i just tore dowm a 468 that i used to bracket race with. i had bought it from a freind who builds race engines. im going to be taming this engine dowm a bit for the street. lately i have been taking engine building very seriously hitting the books like crazy as i want to start building engines out of my garage. but anyway i have been practicing using my dial bore gauge. my crank has been turned down .020 which now measures 2.728. i checked the main bearing clearance and it came out to .004 thats more than normal. i know the ideal clearance should be around .0025 to .0028. know wonder my oil pressure was low than normal. i triple checked this. and all 5 times came out to .004 the main bearings are a federal mogul brand. the number on it is 3191cp_cpa u-020 2-99 would anybody happen to have the specs on these bearings. im trying to figure what i need to come up with a .0025 bearing clearance. anyhelp would be greatly appreciated. thanks

Rip,
How are you measuring the clearance ? Plastigage is not all that accurate .. I use a micrometer to measure the crank and then set a bore gauge with the mike. Personally, I doubt that the extra .001 was hurting your oil pressure that much. The only way you can get the clearance exactly where you want it is to follow these steps:
1. Have the block align honed. Preferably at the small end of the specs for maximum bearing crush.
2. Decide what size the crankshaft will have to be reground to (.010,.020, .030 etc.) in this case it would have to go to .030
3. Get a set of bearings for that size.
4. Install those bearings in your block and torque everything properly.
5. Take a dial bore gauge and put it in the main bearings and set it to "0"
6. Take your crankshaft to the crank grinder along with the preset bore gauge, and have him use his micrometers to measure the gauge and then add however much clearance you want (in this case .0025")
7. Listen to most crank grinders "snitch" and moan about having to do it right. :rolleyes:
8. Then he can grind the crank to the exact size you need to get the clearance you want.

This is the ONLY way to get it exactly where you want it.
In your present case, unless you want to regrind the crank, you are pretty much set with the clearance you have. You could check the align hone to see if it is way big .. if so having it redone might help some. If the crank was standard .. you could get some .001" undersize bearings. You could also purchase a bunch of sets of main bearings and measure each one with a bearing micrometer and hope you can find a set that was made a bit thicker than the rest, but QC now days pretty much keeps them all the same.
I am sure this is not what you wanted to hear, but it is the only way I know to do it.

So ... you want to be an engine builder :D

You have a small problem :(
I know of no one that makes .001 series bearings for anything but standard & 010 sizes unless possibly King but I don't use them so someone else will have to chime in on those.

==========EDIT================
I just looked & Fed Mog makes a performance bearing in .021. The set is the 141M .021

==========================================

About the only way I know of is to close up the main bores assuming they are on the high side & add coated bearings.
I have run the main bores at a half thou under spec without any problem but I probably would not go any more as it can distort the bearing from too much crush.

Another member on the board ordered coated bearings to close his clearance by a half thou but you are needing a bit more that that.
If you can pull a thou out line honing you will be fine. .003 is looser than I prefer but will work ok.
.004 is something I would try to close up as much as you can.

How exactly are you measuring? I don't care what the mikes say as long as you are using them as a setting standard for your bore gauge.
Set the bore gauge to zero with the mikes after measuring the crank & use this.
If you lock the mikes, do it while it is still on the crank not after you remove them.
I normally do not lock the mikes, just be sure they do not move.

hi bill, thanks for the responce. i measuring the bearing clearance the same way you do. i mike the
main journals then i place my dial bore gauge inside the mike using it as a standard then i zero the gauge. the crank is in great shape. i was thinking that these were a set of custom bearins that have a +.002 to come up with .004 clearance.

thanks for the info guys. im also going to try to get the specs on these particular bearings. im also going to find out what the stock housing bore measurement is so i can find out how much they took off. thanks

Originally posted by RIPPERS 67:
thanks for the info guys. im also going to try to get the specs on these particular bearings. im also going to find out what the stock housing bore measurement is so i can find out how much they took off. thanks =
2.9370-2.9380 ;)

well i just went to go measure my housing bore at 2.9370 with my dial bore gauge and it came out too
2.9355 which is .0015 . i ran out of time or else i would have triple checked this measurement. im aslo going to buy a new set of .020 umdersize bearings and see were that lands me aslo. i have made some phonecalls today but nobody can give me any information om these bearings. i will let you guys know tomorrow what my measurements are. thanks

Rip,
If you want, give me a call on Monday ... I have the FM catalog and it should give the specs. 301-843-5700

Doesn't a dial bore gauge have three points of contact?? And aren't they very expensive??

well i think i know what the problem is. im thinking who ever aligned this block took too much material off. i measured the housing bore with my preset micrometer at 2.9370 set my dial bore gauge and came up with 2.9355 which is .0015. now couldnt the machinist just take off .0005? i would have had .002 clearance if he did. but if the the housing bores didnt need any align honing than i would have had my clearance at .0025 does this make sense.

Rip,
If anything, yoou should have less clearance by the measurements you are getting. If the main bore is 2.9355, that is .0015 smaller than normal, which would make the clearance LESS. If you make it the correct 2.937, you will open up the bearing even more and you will have more clearance.
You may want to check the calibration of your micrometer too, thats a fair amount off on the main bores.

your right bill. i was thinking the + plus side was - and the - side the + side graemlins/clonk.gif . im going to remeasure everything and recheck my mics with my standard i will get back to you on this. thanks help