Correct rod and main bearing clearances? - Team Camaro Tech
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post #1 of 17 (permalink) Old Mar 30th, 11, 08:55 PM Thread Starter
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Matt
 
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Correct rod and main bearing clearances?

I am beginning to assemble my 406 and measured the rod bearing clearances at .0021 to .0023. I plan to use the engine mostly on the street with a few trips to the strip a year. Hoping to make a little more than 500hp and rev to 6500 RPM.

The book I have says .0017-.0030 for a Stock engine, .002-.003 for Hi-Po Street and .0025-.0035 for High-RPM Racing.

My clearance seems to be on the tight side. Should I increase the clearance? If so, how?

Matt

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post #2 of 17 (permalink) Old Mar 30th, 11, 09:07 PM
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Michael Gekko
 
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Re: Correct rod and main bearing clearances?

You could get oversize bearings. Or you might be able to get the crank polished a little .
Personally I wouldn't worry about it, you are in spec......and tbh 6500 rpm isn't a lot of rpm.

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post #3 of 17 (permalink) Old Mar 30th, 11, 11:49 PM
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darrell
 
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Re: Correct rod and main bearing clearances?

i would leave it--a big concern is clearance between rods- eagle cranks are always off
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post #4 of 17 (permalink) Old Mar 30th, 11, 11:53 PM
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darrell
 
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Re: Correct rod and main bearing clearances?

i personally run those clearances but i run 30 on back main ( alittle less oil pressure but it makes more power because of less rotational drag
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post #5 of 17 (permalink) Old Apr 1st, 11, 02:31 AM
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Re: Correct rod and main bearing clearances?

Quote:
Originally Posted by MW67RS View Post
I am beginning to assemble my 406 and measured the rod bearing clearances at .0021 to .0023. I plan to use the engine mostly on the street with a few trips to the strip a year. Hoping to make a little more than 500hp and rev to 6500 RPM.

The book I have says .0017-.0030 for a Stock engine, .002-.003 for Hi-Po Street and .0025-.0035 for High-RPM Racing.

My clearance seems to be on the tight side. Should I increase the clearance? If so, how?

Matt
Your clearences are PERFECT
Assemble it, then rod the piss out of it!!!

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post #6 of 17 (permalink) Old Apr 1st, 11, 03:55 PM Thread Starter
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Matt
 
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Re: Correct rod and main bearing clearances?

Thanks guys. I will run them as they are.

I checked the main bearing clearance and have .0021-.0024 on the first 4 and .0036 on the rear. I think the .0021-.0024 are a little tight and the .0036 is a little loose. Is that correct? Should I get different bearings or run it like it is? I heard somewhere that you can scotch brite the back side of the bearings to make them a little thinner and then install them to get more clearance. Has anyone done that? Will that reduce the bearing crush and cause a problem?

Thanks again for all the help,

Matt

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post #7 of 17 (permalink) Old Apr 1st, 11, 08:27 PM
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Don
 
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Re: Correct rod and main bearing clearances?

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Originally Posted by MW67RS View Post
Thanks guys. I will run them as they are.

I checked the main bearing clearance and have .0021-.0024 on the first 4 and .0036 on the rear. I think the .0021-.0024 are a little tight and the .0036 is a little loose. Is that correct? Should I get different bearings or run it like it is? I heard somewhere that you can scotch brite the back side of the bearings to make them a little thinner and then install them to get more clearance. Has anyone done that? Will that reduce the bearing crush and cause a problem?

Thanks again for all the help,

Matt
Your clearances are good for start up. Use good oil and break it in slowly. Leave the scotchbrite trick for the pro racers. I usually call .001-.0036 good. I would check the rear crank flange thrust clearances. Thats between the crank flange and main bearing thrust surface. .005-.007 is my number. This is especially important on a manual trans car.

Don
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post #8 of 17 (permalink) Old Apr 1st, 11, 08:35 PM Thread Starter
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Matt
 
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Re: Correct rod and main bearing clearances?

Don,

My thrust endplay is .0035. Any way I can increase it a little?

As for the bearing clearance. I have been doing a lot of searching on this site and find that some people like to run around .0035 for the mains and others prefer .0025. I have learned that a larger clearance will cause more oil flow through the bearing/crank journal interface and cool them better. What is the advantage of the tighter clearances. What is the draw back to running larger clearances?

Matt

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post #9 of 17 (permalink) Old Apr 1st, 11, 09:50 PM
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Michael Gekko
 
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Re: Correct rod and main bearing clearances?

Quote:
Originally Posted by MW67RS View Post
Thanks guys. I will run them as they are.

I checked the main bearing clearance and have .0021-.0024 on the first 4 and .0036 on the rear. I think the .0021-.0024 are a little tight and the .0036 is a little loose. Is that correct? Should I get different bearings or run it like it is? I heard somewhere that you can scotch brite the back side of the bearings to make them a little thinner and then install them to get more clearance. Has anyone done that? Will that reduce the bearing crush and cause a problem?

Thanks again for all the help,

Matt
Nah, the thrust bearing can handle the larger clearance. Matter of fact I set mine up in that fashion. You are good to go, imo.

1968 Camaro NHRA/IHRA SS/C 'Super Stocker' 396/Jerico
1968 Street/Strip Camaro 350 w/PG
1968 Caprice NHRA/IHRA Stock ELiminator O/SA 327-250 HP



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post #10 of 17 (permalink) Old Apr 3rd, 11, 08:44 PM
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darrell
 
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Re: Correct rod and main bearing clearances?

bearing clearances fine i would run that way --dont like that much thrust clearance and wondering why if its new or reground--too much clearance will make it sling a rod at high rpm--if you dont turn 6600 rpm or higher i think it will be fine=the more bearing clearance you have , needs more oil volume and it will have lower oil pressure at idle but yields more hp--too tight more friction less hp and can kil a crank higher oil pressure--i wouldnt run a 3 or more accross the board for the street
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post #11 of 17 (permalink) Old Apr 3rd, 11, 10:00 PM Thread Starter
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Matt
 
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Re: Correct rod and main bearing clearances?

My thrust endplay is only 3 1/2 tenths. I thought that is too little not to much.

Matt
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post #12 of 17 (permalink) Old Apr 3rd, 11, 11:08 PM
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Todd
 
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Re: Correct rod and main bearing clearances?

.0035 is three and one half thousanths. The rear main being that loose will hurt your hot oil pressure at idle. Sounds like you could order a different rear main bearing that is a little tighter bearing wise and loosen up the end play a touch.
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post #13 of 17 (permalink) Old Apr 4th, 11, 08:09 AM Thread Starter
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Matt
 
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Re: Correct rod and main bearing clearances?

Todd,

Thanks for the correction. You are right. 3 and 1/2 thousandths. How do I loosen up the end play a touch?

Matt

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post #14 of 17 (permalink) Old Apr 4th, 11, 09:09 AM
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Todd
 
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Re: Correct rod and main bearing clearances?

I was thinking you could order the new rear main with a little less clearance on the bearing surface and a little more clearance on the the thrust.
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post #15 of 17 (permalink) Old Apr 4th, 11, 06:04 PM Thread Starter
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Matt
 
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Re: Correct rod and main bearing clearances?

The book I have on building a small block says to hit the crank with a soft hammer to seat the thrust. I did that and got .0035 clearance. I then heard that you have to hit it with something more substantial. So I hit it with a big brass hammer and now I have .0075 clearance with the main cap only hand tight and .0055 with it torqued to 80 lb-ft. Is that enough clearance.

Also, the local machine shop said the rear main clearance may tighten up once I install the oil pump. I will try that out. I thought it would increase the clearance but they say it will reduce it. I will see.

Thanks again for all the advice.

Matt

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