Rod bearing troubleshooting

I'm cleaning up after hydro lock. 2 pistons showed low protrusion. But all rod/crank bearings have this wear pattern.




Damage appears opposite rod cap only.
Pre ignition or over crush???

Thanks!

Looks like a hard life with high pcp cause true to much advance timing and fuel boost combo. It s normal that wear is on rod side are they afn sputter bearings ?
Hydrolock are hard on moving parts also crank gets a hard bang crusing into bearings

QuickTD said:

Every rod bearing that I have pulled out of a VW diesel has looked like that to varying degrees. It is fatigue damage from high load and years of service. I wouldn't lose sleep over it.

Click to expand...

If you did pull the bearing and they looked like that do you think there would be much benefit from replacing them?

Heck yea, replace them. Running mods for big power really ups the load on shells and you will get some spalling, fatigue, wear, etc. And a hydraulic lock gives at least a few cycles at massive overload (not easy to bend a rod in compression!!). That being said, the shells don't look to bad. But do put some new ones in. Same loading is going on on main cap shells, probably ought to check those too.

If this is a known issue... Has anyone considered Oversizing the oil hole or increasing chamfer?

I wouldn't consider those beat-up. Fairly normal looking wear. Now, if you could see a copper-looking layer of metal in the bearing, that would be excessive wear.

You should see how the bottom cam bearings look on almost every PD cam I've replaced!! Those look way way worse than what you've got here, and a camshaft doesn't reciprocate up and down like a connecting rod/piston assembly do...

You mean like this?



From my 170k mile ALH with 17/22, PP502's, 11mm, RC 4, 5, 6, & TDTuning, etc

I put in new IE rods and checked piston protrusion today. They are all spot on except cylinder 1.
Here are the measurements:
Cyl 1 - 0.030
2 - 0.0350
3 - 0.0345
4 - 0.0345
5 thousands of an inch seems like a lot. What is the speck for variance between cylinders???
I measured it twice to make sure I was seeing correctly.

Cyl 1 before tear down measured 0.034 (rosden rod unbent)
So I did not mix up the rods.

On the last build All piston protrusion was 0.032 to 0.034". 0.002" variance.

My book says 0.0350 to 0.0395" get a one whole gasket.

Possible causes???
A missing bearing half? Bearings are more like 0.060" thick.


Did I get a mixed up set of rods???

I had similar issues in my re-build

Summary is on Post 243 in my build thread

Make sure you're measuring as close to the wristpin as possible and are getting accurate repeatable measurements. Non repeating measurements threw me for a loop. I ended up with a similar difference in piston protrusion on my #1 cylinder as well - which is curious.

Generally speaking, you have plenty of room to play with given 0.035" piston protrusion.

The rough math is that each 0.001" of piston protrusion will change your compression ratio by ~0.1 point so as it sits cylinder 1 would be ~0.5 lower than the others. Not the end of the world, but obviously better if you can get rid of it.

There's a myriad of possible causes - block, crank, rods, bearings, pistons, dirt, etc.

I don't mean to keep beating a dead horse on the measurement method, but are you sure you're at TDC on each piston, individually, always approaching from the bottom and from the same direction of crank rotation, never going past (and if you do going back 45 degrees and making sure all the rings are pushed to the bottom of their grooves, etc). I spent an entire weekend figuring this stuff out the hard way.

Once you've confirmed that you have accurate and repeatable measurements on both sides of the piston, you can start swapping rods/pistons, flipping the rods 180, etc to get the most even protrusion across all the cylinders.

Be patient and careful, put something soft under the engine so if you drop a piston you don't damage it (speaking from experience here). You'll get the right combination.

Just double checking that you are measuring directly over the piston pin, in two places- otherwise piston slop in bore creeps into the measurment.

Thanks FUB! Thats good beta! I'll remeasure.

@ ski:
But measuring over the center of the wrist pin places the dial indicator in the valve relief of ASV pistons and not on the actual piston top.

I went back this morning and remeasured everything a few times.

Piston rock effect on height was only 0.001".

Max variation in repetability 0.005 (same as FUBs)
Average repetability 0.002.

I am willing to say that my pistons sit square timing belt to flywheel.
The fire wall side sits about 0.010 lower than the bumper.
(Measuring as close to the wrist pin as possible without dropping into the valve relief.)

I got some numbers I am much happier with and matching the previous (professional) build numbers.

coronan - are you sure you've got all the right number of zero's in your repetability number?

I tired a caliper, dial indicator, straight edge + feeler gauges and finally settled on a depth micrometer to be the best for me. You can bridge the valve relief and put the pin of the micrometer right between the cylinders on the axis of the wristpin.



The 0.010 you're seeing from front to back is the rock of the piston.

Are you getting the same protrusion on the timing belt side of the piston as on the flywheel side?

I'm measuring with a dial indicator on piston and a bridge on the deck. I can roll each piston up to tdc until I see the dial begin to sweep the other way.
Like here but not with a digital.
http://forums.tdiclub.com/showthread.php?t=345557

I recheck zero each time. Place the piston flush with the deck by my finger then move the dial indicator into place over the piston and its always with in 0.001" of zero. Its amazing what the finger can find.

Yes, I get the same measurement on the t belt side of the piston and flywheel side.
Rocking the piston by hand only changes the measurement 0.001.

I use a mag base and dial indicator. Slide mag base so probe is over block, zero, slide mag base to put probe over piston, rotate crank to get max reading, slide mag base again to put probe over block deck, then verify zero is still good.

Another way is put straightedge over cyl bore, spanning both sides. Mag base indicator zero'd on straightedge. Rotate crank and piston lifts s-edge off block deck, measure lift.

Zillion ways to do this.

I had a mag base. I felt there was too much human interferance for measuring thousands accurately. If you post is on a screw then it will raise and lower as you swing the dial indicator. But of course it will come back to zero when you swing it over the block agian.
So i go a bridge.

What was your repetability???

I use the mag base with the on-off button, so push the button and now the base is easy to reposition. I never touch the joints holding the indicator to the base, that would screw it up fo' sure. Repeatable within 0.001". But the bridge is a cool way to do it.

I finially got all the bells and whistles bolted back on and crankded for oil pressure.
Primed fuel pump and injectors. (easy with a lift pump.)
I still have a tapping / knocking While turing it over with the starter.

I replaced all rod bearings.
Main bearings only have 20k mi on them. I checked oil clearance and it was still good.

I understand that no one has ever bent a crankshaft.

What could it be?

crap have you replace mainbearings? maybe this have some damage tru hydrolock.