Your prefered minimum bearing clearances?

I figure I don't want to go tighter than .00275 at an absolute minimum on 2.750 mains, .0025 0n 2.375 rods, and I am nervous about being that tight. I only figure I could get away with it due to running my motor so warm. What hp level and rpm would also be a factor, in my case 880 hp at 7500 max rpm.
I don't think I am going to push it that tight on the mains, maybe .003 if the three sets of bearings I have will get me there. Rods, I won't go below .003 . What are your safe minimums?

Im in the same boat as greg and ill be starting the assembly process of my low deck within the next month and would like to know this info as well, Class is in session
This will be the first stroker motor ive assembled im not looking to turn more then 7000rpms but the mill will see some boost and I'll be running e85.
Thanks all

I like to run .003/.003 on my SB junk.. I do turn up
the rpm... so that .003 is my min... .0035 is my normal
max unless its a alum rod engine..I am talking race only

People get stressed over large clearances, or what they perceive as large, but I have never seen them be a problem. Tight on the other hand, gets a you a pan full of shrapnel. 003 on mains and rods is generally my minimum, even on a driver motor. Alum rodded motors...........I don't know how many have ever heated one up and THEN checked it, but an alum rod that has .003 cold, can be .005 or better at 150* and they never present a problem. Less than .003 is just too tight for my tastes.

It was mentioned about "getting away with it" because you run your engine warm. Well it isn't warm when you FIRST fire it and THAT is when 90% of bearing damage is done on a tight motor. NOT at normal temp and high rpm. You hurt it cold and THEN spit it out

I am in the .003 minimum crowd as well.

I am probably wrong, but I thought from the factory, back in 68, motors came with .0025 clearance didn't they?

Not sure why that would be relevant to this discussion

I've ran a bunch of steel rod street and strip 7000 RPM motors with .004+ on the mains and .0035+ on the rods, no problems other than having 20 lbs oil pressure at 650 RPM idling in gear with 5W20WT oil at 180 +F oil temps, 30 lbs at 1200 RPM

I agree.

there is a old saying, "if you have too much clearance only you will know, if you have too little everyone will know".


Joe

.0025" rods / .0030" crank / .0035 camshaft.

New bearings on the way, and since I have to buy one set, I may as well get em right and spring for the +.001 second set if I need to. Shooting for .0035 mains and .003 rods, where I always have been in the past. Thanks, all.

Sorry I did not ask your permission before I asked my question, but It IS relevant Monte. Because if the factory could get away with .0025 clearance on a factory hemi, that had to be warrantied if it broke, then would it not be safe to assume .0025 was a safe clearance today with the better oil and metal we have available now?
By the way have you ever destroyed the bearings in a motor you built that had clearances tighter than .003. Not trying to start an argument, just asking.
Hope you have a blessed day

No that wouldn't be safe to assume....... That was a street car, that was to be driven on the streets. Not make pass after high rpm pass on a race track. Racers "blueprinted" factory engines, which almost always included MORE bearing clearance than a street engine, as well as a multitude of other "improvements". If they were perfect from the factory, that would mean all one needed to do was drop it in a car with proper gearing etc and go set stock class records. THAT didn't happen.

As to your other question, answer is NO, because I don't build anything tighter than .003 and never have. But we have recently seen several posts about destroyed engines on this forum, with engines that were what I myself consider "tight". Many have the same response as you, "well the factory....". Personally, I don't care what they did at the factory, because everything we do to a performance engine is to make it BETTER than factory. Also, speaking of factory, talk to some techs that actually worked at dealerships in the 60s and 70s. Spun bearings were very common in Hemi and Six Pack motors that were thrashed hard on the weekends.

You want to set YOUR engines up to factory specs, or tight, or whatever you want, that's fine.........but the OP asked for opinions on a race motor clearance and that's what he got. Same as you, he can form his own conclusions.

Someone already repeated the tired old adage......."build it loose, nobody knows, built it tight, everybody knows". That rings VERY true

so is it the same for a street strip motor that's gonna see alot of street miles?
.003-.0035 mains and rods there too?

Basically.. yes... my currant 416 which is street/strip
but maybe a bit more strip minded.. I built it .003/.003
with a HV oil pump.. its a 7200 rpm engine

My junk is roughly .025-.028 on the rods and .032-.035 on the mains.............

I am guessing you run 2.200 rod bearings?

I've had the priviledge to take apart several factory OEM 426 street Hemi, one 1968 and sevaral 1966 and one 1970, none of them had .0025 main bearing clearances, same on the rods.(more like .0038+ on the mains and .0030+ on the rods) That was using a inside mike for the bearing I.D. and then measuring the inside mike with the same outside mike used to measure the rod and main journals. Keep in mind these motor had been driven for some miles, one had over 42,000 miles on it, not sure about the true mileage on the others BTW, I have seen 318 motors that had less than .0030 on the mains, I had to scotchbrite the mains to make the cranks rotate on them due to slightly bent cranks on both

I was reading something the other day that said nascar engines run as little as .001 on bearings and those engines spin 9000+ for hours at a time. Also, used to know an old guy that built many circle track engines. He once told me he sets all bearing clearace to .002, when the overlayment wears off there at .0025. Interesting stuff.

Yes sir..........

You are correct. They also have 1.88 rod journals, as well as mains under 2.0. They have some of the most precisely machined and engineered parts in the world, run oil about the weight of water, with LOTS of friction modifiers in it and also run at a more or less steady rpm for 500 miles or so. When the motors come down after a 500 mile race, the bearings, rods and usually the crank are junk from the intense heat. Tight clearance also equals HIGH heat in both the oil and the bearing. The cranks are machined perfectly and micropolished to a 2 or less microinchess RA. And even though the motors don't make huge power, they run very expensive, high quality steel rods. Why?......because rods deform at both TDC and BDC elongating the hole an changing bearing clearance. Cheap rods deform MORE. Cheap heavy cranks also deform. So comparing a CUP motor to your run of the mill performance motor, is about like comparing a Pro-Stock motor to the one in your minivan. Guys who try and apply cutting edge racing technology to their motor with run of the mill, Chinese made parts are ASKING for trouble. Makes no difference if it checks perfect in the shop. It will NOT be when it's running. THIS is the part guys don't get. .....So, can you run a motor tight and it live? yes sir, but you better have some damn good parts and that list doesn't include $1500 rotating assemblys

Mine just freshened. 2.2 rods@.0028, mains .0039 both+/- .0001. Has 55psi hot idle, 80psi at speed with 5w30. Lifter bores are up towards .0025 as well. Single line Indy pump. More than enough oil pressure. I will trim the relief spring and bring it down.
Doug

I run tighter clearance used nascar stuff. The cup engines I have show no heat in the bearings. Restrictor plate engines run the 2.000" main journals, I don't.

I got talked into tighter clearances years ago. But, I run top quality American cranks and rods.

NASCAR engines never start cold. Racers shouldn't either. But, I'm lazy when it comes to that. Treat it like Herb McCanders suggested with aluminum rods. Crank it fast idle until tge temp gsuge moves then shut it down.

My 2.00" Dyers rods are .0018". 2.500" mains in aluminum block with steel caps are .003". It gets bigger when hot. I want to find coated bearings with a .001" tight top half. The dry sumps are set up for tight clearance as they pressure oil everything in these engines. I have sped the pump up and the idle pressure will just keep the idiot light out.

Previous builder ran tighter coated mains. They had no trouble running outlaw late model with 50 weight oil and always preheated and primed the pump. I run 10w30 only preheat in freezing temps. Prime only after oil changes or repairs.

The only bearing hurt in 20 years was on my W8 na combo. It ran a real tight main. Took 4 years of racing to do it. But, index racing not shutting engine down for hard braking and starving the sump ignoring the idiot light eat this one up. Big clearance molasses combo would have survived.