Unsure what to do with 0.0020" Main Clearance

[n2omike]

Brand new engine
Dart Sportsman 8.2 Ford block
4340 Scat Crank
Oliver Rods
7800 rpm

Double checked my clearances, and also verified with Plasti-gage. 0.002" on the mains, and that is using Clevite MS-590 HX 'extra clearance' bearings that are supposed to give an extra 0.001". Crank mics out to 2.2490". Ideal is 2.2480".

What should I do? 0.002" seems a little tight.

Thanks

[RW TECH]

The only way that would ever be a problem is if something or another is not straight, round, stuff, and smooth.

I've dealt with 2.750" main combinations (larger than 302 - BBC, 351C/SVO) and usually targeted .0019"-.0023" for main bearing clearance in severe off-road truck racing applications with 4" stroke at 8500-ish peak RPM for 15 minutes per race, about a dozen per season.

I've also done this on 1100 HP 4.5" stroke BBC turning 7800 trap RPM.

I don't think I'd worry about .002" on a 2.25" main. That's likely to be where similar size NASCAR engines are built to.

[n2omike]

The only way that would ever be a problem is if something or another is not straight, round, stuff, and smooth.

I've dealt with 2.750" main combinations (larger than 302 - BBC, 351C/SVO) and usually targeted .0019"-.0023" for main bearing clearance in severe off-road truck racing applications with 4" stroke at 8500-ish peak RPM for 15 minutes per race, about a dozen per season.

I've also done this on 1100 HP 4.5" stroke BBC turning 7800 trap RPM.

I don't think I'd worry about .002" on a 2.25" main. That's likely to be where similar size NASCAR engines are built to.

Yea, the tighter the clearance, the less room there is for error. In an absolutely perfect world, that clearance would likely work... especially with something thinner than the Mobil 1 15w50 I normally run... and the crank is 4340, but Scat, not a Crower or something.

I called my machinist, and he mentioned Shaft Tech in Findlay, OH... which is about a 4.5 hour drive. No reliable crank grinders around here, anymore. He said they have a $30k machine that can reliably polish off 0.001", and make things perfect. Of course, they charge $400 just to turn one.

Another option is to get a new crank. This one is internally balanced. It was done close to 10 years ago, back before any internally balanced cranks were available, so it's got a few slugs of Mallory. Anyway, it's got a 1502 gram bob weight. (Oliver extra light rods and Mahle pistons) Looking into what is available under $1k that comes highly recommended. (4340 forged, internally balanced with a 3.4" stroke)

I'm just not comfortable with 0.002" clearance. It took me a long time to acquire all the parts for this engine, and I can't take any chances on doing something unwise that might kill it.

[piston guy]

I would have Adney Brown at Performance Crankshaft in Detroit ( only another hour more) grind it . SUPER quality work. "Realistic" prices.

[n2omike]

I would have Adney Brown at Performance Crankshaft in Detroit ( only another hour more) grind it . SUPER quality work. "Realistic" prices.

Thanks. I'm in WV... so nothing is all that close. I did call Shaft Tech, who comes HIGHLY recommended by my machinist. They said to take 0.001" off the mains and re-harden the shaft was $340. If they did the rods as well, it was $425... and about a 4 week turnaround.

I miss the days of having a GOOD reliable crank grinder an hour away, who you could simply take the crank there and have it ground to the 'low' side of the spec for $120... and have it back in a couple days. Heck, there were two places right close to each other who both did excellent work. Now, only one is there... and the old guys who use to do the work have long since retired. The quality/precision isn't near what it use to be. GOOD machinists are few and far between, anymore.

I don't feel comfortable shipping a crank both ways, as I don't want it to get bent/damaged... and it's too far to drive... twice.

My machinist is a dealer for Callies, and is seeing what he can get a Compstar for.

[n2omike]

Okay... Looks like I found an alternative.

My machinist said he could get a Compstar for $781 plus $50 freight, and would balance it for $175... but also referred me to a man named Rod McBride in Fresno, OH. McBride Crankshaft. He works from his home, is very experienced, and has a good reputation. I called him on the phone, and he said he has a micro-polisher... not a belt... that will accurately remove between a half thou to a thou of material, putting me right where I need to be. He reiterated that a belt would would be a bad idea, but his machine could fix it right up. I believe he said it was around $100... and turnaround was about a week... and it's about a 2.5 hour trip, which is do-able. Crankshafts are all he does. He also has reasonable prices to turn a crank.

McBride Crankshaft
(330) 204-5571

[Charliesauto]

Brand new engine
Dart Sportsman 8.2 Ford block
4340 Scat Crank
Oliver Rods
7800 rpm

Double checked my clearances, and also verified with Plasti-gage. 0.002" on the mains, and that is using Clevite MS-590 HX 'extra clearance' bearings that are supposed to give an extra 0.001". Crank mics out to 2.2490". Ideal is 2.2480".

What should I do? 0.002" seems a little tight.

Thanks

Buy a set of ACL 5M590HX bearings if you want more clearance than the Clevites. That being said, I have ran .0018"-.0020" on SBF circle track engines with 302 main size and over 800HP with zero issues.

I would not consider letting someone polish .001" from a crank, no matter what kind of polishing apparatus they have.

[vortecpro]

This easily fixed.........you sand the back of the bearing counting sand strokes. You want to sand the bottom 1/3 of the radius, so as too increase the vertical clearance. This is done all the time. Of course you want to CK clearance with a Sunnen bore gauge. You can easily get 4 tenths......easy.

[SupStk]

Another vote for Adney Brown. That guy is a magician with a crank grinder and this is from someone who grinds cranks.

[Walter R. Malik]

Brand new engine
Dart Sportsman 8.2 Ford block
4340 Scat Crank
Oliver Rods
7800 rpm

Double checked my clearances, and also verified with Plasti-gage. 0.002" on the mains, and that is using Clevite MS-590 HX 'extra clearance' bearings that are supposed to give an extra 0.001". Crank mics out to 2.2490". Ideal is 2.2480".

What should I do? 0.002" seems a little tight.

Thanks

That main journal is only 2.249" maximum...? With a 4340 crank, Run it; (unless there is shoddy machine work).

Low limit dimension is 2.2482" and 2.2490" is the high limit.

[xanadu]

I used to be a bit weary on tighter clearances. With quality products and machine work, i now shoot for them.
0.002" will be fine IMO.

[Mark O'Neal]

Polish the crank?

[Mark O'Neal]

This easily fixed.........you sand the back of the bearing counting sand strokes. You want to sand the bottom 1/3 of the radius, so as too increase the vertical clearance. This is done all the time. Of course you want to CK clearance with a Sunnen bore gauge. You can easily get 4 tenths......easy.

That is easy.

I caught one of my engine builders doing that one time. I fired him on the spot.

[tuffxf]

Gday,
Try a different brand, acl or king, I would rather use acl or clevite but king are usually looser and have a great range of sizes
If you are going to attack the crank do it properly , get a good crank grinder don’t try to polish those amounts
Cheers

[Momus]

Run it. Will be fine.

At the moment with all the crap there could be a logistics issue sending it out or any number of QA adverse possibilities
trying to correct such a small error.