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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHM96 3.4L Crankshaft Journal Measurements
Leading reported evidence
Use rather cheap micrometer
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Leading evidence: 'Use rather cheap micrometer' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check rod bushings' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
If you need journals welded/repaired, I’d talk to Nick at Shaftech.
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Suggestion
Suggest you use the old bolts for torqueing and testing/measuring.
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Tonight I measured the crankshaft main & rod journals from my M96 3.4L. It was removed from a re-manufactured engine (by Porsche) with approximately 37,000 miles. What measurements do you guys have? In a few days, I'll be shipping the crank out for magnaflux, balancing, and journal polishing. Photos below.
See updated measurements in post #16 below:
https://rennlist.com/forums/996-foru...l#post15250757
7 Main Journals, Inches
Direction: Crank Pully (A) --> Flywheel (G)
A: 2.360
B: 2.360
C: 2.360
D: 2.360
E: 2.360
F: 2.359
G: 2.360
Rod Journals, Inches
1: 2.086
2: 2.084
3: 2.084
4: 2.086
5: 2.086
6: 2.085
So you just measured the diameters? I would think the runout would be more useful, will tell you how out of round they are if at all.
Another measuring tool you should consider when putting this back together is plastigauge, it will give you a measurement of the shell to crank surface clearance on each.
I have measurements for a 3.6 (not on me right now though) so don�t know how helpful my data is to you. Considering how your measurements are so consistent, you are probably good. IIRC, clearance should be around 0.0015. Torqued bearing carrier and rod caps with bearings and measured diameters might be worth doing to check.
Looking at your measurements you have a problem. .002 variation on rod journals is WAY too much. There are no "select fit" bearings available So there is no way to correct the variation. Even the coated bearings are only coated to .0005.Suggest you remeasure with a micrometer with accuracy of ten thousands, or have someone else measure.
Sorry, only saw the crank journals measurements and I agree, you need an additional decimal place.
If you need journals welded/repaired, I’d talk to Nick at Shaftech.
Good point! I'll mention this to the shop doing the balancing.
That's a great suggestion. Is there concern with torquing brand new main bearings more than twice?
Mobile 0-40 every 3000 miles. However, at the time, I didn't realize the AOS was the reason for running lean... and with a VF Eng. supercharger. Thus this preemptive complete tear down and rebuild (DIY style. I attended the Knowledge Gruppe class back in March.)
I haven't measured the bearings yet. I need to invest in more precise micrometer.
I used a rather cheap micrometer. It's time to invest in a Fowler brand. I purchased the coated main & rod bearings from LN.
I hope I can chalk up these variations to a cheap micrometer, and my inexperience. Thanks for the lead!
He has measurements for the 3.6, not the 3.4.
I appreciate all of the input, guys. I'm leaning towards purchasing a Fowler micrometer and re-measuring. This is more for peace of mind, before shipping the crank to the shop that will magnaflux, rotate, and balance.
Check your rod bushings. They might still be in spec relative to the broad, older model specs, but the engine quench is very tight so I would recommend replacing them.
New factory OEM main bearing carrier bolts and rod bolts can only be torqued 4 times. Suggest you use the old bolts for torqueing and testing/measuring. Arp2000 bolts (should be included with Corillo Rods) can be torqued many times. No problem from torqueing the bearings many times. Since you are balancing the rotating assembly, you will be sending the rods and bearings with the crank, so have the machinist assemble the rods and bearings , torque and measure, and measure the crank journals and provide/record bearing clearance. It's more accurate than plastigauge, but plastigauge done correctly is acceptable.
Here are two sets of updated measurements recorded with a Fowler micrometer. I'm feeling much better now, given the fact that machinist who will be doing the balancing and crankcase assembly said the rod journal specs are:
2.0855 to 2.0862 inches
.
As you can see from the photo, I measured twice. One day while in the garage where it was 82 degrees Fahrenheit. Then a few days later, I took the crank and micrometer to the basement of my home where it the temp stays steady around 65 degrees Fahrenheit. I left the parts down there to adjust to the temp for 2 full days.
I'm documenting the measurements in plain text here too, in case this image doesn't resolve one day in the future.
The final measurements will come from the machinist, but I don't anticipate there being any major discrepancies.
Rod Journals, Inches, 65 Degrees Fahrenheit
#1: 2.0857
#2: 2.0857
#3: 2.0858
#4: 2.0857
#5: 2.0858
#6: 2.0858
Main Journals, Inches, 65 Degrees Fahrenheit
#1: 2.3615 (belt pulley side)
#2: 2.3614
#3: 2.3614
#4: 2.3614
#5: 2.3614
#6: 2.3614
#7: 2.3614 (flywheel side)
This is a source reference. Confirm exact model applicability in the original material.
