SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: eliminator18 on June 22, 2015, 11:37:24 AM
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What if my bearing clearance is .002 - .0025? Can I still run the motor with a lower wt oil? Or will I have catastrophic bearing failure?
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Very loaded question.
It boils down to depending on oil temperature, oil weight, journal size, rpm, hp. Among others.
Jmo
GT
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5k rpm just a cruiser, not a race motor
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Or should I send the crank in to have .002 ground off to make the clearance at .003
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What are you using to measure the clearance? Why are they so tight?
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Brown & sharpe o.d. Mics and a fowler bore gun with a calibrated ring gage!
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I'm using king bearings c808 si std, do you know if they make smaller bearings? That way I wouldn't have to grind the crank
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Are you finding that the crankshaft journals are oversized or the bearings undersized? Is this on both the rods and mains? If the crankshaft is within tolerance, have you checked the line hone in the block and bores in the rods (measured perpendicular to the parting line)?
Just curious, did you qualify your OD micrometer to your bore gauge?
Not doubting your skills or technique, just trying to help you find the source of the problem.
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The mains are .0025 except #5 it is .003. As far as calibrating the od mic, I used a calibrated ceramic gage block set. I just had the block line honed and and the crank is new from scat, it came as a stroker kit
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I'm not sure what to do,
1. Have the crank polished to allow .003-.004 clearance
2. Find someone that make undersized bearings?
3. Just leave it, and run it!
** if I was to run it with these tolerances would I have problems running melling hv oil pump? Or would I have to run a std pump!
Thanks flusher for helping me out
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Sounds like you have some nice tools.
What I meant about qualifying your OD micrometer and your bore gauge is, did you actually check them to each other? Because you are measuring two different features with two different tools that operate in different directions, setting the OD micrometer to a known setting and comparing that known number to the actual as-measured indication of the bore gauge measuring across the anvils of your micrometer to verify that they repeat. When directly measuring the micrometer with the bore gauge, you will see if they both indicate the same.
This is something I always do to take as much error out of the equation as possible and gives you more of a direct measurement rather than a calculated indirect measurement.
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The mains are .0025 except #5 it is .003. As far as calibrating the od mic, I used a calibrated ceramic gage block set. I just had the block line honed and and the crank is new from scat, it came as a stroker kit
What are the actuals on the crankshaft? I will look up the factory blueprint specs when I get home unless someone knows them off hand.
I really don't trust production tolerances. I measure everything!
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I will have to check tomorrow, crankshaft is at work
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I'm not sure what to do,
1. Have the crank polished to allow .003-.004 clearance
2. Find someone that make undersized bearings?
3. Just leave it, and run it!
** if I was to run it with these tolerances would I have problems running melling hv oil pump? Or would I have to run a std pump!
Thanks flusher for helping me out
1. I'm not a fan of taking that much off by polishing, it will make the journals out of round. Polishing is really a micro-deburring process intended to remove the microscopic burrs left by the grinding process.
2. Check the crankshaft to blueprint specs and proceed from there.
3. I would definitely not run a HV oil pump. Please consider a factory L-88 pump. In most engines, with reasonable clearances, the oil pumps operate in bypass all the time, which unnecessarily heats the oil, not to mention the stress on the distributor gear. Yes, I too used to subscribe to "more's law," if some's good, more's better. Been there, done that, bought the T-shirt, and I have a really expensive pile of busted up junk to show for it.
Always happy to help brotherman. I hope something positive comes from it.
Cheers,
Joe
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Crankshaft main bearing journal diameters are 2.7482-2.7492 with the rear main journal diameter of 2.7478-2.7488. Rod journal diameters are 2.1988-2.1998.
Connecting rods should have a bearing bore diameter of 2.3247-2.3252
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What if my bearing clearance is .002 - .0025? Can I still run the motor with a lower wt oil? Or will I have catastrophic bearing failure?
Which bearings? Your rod bearings?
Based on what I can gather through this thread, if:
- Your rod bearings are .0020" - .0025"
- Your main bearings are .0025" (except #5 is .0030")
- Your engine is "5k rpm just a cruiser, not a race motor"
Then you're ball parked just fine for your application.
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Ignore the ring gauge....measure your crank pin, then zero your bore gauge in the mic, then measure your bearing and see the difference.