Main Bearing Clearance

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yup. I'll bet you found the issue. A "thin film" is probably .002" by itself. So clean the surfaces (backs of bearings and block/cap saddles) and try again. Don't move the crank once you lay it in place. Lubricate the studs, nuts, and washers with the ARP lube, torque in steps.
 
Everything is prepped and ready to go when I left home yesterday,,,now I have to work 2 weeks untill I get another crack at it :-(

Thanks for everyones input, I will update with "Dry" results when I get the chance.

Cheers
 
Tryed again with bearings totally dry and the clearances are still crap. Best one was marginally better then .0015" and worst was still a .001", so I guess my crank is off for more polishing. I like the full grove style of clevite bearings I have so I don't really want to change those out.
I need my heads dropped off anyway to have them gone thru since I can't trust the clown who built them,,,refer to my "ripped off" thread in General Discussions for that story, STILL ripped off at this point.
 
Just ran into this exact issue. All my mains are coming out .001-.0015. Just going to order new bearings rather than trying to polish crank. These are .030 over so should I go .020 or just .010 ?
I have pictures of plastigauge if someone wants to diagnose for me.
 
Are you saying your crank is turned .030 now? If so .020 bearings will give you .021-.0215. That would be way to lose.You will have zero oil pressure!
 
Make sure the saddles of the block and caps are clean. The bearings may be not seated all the way.
 
SGBARRACUDA said:
Make sure the saddles of the block and caps are clean. The bearings may be not seated all the way.
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I like to torque all the mains to specs first and then remove one cap at a time to plastigage. That should seat all the bearing shells and keep you from getting false readings. Rods can be done one at a time. Remember to lightly tap on the bearing caps with a brass hammer to make sure they're seated properly before you do the final torquing.
 
I cleaned the saddles and caps with acetone before I put the bearings in, placed them in place, tapped with a dead blow, then torqued down to 85ft lbs in stages 20, 40, 65, 85. Middle first, then 2, 4, 1, 5 Should I do it differently? I did place the plastigauge on there before I torqued any of them down though.
 
bigrobsRT said:
I cleaned the saddles and caps with acetone before I put the bearings in, placed them in place, tapped with a dead blow, then torqued down to 85ft lbs in stages 20, 40, 65, 85. Middle first, then 2, 4, 1, 5 Should I do it differently? I did place the plastigauge on there before I torqued any of them down though.
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No that is good enough. You may just have to get the crank polished.
 
Reread that you are .030 under, looks like you just need a bit of a polish to give you the needed clearance.
 
Machine shop told me to order .030 undersize bearings for mains and rods. So I ordered that and I guess the clearance for it is off by .002" So crank is .002 oversized from .030 undersize spec is what I am understanding. I don't have my own measuring tools for this. All I have is my 6" harbor freight caliper. haha
 
Rod bearings had .001-.0015 clearance also. Going to call machine shop in morning. Thanks.
 
moper said:
Nope. If the crank is laying on the bearing on the bottom, and you torque the cap, the space left is the clearance.
So if your plasitgage says ".001" because that's how wide it squished and that's what you matched up, you have .001 total clearance, or .0005 per side, and yes that is too tight. You need an undersize bearing for one that is too tight. And oversize bearing for one that is too lose.

If you are measuring you measure the bearing bore top to bottom with the cap torqued, and then the crank journal, and subtract the crank measurement from the bore measurement.

Please answer the question on how you're measuring and was the crank was just turned or used?
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this is correct !---------
 
Rodzilla said:
This I agree with, but it would equal a .002" difference in the OD of the crank journal and the ID of the bearing. So is that how it works? Or do you need a difference of .004" to get a clearance of .002"?
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how do u figure that w/ the crank laying in the bearings w/ no oil, the block upside down on an engine stand ? the crank will have no clearance against the top bearing, which is actually down . w/ the cap torqued on, the clearance will be in the top, or cap, think about it ! if you take a coffee can laying on its side, and put a tennis ball in it, is there clearance on the bottom of the can or the top ??
 
fishy68 said:
Exactly! Oil can take up a lot more room than you think. Without oil you may have .002~.003" clearance. And I agree with ramcharger's earlier statement that with your build you should shoot for .0025" clearance. Even .003" is fine. I wouldn't go any tighter than .002" for sure. Even though you say your not going to race it your description of it being a stroker that will make up to 600 hp and turn 6800 rpm that's an area that requires looser than normal bearings. Not as loose as a race engine but definitely a lot looser than a grocery getter. Don't worry about torqueing it down with no oil on the bearings. Won't hurt anything.
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-------------------------------------don`t rotate the crank very much w/ dry bearings, and do it easily , makng sure their squecky clean if u do, better not to! Oil "will" take up some space if its in the upper bearing when plastigauging.
moper said:
yup. I'll bet you found the issue. A "thin film" is probably .002" by itself. So clean the surfaces (backs of bearings and block/cap saddles) and try again. Don't move the crank once you lay it in place. Lubricate the studs, nuts, and washers with the ARP lube, torque in steps.
Click to expand...
agree w/ this-----------------
 
I cringed when I read about using plastigauge,,,,,,,, and a motor with a stroker crank and high rpm. Please take the time to find a way to get it measured with a dial bore gauge and a good mike. An ounce of prevention here is worth a hundred pounds of cure here. If you plan on doing more motor assembly, invest in these items. Then you can know exactly what you have for clearances. The reason for more than factory clearance is two fold. A little less turning resistance, but more importantly, allowing for more flex and distortion at higher stress levels, like more stroke and more rpm. If you aren't familier with how much metal deforms when pushed on, pulled, or squeezed, get a rod bolt stretch gauge and measure it un torqued. Then tighten with your FINGER tips only and remeasure. You will see at least .0002 stretch! I did this on an ARP2000 7/16 bolt. Now think of what is going on inside your motor at 6800 rpm with a 4 inch stroke. A quality set of mikes and a good dial bore gauge are not cheap, but niether is your mileage hauling stuff around to get it rechecked or redone. On top of that you will also be able to double check machine work done. That is essential in protecting your investment. I found the clearances varied by .0005 on my race motor from one side of the bearings to the other. It turned out to be a line hone I requested on a race block must never have been done!! Now that motor is .0035 on all main bearings, + or- .0001, rather than .0034 on one side of a bearing and .0040+ on the other side!
 
gregsdart said:
I cringed when I read about using plastigauge,,,,,,,, and a motor with a stroker crank and high rpm. Please take the time to find a way to get it measured with a dial bore gauge and a good mike. An ounce of prevention here is worth a hundred pounds of cure here. If you plan on doing more motor assembly, invest in these items. Then you can know exactly what you have for clearances. The reason for more than factory clearance is two fold. A little less turning resistance, but more importantly, allowing for more flex and distortion at higher stress levels, like more stroke and more rpm. If you aren't familier with how much metal deforms when pushed on, pulled, or squeezed, get a rod bolt stretch gauge and measure it un torqued. Then tighten with your FINGER tips only and remeasure. You will see at least .0002 stretch! I did this on an ARP2000 7/16 bolt. Now think of what is going on inside your motor at 6800 rpm with a 4 inch stroke. A quality set of mikes and a good dial bore gauge are not cheap, but niether is your mileage hauling stuff around to get it rechecked or redone. On top of that you will also be able to double check machine work done. That is essential in protecting your investment. I found the clearances varied by .0005 on my race motor from one side of the bearings to the other. It turned out to be a line hone I requested on a race block must never have been done!! Now that motor is .0035 on all main bearings, + or- .0001, rather than .0034 on one side of a bearing and .0040+ on the other side!
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What's your oil pressure in July when you pickup your time slip?
 
Sorry I kind of butted in on this 5 year old thread with my new same issue. I dont know if the original poster still watches it or not. haha But I got this back from the machine shop. As far as they are concerned it is in spec. ( .0005" - .0026")
https://goo.gl/photos/DLqFoqyCN9GW6bK17
 
As Famous Bob says above, don't have any oil in the bearings when you use Plastigage; it'll throw off the readings (and may also make the P-gage flow a bit more than it should due to oil wanting to dissolve it). Use it dry like it is supposed to be done, and don't rotate the parts I also avoid tapping the caps when assembling with P-gage just in case the momentary distortion of the cap might hit the P-gage and crush it.

bigrobsRT, what are you going to use this engine for? I run .001-.0015-.002 on street engines all the time and never have issues. I polish journals up to .0025-.003 on my race engines (which are all 4 bangers BTW). So a lot of this has to do with use and engine particulars.
 
nm9stheham said:
As Famous Bob says above, don't have any oil in the bearings when you use Plastigage; it'll throw off the readings (and may also make the P-gage flow a bit more than it should due to oil wanting to dissolve it). Use it dry like it is supposed to be done, and don't rotate the parts I also avoid tapping the caps when assembling with P-gage just in case the momentary distortion of the cap might hit the P-gage and crush it.

bigrobsRT, what are you going to use this engine for? I run .001-.0015-.002 on street engines all the time and never have issues. I polish journals up to .0025-.003 on my race engines (which are all 4 bangers BTW). So a lot of this has to do with use and engine particulars.
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Thanks! The machine shop said .001 is fine for a driver/ cruiser motor. I think I will just go ahead and put this together. Its just going to be a street cruiser and occasional car cruise type car. A 273 is hardly a race engine! It wont be seeing any 6000rpm duty while I own it.
 
And if you are still worried, break-in the rings for a few hundred miles, and then switch over to Mobil1 or another full synthetic, and you'll never have to worry over it.

The protection of bearings with a good synthetics is unreal: I suffered an oil leak in a race (rally) and raced a turbo'd 2.6L Mitu for 2 minutes with 0 to 1/2 pressure and then the final 2 minutes at 3/4 throttle with ZERO oil pressure. (I was pissed; so it became 'finish or blow'! LOL) I pulled the motor apart afterwards and found NO scratches or wear on the bearings. No way that would have happened with straight petroleum oil; I woulda lost the whole crank trying that stunt of running with zero oil pressure! The assembled bearing clearances in that motor were around .002, and maybe .0025" on the mains. RPM's were 2500 to 6000 in racing conditions.
 
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