Max. bearing clearance

[Dusterguy]

i have started rebuild 360 -75 engine. What is maximum crankshaft bearing clearance that is acceptable? I Have stock crankshaft and it is worn.

I have allready new STD bearings so i think if i could use them. Engine is +300hp. Use is street cruising, no racing.

 

[ramcharger]

On the street, you should have no more .0015" clearance, racing is .003" but that's with a HV oil pump. Crank condition is just as important as clearance. I would have have the crank cut undersize and install the appropriate oversize bearings.

 

[Dusterguy]

Clearange is now far more than .0015. Because crankshaft is worn. I have not measured it yet. What if clearange is .0040 or so ? I think that is about that much. Will it work at all?

Im planning to go whit this engine max 2 drive seasons. so engine doesnt have to last lifetime..

 

[daredevil]

Will work with a high volume pump to control the bleeding. Probably have a lot of pressure drop on a hot engine though.The following is stolen off the net.Excessive bearing clearances (more than about .001 inch per inch of diameter of the crankshaft journal) can allow a drop in oil pressure that can adversely effect lubrication elsewhere in the engine such as the camshaft and upper valvetrain. Excessive clearances also increase engine noise and pounding, which over time can lead to bearing fatigue and failure. Fatigued bearings will typically be full of microscopic cracks and have flaking material on the surface.

The amount of clearance between the bearings and crank journals will obviously vary depending on the application and the preferences of engine rebuilder. Some want closer tolerances to maximize oil pressure while others want looser tolerances to allow for machining variances and contaminants that often end up in the crankcase.

One large production engine rebuilder says they try to build all their passenger car and light truck engines with about .001 to .002 inch clearance in the main and rod bearings. This compares to as much as .004 inch of clearance that may have been present in the OEM engine. But on some engines, such as the General Motors 173, more than .0015 inch of clearance can result in noise problems.If oem was .004 you should be ok. I would worry more about finish and concentricity. Mike the journals and if they arent round turn it.

 

[oliver]

stock rod bearing clearance was between .0020 and .0035, just pulled a 360 out of a truck that was wrecked with 300 miles on it, clearances were at .0028.

 

[dodge freak]

too tight isn't any good. Bearings grab and spin. IMO, .0015 is too tight on mains and borderline on rods.

Engine will last longer with .004 clearance vs .001. .0025 is a good clearance, yeah too much and too much oil gets thrown on the cylinder walls but better than scuffing the bearings cause its too tight.

Run 30 weight oil or 20w-50 with .004 clearance, not 5w-30

 

[1wild&crazyguy]

if you plan on reving it on the street, .002-.0025 is what i recommend.

I would never want less than .0015 even on the street

 

[Dusterguy]

Thanks all for reply!

My oil pressure was 13psi@1000rpm hot , 36psi@2000rpm hot, 72psi when cold idling.. All this whit this worn crankshaft AND bearings that was worn so much they showing copper surface. So if i put new bearings oil pressure will raise little bit.

I have hi volume oilpump and i used 20w50 mineral oil (is that right word?)

Overall if i polish crankshaft and put new bearings it could be OK ?

 

[dodge freak]

Well if the crankshaft is out of the engine and your buying new bearings, why not get the crank turned and not just polished ? that is why they sell .010 and .020 undersize bearings.

 

[1wild&crazyguy]

Thanks all for reply!

My oil pressure was 13psi@1000rpm hot , 36psi@2000rpm hot, 72psi when cold idling.. All this whit this worn crankshaft AND bearings that was worn so much they showing copper surface. So if i put new bearings oil pressure will raise little bit.

I have hi volume oilpump and i used 20w50 mineral oil (is that right word?)

Overall if i polish crankshaft and put new bearings it could be OK ?

The idle oil psi when hot will go up probably 15 psi with proper clearance, good bearings, fresh journal

 

[Dusterguy]

Well if the crankshaft is out of the engine and your buying new bearings, why not get the crank turned and not just polished ? that is why they sell .010 and .020 undersize bearings.

I have already STD bearings. What you mean turned? I dont understant that word. Do you mean "cut" it to undersize? Well it cost so much here that i dont wanna do that. (but if i have to do it, i have to do it)

Polishing i mean that i "polish" crank journals, firstly 400 paper then 800 paper.

 

[dodge freak]

I have already STD bearings. What you mean turned? I dont understant that word. Do you mean "cut" it to undersize? Well it cost so much here that i dont wanna do that. (but if i have to do it, i have to do it)

Polishing i mean that i "polish" crank journals, firstly 400 paper then 800 paper.

yeah, cut-turn, well if you got new std bearings then go for it--do it your way. Just take care in the polishing, in fact I might just skip that part. All its going to do is take more metal off the crank, well maybe it clean some of the old bearing grit off the crank--but don't over do the polishing

 

[1wild&crazyguy]

and do it evenly...

I did a 400 grit polish on a 225 crank, lasted many wot blasts & 6 yrs till I sold the car.