3.0 rod bearing clearance... Upper end of spec

IXjamesXI · 08-08-2015, 03:30 PM

Finally mic'd my crank and put the bore gauge on my reconditioned rods and finding clearance around .077-.087 mm which I think is the upper end of spec. OK to run em? Suffering from porsche paranoia and looking for others experiences on the rebuild forum but can't find anything from my searches. Ok to run at the looser end of spec? Thanks all

3literpwr · 05:12 PM

I rebuilt my 3.0 this year and here are my dims after my rod work.

Clearance 0.0280 0.0348 0.0407 0.0466 0.0466 0.0525

Standard tol 0.030 - 0.088

Trackrash · Trackrash's Garage

You are in spec. However, I would use plastigage to confirm your clearances.

IMO. If the crank mics within spec, you should be good to go with new bearings, assuming the rods are in spec.

Did you use the bore gauge, or mic to check the big end diameter without the bearings? That is the number I would want to confirm as within spec, since the rods were resized.

IXjamesXI · 08-11-2015, 04:25 AM

hi guys, thank you for your insights.

Crank is within spec, albeit at the "smaller" end. Rod journals avg 52.976 (Spec 52.971-52.990)

Rods measured out ok when I got them back from machine shop.. double checked those.

Plastigauged for peace of mind and got clearance in the 0.038 range, re-set my bore gauge and came up with clearance more like .076mm. Both via gauge and plastigauge are within the spec so I feel ok. I also feel like every time I use the bore gauge on the bearings, maybe I am putting a small gouge (to the tune of like .038 mm?) in them just from the pressure and the slight motion of the gauge. Slightly regretting doing it so much, don't want to chew up my bearings..! But now I know.

I have been trying to measure the crankshaft bore in the case and that's another handful too. Got great numbers with plastigauge but every time I stick the bore gauge in there I come up with numbers that are too large.. not sure what I am doing wrong but I am going to give it another shot later on. Very very consistent readings but just too big by about 0.040 mm if i recall.. Don't have my notebook in front of me. I probably should be content with the plastigauge but don't want to miss an opportunity to learn something. You know, for the next time I do this.