Thread: D3 spun bearings video

Why do 2.7 cranks break?

In the vid, bearings have spun, he says something like the block has spread as he takes out the centre caps over the offending mains and then he's just going to line bore it?

The next vid will be interesting. Great stuff.

DL

I am amazed that the bearings don't have tabs that locate in a notch to stop them from rotating, every motor I have pulled down has then.

she is at least rather cute and amusing. Funny little quips.

Originally Posted by loanrangie

I am amazed that the bearings don't have tabs that locate in a notch to stop them from rotating, every motor I have pulled down has then.

They are really only for assembly and do bugger all in preventing a spun bearing. The bore itself should be providing enough friction to prevent the rotation if the sizings are correct. Dont under estimate the power of friction - I've worked on turbines in the 2-5gigawatt power range and the drive couplings are simply friction fit taper - there is no drive keyways, splines etc

Originally Posted by shanegtr

They are really only for assembly and do bugger all in preventing a spun bearing. The bore itself should be providing enough friction to prevent the rotation if the sizings are correct. Dont under estimate the power of friction - I've worked on turbines in the 2-5gigawatt power range and the drive couplings are simply friction fit taper - there is no drive keyways, splines etc

I disagree, the tabs are on opposite sides and prevent them from spinning 100%, sure they aid in assembly but will also prevent them moving.

Originally Posted by shanegtr

They are really only for assembly and do bugger all in preventing a spun bearing. The bore itself should be providing enough friction to prevent the rotation if the sizings are correct. Dont under estimate the power of friction - I've worked on turbines in the 2-5gigawatt power range and the drive couplings are simply friction fit taper - there is no drive keyways, splines etc

My ex-Porsche GT3 had friction fit cam gears onto the cams. The power of friction didn’t help me though. During a high speed driver training event where the task was to drive with your feet flat on the floor and not touch the pedals whilst turning a corner at speed (skid pan) and maintaining within the line (learning how to let the wheel move loosely under hand and follow the undulations to avoid skipping the surface), I spun.

The engine actually ran backwards (yes this IS possible), popped the intake apart (runners connected by rubber joiners between sections) and unbeknownst to me at the time, had shifted a cam gear out of position/alignment. Not enough to cause damage, but enough that the next time I had an MOT I couldn’t pass the emissions test. £3500 later and the engine removed and Porsche Germany involved, they worked out that was what had happened and why it wouldn’t meet emissions.

Anyhow, I digressed!

Originally Posted by shanegtr

They are really only for assembly and do bugger all in preventing a spun bearing. The bore itself should be providing enough friction to prevent the rotation if the sizings are correct. Dont under estimate the power of friction - I've worked on turbines in the 2-5gigawatt power range and the drive couplings are simply friction fit taper - there is no drive keyways, splines etc

Yes, but you mention a slight taper which is totally different to the crankshaft bearing/shells simply placed into the block and 'hope' they won't spin. I firmly have always felt that not having the locator tabs is the principal reason of the failures.

As you'd be aware large drill bits are tapered and that taper is the only thing that prevents turning whilst drilling the hole.