Rod re-sizing gone bad?

brighton911 · 05:05 PM

After I installed the ARP rod bolts, I checked the big ends and one was definitely out of round with the rest being reasonable. I figured with new rod bearings, why not make it 100% right. I had a local shop with a good reputation re-size them. I got my rods back today but I am not happy with what I see Have a look at the pictures and give me your opinion on how the caps and rods look where they have been ground. Hot spots galore, this can't be a proper job. Also note a tooling scratch on the bearing surface that you can feel with a fingernail.

RedCoupe · 01-23-2014, 06:51 PM

Perhaps there are some metallurgists or mechanical engineers looking at your pictures who would care to comment about the effect of the overheating on the strength and ductility of the rods and caps. Personally, I would insist on a new set of rods if mine back looking like that.

tharbert · tharbert's Garage

Disclaimer: amateur only, non-expert: I just got my rods back from my local machine shop. I'll go take a look at the mating surfaces. If I find anything like that that, I'll be surprised. Because of the spots, I'd be a little worried that the mating surface isn't square. As for the other, it doesn't require a finely honed/polished surface. It simply supports the bearing. This is a supposition on my part but I'm not sure you want that very smooth as your goal is to keep the bearing captured. It certainly must be uniform and within tolerance. Yes, you certainly want this to be a perfect as you can get it.

Lapkritis · Lapkritis's Garage

The staining on the surfaces is normal from use (not on a brand new rod though). Nothing to worry about here as long as the geometry and plasti-gage are in spec.

Steve@Rennsport · 01-24-2014, 01:39 PM

Hi,

I cannot tell you anything definitive from just looking at your pictures, however the finish honing doesn't look quite right to me and they should be measured to confirm concentricity, alignment, length, and parallelism.

Normally, you don't see those dark stains on the cap surfaces since these are usually ground for bearing clearance and fitment.

If it was my car, I would have them checked and possibly redone before installation by someone who only does 911 engines.

brighton911 · 01-24-2014, 04:55 PM

Update Thanks to those that gave their input, without this forum, it would not be possible to achieve the level of quality I want.
So I went back to the shop that sized the rods and politely (Canadian eh) asked the tech about the marks on the parting surfaces. He said that some rods, depending on the material. were more prone to those marks than others. He assured me he had taken great care and the sizing was bang on. I searched out two other shops in the area and showed them the rods and asked for their opinion. They pretty much corroborated the story and the marks were not a big deal. Hopefully they are not all brothers sticking up for each other!
So far, I have checked two rods installed on the crank for clearance using Plastigauge and they are good, coming in at .001" with new bearing shells. I'll check the rest tomorrow and report back if anything is not good. I also checked the rods with my bore gauge and there was no discernible variance so it appears they are round. Maybe I was worrying for nothing, then again, better safe than rod through the bottom I say.