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Discussion Starter #1
Sbc dart shp block lunati crank and rods
Solid roller cam 7500 rpm around 550 hp
Some street mainly drag racing
Currently have 2 thou on rod and main of clearance is this too tight ?
 

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Consider .001" per 1.0" of shaft dia. as a good starting point.
 

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I’d open up the mains to .0025” and build it. Don’t use heavy oil like Ron said.
 

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Sbc dart shp block lunati crank and rods
Solid roller cam 7500 rpm around 550 hp
Some street mainly drag racing
Currently have 2 thou on rod and main of clearance is this too tight ?
.002" Will work very well in your application. We build dozens of engines very similar(SHP block, 515HP) every year with mains @ .002"-.0025" and rods @ .0018"-.0023". We use the standard volume Melling select(10553) with a yellow spring(60 psi). use either a -30 or -40 oil.
 

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Discussion Starter #7
Thanks for your help guys
I brought a set of .009 mains and going to use half and half so will end up with 2.5 on mains
Leaving the rods at 2
Measurements were taken using micrometer and inside bore dial gauge
 

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There are better and not so good inside bore dial gauges.
Sunnen (floating fingers) is a good choice.
That is why some will add an extra 0.0005 to clearances just to make sure.
 

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There are better and not so good inside bore dial gauges.
Sunnen (floating fingers) is a good choice.
That is why some will add an extra 0.0005 to clearances just to make sure.
By choice the best bore gauge for checking bearing clearances is Sunnen. I have had a lot of bore gauge wars at my shops against the 150.00 gauges not even close.
 

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Depends one ones measurement tools!
Half a thou too loose will not cost and engine.
Half a thou too tight will!
Your choice.
You don't make a bad point I suppose. I don't build engines all day long but I am a machinist every day, and trusting numbers down to a few tenths is not something I would do for the majority of engine machine shops. Not to make a stab at the shops at all it is just the reality.. But with all the tolerance stack up that may be missed, adding half a thou probably wont hurt...
 

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You don't make a bad point I suppose. I don't build engines all day long but I am a machinist every day, and trusting numbers down to a few tenths is not something I would do for the majority of engine machine shops. Not to make a stab at the shops at all it is just the reality.. But with all the tolerance stack up that may be missed, adding half a thou probably wont hurt...
If you're a machinist and are comfortable to working in tenths, engine parts are no different than any other parts. You have to take all the regular things into consideration like temperature, handling your mics, properly setting up your bore gauges, etc. No reason to "guess" at your clearances or arbitrarily add something that's not needed "just in case". Mic your crank, install your bearings in the rods and block and measure them vertically at 12:00/6:00, do the math, there's your clearance. That's a little bit of an oversimplification, but none the less... Don't be surprised if, by the end of the day, you're as frustrated as you've ever been, though. Bearings are not consistent and accurate machining is hard to come by in this industry. Not like what we're used to as industrial machinists (how I got my start). Most automotive/engine machinists couldn't make a part form a drawing if their life depended on it. Oil control is huge, and it's power. Oil control starts with bearing clearances. Personally, I work real hard to get mine right on the money and run the tightest clearances the application calls for. If the application calls for being really anal about tight clearances, then I do that. If it doesn't then I have some wiggle room. You have to be the judge there. JMO.
 

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How much do builders figure tolerance needed based on crank and/or block flex due to engine tq, crank or block used, chassis stiffness, eng plate or mounts, etc?
 

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How much do builders figure tolerance needed based on crank and/or block flex due to engine tq, crank or block used, chassis stiffness, eng plate or mounts, etc?
It all plays into it.
 

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If you're a machinist and are comfortable to working in tenths, engine parts are no different than any other parts. You have to take all the regular things into consideration like temperature, handling your mics, properly setting up your bore gauges, etc. No reason to "guess" at your clearances or arbitrarily add something that's not needed "just in case". Mic your crank, install your bearings in the rods and block and measure them vertically at 12:00/6:00, do the math, there's your clearance. That's a little bit of an oversimplification, but none the less... Don't be surprised if, by the end of the day, you're as frustrated as you've ever been, though. Bearings are not consistent and accurate machining is hard to come by in this industry. Not like what we're used to as industrial machinists (how I got my start). Most automotive/engine machinists couldn't make a part form a drawing if their life depended on it. Oil control is huge, and it's power. Oil control starts with bearing clearances. Personally, I work real hard to get mine right on the money and run the tightest clearances the application calls for. If the application calls for being really anal about tight clearances, then I do that. If it doesn't then I have some wiggle room. You have to be the judge there. JMO.
For sure, I guess the one thing I always come back to think is you are just individually checking each housing bore to its corresponding crank pin. How can you accurately measure each main bore relative to one another to make sure they are perfectly in line with each other? I get they are honed on a line hone , but how can you check it to make sure they are straight?

Or else your clearance will not be the same at all point of the crankshaft rotating, same with any run out in the crank. Maybe I am over thinking it, as I said I don't build engines for a living . Just making some conversation about this because I have never got a great answer whenever I bring this up.
 

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For sure, I guess the one thing I always come back to think is you are just individually checking each housing bore to its corresponding crank pin. How can you accurately measure each main bore relative to one another to make sure they are perfectly in line with each other? I get they are honed on a line hone , but how can you check it to make sure they are straight?

Or else your clearance will not be the same at all point of the crankshaft rotating, same with any run out in the crank. Maybe I am over thinking it, as I said I don't build engines for a living . Just making some conversation about this because I have never got a great answer whenever I bring this up.
I tried laying a machinist's rule down them but I didn't think it was worthwhile (at least with my skill).
 
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