Bad knock from worn rod bearing?

[jlevie]

^ your mic is not accurate enough. You need one that reads in .0001 inches or metric equivalent. Measure each journal at 4 positions: left side of journal 12o clock to 6o clock, and then 3o clock to 9o clock. do the same on the right side of the journal. You want to find out if the journal is oval or tapered. I wouldn't run it if it has more than .0003- .0004 inches of either.

Correct! In addition to checking for out of round or taper you need to precisely know the journal dameters in order to pick the bearings by color code. Tenth reading micrometers are essential.

[ForcedFirebird]

Haha , thats a good one. All these years i've spent building high performance engines and i've never heard that one before.

The CNC machine I program will hold .0002" for hundreds of parts, fully aware of being able to measure parts. My surface grinder will hold 50 millionths, measure that with your calipers.

[LJ851]

caliper is going to give a more accurate reading, and you can roll it around the journal. my $.02.

Haha , thats a good one. All these years i've spent building high performance engines and i've never heard that one before.

[ForcedFirebird]

caliper is going to give a more accurate reading, and you can roll it around the journal. my $.02.

What? Even the Mitutoyo digital calipers I use aren't as accurate as mics. Calipers are lucky to be within .0005" never-mind less.

[riceh8r]

caliper is going to give a more accurate reading, and you can roll it around the journal. my $.02.

[ForcedFirebird]

Yeah that 1/50th mm mic is only accurate to about .0008".

[LJ851]

^ your mic is not accurate enough. You need one that reads in .0001 inches or metric equivalent. Measure each journal at 4 positions: left side of journal 12o clock to 6o clock, and then 3o clock to 9o clock. do the same on the right side of the journal. You want to find out if the journal is oval or tapered. I wouldn't run it if it has more than .0003- .0004 inches of either.

[tommye]

Measured the crank today, it's pretty close to 45mm all the way around.
So the crank is probably ok. Dont have any scratches either.

So the solution for my knock is most likely some new rod bearings?
Maybe open the oil pump to check for wear and tear?

[ForcedFirebird]

If the engine was run with water/coolant in the oil, it will wipe out the bearings. I have done more than one repair where the customer was advised about possible bearing failure when they drove the car with water/coolant in the oil. Last 2 times I replaced the head at their request spite the warning, one had knock after, the other had no oil pressure. Water is not a bearing lubricant.

[tommye]

I did try to rock them, didnt feel any play or maybe a tiny play on cyl 4.
The oil pressure light came of right away after start.
But the engine has been run with a blown headgasket, may that be the cause?
The main bearings look fine, just like new.

[sweet6e30]

x2^

[Cinnabar325is]

Before undoing the rod caps, you should have taken your hand and tried to rock each cap back and forth to see if there was any play in it. That would have told you which rods were knocking.

Even if only one or two rods were currently knocking, it looks as though all your bearings were wearing out and eventually, you would have had more rods knocking.

I'd highly recommend checking to see if the rod bearing journals and the rod big ends are within spec! You don't want to find out they aren't the hard way.

[jlevie]

This engine has experienced a lack of oil pressure. You need to mike the crank and see if it is still within spec.

[sweet6e30]

i smell rebuild

[matt0300]

It could be, did ur oil pressure light come on at all? Cause if ur main bearings are bad ur oil pressure would be fluctuating all the time. Main bearings cause knocking too.