Main Bearing Tolerances Question

[nuggets]

Hello,

Alright, I'll try to keep it short. I am re-building a stock 6 bolt. Crank was micro-polished, block was decked, honed, and cleaned up. It looks good

I've been struggeling with the main bearing clearances for quite some time now using, plastigauge, telescoping gauges, and now an Electronic bore gauge. I've finally gotten some correct readings with the dial bore gauge but my main bearings are still too loose.

I first tried Topline, and now am using Engine Pro ACL bearings. The Engine pro bearings yielded better results but are still a little out of spec. Spec being: (0.0008 - 0.0020)
I got only one reading of, 0.0018.

I used a micrometer on my crankshaft to see if it was within spec and it is... but it's at the bottom of being within spec. After averaging all the measurements I took at different angles on each journal, the mains came out to this.

#1 - 2.2433
#2 - 2.2433
#3 - 2.2432
#4 - 2.2433
#5 - 2.2433

Consistent, yes but unfortunatly the crankshaft main journal specifications are: (2.2433 - 2.2439)

My rod journals were just fine. Anyways, what I'm looking for is some advice as to what direction I might want to go in order to get my main bearings within spec. Keep trying different brand bearings? Brand new 6 bolt crank? Align bore? Or maybe even take .10 off? I'm trying to do this right the first time so I'd appreciate any advice or input.
Thanks.

 

[thekyguy11]

 

[nuggets]

I promise that thekyguy11 and I will make another Building a DSM ENGINE in 10 minutes video.. if I get the answer to this within the next few days...


.. i really want to do another one..

 

[alex99gst]

I would see if you could pick up a nice used crank that is still within spec, especially since yours is barely within spec. Be sure to make another video. I really enjoyed that last one.

 

[nuggets]

that's possible, but that means it would have to be local and i would have to go over to the person's house, check all the journals for their measurements and then consider if its worth the purchase. i'm trying to avoid such complications.

 

[snox135]

I would take to the shop to see what they say. But they will probably suggest going .010 under.

 

[kiggly]

I wouldn't worry at all about even 0.003" main bearing clearance. It will increase oil flow and cooling for the bearing. The only thing it might do adversely is drop oil pressure at idle a little. If you have the balance shafts removed, you will still have plenty of pressure.

Kevin

 

[nuggets]

thank you for the replies. Yes i'm just worried about the engine not lasting very long at all. I have the balance shafts removed with fresh bearings covering the oil galleys..


so you think that with the clearances I'm getting.. even thought slightly out of spec.. I should still be good?

 

[thekyguy11]

I would take to the shop to see what they say.

We tried this, many times actually. It seems like people at the shops around here don't want to give answers on stuff like this. They act like this is top seceret information that they don't want to give out. Also, different shops keep giving different suggestions, so who do we believe?

 

[pneumo]

...so who do we believe?

Believe the DSM'er who runs 9's, the one who advised you to go with what you have.

I have my bearing clearances listed in my profile if you want to check. I've been running this motor for two years now, still going strong.

 

[fourreGsixty3]

Sound's like you got your awnser...but I will add this. I wouldn't be using plastiguage, it put's indent's into the bearing's.

PS: Loved the vid you two made.

 

[Maglin]

Plasti gauge doesn't leave "indents" in the bearing. And if it did it would be so minor. You would probably do more bearing damage with a vernir caliper or bore gauge than with plasti gauge.

Personally if it was me and I wasn't planning on making over 450 HP and not turning over 8K RPM I would probably run with what you have. But I don't roll like that. I prefer to go on the low side of the spec and run thinner oil. I like 0w-20 oil. Anyways. You can also try a set of mitsu bearings if you haven't already. You might be able to get them in a slight oversize. I know you can with Toyota but never tried with Mitsu.

 

[thekyguy11]

Believe the DSM'er who runs 9's, the one who advised you to go with what you have.

Absolutely, we already knew to go with Kiggly's advice, . Sorry, I was referring to the discrepencies we keep getting from local machine shops. that's the reason Al started this thread in the first place. And thanks to you and kiggly, we don't have to worry about the .0022-.0023 clearence we have.

Also, is there something we should be doing to minimize the tiny marks the bore gauge leaves on the bearing? should we lube the tips of the gauge or something? maybe lube the bearing?

 

[nuggets]

Yeah the dial bore gauge has managed to leave some semi-nasty indents/scratches in my bearings. Our local machinist told us to use a solvent and a scotch bright pad to clean them up a bit, and not to worry about the blemishes.

I also just got a PM from somebody telling me there are ACL bearings that can go up .001 if you want them. He gave me the part numbers and told me what they are capable of doing.. here..

Originally Posted by sawnuoff which acl's do you have because they actually sell a bearing that is .001 oversized to tighten up the clearance, they are for the standard crank journal sizes only.


acl race series bearing
mains - 5m1144hx is the +.001
for the 6 bolt cranks the "x" indicates .001 over drop the "x" for the standard
rods - 4b1146hx is also a +.001
just drop the "x" for standard bearing size

 

[thekyguy11]

anybody? Thoughts on minimizing damage to bearings from the bore gauge?

 

[pneumo]

Don't push so hard on the bore gage?

Seriously, if you're pushing hard enough to make an imprint on the bearing, then your reading won't be accurate. You're measuring the bearing plus the divot you just made. The reading will be different depending on how hard you push on the gage.

Use a light touch. Stop pushing as soon as you feel resistance. Good Luck.

 

[thekyguy11]

Push? I don't think there is any pushing involved with this tool. Its a bore gauge, not an inside micrometer. The tool expands inside the hole with its own pressure, and measures that way, All I am doing is inserting it and slightly rocking it to ensure a minimum reading is taken.

We had a similar problem with the expanding snap gauges that would leave a dent when it expanded inside the bearings, so I took the snap gauge apart and cut sections of the spring away until the spring pressure was significantly reduced. That made a difference.

I wonder if I can do the same thing with this tool. It was pretty expensive, so I'd rather not do anything that will mess it up, but I'll check it out and let you guys know what I find. The tool can be seen here http://cgi.ebay.com/ebaymotors/ws/e...0091994017&category0=&fvi=1&item=190091994017

 

[danl]

Hello,

Alright, I'll try to keep it short. I am re-building a stock 6 bolt. Crank was micro-polished, block was decked, honed, and cleaned up. It looks good

I've been struggeling with the main bearing clearances for quite some time now using, plastigauge, telescoping gauges, and now an Electronic bore gauge. I've finally gotten some correct readings with the dial bore gauge but my main bearings are still too loose.

I first tried Topline, and now am using Engine Pro ACL bearings. The Engine pro bearings yielded better results but are still a little out of spec. Spec being: (0.0008 - 0.0020)
I got only one reading of, 0.0018.

I used a micrometer on my crankshaft to see if it was within spec and it is... but it's at the bottom of being within spec. After averaging all the measurements I took at different angles on each journal, the mains came out to this.

#1 - 2.2433
#2 - 2.2433
#3 - 2.2432
#4 - 2.2433
#5 - 2.2433

Consistent, yes but unfortunately the crankshaft main journal specifications are: (2.2433 - 2.2439)

My rod journals were just fine. Anyways, what I'm looking for is some advice as to what direction I might want to go in order to get my main bearings within spec. Keep trying different brand bearings? Brand new 6 bolt crank? Align bore? Or maybe even take .10 off? I'm trying to do this right the first time so I'd appreciate any advice or input.
Thanks.

I didn't read the other replies but after doing a few motors here are my comments..

Those numbers are more than ideal. That is a perfect clearance for a street/strip motor if I were to build it. If it were a race only motor I'd approach 2 and a half or 2 and a quarter. The numbers are so close actually that its scary. When I measure mine they vary by .0001 either way. Its not always possible but you can make tolerances work to your favor when building an engine. Put looser ones on one side and tight ones on the other. I make my center bores looser if I have a piston that is a fraction of a thousandths loose.

Plasticguaging as a fine way to double check your bore guages but don't use it alone. I've also noticed that some brands of plastic read tigher than your bore guages and math method.

My stock motor from last year was looking at about 3 and a half thousandths on the mains and about the same on the rods. I could hold 10psi oil pressure at idle with 15w/50 oil no balance shafts. It held mid 11's at 130 and 32psi boost. That is noooooooooo problem, motor wanted more abuse even with those extreme clearances. Some v8 guys will build a motor for 3 and a half out of the box!

 

[thekyguy11]

So why does the factory recommend such tight clearences then? Only thing I can think of is so the motor lasts longer.

I havnt had a chance to attempt to modify my bore gauge yet, but does anyone else have any idea's on how to avoid damaging them when I measure em?

 

[alex99gst]

So why does the factory recommend such tight clearences then? Only thing I can think of is so the motor lasts longer.

I havnt had a chance to attempt to modify my bore gauge yet, but does anyone else have any idea's on how to avoid damaging them when I measure em?

The only thing I could think besides cutting the spring so that it doesn't push as hard would be to place something on the end of the gauge or lube it with oil, which would throw off the readings.

 

[nuggets]

yeah so for the future motors we are going to try to reduce as much gouging as possible.. we actually played with the bore gauge today and made the spring resistance much more gentle. As for my GOUGED bearing.. I tried to use a scotch bright pad and solvent to get it out but it's deep... so I'm not going to use it. I think I'm going to simply use one of my topline bearings on the bottom of that journal, and an ACL or engine pro on the girdle side. Any objections to this? The rest of my ACL's are untouched.

 

[thekyguy11]

why didnt you ask me? I would have objected and prevented you from posting that.

 

[nuggets]

okay my crank is in and bolted down. we also started making another video so in due time we should have the engine completely built and another building a DSM video for your viewing pleasure.



thank you everybody for all your advice and help.