M96 crank

[Newsguy]

I'm looking for input from someone with experience rebuilding these.
I have a 3.2 which suffered from a clogged oil pump inlet as a result of cam pads disintegrating. The end result was a trashed rod bearing and some very unhappy mains but without scoring. A pro engine builder polished the crank and called it good.
I have reassembled with new bearings and ARP case bolts. It spins freely--to a point. There seems to be a tight spot. Now i have another crank which is undamaged, and I intend to mic. The question is should I just move to the other crank, or go through all the bearings to see if one is out of spec?

[Homeoboxter]

There should not be any tight spot. Make sure you torque the bolts to spec and in the correct sequence. If still there is a tight spot, disassemble the unit and re-inspect each part. Did you replace the thrust bearing? The endfloat also should be checked.

[JFP in PA]

Originally Posted by Newsguy

I The question is should I just move to the other crank, or go through all the bearings to see if one is out of spec?

You shouldn't be assembling the engine without first assembling the rods and crank carrier with just the bearing shells in them and checking them with an inside micrometer or bore gauge, and then comparing those values to crank journal diameters to determine the actual bearing clearnaces.

[Homeoboxter]

At the very least measure the clearances all around with plastigauge.

[Newsguy]

I did plastigage the clearances and they were within tolerance.
New thrust bearings also checked.
I will be checking clearances with a mic.
Thanks for the input.

[Bebbetufs]

Some people claim these cranks can't be ground because the hardened layer is too thin. Did the machinist test the hardness of the reground rod pin?

I just measured my own crank and found 0.0012" / 0.03mm runout. I was told by LN engineering to throw it away. It seems strange to me that the tolerance is that tight. The 944 crank has a tolerance of 0.0031" / 0.08mm. The 2JZ has a tolerance of 0.0024"

Have you measured the runout?
What tolerance did you use for the bearing clearances?

If I were you I'd have both cranks checked before continuing with the build. Also the carrier bearing saddles should be checked, just to be sure.

[JFP in PA]

Originally Posted by Bebbetufs

Some people claim these cranks can't be ground because the hardened layer is too thin. Did the machinist test the hardness of the reground rod pin?

I just measured my own crank and found 0.0012" / 0.03mm runout. I was told by LN engineering to throw it away. It seems strange to me that the tolerance is that tight. The 944 crank has a tolerance of 0.0031" / 0.08mm. The 2JZ has a tolerance of 0.0024"

Have you measured the runout?
What tolerance did you use for the bearing clearances?

If I were you I'd have both cranks checked before continuing with the build. Also the carrier bearing saddles should be checked, just to be sure.

LN is correct.

[Bebbetufs]

Thanks for your input.
What do you consider acceptable in your builds?

[JFP in PA]

Let's just say much tighter than those values. And before you ask more, you are in an area of very limited information that is very dear to come by as Porsche has never published it.

[Homeoboxter]

Originally Posted by Bebbetufs

Some people claim these cranks can't be ground because the hardened layer is too thin. Did the machinist test the hardness of the reground rod pin?

Where did he mention reground pin? I think he just got the crank polished.

[Bebbetufs]

Originally Posted by Homeoboxter

Where did he mention reground pin? I think he just got the crank polished.

My bad. I assumed a thrashed pin would equal grinding.

[Bebbetufs]

Originally Posted by JFP in PA

Let's just say much tighter than those values. And before you ask more, you are in an area of very limited information that is very dear to come by as Porsche has never published it.

Thanks for responding.

Yes, I have found that people won't share info about this particular engine. For other cars I work on people share willingly and freely what they have

[tcoradeschi]

Originally Posted by Bebbetufs

Thanks for responding.

Yes, I have found that people won't share info about this particular engine. For other cars I work on people share willingly and freely what they have

Perhaps this point has escaped you - people can’t share what they don’t have. The root cause of that is an organization headquartered in the same time zone you are.

[Bebbetufs]

Originally Posted by tcoradeschi

Perhaps this point has escaped you - people can’t share what they don’t have. The root cause of that is an organization headquartered in the same time zone you are.

Perhaps.English is not my first language It is also possible people have workable information, but don't want to share. which was how I read, and still read the response.

I'm sorry if I came across as rude. I understand why people won't want to be associated with unofficial values, even though they are proven to work. I should have directed my frustration at the organisation you mention.

OP, sorry for hijacking your thread. I hope your build goes well.