Main Bearing Measurements

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T56MaxTorq

T56MaxTorq

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Putting a different oem mag crank (10/10) in my turbo 318 with arp studs (never line bored for studs) and started taking some measurements. Plastigauge and a mic. Plastigauged all 5 by putting it in 4 places, 2 on the bottom and 2 on the cap, 90* apart, 45* off bearing half split line. All is well there, .001-.0015 on all. Grabbed my mic and read .003. The split line is .0055. I know the split line is eccentric but is this too much?? I don't have a fancy dial bore gauge so I used the regular type and found it difficult to use and set. So I set the mic to XYZ and locked the bore gauge on this measurement, basically using the bore gauge as a go-no go. Mic is excellent quality and recently callibrated. I've only measured #1 so far.

Wanting to cover all bases on this as I had a bad bearing on the old crank and this new one is not the original. Plus I added the studs. I plan on only street use, maybe a 1/4 mile or two. 15w40 or 20w50 synthetic oil. Basic oil pump with oil mods - smoothed out #5 cap and oil filter mount ports, opened up the pump intake and put in a bigger homemade pickup. Have a roller cam so no top end or cam oiling mods.

Will also check crank out of round, freedom of movement, and end play. Is there anything else I could be missing?
 
I think if you rechecked with plastigage only on the top of the crank you would see the .003 the measurements are telling you. Never heard of putting it on top and bottom and checking it. As far as studs and no line bore/hone and .003 clearance maybe some others will chime in. .003 is big for me, maybe some .011 shells.
 
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You don't put plastigauge on top and bottom. You check in one place, on the cap side 90* from the parting line. If you put it on the top and bottom your readings for both will be off. Installing studs without have it line honed isn't a good idea IMO because studs generally fit tight in the main caps and can move them slightly. For a hi-perf engine like your building I shoot for .0025~.003" on the mains so your in the ball park
 
fishy68 said:
You don't put plastigauge on top and bottom. You check in one place, on the cap side 90* from the parting line. If you put it on the top and bottom your readings for both will be off. Installing studs without have it line honed isn't a good idea IMO because studs generally fit tight in the main caps and can move them slightly. For a hi-perf engine like your building I shoot for .0025~.003" on the mains so your in the ball park
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I agree on the plastic gauge to use only one place at a time...

Would the studs make a difference, there is the machined channel that the main caps fit in which locates the cap, not the bolts/studs... If the studs aren't used to locate the cap, then it shouldn't need an align bore...
 
another thing to remember is that plasti gauge has a shelf life. If it's not fresh, it can get hard and give inaccurate readings. Don't get me wrong, I think it is very useful and normally quite accurate, just has to be "fresh".
 
fishy68 said:
Installing studs without have it line honed isn't a good idea IMO because studs generally fit tight in the main caps and can move them slightly.
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Are the mating of the caps and saddles at the parting line very smooth with the studs installed? If the caps move with the studs inside of them, you will be able to catch a fingernail on the parting line if the cap shifts off.

OP, I am assuming the studs used have a higher torque that the stock bolts. This higher torque can distort the cap/saddle area a bit. You are fully toquing the studs to spec right?

But my concern with the largish diameter across the parting line is that the main bearings are not seeing enough crush. They are very slightly tapered at the ends to account for the crush that should occur when the caps are torqued to the saddles. But, honestly, I have never made this measurement across the parting line to know what is normal when properly crushed. Which I guess is your question and concern...

Also does this 'over-diameter' reading stay consistent if you turn the bore gauge a few degrees off of the parting line?
 
I only used the plastigauge top and bottom to check for out-of-round and taper. I wanted to mainly look at the clearance throughout the entire bearing surface for concentricity. The plastigauge was bought the other day so I assume it's somewhat fresh. I wasn't too worried about the .001-.0015 on the plastigauge smear for top and bottom because if I have .0015 on bottom and .0015 on top, I have .003 total.
 
nm9stheham said:
Are the mating of the caps and saddles at the parting line very smooth with the studs installed? If the caps move with the studs inside of them, you will be able to catch a fingernail on the parting line if the cap shifts off.

OP, I am assuming the studs used have a higher torque that the stock bolts. This higher torque can distort the cap/saddle area a bit. You are fully toquing the studs to spec right?

But my concern with the largish diameter across the parting line is that the main bearings are not seeing enough crush. They are very slightly tapered at the ends to account for the crush that should occur when the caps are torqued to the saddles. But, honestly, I have never made this measurement across the parting line to know what is normal when properly crushed. Which I guess is your question and concern...

Also does this 'over-diameter' reading stay consistent if you turn the bore gauge a few degrees off of the parting line?
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The overdiameter is about 10 degrees off the the split line on each side. So 20 degrees total.
 
BTW here is one article showing range of installing bearing eccentricity; it mentions around .001" + or - for performance engines. So you are above that number, if you gauges are accurate.
Geometrical parameters of engine bearings [SubsTech]

Since, the forces on the crank will be pushing it down into the cap and so the added gap at the sides should only allow a bit more oil to be carried in the bearing area, I doubt that a short length of increased gap at each side will allow the oil to flow out badly. That is especially so with your thicker oil weights. AND, the synthetic will add even more protection.

BTW, now that I think of it, I HAVE run one bearing on one engine at about .001-.0015" larger gap on one side at the parting line. (Due to a small cap misalignment on just one side... it was weird, like someone had lifted it by the front cap and saddle and tweaked the cap sideways.) It has run fine so far. YMMV

Another question: If .005" IS too much, how will that be corrected? Sink the crank up into the block? Try different bearings? New crank that is .001" larger? From the measurements, the crank does seem like it is worn or was cut a bit undersize.

And maybe try to borrow a better bore gauge to make sure your numbers are right.
 
Measure the main bore and see where it's at. Also, you can buy a ball to go on your mic and you can accurately measure the amount of taper the bearing shell is. .003 doesn't sound outrageous if you are boosting over 10 pounds.
 
T56MaxTorq said:
The overdiameter is about 10 degrees off the the split line on each side. So 20 degrees total.
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Is the over-diameter above the parting line on one side, and below the parting line on the other side? If so, that sure sounds like a cap shifted a bit, like fishy68 suggests. If that is the case, you ought to be able to catch a fingernail on the parting line, while moving upwards on one side and downwards on the other side.
 
The split lines of the bearings are flush. No raised edges of any kind. I took a measurement above and below each split line and it's an even .0055 total clearance vs the .003 measuring 90* from splitline. And to answer a previous question, the caps are torqued to a final 110 ft lbs in 3 steps. The studs don't contact the walls of the caps, either.
 
Plastigage cannot read taper. It's not fine enough. Buy a dial bore gage and actually measure everything. You already used the plastigage wrong regardless of intentions. You didn't take advice to have the main bores at least checked and honed as needed (which they would have in all likelyhood). I think it's a big mistake in either having it checked by someone better qualified, or at least buying the tools to be able to properly assess the situation. Least that's my opinion.
 
Yeah you need a bore gauge, jegs has one for a buck. I'd think you would see tighter readings in the parting line.
What are you going to do if it's too o.o.r or big, sand the cap and swedge the saddles a tad? Lol you can do a lot of things and get by...but you gotta love building engines to be playing like that.
 
moper said:
Plastigage cannot read taper. It's not fine enough. Buy a dial bore gage and actually measure everything. You already used the plastigage wrong regardless of intentions. You didn't take advice to have the main bores at least checked and honed as needed (which they would have in all likelyhood). I think it's a big mistake in either having it checked by someone better qualified, or at least buying the tools to be able to properly assess the situation. Least that's my opinion.
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So, I may have not used the plastigauge as tradition would have, but that doesn't make it less effective. The math adds up. It squeezed out to a smear of .0015 on top and bottom. I confirmed it with the mic. Same exact readings. I bet if I go behind and put it just on the cap it would squeeze .003

Problem is, I've lost all my machinists. One passed away a couple years ago and the other shop is fully retired after 40 years. I've outsourced to others in the past but have received mediocre work at best. I can work a mic and a bore gauge, I've been rebuilding and maintaining 5000hp turboprops for the last 12 years, use them all the time to measure tolerances. Problem is my bore gauge uses a collet style lock and getting it to fully lock while being steady is tough. So I measure the crank, and then add .0005 at a time to my bore gauge then use it as a go-no-go gauge, then recheck against the mic. I know what the proper drag feels like. If I can measure my own bearings and crank, I save a trip to an unknown shop for a problem I probably don't even have.
 
T56MaxTorq said:
So, I may have not used the plastigauge as tradition would have, but that doesn't make it less effective. The math adds up. It squeezed out to a smear of .0015 on top and bottom. I confirmed it with the mic. Same exact readings. I bet if I go behind and put it just on the cap it would squeeze .003

Problem is, I've lost all my machinists. One passed away a couple years ago and the other shop is fully retired after 40 years. I've outsourced to others in the past but have received mediocre work at best. I can work a mic and a bore gauge, I've been rebuilding and maintaining 5000hp turboprops for the last 12 years, use them all the time to measure tolerances. Problem is my bore gauge uses a collet style lock and getting it to fully lock while being steady is tough. So I measure the crank, and then add .0005 at a time to my bore gauge then use it as a go-no-go gauge, then recheck against the mic. I know what the proper drag feels like. If I can measure my own bearings and crank, I save a trip to an unknown shop for a problem I probably don't even have.
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I feel your pain. I sent a crank out to be reground at a supposedly reputable shop(A&W) on Capitol Hill in Seattle. When I got it back they ground it more than std undersize. When I complained, they said I didn't know what I was talking about. I told them I was a journeyman machinist and I miked it with a Starrett micrometer with a calibration sticker less than two months old , and asked when theirs had been calibrated, they told me to get the he'll out or they were calling the police.
 
rustycowll69 said:
I feel your pain. I sent a crank out to be reground at a supposedly reputable shop(A&W) on Capitol Hill in Seattle. When I got it back they ground it more than std undersize. When I complained, they said I didn't know what I was talking about. I told them I was a journeyman machinist and I miked it with a Starrett micrometer with a calibration sticker less than two months old , and asked when theirs had been calibrated, they told me to get the he'll out or they were calling the police.
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I'm not surprised. Finding anyone to run manual machines is getting tougher every day.
 
That sucks, Rusty. I too have been scammed. It's a shitty feeling and there is likely nothing to be done except small claims court but proving it is almost impossible. Even just explaining something like this in laymans terms to a magistrate is difficult when it's one mans tools and words vs the others.

So this is where I'm at, I measure bearing clearance and get .003, I measure the sides near the splitline to see if the studs' higher torque have effected anything drastically. So the splitline clearance is .0055 over crank diameter. I just want to know if this is way to much/little. I know the bearings are designed to have this section have larger clearance. I'm pleased with the .003 I'm getting 90* off splitline. I followed this as a guide:

http://www.mahle-aftermarket.com/media/local-media-north-america/pdfs/cl77-1-205r.pdf

Nm9stheham also posted a good article that says .001 over in the splitline is too much. I'm .0025 over.

Im using Clevite bearings, specifically. Doesn't say how much extra clearance in the splitline area is acceptable, in their tech article. Everything slightly off the splitline is within limits. I wanted to make sure that the bearings are "crushed" properly. Am I just overthinking all this???

Maybe I should torque all caps without bearings, with the studs and then take some measurements all around, then compare to the oem bolts. Probably do the same with the bearings installed too. Overkill probably but how else would someone gain confidence in a new crank with new studs? Taking it to the shop is a slim option at the moment. Plus I'd like to find a defect, then confirm the defect is corrected by the shop before being taken for a ride.
 
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I usually don't get excited over parting line clearance as long as the hole is ROUND.
.003 is ok if you use a grade 50 oil. You can use a 40 in the winter.
 
as an aside, have you spun the crank and checked for runout? I went thru 3 360 reground crank kits from some jobber before I found one that wasn't bent too bad. Maybe you'll need that extra clearance to accommodate a bent crank, hahaha.
 
Have you miked the main bearing bores themselves for concentric? I got a line honed block(supposedly done!) Back that measured .0005 bigger on one side of the bores on three out of five. It showed itself when I measured the bearings, which led me to double check the line bore work.
 
I use the same telescoping gages that you have and yes, they are tricky to use well but I have used them enough to find that I can get to around .0005" accuracy with them. If I had a shop, I would not be using them, and I may buy an easy-to-use gage eventually, but I am not anymore doubting your measurements with the way you described using them. The only trick to using them the way you describe (go/no-go) is to make sure they are straight in line with the micrometer axis when you lock them to a set length.

I would do as you say with checking the bores in the block without bearings to see if they are round. Do it first with the original bolts torqued to 85 ft lbs with dry threads, and then again with the studs torqued to 110 ft lbs to see how much the extra torque is distorting the bores. That extra 25 fl lbs of torque does not sound like much, but sometimes iron castings move around in strange ways with torqued bolts. (Lemme tell you about the #4 bore in a 1.9L Opel block....) AND, if the studs are ARP's and you are torquing them with the lube on the threads, the actual clamping force is somewhere in the range of 50-75% greater than the stock bolts with dry or oiled threads.

Has this blocked been bored or honed in the mains before? If not, then I can't see the crush likely being bad, and those bearings have been reliably made for decades. (Do the boxes say "Made in China"? ACK!) If the holes themselves are round when torqued, then I'd go ahead and run it. And as far as that article, it is interesting but I am not sure it is the final word; I linked it as an example but it may be more for newer, production designs, and not a good indicator of what you can actually run and get away with. Measuring the split line bearing clearance is an oddity, and I just have to wonder how many people, including builders, have ever looked at it in depth.
 
The main bores have never been touched, nor have the cylinders! I run the oem pistons to 10lbs boost on E85. I haven't touched the crank and bearings since the other day, haven't found the time. But I will take all this advice and try to find something wrong with it before taking it in to a shop. This build is slow but I will keep this thread updated when there is news. I think if I can measure everything and have consistency across the board I'll be happy to set the crank to bed.
 
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Again - order the right tool, and measure it properly. I understand your situation. What I don't understand is your lack of motivation to do it the right way. It's simple: You have doubts about the setup, and about relying on anyone who might be able to fix it. So get the tool (doesn't have to be a top of the line deal - you're not using it every day and paying for your house with it, and it can be shipped to you). Torque it properly, and measure. Then you will know. .0005 does actually matter if one cares about "good" rather than "good enough".
Bearings are made with some eccentricity. It's not crush that makes them round. It's crush that transfers heat out from the oil to the block, and crush that helps hold them in place. It's the manufacturer that puts in the eccentricity. But you have to know, not guess, not estimate and average and stack numbers, actually KNOW what that amount is, so you can choose a bearing that provides what's needed.
 
Agree with Moper. A dial bore gauge isn't all that expensive. I think I paid about $85 for mine from Eastwoods. Summit has them for about the same price too. If your putting this much into building something running boosted you need to make sure the bottom end is correct or it won't last. JMHO
 
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