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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHDifferences in updated crankshaft.
Reported or suspected cause
carrier bolts are not torqued correctly
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
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Reported cause
Most common with this issue is the carrier bolts are not torqued correctly.
Leading evidence: 'carrier bolts are not torqued correctly' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'carrier bolts are not torqued correctly' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check thrust bearings' (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
The pic doesn't have he detail I need to make the change for sure.
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Suggestion
Yes, 987 Boxster would not have the larger diameter mains until 2007, when the Boxster got the 3.4 engine, and used the M97.21 engine, just like the Cayman.
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Since we are rebuilding my engine again today I noticed two differences on the newer generation crankshaft I'm installing compared to my stock crankshaft. Just wanted to share with you guys.
There seams to be more lubricaci�n holes on the newer crankshaft. It came from a 987 Boxster S engine. You can see an example of the additional lubrication hole on the first picture.
Also in the second picture the interior of the crankshaft cavity is at least double the depth of the original crankshaft. I don't know the reason it's like that but it's probably improved in some way.
Lubrication holes on the newer crankshaft on the left. A single hole on the original shaft on the right.
The cavity is deeper on the new one
What engine are you working with? The 987 uses the same diameter main journals as the 3.6 996/ 997. The stroke is 78mm vs 82.8mm
Just look at the revision numbers on the crank to see how new it is. That said, newer is not always better... too often the newer units are not changed to become better, but often to save money.
As cranks got newer the fillets became wider, and the rod journal radii became wider.
The crank on the right looks like it has 3.6 mains, and the one on the left looks like it has the smaller 3.4 mains. The pic doesn't have he detail I need to make the change for sure.
The crank on the left with the additional holes is from a 987 Boxster. The crank on the right is broken but is from my 99 996 3.4 engine. We measured them and they have identical measurements.
I'll get the revision number tomorrow. I didn't take a picture of the numbers when I was at the shop.
Yes, 987 Boxster would not have the larger diameter mains until 2007, when the Boxster got the 3.4 engine, and used the M97.21 engine, just like the Cayman. If you try to fit this to the early carrier, you'll find the journal radius is too fat, and you'll lose end play.
The revised crankshaft actually has more issues than your early 3.4 crank, which looks to be a 2nd revision part. These cranks were revised 4 times.
The new crank I'm installing was from a 987 Boxster S. I'm not sure if it was a 3.2 or 3.4 engine. We are also using the carrier from that engine. What kind of issues does this newer revision crank have? Anything I should consider if I track the car 5 or 6 times a year?
The carrier isn't compatible as it is.. Fit the carrier to your case now. You may find that the alignment dowels are not properly spaced to allow this.
The whole game changes when tracking an engine. Measure all running clearances from A-Z,a nd ensure that you have proper sizing.
Thanks for your help Jake.
We joined the case case and the alignment dowels lined up. So far it works. But now we have a new problem.
We installed new stock main bearings and new thrust bearings and the crankshaft is too tight. It doesn't spin at all and it's well greesed and oiled. We don't know why. It's as if the new main bearings are too large.
What could it be?
We can have the parts adjusted and precisely measured but as far as I know it shouldn't have so much resistance. .
What a pity .You were so close. But glad you caught it now. You are correct,it spin smoothly and consistently as you rotate the crankshaft in the assembly with the carrier.
What happens if you slacken the main bearing bolts say 180 degrees in stages? I ask because we need to start figuring out if it is a main bearing problem or thrust washers. Did you get the thrust washers in the 'right' way around ? See Post #5 above for an expert prediction this could happen. Follow his advice over mine !!!
we checked the thrust bearings. They seam fine. It seams the main bearings might be .10 larger and that's why it's so tight. If this is the case then the parts supplier sold me the wrong bearings. I'm about to find out.
You really mean the new main bearing shells are 10 thou" larger o.d. ? When I rebuilt mine we line bored the crank carrier as a test. We did not actually remove any material .It was just to test for alignment.Yours is more complicated because it is mix and match.
Did you understand about the thrust washers being 'the right way around'? They are not symetrical/mirror image.
Yes. We removed the thrust bearings and it was still too tight.
It it may be that the main bearings are .10 thicker not wider. If they are it means the parts supplier sent me the wrong part since i ordered standard bearings. Here is a picture of the markings on the bearings.
Picture of Main bearing
Most common with this issue is the carrier bolts are not torqued correctly. Did you replace the bolts? Did you lube the bolts prior to install, and if so, with what?
What were your bearing clearance measurements? Assume nothing, and quantify everything. That's the first rule in engine building. You can't just bolt things together.
Thanks for your response Jake. We didnt even torque the bolts and it was still too tight. The bearings seam to thick. We are measuring everything today with precision instruments to see why its happening. I should know by the evening.
ah hah!
Youve screwed yourself... being too reserved and incomplete is giving you a false indication of an issue. If the carrier is torqued completely, using the entire procedure, and correct torque specs, this exact issue will occur!
This is why I offer classes. If you were in y hands on class the very first topic on the second day of the class would have gone over this exact issue, and situation to the T.
These are the tricks that make the class priceless.
That said, I'll give you some free information.
Torque the carrier up and magically as you torque the final fastener to full value, the crankshaft will miraculously spin with no tightness, or issues.
Amazing . Who knew?
I must have watched & read almost every Internet item on this subject and rebuilt the engine. But I never came across this issue that Jake generously shared. Thank you on behalf of future M96 rebuilders.
As long no obnoxious person interferes (yes it has happened !) , my hope is that The M96 Definitive Guide will come out in time for the Porsche Literature Fair which is March 4th ! Just hopeful speculation on my part.I would go and collect it from the Fair if I thought I could buy one there !
http://www.lalitandtoyshow.com/shoppers.html
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