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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
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.
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.
Good point! I'll mention this to the shop doing the balancing.
Originally Posted by Chris(MA)
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.
That's a great suggestion. Is there concern with torquing brand new main bearings more than twice?
Originally Posted by Noz1974
Those upper bearing shells look like they have had a bit of hammer, what oil where you runnning at what interval ?
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.)
Originally Posted by TexSquirrel
Yeah the bearings have heat marks. Are they evenly worn?
I haven't measured the bearings yet. I need to invest in more precise micrometer.
Originally Posted by Porschetech3
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.
I used a rather cheap micrometer. It's time to invest in a Fowler brand. I purchased the coated main & rod bearings from LN.
Originally Posted by tomcat
If you need journals welded/repaired, I’d talk to Nick at Shaftech.
I hope I can chalk up these variations to a cheap micrometer, and my inexperience. Thanks for the lead!
Originally Posted by 808Bill
Ahsai might have them, send him a message.
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.
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.
08-10-2018, 01:49 AM
M96 3.4L Crankshaft Journal Measurements
