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Author Topic: Mid- Engine Modified Sports  (Read 343668 times)
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fordboy628
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« Reply #1575 on: December 30, 2018, 07:30:33 AM »


Fordboy, I appreciate your (and everyone else's) opinion. It does look like loose soft metal (aluminum?) swarf that was not completely flushed out of the block. That is completely my fault, I should have been more careful.

Regards, Neil  Tucson, AZ


Neil,

x2 about Line-to-Line.

Some other, random thoughts . . . . .

A/    It's your Lucky Day!    rolleyes   Well, because it's a Chevy.   Race bearings are available in .001" under size, so if your crank polishes up slightly under spec, you can use a set of those.   And .001" unders, are available for many engines.   King lists .002" u/s for Chevys, in both mains & rods.

2/    Don't get paranoid about getting all the cylinder "scratches" out by honing the bore.   Tiny, fine scratches, (not DEEP ones), while not ideal, can be ignored.   Anything that is equivalent to service wear is acceptable, UNLESS the cylinder is "out of round".    O/o/r conditions prevent ring seal with "tool steel" rings.   Softer rings can accept more o/o/r.   And, BTW, forget about cylinder scratches in the lower 1/3, or so, of the bore.   Rings don't go there.   Bore should be smooth enough so that the piston skirt is not "compromised".    Chromed, steel aircraft cylinders are purposely "scratched" by specialized honing methods and/or reversing the plating polarity.    Those small to tiny "defects" hold oil essential for piston skirt lubrication.

d/    On most "conventional" engines, the mains are fed oil first, and then oil flows to the rods from a combination of oil pressure and rotating forces.    "Nose fed" crank oiling is an exception to this convention.    Crank oil passage drillings & rpm range used, determine whether a crank requires a "low" or "high" pressure for bearings to receive adequate oil.   Additionally, pressure is somewhat misleading as it is the oil pressure, plus the volume of flow, plus the flow timing, that keeps the surfaces out of contact.   Note that many specialist produced "Chevy" type blocks use "priority main oiling systems".    These systems are designed to prioritize oil feed to the crankshaft.    Mains first, then rods.   Everything else, after that.

JMHO and YMMV

 cheers
Fordboy
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wobblywalrus
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« Reply #1576 on: December 30, 2018, 10:53:19 AM »

The contamination particles embed themselves in the shell surface and in other respects, the shell looks OK, based on what I have seen in the past.  The scoring and color of the one shown are a concern.  The main idea is to make sure that there are not multiple problems happening.  Gross contamination can score the oil pump so it does not produce the needed pressure.  Also, junk can lodge in the excess oil pressure bleed valve and cause a pressure loss there.  Or, there might be two problems happening independent of each other.

At a minimum, it might be smart to send an oil sample to a lab, cut apart the filter and look at contaminates on the paper, get a second opinion on the bearing shells, take apart and inspect the oil pump and check valve, and recheck all crank and rod bearing clearances and crank end play.  Also, prussian blue is put on the back side of all bearing shells and the motor is assembled.  Then it is taken apart and the shell seating on the block and rods is examined.  The goal is to verify that oil is not escaping out from under a shell. 

Keep in mind that I know very little about this engine.  This is only some things I have learned from experience with bike motors.   
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manta22
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« Reply #1577 on: December 30, 2018, 10:59:35 AM »

Big decisions Neil.

So you think there was swarf in the oil passages?.

Yes, Mike, from the condition of the rod & main bearings it is clear that there was some debris in the oil passages that did not get completely cleaned out.

I originally used Clevite H-series bearings but this time I think I'll try King XP bearings.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
manta22
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« Reply #1578 on: December 30, 2018, 11:07:47 AM »

Neil, sometimes the coating comes off of a shell and it is pounded back into the shell at a different location.  This appears to be contamination from an external source, but it is not.  Shells contaminated from an outside source often show embedded particles without a lot of pitting elsewhere on the shells.
The dark color of the big end in the photo suggests another problem source, like low oil pressure.  I am not sure how the oil passages go, but if the rod big ends are downstream from the main bearings, and they show more distress, this is another indicator of an oil pressure problem.   

I think the "dark color" in the photo is just the lighting. I just put the bearing on a table and used my cell phone camera. The oil pressure gauge showed 60 psi during the run so it looked OK.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
manta22
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« Reply #1579 on: December 30, 2018, 11:20:18 AM »

Fordboy;

Thank you for your observations. I've tentatively already decided to switch to King XP bearings and they do offer a slightly undersize choice. I'll clean out the block oil passages with a set of brushes that I'll order from Speedway Motors. I'll clean out the Melling oil pump as well.

Re your comment about hard chrome aircraft cylinders: I had a few 4 cyl McCulloch drone engines and they had hard chrome plating on their aluminum cylinders. McCulloch's solution for oil retention was a series of thousands of little indentations about the size of this "_" in the cylinder walls.

L-to-L is sounding better all the time.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
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