Oil Clearance Question



Oil Clearance Question

Postby bytor » May 12th, 2012, 6:38 am

I got started on my 383 pre assembly recently. One of the first measurement tasks was the crank main oil clearance. I measured the crank journals with a mic and then zeroed my bore gauge to that diameter and then measured the oil clearance. Being inexperienced on the ways of the mic and bore gauge, I spent a good amount of time getting good consistent measurements with both. I then made Plastigage measurements to cross reference. I wanted to share my results and get some feedback because the clearances look a bit on the big side, especially the #5. Should I consider reducing these clearances?

My setup:
4 bolt main block
SCAT 350-3750-6000 crank
King Bearings MB557SI

Image
Ive generally found the H-series bearings are the best choice
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Re: Oil Clearance Question

Postby grumpyvette » May 12th, 2012, 7:33 am

if those are the true bearing clearance measurements they are very close to ideal, and in fact a smidgen on the tighter end of the tolerance, ID be very pleased if those were my main engine bearing clearances

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Re: Oil Clearance Question

Postby bytor » May 12th, 2012, 10:41 am

grumpyvette wrote: ID be very pleased if those were my main engine bearing clearances

viewtopic.php?f=50&t=1222


Thanks for the conformation Grumpy. The clearance difference on the #5 stood out but I suppose a little extra oil flow on the rear main for the thrust bearing is not a bad thing.
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Re: Oil Clearance Question

Postby grumpyvette » May 12th, 2012, 11:27 am

rear mains DO generally have slightly larger clearances ON purpose, you look fine.
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http://kingbearings.com/files/Engine_Be ... erials.pdf

Influence of Grooved Main Bearings on Performance
http://www.enginebuildermag.com/Article ... mance.aspx

http://www.stealth316.com/misc/clevite- ... ooving.pdf

Manufacturers are frequently asked what difference grooving makes. Various forms of main bearing grooving have been used over the years.


It’s essential to understand that bearings depend on a film of oil to keep them separated from the shaft surface. This oil film is developed by shaft rotation. As the shaft rotates it pulls oil into the loaded area of the bearing and rides up on this film much like a tire hydroplaning on wet pavement.

Grooving in a bearing acts like tread in a tire to break up the oil film. While you want your tires to grip the road, you don’t want your bearings to grip the shaft, so grooving is bad for maintaining an oil film. The primary reason for having any grooving in a main bearing is to provide oil to the connecting rods. Without rod bearings to feed, a simple oil hole would be sufficient to lubricate a main bearing.

Many early engines used full grooved bearings and some even used multiple grooves. Those choices were based on what engineers knew at the time. As engine and bearing technology developed, the negative effect of grooving was recognized and bearing grooving was removed from modern lower main bearings. The result is in a thicker film of oil for the shaft to ride on.

This provides a greater safety margin and improved bearing life. Upper main shells, which see lower loads than the lowers, and hence don’t apply the same load to the oil film, have retained a groove to supply the connecting rods with oil.

In an effort to develop the best possible main bearing designs for high performance engines, manufacturers have investigated the effects of main bearing grooving on bearing performance. The graphs (Figure 1) illustrate that a simple 180° groove in the upper main shell is still the best overall design.

While a slightly shorter groove of 140° provides a marginal gain, most of the benefit is to the upper shell, which doesn’t need improvement. On the other hand, extending the groove into the lower half, even as little as 20° at each parting line (220° in total), takes away from upper bearing performance without providing any benefit to the lower half. It’s also interesting to note that as groove length increases so does horsepower loss and peak oil film pressure, which is transmitted directly to the bearing.

Notes: You will still find some full-grooved main sets offered for older engines where demand is low and the engineering cost to bring the sets to current standards is not warranted (bearings generally represent the technology of the time the engine was developed).
Image
Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Oil Clearance Question

Postby bytor » May 13th, 2012, 9:05 pm

Are the marks on the bearings left behind by the bore gauge something to be concerned about of purely cosmetic?
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Re: Oil Clearance Question

Postby grumpyvette » May 14th, 2012, 10:30 am

they look rather more COSMETIC in nature in the picture,you posted, than anything ID be concerned with having any detrimental effect on engine function, I doubt youll have any serious issues but Id also suggest a good layer of assembly lube be used during the engine assembly
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Oil Clearance Question

Postby bytor » May 15th, 2012, 7:13 am

It seems my bore gauge has a lot of pressure on the anvil measurements points I found that if you remove the intermediate spring in the bore gauge handle and alignment mechanism spring 'the thing with the wheels to center it'. This all but eliminates the marks on the soft bearing material while measuring. The spring in the dial gauge seems to provide enough pressure to get accurate readings along with better a 'feel' while measuring. I got the idea from this link and found the comment about the non professional bore guages having very small anvil points compared to Sunnen interesting.
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