Rod bearing clearance

[phat46]

What are you comfortable running for minimum rod bearing clearance? On a SBC 383 stroker with Scat rotating assembly.

[kb426]

This article has some good info. http://www.superchevy.com/how-to/engines-drivetrain/4380-bearing-clearance-info
An engine is an engine to me. I never run tighter than 2 or looser than 3.5 unless it's a blown fuel engine with 50 wt. oil and at least 100 lbs. of pressure. That would be an engine with steel rods and normal rpm operating limits. I always use a mic and a dial bore gauge to measure. You might get by with plastigauge but it will be incorrect in the right circumstance. I'm sure you want to do this the best you can. I don't think you need to think it's any different than any other chevy you've put together in your life. If your crank and rods are new and measure to standard, I don't think you need to worry. Even if the crank measures low standard and the rods measure high standard, you shouldn't have more than 3. However, that is why we measure everything. I think the rule of 1 thou per inch of size applies to most parts in an engine.

[phat46]

This article has some good info. http://www.superchevy.com/how-to/engines-drivetrain/4380-bearing-clearance-info
An engine is an engine to me. I never run tighter than 2 or looser than 3.5 unless it's a blown fuel engine with 50 wt. oil and at least 100 lbs. of pressure. That would be an engine with steel rods and normal rpm operating limits. I always use a mic and a dial bore gauge to measure. You might get by with plastigauge but it will be incorrect in the right circumstance. I'm sure you want to do this the best you can. I don't think you need to think it's any different than any other chevy you've put together in your life. If your crank and rods are new and measure to standard, I don't think you need to worry. Even if the crank measures low standard and the rods measure high standard, you shouldn't have more than 3. However, that is why we measure everything. I think the rule of 1 thou per inch of size applies to most parts in an engine.

Yeah, I was using Plastigage, it was right between .0015 and .002. I have a guy coming tomorrow to check it with instruments; better safe than sorry. Not sure how to fix if it is too tight, I have read of using one shell of a .001 under bearing.

[kb426]

There are one unders and one overs in most bearing sizes. It if checks at 2, I'd be happy. Many run there's at 1.5 but I spin mine sometimes so the extra clearance is something I feel is needed. Once you have accurate measurements, it will be easy to make a decision. Just so I'm clear, I use the dial bore gauge for the rods and the mic for the crank. Same with main journals. I don't trust snap gauges unless you can get the same reading many times in a row. Accurate measurement is based upon repetition and getting the same result. I use a checking standard to set up the dial bore gauge and to check the mics.

[phat46]

There are one unders and one overs in most bearing sizes. It if checks at 2, I'd be happy. Many run there's at 1.5 but I spin mine sometimes so the extra clearance is something I feel is needed. Once you have accurate measurements, it will be easy to make a decision. Just so I'm clear, I use the dial bore gauge for the rods and the mic for the crank. Same with main journals. I don't trust snap gauges unless you can get the same reading many times in a row. Accurate measurement is based upon repetition and getting the same result. I use a checking standard to set up the dial bore gauge and to check the mics.

The guy coming to check them is my nephew, he's a machinist and has built several strokers with the Scat kit, his latest was a 788 h.p. e85 blower motor. He said his gauges are all set! He also suggested the .001 under half shell. I'll let you know what we find. Btw, is there any other way to fix this?

[kb426]

It is possible to polish a crank some and use a set of one under's. The crank is probably hard enough that the next step is to grind it undersize and use a 10 under bearing. What is the desired clearance you are looking for? I haven't run across a scat crank that wasn't on spec. I have found bearings mis-stamped or out of tolerance.

[phat46]

It is possible to polish a crank some and use a set of one under's. The crank is probably hard enough that the next step is to grind it undersize and use a 10 under bearing. What is the desired clearance you are looking for? I haven't run across a scat crank that wasn't on spec. I have found bearings mis-stamped or out of tolerance.

I'm looking for .002 -0024. I wondered if the rods could be honed.

[chimp koose]

.001" per 1" diameter is the minimum clearance required . There are shells available to fix a rod bore that is large or small last time i looked . There are also shells that are for an extra .001 clearance . I have heard of using different shell halves in the same rod to obtain the right clearance . I do a lot of measurement with telescoping gages and always set the gage and measure at least 2 times before accepting a measurement as correct. I find that my students will almost always get a smaller size when they measure compared to me . Beginners or those who dont use telescoping gages often enough tend to get too tight of a 'grip ' on the gage with the micrometer. I had also heard that the company that made plastigage is no longer making it any more . side clearance between the rods has no bearing on oil pressure or how much oil the crank throws off . Just make sure the chamferred side of the rod goes toward the fillet of the crank . this is all stuff i am sure you already know .

[kb426]

Resizing new rods would be my last choice. That is where I find most problems. A one under bearing would be my choice. I think when you get your measurements, you will be happy with the results.

[phat46]

.001" per 1" diameter is the minimum clearance required . There are shells available to fix a rod bore that is large or small last time i looked . There are also shells that are for an extra .001 clearance . I have heard of using different shell halves in the same rod to obtain the right clearance . I do a lot of measurement with telescoping gages and always set the gage and measure at least 2 times before accepting a measurement as correct. I find that my students will almost always get a smaller size when they measure compared to me . Beginners or those who dont use telescoping gages often enough tend to get too tight of a 'grip ' on the gage with the micrometer. I had also heard that the company that made plastigage is no longer making it any more . side clearance between the rods has no bearing on oil pressure or how much oil the crank throws off . Just make sure the chamferred side of the rod goes toward the fillet of the crank . this is all stuff i am sure you already know .

Yes stuff I know, but it's nice to get input from more experienced folks. Mains are set at .002-.0024. Rings gaps were perfect right out of the box!!! (Checked all rings in multiple holes)  Thrust bearing is .006. I see online that some guys feel that .0015 is o.k., depending on what oil your going to use. It does increase oil temps though. I've even seen some sites that claim .0007-.001 per inch is safe clearances. I would not be comfortable with it so it will get fixed if needed. My nephew uses his gauges daily, so I am confident in his ability with them, moreso than mine. He runs a mud truck with his blown e85 motor in it, that thing sounds nasty. I'll update later with what we find.

[phat46]

Update: we checked the journals and rods with a mic and bore gauge. All were between .0021-.0024. Sounds good to me, onward

[kb426]

[chimp koose]

My son in law and i are just starting a 6" rod 406 build for him. 11.3:1 with 187cc intake aluminum heads. They flow 240cfm@.500 lift . Same heads as my T motor.  The car has a 5 speed /3.73 gears. Goal is a reasonably streetable 500hp. 800 cfm carb or better,street dominator intake ,long tube headers ,6000rpm or slightly higher . Next thing is to pick the cam, we have 1.6 and 1.5 roller rockers and I have a 200hp nitrous plate system kicking around . We want to make 500hp on motor and throw nitrous at it after it is all sorted out on motor. This motor could end up in my 125" roadster chassis also with a powerglide and a trans brake. Alterior motive with this is to use up a lot of my drag race leftovers so I dont go and start a FED project . I have never actually finished the 12 step program to stop drag racing