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Crankshaft main journal tolerances on 383 rebuild #1044230
07/31/11 09:31 PM
07/31/11 09:31 PM
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Tri-Cities, Washington
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VITC_GTX Offline OP
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VITC_GTX  Offline OP
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Tri-Cities, Washington
Shop manual shows main journal specs of a 383 at 2.6245”-2.6255”.

I measured mine at the following (two axis):

#1
2.6243”
2.6242”

#2
2.6236”
2.6238”

#3
2.6238”
2.6237”

#4
2.6241”
2.6241”

#5
2.6241”
2.6240”

So I’m out of tolerance (.0009" under) but I believe I’ve heard that I can buy .001” under main bearings, is that correct? If so, it should put my oil clearance within specs, correct?

This engine will be a stock build and will rarely, if ever, see anything over 4500 rpms.

Re: Crankshaft main journal tolerances on 383 rebuild [Re: VITC_GTX] #1044231
07/31/11 11:22 PM
07/31/11 11:22 PM
Joined: Dec 2007
Posts: 85
central illinois
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65dodgebob Offline
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hey there, your measurements are already under min. spec.,but you would not want to buy .001 undersize bearings. that would add .001 clearance to what you already have! however, ideal bearing clearance in performance engines is generally considered as .001 per 1 inch of crankshaft diameter.so, ideally you could have as much as .0026-.0027 and be o.k.

Re: Crankshaft main journal tolerances on 383 rebuild [Re: 65dodgebob] #1044232
07/31/11 11:54 PM
07/31/11 11:54 PM
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Tri-Cities, Washington
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VITC_GTX Offline OP
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Quote:

hey there, your measurements are already under min. spec.,but you would not want to buy .001 undersize bearings. that would add .001 clearance to what you already have! however, ideal bearing clearance in performance engines is generally considered as .001 per 1 inch of crankshaft diameter.so, ideally you could have as much as .0026-.0027 and be o.k.




Yeah, I understand I'm under spec that's why I wanted the .001" bearing to take up that difference. I guess I should have said .001" over bearing

This will not be a performance engine but a stock build.

Re: Crankshaft main journal tolerances on 383 rebuild [Re: VITC_GTX] #1044233
07/31/11 11:56 PM
07/31/11 11:56 PM
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Tri-Cities, Washington
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VITC_GTX Offline OP
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I was thinking of these. Are these .001" over or under? It doesn't say.

http://www.competitionproducts.com/Clevi...info/CB527P001/

Re: Crankshaft main journal tolerances on 383 rebuild [Re: VITC_GTX] #1044234
08/01/11 01:58 PM
08/01/11 01:58 PM
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Tri-Cities, Washington
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VITC_GTX Offline OP
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Thank you.

Re: Crankshaft main journal tolerances on 383 rebuild [Re: VITC_GTX] #1044235
08/01/11 02:11 PM
08/01/11 02:11 PM
Joined: Jan 2003
Posts: 25,200
Upper Midwest
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MoparforLife Offline
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Upper Midwest
Quote:

I was thinking of these. Are these .001" over or under? It doesn't say.

http://www.competitionproducts.com/Clevi...info/CB527P001/


They will give .001 less clearnce. Used to slightly tighten the clearance.
Take that shaft and have it professionally checked for out of round and taper. Just because it may look good it may not be. It is not that spendy to have the shaft at least polished or turned .010. Then you know where you are and the bearings will be the same price.

Last edited by MoparforLife; 08/01/11 03:28 PM.
Re: Crankshaft main journal tolerances on 383 rebuild [Re: VITC_GTX] #1044236
08/01/11 02:58 PM
08/01/11 02:58 PM
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dogdays Offline
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There used to be 0.001" UNDERSIZED bearings available as the OP said. They could still be available. There are also 0.001" oversized bearings for when you want to have a bigger clearance.

Sounds doable to me, although I'd say that extra 0.0009" won't kill you if you use standard sized bearings.

R.

Re: Crankshaft main journal tolerances on 383 rebuild [Re: dogdays] #1044237
08/01/11 03:29 PM
08/01/11 03:29 PM
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Upper Midwest
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MoparforLife Offline
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Quote:

There used to be 0.001" UNDERSIZED bearings available as the OP said. They could still be available. There are also 0.001" oversized bearings for when you want to have a bigger clearance.

Sounds doable to me, although I'd say that extra 0.0009" won't kill you if you use standard sized bearings.

R.


You are right - my mind was in reverse. Use them to slightly tighten the clearances..

Re: Crankshaft main journal tolerances on 383 rebuild [Re: MoparforLife] #1044238
08/01/11 03:56 PM
08/01/11 03:56 PM
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Posts: 2,495
Oregon City, OR
Baxter61 Offline
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You could also buy the bearings and measure the actual clearences. Your crank may be undersized out of spec but if your main bores are small as well you may end up with a useable clearance. Or grind the crank to .010 under as previously mentioned and just buy the right bearings from there, although it does appear you are doing this on a mega-budget so that may be money you dont have to spend.







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