Crankshaft Roughness

[langeberg]

Can some on please tell me the max tolerance on roughness on a crankshaft surfaces in Ra

my crank is 0.6-0.8 Ra

A well know motor guru in denmark Torben Alstrup / Farmer is convinced that my re grind crank is in a good con dision ? but i disagree with him

he tell my that the roughness is better for at good oil film 

Jan from denmark

[langeberg]

hey all

like to hear if some of you engine people dare to used this crank in an engine ?

please let me know..

[Fast Bug]

http://www.enginebuildermag.com/Article/2557/crankshaft_polishing_make_sure_the_journals_on_the_crankshaft_are_properly_polished.aspx

According this article the surface should be between Ra 0.15 and 0.3
Remember the Ra numbers in this article is in micro inches so you have to divide the numbers by 40 to get them in metric.

[langeberg]

Ok to get i total clear

The ultimate goal when polishing crankshaft journals is to achieve a relatively flat and smooth surface finish (an average roughness of 10 microinches or less) with plenty of bearing surface to support the oil film.

10/40=0,25 micrometer

and my crank is

0,6 X 40 = 24 micro inches
0,8 X 40 = 32 micro inches

is this correct ??

is that to far away from the 10 micro inches ?

or do anyone dare to run this in an engine ?

please give me some feedback on this

thanks Jan from Denmark

[Fast Bug]

Yes, the calculations are right. 40 inches is approx. 1 meter.
I would get that crank polished. You don’t want any peaks on the journal surface of a greater thickness than the oil film, metal-to-metal contact will hurt the bearings.
Bearings are very soft. The cranks I have measured (DPR and CB super race) are better than 0.3 micro meters. Nitrated and nice polished journals are what you need.

[langeberg]

oki and thanks then i was right the man Torben Alstrup alias Famer is NOT a fair vw pusher......keep away for him ....he is no good for the vw world in my opinion


Jan from denmark.....

[JS]

oki and thanks then i was right the man Torben Alstrup alias Famer is NOT a fair vw pusher......keep away for him ....he is no good for the vw world in my opinion
Jan from denmark.....

Please be advised there exists different opinions on the matter.

Sorry to hijack the thread.

Johnny Steiro
NOT from Danmark.

[langeberg]

Js

 Iknow then tell me you opinions,,?? or

[nicolas]

if you can get access to a lathe i would just do that and polish it on it. no big deal just be careful not the wrap the polishing cloth around it  if you want you can get it mirror finished (if that is even a word). i have more concerns about the flatness of the journal from radius to radius.