Crankshaft dimensions

[John Druckrey]

Got my 2.7 crank back from being polished; the rod throws read a couple of ten thous under. Any way to "coat" these and bring them back up to spec?

[snowman]

Whats the overall oil clearence now? couple of ten thousands shouldn't make any difference normally. Anywhere between 1.8 to 2.4 thousands oil clearence is ok. more or less may be ok, depending on how much. for example, 2.5 thou wouldn't be a problem.

What did you use to measure the crank and was it checked with a cal block?

Rather than plate up a crank you would go to the first size under and repolish to fix a problem.

Polishing a crank shouldn't remove any perceptible ammount of material as something like 800grit or higher is used to polish it.

[camgrinder]

You can Nitride the crankshaft. I have seen .0005 to .0007" growth depending on the cycle length. Nitriding will also stress relieve the crank if you are going to be abusing it.
Jack is right about polishing the crank, I have seen someone try and remove a few tenths. The Porsche cranks are very hard from the factory and it would take a half hour to polish a crank journal down a few tenths.

[John Druckrey]

Actualy used a go/nogo gage set-up on gage blocks. The minimum gages out at 2.0458" - 2.0459". (51.963 - 51.965mm). Would not like to grind undersize and was hoping that some type of applied coating would bring it up in size.

[snowman]

I would check your oil clearence. Use plastiguage and your rods with new bearings if possible. The reason is that your rods also have a tolerance and could be on the small side of things. You could also resize the rods and force them to be on the small side of the tolerance or even slightly smaller. Some bearings may be available in increments of 1 thou up to 3 thou oversize.

If your using go no go testing then you have no idea how far off you really are.

As to grinding the crank undersize, if done correctly makes absolutely no difference in strength or performance. Plating up the crank is prone to more error and more expense. The plating has a tendency to peel if not done absolutely correctly, and the crank still has to be reground. Its only a last resort for exotic and non replaceable cranks in general and prone to a lot of problems. Plating has been used on race engines, but I couldn't recommend it

[John Druckrey]

I checked the journals several times with the same results (one - two ten thousands under. I was thinking that I could have my rod big ends trued slightly under the minimum but wouldn't that put a "bind" on the bearing?

Thanks
John

[snowman]

If you are talking about one to two ten thou out of spec, forget it. Its not a problem.

[Wayne 962]

It it's within the spec provided by Porsche (at first glance it does seem to be), then don't worry about it...

-Wayne

[BReyes]

I would measure with plastigage. You may want to send it to be nitrided.

Regards,

[snowman]

I think the crank should always be nitrided.