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Hey guys well I have a 400 crank im running in my 400 that im currently building. its a stock cast crank. but on further inspection, the crank has some scratches in the journals. they are not serious scratches by any means. now what im wondering is, will it be fine to run in my 400? I just got it polished at the machine shop. Does that put a slightly rounded edge to the scratches when polished? Whats your opinions on this guys?
Thanks
It depends on what you mean by a scratch - if you can catch a finger nail while dragging it across the scratch, it needs to be ground to the next undesize. If it is a very minor surface scratch, and is cosmetic mostly, it MAY be fine and run forever. I have seen nasties run for many miles with good oil pressure, but..... it's your final decision (or with a good automotive machinists' input after seeing it in person)Quote:
Originally Posted by facemelter
well they can not be that bad if they polished it .the belt takes the hi.s off the crank the low spot is left . all this will do is hold oil
Yeah when i brang it there I originally just had the assembly balanced, but then they noticed some scratches. So I asked what they thought and they just said we'll polish it up. The high spots I suspose is what would rip the bearings up.Quote:
Originally Posted by pat mccarthy
And if the scratches ARE too bad, which im thinking they probably are not, like you said, I could get it cut undersized. Didnt honda make they're cranks to have smaller journals for more horsepower? As a result of less surface contact?? lol anyways, ill keep that in mind. Oh, and lets say if i do need to cut it undersized, will that make the crank unbalanced? as i just paid 175 to get it balanced! :CRY:Quote:
Originally Posted by Irelands child
Thanks for your opinion
Face, Pat's got ya covered. We just call it "oil clearance. Seriously, you should be fine if they don't appear to be the Grand Canyon.
yes it would .i have polish cranks that see hi loads and grab the bearings a bit and polish them and run them i try to not get them turn down in drag engines. to get some use out of the cranks and have run some that have been scratch a bit long as size of the crank is not way off i do not grind them i like them abit loose any ways for racing and they make plus bearings any waysQuote:
Originally Posted by facemelter
had one 454 crank oil grooved 360 mains work just fine and is still out there some were ?if you read this call home :confused: :LOL: grinding the crank will not throw any thing offQuote:
Originally Posted by DennyW
i have had crank at my shop done with tape were they came from they look wavy . i can do a better job with my hand held polisher with 400 to worn 400 belt with belt dresser then with belt rouge sometimes or the 3m scotch brite belt.
that.s cool i just was saying that i was not happy with there new tape machine .i hope my new crank will not look like the ones i have seen from the other crank company:confused:Quote:
Originally Posted by DennyW
hey denny thanks for that info, I read it all, and it makes things much easier :3dSMILE:
If you buy that the oil film thickness is only .00005 from the article then a 32 finish would be the worst you would want. According to some bearing studies we did a (long) while back in school I think the minimum film thickness is more like .0001 to .0003. In this case the 32 finish would work great as your experience has indicated.Quote:
Originally Posted by DennyW
In high speed bronze hydrostatic bearing applications we usually spec out a ground 16 finish. These are bearings up to 8 inch diameter with a 3 mil per side clearance and a minimum film thickness of 1 mil.
Kitz
My days in manufacturing, a long time ago, we spec'd a 64 finish on high speed turbine and generator shafts. These ranged from 6 inches up to 24 inch diameter shafts. The turbines were operating at 3000 to 6000 rpm while the gear driven generators operate at 1500, 1800, 3000 or 3600 rpm, depending on the frequency of the country of destination. The bearings in these applications were not round but eliptical (wide at the horizontal joint, allowing for an oil wedge and the climbing factor of the shaft (hydrodynamic wedge) - the shaft would rise and rotate about 10-15 degrees from the vertical centerline of the bearing shell. The oil film was based on a rule of thumb bearing to clearance of .0015/in of diameter, the shaft climbing at rotational speeds and the flow in GPM at 25psig.
Then, to complicate this even more, throw in a rotated tilting pad bearing and try to make some sense out of that feed and drain system - I tried including talking to the designer.:CRY:
How does that translate to automotive technology? You still have clearances to worry about, pressure and flow and a hydrodynamic wedge - look at the direction of the feed holes in the crankshaft to determine where the wedge is formed. This provides the semi metered flow to the babbited bearings, and provides the cushion for wear resistance. This flow can be disrupted by heavy scratches or it can introduce early wear to the bearings. If the measured fit, by micrometers is correct, and there are no significant scratches, i.e. feel by dragging your fingernail across the journal, there should be no problem. But you also need a good finish in the 64 range as well. Pur it together and run it!!!!:LOL: :eek:
I wouldnt consider them "significant" scratches, but as Denny stated, even if I have scratches, I have it polished, and the scratches will just hold oil.Quote:
Originally Posted by Irelands child
I'm halfway done with the rotating assembly at the moment. Starting to look pretty nice!
Thanks for this info
You put it like it is. Thats how it should be all the time :LOL:Quote:
Originally Posted by DennyW
Glad to hear that - post some photos if you can (sorry about the hijack in my last spiel, but....)Quote:
Originally Posted by facemelter
No lol its fine! I like to hear everyones point, and all in all it just makes me more knowledgeable thanks to you guys.Quote:
Originally Posted by Irelands child
Thanks again!