Rod Bearing Clearance
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Teching In
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Rod Bearing Clearance Question about connection rod bearing clearance.
Crank is a K1 4" crank going into a 05 LQ4 block. Rods are also K1 and I was supplied with Mahl/Cleviete bearings (PN #CB663HN) which is a coated standard bearing. Crank journals measure out to 2.0992"-2.0993". With the bearing in the rod and bore guage zeroed to mic, I'm coming up with .0024" clearance.
After searching, I'm not quite sure if this is too much clearance. I was planning on running a 10w40 oil due to the south Texas heat. Oil pump is a Melling M295 shimmed .080". Motor will be 408ci, 11.7:1, PRC heads, fast 102 and will be primarily a weekend street car.
If I order a set of .001 tighter bearings and run half shells, I wind up around at .0019"-.0020", which seems a little on the right side.
I'd just like to get some insight from some more experienced engine builder here. Should I run what I've got now or go for the smaller clearance?
Crank is a K1 4" crank going into a 05 LQ4 block. Rods are also K1 and I was supplied with Mahl/Cleviete bearings (PN #CB663HN) which is a coated standard bearing. Crank journals measure out to 2.0992"-2.0993". With the bearing in the rod and bore guage zeroed to mic, I'm coming up with .0024" clearance.
After searching, I'm not quite sure if this is too much clearance. I was planning on running a 10w40 oil due to the south Texas heat. Oil pump is a Melling M295 shimmed .080". Motor will be 408ci, 11.7:1, PRC heads, fast 102 and will be primarily a weekend street car.
If I order a set of .001 tighter bearings and run half shells, I wind up around at .0019"-.0020", which seems a little on the right side.
I'd just like to get some insight from some more experienced engine builder here. Should I run what I've got now or go for the smaller clearance?
Clearances are setup by intended usage and power output. The more power it’s going to make, along with time sent at rpm, the more clearance needed. .0019-.0020 at the rods, sounds ok for a weekend warrior with occasional WOT runs and say…650hp. Let’s say your shooting for a max-effort build, 440 cu inch, 12.5+ compression, 800+ hp and planning on a LOT of WOT runs, I’d lean more toward the .0024 number.
Fun fact here that I’ve never shared with anyone on a forum…It’s no secret that I have a background in early 90’s Cup engines, back when teams farmed out their power. Because of my relationships there I use a machinist today that is heavily involved with Joe Gibbs Racing. Tony Stewart was hard on parts. I’m talking…very hard on parts. Tony went through a spell of constant blown engines for a stint and my machinist discovered at the time, that they had to open up the main clearances on Tonys stuff to .0045” to finally make his stuff live, and almost that much on the rods. Very similar numbers for Jimmie Johnson also while on his ‘06-‘10 winning streak at Lowes Motor Speedway. Jimmie could flat-foot the car down the back chute, through three and four and up the front chute, only lifting in one and two briefly. Basically holding the car WOT for 20-25 seconds at a time. Hard on bearings.
Fun fact here that I’ve never shared with anyone on a forum…It’s no secret that I have a background in early 90’s Cup engines, back when teams farmed out their power. Because of my relationships there I use a machinist today that is heavily involved with Joe Gibbs Racing. Tony Stewart was hard on parts. I’m talking…very hard on parts. Tony went through a spell of constant blown engines for a stint and my machinist discovered at the time, that they had to open up the main clearances on Tonys stuff to .0045” to finally make his stuff live, and almost that much on the rods. Very similar numbers for Jimmie Johnson also while on his ‘06-‘10 winning streak at Lowes Motor Speedway. Jimmie could flat-foot the car down the back chute, through three and four and up the front chute, only lifting in one and two briefly. Basically holding the car WOT for 20-25 seconds at a time. Hard on bearings.
Thread Starter
Teching In
Joined: Feb 2022
Posts: 13
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Clearances are setup by intended usage and power output. The more power it’s going to make, along with time sent at rpm, the more clearance needed. .0019-.0020 at the rods, sounds ok for a weekend warrior with occasional WOT runs and say…650hp. Let’s say your shooting for a max-effort build, 440 cu inch, 12.5+ compression, 800+ hp and planning on a LOT of WOT runs, I’d lean more toward the .0024 number.
Fun fact here that I’ve never shared with anyone on a forum…It’s no secret that I have a background in early 90’s Cup engines, back when teams farmed out their power. Because of my relationships there I use a machinist today that is heavily involved with Joe Gibbs Racing. Tony Stewart was hard on parts. I’m talking…very hard on parts. Tony went through a spell of constant blown engines for a stint and my machinist discovered at the time, that they had to open up the main clearances on Tonys stuff to .0045” to finally make his stuff live, and almost that much on the rods. Very similar numbers for Jimmie Johnson also while on his ‘06-‘10 winning streak at Lowes Motor Speedway. Jimmie could flat-foot the car down the back chute, through three and four and up the front chute, only lifting in one and two briefly. Basically holding the car WOT for 20-25 seconds at a time. Hard on bearings.
Fun fact here that I’ve never shared with anyone on a forum…It’s no secret that I have a background in early 90’s Cup engines, back when teams farmed out their power. Because of my relationships there I use a machinist today that is heavily involved with Joe Gibbs Racing. Tony Stewart was hard on parts. I’m talking…very hard on parts. Tony went through a spell of constant blown engines for a stint and my machinist discovered at the time, that they had to open up the main clearances on Tonys stuff to .0045” to finally make his stuff live, and almost that much on the rods. Very similar numbers for Jimmie Johnson also while on his ‘06-‘10 winning streak at Lowes Motor Speedway. Jimmie could flat-foot the car down the back chute, through three and four and up the front chute, only lifting in one and two briefly. Basically holding the car WOT for 20-25 seconds at a time. Hard on bearings.
I couldn’t count how many iron block engines, of many manufactures and styles, that I’ve set up the mains at .0025 with great results. Long life, 35-40 psi oil pressure hot idle with 30w oils. Your rod bearings have the final say about oil pressure on an LS platform, as they oil last.
Thread Starter
Teching In
Joined: Feb 2022
Posts: 13
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I couldn’t count how many iron block engines, of many manufactures and styles, that I’ve set up the mains at .0025 with great results. Long life, 35-40 psi oil pressure hot idle with 30w oils. Your rod bearings have the final say about oil pressure on an LS platform, as they oil last.
This is the kind of reassurance I was hoping for. They seemed a bit on the high side, but then you read so many posts and opinions on both side of the argument, with some people stating those clearances will "bleed oil' and you'll suffer low oil pressure. I've even spoken to a few machine shop and they seem to agree that the clearance will be fine. I guess once it running, if pressure is low, I can throw on a higher pressure pump. Hopefulle my shimmed M295 will be sufficient.
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It does not, as long as it’s consistent. If you stagger it, it will matter a lot on the mains. I personally like to go larger on top (bottom when assembled on an engine stand. Conn rods need to be consistent as well to keep out of the hole numbers equal, and to help balance compression. I put larger half shell on top part of rod also, smaller shell on cap side. Again it doesn’t matter really as long as you do it the same way throughout. Use a fine tip sharpie and label the shells so nothing gets turned around.
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