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Title: Crankshaft Roughness Post by: langeberg on May 13, 2012, 16:00:49 pm 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 Title: Re: Crankshaft Roughness Post by: langeberg on May 13, 2012, 19:12:37 pm hey all
like to hear if some of you engine people dare to used this crank in an engine ? please let me know.. Title: Re: Crankshaft Roughness Post by: Fast Bug on May 13, 2012, 19:26:25 pm http://www.enginebuildermag.com/Article/2557/crankshaft_polishing_make_sure_the_journals_on_the_crankshaft_are_properly_polished.aspx (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. Title: Re: Crankshaft Roughness Post by: langeberg on May 14, 2012, 17:04:40 pm 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 Title: Re: Crankshaft Roughness Post by: Fast Bug on May 14, 2012, 22:16:14 pm 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. Title: Re: Crankshaft Roughness Post by: langeberg on May 16, 2012, 21:18:39 pm 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..... Title: Re: Crankshaft Roughness Post by: JS on May 16, 2012, 23:55:43 pm 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. ;) Title: Re: Crankshaft Roughness Post by: langeberg on May 17, 2012, 13:17:30 pm Js
Iknow then tell me you opinions,,?? or Title: Re: Crankshaft Roughness Post by: nicolas on May 21, 2012, 19:30:26 pm 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.
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