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Author
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Topic: Bearing clearance questions
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BLstangin
Gearhead Posts: 779
From: St. James, MN
Registered: Apr 2002
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posted 03-06-2004 04:42 PM
   
O.k., I got the 306 apart to open up the top ring gap, and evertything looks o.k. The bearings look good, but I plastigauged the back main with the red plastigauge and came up with .004 clearance. That one was .001 looser than the rest when we put it together the first time. I have 20 pounds of oil pressure at and idle and 50 at 6,500 with 10w30 in it, and when I switched to 20w50, then I have 40 at idle and 70 at 6,500. I haven't checked the rods yet, but when I put it together the first time the mains were at .003 and the rods were at .002. So is .004 to much and should I go to an undersized bearing, or should I just put these back in and use 20w50 and drive it? I do drive it rather hard, but I would like it to last a while. I checked the rest and the front one is at about .0035, and the back one is at .004, the other 3 are at .003.
I've heard run them loose so that they get extra oil, and I've heard run them tight so that they don't hammer, so what should I do?
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1970 coupe restored with the help of my dad. 306 with 600 holley, Weiand Stealth intake, headers, Comp cam, harland sharp roller rockers, kb pistons, 10.3:1 compression ratio, pertonix ignitor 2 with matched coil, lakewood bellhousing, 4-speed toploader, and 2.79 open 8" rear. Soon to be 9" 3.50 trac-lok
1986 f-150, 5.0, factory towing package with original c-6 trans
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steve'66
Gearhead Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 03-06-2004 05:28 PM
If everything looks good I'd put a hi-volume pump in it and run it.  SteveW
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bigblocked85
Gearhead Posts: 163
From: Waterford,MI
Registered: May 2003
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posted 03-06-2004 11:17 PM
I'm of a different mind. For one thing, plastigauge is a cavemans method of bearing measurment. It HAS to be measured with mics. Preferably calibrated at that. The differances you mention of are absolutely not tolerable. I see the norm going to around .0020-.0025. Depending on the bearing. At .0040 you would make a pro engine builder cry. Especially having a variance of .0010 between bearings.
Now on drag only machines, very loose tolerances may be the norm on VERY competitive engine combos like Alex's, but for a street strip combo, I would be very leary. My suggestion is to take it to a dependable shop and have accurate measurements takin and then make your decision.
Not the gospel, but I try to run .0025-.0025. ------------------
Gordon Ross
85 Mustang GT
466 C-4 mini tubbed
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BLstangin
Gearhead Posts: 779
From: St. James, MN
Registered: Apr 2002
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posted 03-07-2004 02:13 AM
I already have a high volume pump in it. I am going to school to be a machinist, so I have the tools and they are calibrated, but the problem is during spring break when I have time to work on it, the tools are , locked in the school because I didn't think about it beforehand. Also, I am just running the stock crank, which had about 90,000 miles on it, and it looked great, so I didn't have it ground. I think that maybe the back main has more wear because of the clutch in the back, I don't know.------------------
1970 coupe restored with the help of my dad. 306 with 600 holley, Weiand Stealth intake, headers, Comp cam, harland sharp roller rockers, kb pistons, 10.3:1 compression ratio, pertonix ignitor 2 with matched coil, lakewood bellhousing, 4-speed toploader, and 2.79 open 8" rear. Soon to be 9" 3.50 trac-lok
1986 f-150, 5.0, factory towing package with original c-6 trans [This message has been edited by BLstangin (edited 03-07-2004).]
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thumpin cat
Gearhead Posts: 458
From: Santa Barbara, California
Registered: Mar 2002
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posted 03-07-2004 02:41 AM
Plastiguage is no good, and if you are measuring rod/main bearing clearences with plastigauge you should be using the green stuff, the red stuff tends to show clearences larger than they really are.
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BLstangin
Gearhead Posts: 779
From: St. James, MN
Registered: Apr 2002
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posted 03-07-2004 02:54 AM
Also, which bearings are the best for street driving, with a lot of abuse, but I don't want to tear it down all the time. Should I use clevite "p" series, clevite "h" series, federal mogul standard bearings, or federal mogul perfomance bearings? I will do it with micrometers when I get a chance.------------------
1970 coupe restored with the help of my dad. 306 with 600 holley, Weiand Stealth intake, headers, Comp cam, harland sharp roller rockers, kb pistons, 10.3:1 compression ratio, pertonix ignitor 2 with matched coil, lakewood bellhousing, 4-speed toploader, and 2.79 open 8" rear. Soon to be 9" 3.50 trac-lok
1986 f-150, 5.0, factory towing package with original c-6 trans
IP: Logged |
BLstangin
Gearhead Posts: 779
From: St. James, MN
Registered: Apr 2002
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posted 03-08-2004 04:20 PM
O.k. I meausred everything with a micrometer and telescoping gauges.
The mains are:
#1 .003
#2 .0032
#3 .0032
#4 .0035
#5 .004So should I just get .001 undersized or isn't that going to tighten it up enough?
The rods have .0025 on the first 3 journals and on the last they have .0022, so should I leave them or tighten them up. Grinding the crank is out of the question, I can't afford it, so what should I do? ------------------
1970 coupe restored with the help of my dad. 306 with 600 holley, Weiand Stealth intake, headers, Comp cam, harland sharp roller rockers, kb pistons, 10.3:1 compression ratio, pertonix ignitor 2 with matched coil, lakewood bellhousing, 4-speed toploader, and 2.79 open 8" rear. Soon to be 9" 3.50 trac-lok
1986 f-150, 5.0, factory towing package with original c-6 trans
IP: Logged | |
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