glen_miss3

What should the be the right clearance to run because I am getting .004 clearance on my main bearings. I had the crank turn 10/10 and bought 10 over main bearings. Just need some thoughts.

I also had the oil holes on the crank chamfered if that matters.

Stekman

I have generally gon eon the rule of .0015" to .0025"

ede

.004 is way too much. .0015 to .0025 is about the clearance range. how are you checking it? if you're using plasti gage i'd check it wit ha bore gage, snap gage, or mics. plastigage is pretty much worthless for truely checking clearances with.

glen_miss3

1 and 2 measure .003 and 3,4,5 measure .004 and I did use the plastigage. I called the machince shop and asked them what they thought and they said that "Its fine." They did want to know how I measured. They did tell me to get a High Volume oil pump since I had the oil hole chamfered on the crank. I dunno?

Oh and thanks for your input guys.

ede

they told you it's fine because they didn't want to admit they ****ed up. after you have it together and it goes to hell in a hand basket there isn't much you can come back on them with. they'll claim it was the assembly not the machine work. the other option is you're checking method isn't very accurate and you need to do like i said in other reply and get some precision tools to check the clearance with. a HV oil pump won't fix anything. with having the crank ground and new bearings the clearances should hit pretty much dead on what they're suspose to be in your manual.

glen_miss3

I called some different machine shops and ask what the clearance should be and they said what everyone else has been saying. So then I called the machine shop I used and talked with them and the guy I talked to said that you want that much clearance when your wanting to run a high performance motor. He said he builds motors every day and for alot of years. He said he runs that much clearance if not more (.005) on his dirt track car with a high volume oil pump. I told him that what he is saying is going against the grain with what other machine shops were saying. He told me that I have to be specific about what I am telling the machine shops. He asked me if I told them that I'm building a performance motor and not a stock motor. What he was talking to me about sounded logical. Less friction=more power is what he was going into detail about. I told him that my main concern is investing all this time and money into a motor and it take a dump on me. I guess I will have to go get a mic and measure it myself and go from there

glen_miss3

The motor I'm rebuilding is a 4 bolt 350 setup for roller. Just thought I would throw that out.

RB83L69

There's a big difference between how you build a dirt-track motor that runs 8 or 10 30-lap events before it breaks a crank; and a street motor that you want to live for hundreds of thousands of miles. In the round-track motor, you want it to be instantly ready to qualify the minute you crank it up, after all there's no 3000 mile break-in procedure on a half-mile track when you install a motor on Friday afternoon after breaking your old one in practice and the feature is on Friday night, you know.

The main bearing clearance for a street-driven motor needs to be about .0015" - .002". .004" is too much. I wouldn't even want .003" in a motor I build.

You don't want a HV pump for a street motor. As long as the oiling system is stock (no grooved bearings and gun drilled rods and extra oil holes in the crank and so on) the extra volume will not help anything. All it will do, is create extra drag on the distributor, which will wear the distributor gear and cause more spark scatter.

Chamfering the crank oil holes does not increase the motor's pressurized oil requirements.

Go buy yourself a micrometer if you're going to try to build an engine. You're just asking for problems without one. Plastigage is not accurate enough for that; about all it's good for is making sure the bearings aren't .020" over when you're running a .010" over crank.

If the machine shop guy continues to insist that the crank is right, tell him you want to trade him that crank for one ground to stock specs; tell him you changed your mind, you're building a stock motor. And remember that next time you get machine shop work done. What happened here, is that his idea of what a "performance" motor consists of, is different from yours. Not so much that he's wrong or bad or whatever about his crank, but rather a matter of suitability for your particular purpose. Basically, if you're going to run a crank on the street, then the crank grind needs to be "stock", unless you're knowledgeable enough (and well enough equipped with test equipment) to specify a particular clearance or crank pin diameter you want.

Vader

New crank time. I wouldn't grind under 0.010" to clean one up. Replacements are just too cheap to risk it.

The front bearing clearance is 0.0008 - 0.0020";
The center three bearings are 0.0011 - 0.0022";
The rear main clearance is 0.0017 - 0.0033". Those are wear limits, not production tolerances. The low ends of all those ranges should be used to blueprint an engine rebuild. 4 thousandths is going to hammer like an LS1 engine when cold, but only until you spin one of your new bearings.

glen_miss3

Well I have a good friend of mine that works at an oil field machine shop and he is going to come over this Saturday and we are going to mic every thing and go from there. I forgot about this earlier but the guy at the machine shop said if I wanted to tighten up the clearances to file the main bearing caps. Would that not make the centerline out of round. I dunno, that sounded a little dumb to me. Maybe I didn't fully understand what he was saying.

ede

you need to quit talking to the guy at the machine shop. so far it sounds like everything he's said or done is wrong. don't file your main caps.

FstBrd6point3

do not file your main caps, you will cause them to be out of round... this guys who did the work sounds like a moron.

Vader

Glen,

In case you didn't already hear, DO NOT file, surface grind, mill, machine, or otherwise alter your main bearing caps.

Your reasoning is absolutely sound, so you already have a better grasp of the mechanical properties and philosophies than your "mechanic", so stop asking himm for anything except the money to pay for repairing his mistakes. (I used the plural form because there are probably other problems of which you might yet be aware.) Better check the rod journals, ring gaps, bore square and taper, cam bearing position and alignment, missing oil bypass gallery plugs, and anything else he may have touched.

Did "the guy" happen to mention that 95% of those engine builds are rewoark and warranty repairs. It wouldn't surprise me a bit. Run away from that place as fast as you possibly can.

glen_miss3

I think that you guys are right I'm going to go to another shop. Today we checked the crank and it was in good shape.

CRANK #'s .010 grind
1. 2.439 main journal O.D.
2. 2.4388
3. 2.438
4. 2.439
5. 2.4388

Then we checked main bearings with an I.D. mic and not so good.

MAIN BEARING #'s .010 oversize
1. 2.4419
2. 2.4422
3. 2.4425
4. 2.4422
5. 2.442

Then we did some swaping around with the bearings and a little better but still not so good.

MAIN BEARING #'s .010 oversize (second time)
1. 2.4415
2. 2.4418
3. 2.4418
4. 2.441
5. 2.442

Well I'm really not sure about all this but do you guys think I should buy some federal mogul bearings instead of clevite 77 the bearings that are in there or what? Does anything look inconsistant or out of place.

Vader

So the best you can arrange is about 3 thousandths clearance. Clevite bearings seem to be just fine, but you could try a new set just to be sure, now that you have a means to measure accurately. The main journal measurements seem to indicate they took about 1-2 thousandths too much in the grind process, and finding bearings to fit won't be easy.

glen_miss3

Yea the best I can arrange is about .0025 - .0032 so I'm going to try a different set of bearings. I just wanted to thank everyone for there input

ede

i have used lot of clevites in the past but after buying some for my 402 i decided i'll never use clevite bearings in any engine of mine. my prefered bearing is from childs & albert but hard to find locally.

glen_miss3

What was the deciding factor to never use Clevite.

ede

their lack of any sort of quality control. having an engine to assemble and a set of bearings i couldn't use.

tom3

Worth mention that when you finally put the torque to the caps you 'crush' the bearings some, really locks them into the caps and might lose just a bit of that clearance. How are you tightening them to check sizes now? Usually a turned crank is right on the money, better than used factory. I'd try a different brand of bearings myself.

glen_miss3

Just waiting to get paid to get some new bearings. I'm torquing the caps to 70 lbs. on the inner two and outer two to 65 lbs.

BASSETT IROC 85

iTrader: (2)

Good job man. You will sleep better knowing that the guts are right.

sofakingdom

iTrader: (1)

Ummm, that stuff all happened 4 years ago....

Sonix

iTrader: (1)

He's been sleeping better for many years by now