Author Topic: Connecting rod bearing clearance  (Read 1377 times)

Offline dieselman123

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Connecting rod bearing clearance
« on: May 18, 2024, 11:28:56 AM »
Im building a 383 with a eagle 383 stroker kit. Im getting .002 on the connecting rod bearing using plastic gauge but want to have .0025 to .003 to be able to run 15w40. This measurement is with the king bearing with the extra .0001 clearance using the upper and lower bearing.What can be done to achieve the extra clearance or am i ok to run 15w40 rotella diesel oil with .002. Could i mix undersized bearings maybe. Please help
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Offline VileZambonie

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Re: Connecting rod bearing clearance
« Reply #1 on: May 19, 2024, 07:11:50 AM »
Sounds like someone give you bad advice. I bet if you were to call Eagle and tell them your plan they would write your name down to void your warranty. Why do you want to build a loose tolerance around a multi-viscosity oil?  ??? .001" is bullseye
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Offline dieselman123

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Re: Connecting rod bearing clearance
« Reply #2 on: May 19, 2024, 07:50:09 AM »
So you would consider. 0025 to be loose?? Without the .0001 bearing im getting .0015 which i feel is too tight. Do not want to run the vr1 20w50 like everyone is saying because i feel it is way too thick. Which is why i chose 15w40 but been going back and forward between rotella 15w40 an driven 10w40
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Offline VileZambonie

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Re: Connecting rod bearing clearance
« Reply #3 on: May 20, 2024, 06:57:38 PM »
From what you describe you have good measurements but want to increase tolerance (which is loosening yes) to accommodate 15w40... Why? Have you seen what 1000 plus HP engines run for motor oil? You choose the oil to fit the engine, you don't build the engine to fit an oil.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline ehjorten

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Re: Connecting rod bearing clearance
« Reply #4 on: May 21, 2024, 10:25:54 AM »
This doesn't make sense to me. You want to increase the bearing clearance to move to a lower viscosity oil? The relationship between oil viscosity and bearing clearance is directly proportional (i.e. tighter bearing clearances require lower viscosity, thinner oil and larger bearing clearance require increased viscosity, thicker oil).

0.0015" - 0.0025" is within a factory spec. Your 0.002" should be about perfect, but to really know you need a micrometer that can read down to the 0.0001". You don't know how tight the out of round is, or if you have slightly tapered journals. Given that you are spending a bunch of money to build your 383, you could take the crank to your machinist and have the journals polished up to take a few tenths off. That might be the best way to gain a little extra clearance.
« Last Edit: May 21, 2024, 10:43:52 AM by ehjorten »
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline JohnnyPopper

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Re: Connecting rod bearing clearance
« Reply #5 on: June 04, 2024, 09:56:50 PM »
A few tenth's off?  8)
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline ehjorten

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Re: Connecting rod bearing clearance
« Reply #6 on: June 05, 2024, 09:17:54 AM »
Yes Johnny...a tenth is 0.0001" in machinist jargon when the basic unit of measure is one thousandth (0.001"). It means one tenth of a thou.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline JohnnyPopper

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Re: Connecting rod bearing clearance
« Reply #7 on: June 11, 2024, 07:29:11 PM »
Yes Johnny...a tenth is 0.0001" in machinist jargon when the basic unit of measure is one thousandth (0.001"). It means one tenth of a thou.

Ahh yes, thanks!
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction