Actually Chris, you may not see it with your eye I just though...but, Im sure the problem lies with the bolts, and nothing else, be it interference under head at radius, or from incorrect torque value, once loose, the small bit of material there were taking all the impact load/torsional vibration and it failed. The bolts would normally dissipate these shocks uniformally thought that area via the clamping forces between spot face and the underside of the bolt head.
I'm following all this closely as I'm about to change my gearbox, and am planning to have a good inspection of the Eurospec flywheel while I'm there. Looks like the bolt heads have sunken into the surface there as well (brinelling?), same as on the OP's flywheel. Would that have happened before or after the bolts worked loose?
This one had the bolts come loose & snap off I believe. It's not obvious in the pics, but the holes were ovalising, so it had to be using them as dowels. Let me know what you need me to do with the flywheel. I can just put a hacksaw in and trim out the cracked section.
I concur 100% with Brian. It is a fatigue fracture. You can see a witness of the bolt threads on both sides of the hole. So, the bolting was not strong enough to stop the flywheel from shuffling backwards as the engine was accelerated and decelerated. Flip-Flop, Flip-Flop. Tension one way. Tension the other. CI hates tension lots and lots and lots. Could be: Incorrect torquing up, and the bolts came loose. Poor contact surface between flywheel and crank, so a little bit of flex causes a little bit of wear, causes the things to come loose. The brinelling, I believe it is just wear as it flopped about, can only have happened after the bolts were loose, unless the flywheel itself was so flexible that it could bend adjacent to the edge of the bolt heads. Brinelling needs massive pressure to indent in compression. Ball bearings on races brinell, as the initial contact area is tiny, thus the pressure between ball and race is v. big.
Thanks Big Engineeering boss. What's brinelling? The circular indentations from the bolt heads? Eurospec ones are showing this too.
brinelling is indentations on the race of a Ball or roller bearings due excessive load or impact of a stationary bearing in the true sense
No. The indentations are more likely to be wear. As mushy says. Ball and roller bearings can suffer from brinelling, cos the contact area is so small that indentation can occur from relatively small loads.. The witness marks on the flywheel are large and quite flat. If it was brinelling, it would be very small, sharp indents, where the edge of the bolt head touched in just the two places, adjacent to where the thread indents. can be seen. ie Circumferentially either side of the bolt hole.
Just thought of a good example. If you want to test the hardness, quickly and roughly, you use a Brinell Testing Machine, or even a hand held Brinell tool. On soft materials like cast iron, or even on relatively hard materials like spring steel, you bash a ball bearing into the surface of the material. To get a relative value of hardness, you measure the diameter of the indent. Standard engineering industry practice. Really hard materials, you use a Vickers machine, for supreme accuracy, or, a Rockwell machine, for rough and ready tests. Hence: Brinell Hardness scales. Vickers Hardness scales. Rockwell hardness scales' Mohr scales for rubber though!
From the pics there it doesn't look like the thin spreader plate was used? I remember always finding these between bolt heads and flywheel on the 020, must have only been <1mm thick.
Thin spreader plate is a waste of time me duck! (That's South Derbys. Not North) Check what I asked TSR about flywheel bolting. No reply though.
OK. It will be 68C. What really matters is the 'U' condition boss. This is 930 to 1080 N/mm2 UTS. So, close to a grade 10.9 bolt. About 300 Brinell. Bit down market for me. I have used Y and Z materials in some of my machines. Up to 1550 UTS!
Ah, thank you Mr Engineering boss. That'll explain why I couldn't drill it. It's the dreaded 'homologation weights' kit car flywheel again! So anyway, back to brinelling, the marks from the bolt heads are not brinelling, so they're from impacts when the bolts were acting as dowels, and the flywheel sitting at angles on the crank face during impacts?
Well sort of. More like rubbing between the under bolt heads onto the flywheel bolting face, as it wobbled all over the place. One of the photos shows quite flat indents. Probably a bit larger than the underside of the head of the bolt. Send the flywheel to me. It'll only cost yous about 30 quids!
Better still. Stanstead to Knock. 5 each way. Have a free Irish Holiday. Bring it with you though! Not kidding, you're very welcome, as we say in Eire.
