Main Bearing Clearance; Am I too tight ???

Main Bearing Clearance; Am I too tight ??? - 11/30/09 05:02 AM

This 451 will be a 10.25:1 street strip motor with a goal of around 500hp, and will likely see between 6000 & 6500 RPM.

413 crank turned down to "B" std.; 400 Block w/ fresh mainline hone.; Cleavite P bearings, std.: ARP main studs.

I don't own a micrometer & bore guage. Plastiguage says I'm between .015 & .020, and is consistant at all journals. Am I too tight? Should I take the crank back to have the main journals polished a bit?

Posted By: Sue

Re: Main Bearing Clearance; Am I too tight ??? - 11/30/09 05:08 AM

if you mean .0015-.002 then yeah .0025-.0035 would be better

Posted By: dodgeboy11

Re: Main Bearing Clearance; Am I too tight ??? - 11/30/09 05:09 AM

I'd like to see .0025" on that one. You can run the tighter clearance but you NEED to make sure the oil is up to temp (200F) before you start beating on the motor.
Could always buy some plus clearance bearings to get the clearance you need. If they're available that is.

Posted By: Cab_Burge

Re: Main Bearing Clearance; Am I too tight ??? - 11/30/09 05:11 AM

I would run .003 and have ran .0038 with no problems on full groove sets. Are the "P" bearings full groove or 3/4 or 1/2 groove? You probally need to have some with a set of inside mikes and outside mikes or a dial bore gauge measure it for you

Don't take a chance on anything your not sure of,

it could kill you if it fails while racing

Posted By: StealthWedge67

Re: Main Bearing Clearance; Am I too tight ??? - 11/30/09 05:18 AM

Yes, I did mean .0015 & .002. And yes, P bearings are full groove.

I was also hoping to see .0025. You guys seem to be of the same opinion as I. Hmmm. I think I'll take the block & crank back to my machinist & have him measure it. If my plastiguage is accurate, can polishing get me to where I need to be?

Posted By: TS3303

Re: Main Bearing Clearance; Am I too tight ??? - 11/30/09 06:11 AM

take the rods and bearings also and have them checked.

Posted By: StealthWedge67

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 05:50 AM

I called the machinist today..... He was a bit insulted at even the thought that I would trust a piece of plastigage over his work. He said his "journal" on my motor showed .0023 - .0025 on the mains. "Bring it down here if you want, I'll mic it for ya.... maybe I'll charge ya, maybe I wont, depends on what sort of mood I'm in" was his comment.

I don't want to insult the guy, but I also want to be 100% positive that the motor I'm assembling is correct. Hope he doesn't get all pissy with me... Question is, if clearances are a bit under where they should be, what can be done about it?

Posted By: Triple Threat

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 06:06 AM

Who's the Machinist?

Posted By: TS3303

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 06:35 AM

if he doesn't respect your fears it's time for another machinist. Tell him you can only afford to do this once and you want to make sure it's right.

my machinist is a "confident" sob

, but neither of us are afraid to tell each other what we think. Then we go out to the track and have a good time. work is not personal it's professional.

Posted By: Moparteacher

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 06:49 AM

I wouldn't call foul from a measurement done with plastigage. I also wouldn't take any s#!t from my machinist, or anybody else I pay for services.

Posted By: R70RUNNER

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 06:59 AM

WOW... I double and even triple check work done. Think I'd be looking for a new machinist too.

Posted By: therocks

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 01:20 PM

My machinist is just the opposite.If I have any questions he will double and even triple check it.He spent like 2 hours just checking the keepers and springs on my new Stealth heads even though I wasnt going to use them.He just wanted to do it for his own knowledge.A good machinist is priceless.That and his prices are super reasonable.Some Ohio guys here know him and all say the same thing .He is one of the best.Rocky

Posted By: dvw

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 01:48 PM

Just because the crank measures corectly doesn't garauntee corrrect clearance. If the rod or crank bore is to tight the clearance can be incorrect. I've taken rods to my machinist on the last 2 builds that I did. Each motor had 1 rod to tight causing insuficient clearance. He resized both at no cost. The rods came machined, so he wasn't the person who did them originally.
Doug

Posted By: Mike Swann

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 02:00 PM

The present machinist's attitude is unaceptable and you should tell him that. At this time, I would find another competent machinist, tell him to check the work that was done and offer to pay him for the inspection. If it is that tight, there is a good chance it will eat a bearing.

Posted By: JohnRR

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 03:05 PM

Quote:

I called the machinist today..... He was a bit insulted at even the thought that I would trust a piece of plastigage over his work. He said his "journal" on my motor showed .0023 - .0025 on the mains. "Bring it down here if you want, I'll mic it for ya.... maybe I'll charge ya, maybe I wont, depends on what sort of mood I'm in" was his comment.

I don't want to insult the guy, but I also want to be 100% positive that the motor I'm assembling is correct. Hope he doesn't get all pissy with me... Question is, if clearances are a bit under where they should be, what can be done about it?

guess what , that's his problem , not yours . I have a block here that needs to go to the next overbore and a set of file fit rings that are useless because the guy that assembles the blocks at the shop I USED TO USE didn't check the bosses work ... hourglass bores .0025 OVERSIZE

...

I don't care who does the work ... CHECK IT ... if the guy gets insulted then that's his problem , even the best make mistakes ...

but he does have a point , checking his work with PLASTIGUAGE ...

Posted By: maximum entropy

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 04:20 PM

Quote:

I called the machinist today..... He was a bit insulted at even the thought that I would trust a piece of plastigage over his work. He said his "journal" on my motor showed .0023 - .0025 on the mains. "Bring it down here if you want, I'll mic it for ya.... maybe I'll charge ya, maybe I wont, depends on what sort of mood I'm in" was his comment.

I don't want to insult the guy, but I also want to be 100% positive that the motor I'm assembling is correct. Hope he doesn't get all pissy with me... Question is, if clearances are a bit under where they should be, what can be done about it?

i wouldn't be surprised if your machinist is right- plastigage ain't worth a damn anymore, imo. in fact, it's decline is responsible for me running out and getting myself a dial bore gauge. in the olden days, plastgage was different. now it just feels like a piece of wax or some such nonsense.

Posted By: B G Racing

Re: Main Bearing Clearance; Am I too tight ??? - 12/01/09 04:46 PM

Not to start a debate or offend anyone but plastic gage serves its purpose when used correctly.We mic every componant and record all our measurements.We are confident with measurements and clearences and at the conclusion of every build we still like to spot check the mains and rod bearings with plastic gage to insure that for a multitude of reasons that nothing changed.We find the gage readings to be very close to our mic readings.We do wipe all lube and make sure we check at the crown or apex of the bearing and journal.Sometimes it the process and person that causes the bad readings.

Posted By: StealthWedge67

Re: Main Bearing Clearance; Am I too tight ??? - 12/02/09 06:52 PM

Well, chalk one up for the machinist in this case. Just got back from the shop, we torqued up the mains & rods, and measured all the journals.... Clearances at mains were between .0021 & .0023. Rods were all at .0022 or .0023.

I'm new at this, and its important to note that prior to machining, I never gave him any specific clearance requests. He said with a performance motor, he shoots for the high side of the bearing manufacturers reccomendations, which is exactly where its all at.

I'm satisfied. And its also worth noting that he treated me very well when I showed up for the double-check process.

In the words of Emily Litella: Never Mind

Posted By: B G Racing

Re: Main Bearing Clearance; Am I too tight ??? - 12/02/09 07:08 PM

Quote:

Well, chalk one up for the machinist in this case. Just got back from the shop, we torqued up the mains & rods, and measured all the journals.... Clearances at mains were between .0021 & .0023. Rods were all at .0022 or .0023.

I'm new at this, and its important to note that prior to machining, I never gave him any specific clearance requests. He said with a performance motor, he shoots for the high side of the bearing manufacturers reccomendations, which is exactly where its all at.

I'm satisfied. And its also worth noting that he treated me very well when I showed up for the double-check process.

In the words of Emily Litella: Never Mind

Did he actually mic each or did he plastic gage them?

Posted By: TS3303

Re: Main Bearing Clearance; Am I too tight ??? - 12/02/09 09:32 PM

Did you thank him and offer to pay for his time? Sounds like the start of a good relationship.

Posted By: todd440

Re: Main Bearing Clearance; Am I too tight ??? - 12/02/09 09:38 PM

The bearing manufacturers usually use the rule .001 clearance per inch of journal diameter. So in your case, they would want .0026 on the mains, and .0023 on the rods.

Posted By: Cab_Burge

Re: Main Bearing Clearance; Am I too tight ??? - 12/02/09 10:07 PM

Loser is way better than a tiny bit(.0002) to tight, especaily on bearings and piston clearances

I like and use .0025+ on the rods and .003+ on the mains