?

Is the wear on the same side of both shells in each conrod?

The dimples on each pair of rods should face each other.
The oil holes in the shells should line up with each other.

The wear marks indicate that you had the shells the wrong way round and or the rods as well.

jacckk · Post by **jacckk** » Thu May 22, 2014 9:05 am

I definitely had the shells installed like this - https://imgur.com/a/Yz3P3

They are in pairs on the pictures you linked to but the wear is on opposite sides (as in the above link).

DaveEFI · Post by **DaveEFI** » Thu May 22, 2014 9:53 am

Just out of interest, the design of the unit is different in later engines? The pics I've shown are from a 3.9.

DEVONMAN · Post by **DEVONMAN** » Thu May 22, 2014 10:30 am

Hi jacckk,
I've just looked at your previous posts.
Is this the engine that was tight to rotate when you were assembling it

Also is it the engine that the cam timing was out and the valves hit the pistons

The dimple on each pair of con rods should face each other on both early and late engine. Same rules apply but the pistons on the later engines (Cross bolted 4.0 & 4.6 units) must be fitted the correct way round with the arrow pointing to the front. This ensures that the offset wrist pin is correctly placed relative to the thrust side of the engine.

Denis

jacckk · Post by **jacckk** » Thu May 22, 2014 2:50 pm

Yeah they're from the engine where the valves hit the pistons. Although the marks on the pistons were quite small and I could see no damage to the valves.

When I put it back together I'm going to use another set of heads I've got and I've also fitted new pistons. I'll make sure I get it right this time!

ChrisJC · Post by **ChrisJC** » Thu May 22, 2014 6:01 pm

DEVONMAN wrote:... on the later engines (Cross bolted 4.0 & 4.6 units) must be fitted the correct way round with the arrow pointing to the front. This ensures that the offset wrist pin is correctly placed relative to the thrust side of the engine.

Denis

Yes, this means that there are four piston / rods in one arrangement, and four in the other. They are NOT all the same.

Chris.

unstable load · Post by **unstable load** » Fri May 23, 2014 6:00 am

It could be the light, but it looks to me like those big end bearings are showing wear that looks like there is a misalignment that is putting a side load on the rod, which would fit in with the dimples/rods being incorrectly aligned.

mgbv8 · Post by **mgbv8** » Fri May 23, 2014 5:16 pm

unstable load wrote:It could be the light, but it looks to me like those big end bearings are showing wear that looks like there is a misalignment that is putting a side load on the rod, which would fit in with the dimples/rods being incorrectly aligned.

Thats what I thought as well. The wear marks indicate a side load. Could the piston being on wrong cause this side load? If so wouldnt there be substantial wear marks on the pistons as well ??

Darkspeed · Post by **Darkspeed** » Fri May 23, 2014 6:47 pm

As the offset is front to back not side to side on the piston, if it was on the rod incorrectly I cant see how it would cause that sort of wear pattern.

Bent rods from an engine that has had a hydraulic lock may well end up like that, or big ends that have been mis-ground with a taper.

I would have thought that you would know if you had assembled with the rods with the chamfers facing each other as the engine would be near impossible to turn over.

Amazed that no damage in the valve train with pistons hitting valves.

mgbv8 wrote:
unstable load wrote:It could be the light, but it looks to me like those big end bearings are showing wear that looks like there is a misalignment that is putting a side load on the rod, which would fit in with the dimples/rods being incorrectly aligned.
Thats what I thought as well. The wear marks indicate a side load. Could the piston being on wrong cause this side load? If so wouldnt there be substantial wear marks on the pistons as well ??

jacckk · Post by **jacckk** » Fri May 23, 2014 7:26 pm

I didn't remove the pistons from the rods when I got them and I'm sure the pistons were on the correct way for both sides when I looked at them.

The valves hit the pistons because the timing was one tooth out. There were some grooves in the pistons where the valves but I couldn't actually see any damage to the valves. The rocker shafts were slightly bent actually. When I reassemble it I've got some different heads that I'll put back on anyway.

So as I said before the only thing I can think that could be wrong is that I put the pistons in with the mark on the rods facing the wrong way.

jacckk · Post by **jacckk** » Tue May 27, 2014 8:12 pm

I've reassembled the crank and the pistons and the marks on the connecting rods are definitely facing each other and the marks on the pistons are all facing towards the front of the engine.

A couple more final questions. When the overhaul manual refers to the LH and RH bank of cylinders is this from the drivers seat or facing the engine. I've assembled it assuming drivers seat meaning the RH bank is the bank with 2,4,6,8 and LH is 1,3,5,7.

It says "Check clearance between connecting rods on each crankshaft journal." and "Check connecting rods move freely sideways on crankshaft.". How much should they be able to move sideways? I can move them sideways a tiny amount which increases the clearance on one side and then reduces the clearance on the other side so does this mean that should be OK?

Thanks.

ChrisJC · Post by **ChrisJC** » Tue May 27, 2014 8:52 pm

Cylinder numbers start at the front of the crankshaft and work backwards. This means 1,3,5,7 are on the passenger side of the car (UK spec vehicle!), and 2,4,6,8 are on the drivers side. No. 1 is immediately adjacent to the distributor.

I think if you look into the bottom of the engine so you can see the gudgeon pin, the con-rod should be centred on it. If you have a rod swapped, it will be pushing one side of the piston with a big gap on the other.

Chris.

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Big End Bearing Wear

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