283 Too Much Main Bearing Clearance

[Thomas H.]

Assembling the 283 for my 58. Crank was cut 0.010 and measures spot on. Using a dial bore gauge (set using the micrometer setting from measuring the main journal) I measure anywhere from 0.0035 to 0.004 for the main bearing clearance. Upper limit is 0.0034 and nominal is closer to 0.0025. Called around (machine shop that did the crank and King bearings) to see if a 0.011" undersize main bearing is available with no luck. Is my next step to take the crank back and have it cut to fit a 0.020 undersize bearing? I could assemble the 0.020 bearings in the block, and take the measurements and let the machine shop cut the crank to fit?

Thoughts?

Thanks,

Tom

[Steven B.]

Re: 283 Too Much Main Bearing Clearance

Are the bearings tight when you torque the caps? If you can take the block in, you might be able to have them take a minimum cut off the caps, and align hone the main line to resize for the correct bearings. I believe that would be possible. Someone else may have a better idea.

Steve

[Joe L.]

Re: 283 Too Much Main Bearing Clearance

Assembling the 283 for my 58. Crank was cut 0.010 and measures spot on. Using a dial bore gauge (set using the micrometer setting from measuring the main journal) I measure anywhere from 0.0035 to 0.004 for the main bearing clearance. Upper limit is 0.0034 and nominal is closer to 0.0025. Called around (machine shop that did the crank and King bearings) to see if a 0.011" undersize main bearing is available with no luck. Is my next step to take the crank back and have it cut to fit a 0.020 undersize bearing? I could assemble the 0.020 bearings in the block, and take the measurements and let the machine shop cut the crank to fit?



Thoughts?

Thanks,

Tom

Tom------

What size were the bearings you removed from the engine before your rebuild? The sizes should be stamped on the rear of the bearings.

[Thomas H.]

Re: 283 Too Much Main Bearing Clearance

Tom------

What size were the bearings you removed from the engine before your rebuild? The sizes should be stamped on the rear of the bearings.

Hi Joe,

Block and crank were obtained at different times. This is the first time they have been assembled together.

Tom

[Thomas H.]

Re: 283 Too Much Main Bearing Clearance

Are the bearings tight when you torque the caps? If you can take the block in, you might be able to have them take a minimum cut off the caps, and align hone the main line to resize for the correct bearings. I believe that would be possible. Someone else may have a better idea.

Steve

Steve,

I spoke to the machine shop earlier today and that was suggested. Told them I'd exhaust trying to find some 0.011" bearings first. Can't find them for a 283 so I may have to go this route. Not a problem getting the block there.

Tom

[Steve G.]

Re: 283 Too Much Main Bearing Clearance

Are you absolutely certain those main caps are original to the block? When bolted in place with the bearings out does the parting line "disappear"?

Not that it really matters now. If your crank is correct the problem is in the block and the way to correct the block is a line bore. You don't machine the crank to fit a faulty block.

Steve

[Joe L.]

Re: 283 Too Much Main Bearing Clearance

Steve,

I spoke to the machine shop earlier today and that was suggested. Told them I'd exhaust trying to find some 0.011" bearings first. Can't find them for a 283 so I may have to go this route. Not a problem getting the block there.

Tom

Tom------

I don't know of any bearing manufacturer that ever made 0.011" undersize bearings.

Also, I agree with Steve and I think the problem is with the block or caps. If you have a crank that is a perfect 0.010" undersize and you use 0.010" undersize bearings, that should get you within the specified clearance range assuming the block and caps are right.

[Steven B.]

Re: 283 Too Much Main Bearing Clearance

I would urge a line hone as opposed to a bore. The cuts to the main caps should be at a minimum so it doesn't tend to move the crank toward the camshaft too much. You should be able to get away with using a stock timing chain (or a stock replacement) and not have any slop.

Steve

[Steve G.]

Re: 283 Too Much Main Bearing Clearance

I would urge a line hone as opposed to a bore. The cuts to the main caps should be at a minimum so it doesn't tend to move the crank toward the camshaft too much. You should be able to get away with using a stock timing chain (or a stock replacement) and not have any slop.

Steve

I'm not a machinist, but my understanding of the process is that you remove the smallest amount of material possible to correct the problem. If that amount is determined to be small enough to do with a hone, that's what you do. If the amount of correction needed is too large for a hone to handle it gets done first with a boring bar then finished with the hone.

Typically when the caps have been replaced or when going to 4 bolt mains they are bored first. If you first bolt the caps in the block and see a large mismatch at the parting line there's a good chance the caps have been changed and that a hone is not going to be the tool to clean it up.

With as much out as his measurements are I'm betting the caps were replaced.

Steve

[Steven B.]

Re: 283 Too Much Main Bearing Clearance

In the original post, it was indicated that it was only out about 1 1/2 thousandths. Boring may be a little aggressive in this case. If it can be cleaned up by honing, I would try that first and save boring for when the mainline needs to be squared up. In any event, his machinist will/should know.

Steve

[Thomas H.]

Re: 283 Too Much Main Bearing Clearance

In the original post, it was indicated that it was only out about 1 1/2 thousandths. Boring may be a little aggressive in this case. If it can be cleaned up by honing, I would try that first and save boring for when the mainline needs to be squared up. In any event, his machinist will/should know.

Steve

I didn't get a chance to work on it last night. Tonight I'll check the parting line.

It could be the caps are not the ones that came on the engine. I'll be in touch with the machine shop today to discuss a direction to go. I'm not a big fan of align boring and I agree that a a bit off the caps followed by a hone should get me back in the ball park.

Thanks for the input. I'll update with the outcome.

Tom

[Steve G.]

Re: 283 Too Much Main Bearing Clearance

I didn't get a chance to work on it last night. Tonight I'll check the parting line.

It could be the caps are not the ones that came on the engine. I'll be in touch with the machine shop today to discuss a direction to go. I'm not a big fan of align boring and I agree that a a bit off the caps followed by a hone should get me back in the ball park.

Thanks for the input. I'll update with the outcome.

Tom

The machinist will of course provide you with direction, but for the sake of discussion, one and a half thou is a lot.

The typical scenario is a block that has come out of service with it's original caps intact. Line honing might be performed to clean up the original machining tolerances and bring them to nominal for a more precise build as well as address any casting shift. Unless a brg has spun in the block this is under half a thou. More importantly, vertical and horizontal centre lines of the block and caps are the same.

One and a half thou off on the circumference is extremely unlikely to be orig machining tolerance and casting shift. It strongly suggests that the caps are not the originals to the block. They just don't grow a thou and a half in service.

When you are dealing with the issue of caps that were machined on a different block than they are now being used on there are two dimensions you have to be concerned with, horizontal and vertical centre lines. The top to bottom diameter does not tell the whole story. If the parting joint of the cap and block sees the cap inside the block bore on one side and outside the bore on the other side, the vertical centre lines of the block and cap are not the same. That means enough has to be cut from the cap mating surface to get both sides of the cap inside the block bore before the bore can be made round again. This moves the one that was already inside the bore in even further. This is what usually warrants a boring bar rather than a honing stone when caps are being replaced.

If boring is required and it moves the crank closer to the cam to where the chain is not tight there are short chains available to deal with this exact issue.

I learned this first hand 40 some years ago when I put together my first engine. Bought a 350 4 bolt main block, then a crank, then rods... Took the block to the machine shop and discovered all about blocks with wrong caps.

Steve

[Domenic T.]

Re: 283 Too Much Main Bearing Clearance

Tom,
I would back up your measurements with plastigauge. Also what I did once was put some shim stock that is about the same as tin foil under the bearing. I have the roll yet in my shop. The edges of the bearing will then be higher and a hand surface stone will trim the bearing in about 2 passes by hand. I then plastigauge it again. A good follow up was spray dye on the bearing to see the contact points. This was done by old timers and I has the roll of tin foil shim stock since I was a kid. We also used to Trim the soft contact babbit if the contact was centered to much on the bearing.
I remember looking at SB clearances in the book and there were main bearing clearances that were close to .005 which blew me away. Think it was a chevy truck block that had the excessive clearance.
I will get called BUBA for this as not to many ever fitted a bearing or know about the VERY THIN foil that was put behind the bearings. When we raced we polished the crank and that took a bit off and after a few tear downs the bearings needed the shim.
You can read the marks on yout main caps as they do on forensics to see see if the projectile was fired from the same gun. A bright lite and you can see if the machine marks match from the block to the cap.

Dom

[Duke W.]

Re: 283 Too Much Main Bearing Clearance

Flint precision align bored the main bearing bores with the main bearing caps torqued to spec. If a cap needs to be replaced in the field, align boring is pretty much a requirement.

Duke

[Mark E.]

Re: 283 Too Much Main Bearing Clearance

Tom,
Also what I did once was put some shim stock that is about the same as tin foil under the bearing. Dom

What about the oil passages?