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Main and Cam Bearing Clearances

sdcbowler

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Good Day, Members

I am a bit confused concerning bearing clearances and how to measure them. I have a stock 383 that came with a 2 bbl carb. I am adding a mild cam (See the pic). I also intend to replace the 2bbl carb with a 4 bbl carb. In the FSM, Page 9-96, it indicates a Connecting Rod bearing clearance of .0005 to .0015 for a 2bbl carb .001 to .002 for the 4bbl carb. Since the engine originally came with a 2bbl, but I am swaping it for a 4bbl, which clearance value should I use, .005 to .0015 (2bbl) or .001 to .002 (4bbl)?

Also, on the same page it gives the Crankshaft Main Bearing clearances of .0005 to .0015. I have looked at the Plastigauge. The green plastigauge has a range of .001 to .003. So, I guess for this clearance I will have to shoot for .001.

Accepting all comments, please

IMG_20230807_200150449[1].jpg
 

MOPARMITCH

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Good Day, Members

I am a bit confused concerning bearing clearances and how to measure them. I have a stock 383 that came with a 2 bbl carb. I am adding a mild cam (See the pic). I also intend to replace the 2bbl carb with a 4 bbl carb. In the FSM, Page 9-96, it indicates a Connecting Rod bearing clearance of .0005 to .0015 for a 2bbl carb .001 to .002 for the 4bbl carb. Since the engine originally came with a 2bbl, but I am swaping it for a 4bbl, which clearance value should I use, .005 to .0015 (2bbl) or .001 to .002 (4bbl)?

Also, on the same page it gives the Crankshaft Main Bearing clearances of .0005 to .0015. I have looked at the Plastigauge. The green plastigauge has a range of .001 to .003. So, I guess for this clearance I will have to shoot for .001.

Accepting all comments, please

View attachment 126580
Doesn't really matter much. It is all relative. .0005,,,...>002, If the lower end of the engine is good, than it is good. Dont worry too much about that. You're splitting hairs... As far as the cam goes, that looks pretty tame. Go fur It.....
 

Chryco Psycho

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Depends on how you intend to drive it , I would lean towards looser clearance & use 10/40 oil with lots of ZDDP to protect the cam .
AS for cam choice you can do far better using Lunati , comps are designed for Chev .
 

MOPARMITCH

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Depends on how you intend to drive it , I would lean towards looser clearance & use 10/40 oil with lots of ZDDP to protect the cam .
AS for cam choice you can do far better using Lunati , comps are designed for Chev .
Or Howards Camshafts..Just make sure the oiling holes are drilled all the way through...AKS me how I know.....
 

sdcbowler

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Depends on how you intend to drive it , I would lean towards looser clearance & use 10/40 oil with lots of ZDDP to protect the cam .
AS for cam choice you can do far better using Lunati , comps are designed for Chev .
Chryco,

Could you be a bit more specific? I don't have any reservations against using 10/40 with ZDDP. What percentage ZDDP? Capacity is 5 quarts. Are you talking 4 quarts of oil to 1 quart of ZDDP, or 3 quarts of oil to 2 quarts of ZDDP?

Also, you say you would lean towards looser clearances. What do you consider loose?

The car will not be on any track, drag strip, or involved in any type of racing. I am in Sothern California. If fuel prices weren't so outrageous, or if there weren't so many car thieves, I could see myself driving it three to fours days a week.
 

sdcbowler

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Doesn't really matter much. It is all relative. .0005,,,...>002, If the lower end of the engine is good, than it is good. Dont worry too much about that. You're splitting hairs... As far as the cam goes, that looks pretty tame. Go fur It.....

Yeah, I did not want a "lopey" cam. Always makes me think the engine is about to die. Otherwise, is there a size cam (not lopey), you would recommend to someone like me?
 

Chryco Psycho

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I would run around .0015-.002
Zddp is an additive in the oil or used to be , only specific oils have it now , there is not enough in modern oil to keep the cam safe , SJ rated oils are best , Brad Penn or Joe Gibbs have special oil formulations for flat tappet cams , Agricultural oils are also SJ still as there are used off road , Valvoline VR1 is good also but I would not use 20-50w
Cam lift is free , if you use a cam in the 220* range at .050 you have a mild cam , 112* LSA is better for manifolds , 110* for headers , you should be able to get close to .490 lift at 220* duration rather than .440 , comp cams are lame
 

sdcbowler

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I would run around .0015-.002
Zddp is an additive in the oil or used to be , only specific oils have it now , there is not enough in modern oil to keep the cam safe , SJ rated oils are best , Brad Penn or Joe Gibbs have special oil formulations for flat tappet cams , Agricultural oils are also SJ still as there are used off road , Valvoline VR1 is good also but I would not use 20-50w
Cam lift is free , if you use a cam in the 220* range at .050 you have a mild cam , 112* LSA is better for manifolds , 110* for headers , you should be able to get close to .490 lift at 220* duration rather than .440 , comp cams are lame
OK,

I understand, but also wanted to know this 'What percentage ZDDP should I use? If oil capacity is 5 quarts should I use 4 quarts of oil to 1 quart of ZDDP, or 3 quarts of oil to 2 quarts of ZDDP?
 

Chryco Psycho

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I would have to look exactly but around 1600 PPM most new oils are 1/2 that or less , it is just added to the oil not like 1 qt added , SJ rated has the correct amount in it
 

sdcbowler

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I would have to look exactly but around 1600 PPM most new oils are 1/2 that or less , it is just added to the oil not like 1 qt added , SJ rated has the correct amount in it

OK. Thanks much for the info. I will research to see what I can find.
 

Xcudame

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Chryco is right on the money! Use 1500-1600ppm ZPPD additive. I like to pour two quarts and part of another quart of oil in the engine, then add the additive to the partial quart, install the cap and shake it up! Then poor it in. Probably not necessary, but it makes me feel better.

And Lunati Voodoo cams are the old Ultradyne cams and my personal favorite as well. 2bbl 383s had lower compression (shorter piston compression heights) so you don't have to worry too much about higher lift cams smacking a piston top! 😀
 

sdcbowler

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Chryco is right on the money! Use 1500-1600ppm ZPPD additive. I like to pour two quarts and part of another quart of oil in the engine, then add the additive to the partial quart, install the cap and shake it up! Then poor it in. Probably not necessary, but it makes me feel better.

And Lunati Voodoo cams are the old Ultradyne cams and my personal favorite as well. 2bbl 383s had lower compression (shorter piston compression heights) so you don't have to worry too much about higher lift cams smacking a piston top! 😀

Xcuda, Chryco

I appreciate the info on using the ZDDP. Will surely do that. Will also look at the Voodoo Cams as well.
 
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