406 rear main bearing issues

Automotive powered airboat discussion.
10X
Southern Airboat Member
Posts: 6
Joined: Sat Dec 12, 2015 8:57 am

406 rear main bearing issues

Postby 10X » Sat Dec 12, 2015 10:41 am

Ive been running a chev 406 and had a piston issue, my machine guy recommended a crank replacement also. So we put an eagle crank in and line bored and balance with the piston replacement. Im also running a 2 to 1 belt reduction unit. Now it will wear out the rear engine main bearing within 5 hrs of operation. Finally traced it to the lower drive gear binding and causing .025 runnout on the rear crank journal. My though is too much line bore causing the lower drive bearing not too line up with the crank. Anyone had this type of issue. Is this block now an anchor.

Rich Andrews
Site Supporter - IV
Site Supporter - IV
Posts: 6775
Joined: Wed Jun 15, 2005 9:20 pm

Re: 406 rear main bearing issues

Postby Rich Andrews » Sat Dec 12, 2015 11:05 am

What all was done and replaced?

Just spent time in a machine shop that cuts cranks straight out of the box. U would be amazed at the shit that is sold.
I'll have my Manatee burger medium please...just say NObama

14x8 deckover FELBER 397ci.. HP ???..just stay back!!

LOHA is AHOL backwards

10X
Southern Airboat Member
Posts: 6
Joined: Sat Dec 12, 2015 8:57 am

Re: 406 rear main bearing issues

Postby 10X » Sat Dec 12, 2015 11:35 am

Crankshaft, Bearings and 1 piston. I had the crank checked last summer at d different shop and said it was fine. i pull the lower gear and the runnout of the crank is .002

10X
Southern Airboat Member
Posts: 6
Joined: Sat Dec 12, 2015 8:57 am

Re: 406 rear main bearing issues

Postby 10X » Sat Dec 12, 2015 11:37 am

They also turned the mains on the crank because it was scored up.

Rich Andrews
Site Supporter - IV
Site Supporter - IV
Posts: 6775
Joined: Wed Jun 15, 2005 9:20 pm

Re: 406 rear main bearing issues

Postby Rich Andrews » Sat Dec 12, 2015 5:04 pm

lots of things can be wrong here.. if you don't know for sure about the block and if it was properly machined and the crank honed right you could be needing a lot. Dumb question but did your builder put in the right mains? Or how about the rods, how do those bearings look?
I'll have my Manatee burger medium please...just say NObama

14x8 deckover FELBER 397ci.. HP ???..just stay back!!

LOHA is AHOL backwards

10X
Southern Airboat Member
Posts: 6
Joined: Sat Dec 12, 2015 8:57 am

Re: 406 rear main bearing issues

Postby 10X » Sat Dec 12, 2015 6:32 pm

Thats the thing im not sure of is the block. Pretty confident the crank was done right. no problems ever with any other bearings. I did plastiguage the crank before install. Not super accurate but seemed to be good.

User avatar
skinny99
Site Supporter - II
Site Supporter - II
Posts: 1182
Joined: Sun Jun 13, 2010 8:20 pm
Location: Deltona, FL

Re: 406 rear main bearing issues

Postby skinny99 » Sun Dec 13, 2015 9:44 am

http://www.robbmcperformance.com/products/dowels.html

Other people make them also. But you can adjust the height on gearbox. What brand box?
Successful people do what others won't or can't!

10X
Southern Airboat Member
Posts: 6
Joined: Sat Dec 12, 2015 8:57 am

Re: 406 rear main bearing issues

Postby 10X » Mon Dec 14, 2015 8:08 am

Its a Century 2 to1 belt drive

10X
Southern Airboat Member
Posts: 6
Joined: Sat Dec 12, 2015 8:57 am

Re: 406 rear main bearing issues

Postby 10X » Mon Dec 14, 2015 8:11 am

Thanks so much for the info. That might be th ticket

User avatar
air-roberts
Site Supporter - IV
Site Supporter - IV
Posts: 1799
Joined: Sat Jun 27, 2009 8:01 am
Location: cocoa / canaveral groves

Re: 406 rear main bearing issues

Postby air-roberts » Mon Dec 14, 2015 8:39 am

line boring doesn't change the distance ofk just adds more bearing material sounds l;ike so true does it have any harmonic vibrations
Air-RobertsImage
experimenting with old step w/t experimental 384.8 c.i. nos 2.68 rotator, 80" three bld ? R
http://www.bcraceengineering.com
Thanks to dave http://waterthunder.com/
New & Used PROPs
WhirlWind prop dealer

User avatar
skinny99
Site Supporter - II
Site Supporter - II
Posts: 1182
Joined: Sun Jun 13, 2010 8:20 pm
Location: Deltona, FL

Re: 406 rear main bearing issues

Postby skinny99 » Mon Dec 14, 2015 5:42 pm

air-roberts wrote:line boring doesn't change the distance ofk just adds more bearing material sounds l;ike so true does it have any harmonic vibrations


Line boring actually does slightly raise the crank in the block. They sell timing chains engineered just for this reason.

http://www.summitracing.com/parts/clo-9 ... /chevrolet

On the other hand I have never messed with a belt box but on a gearbox with soft drive there is more give in the bushings than
the .005-.010 that the crank has moved. JMO
Successful people do what others won't or can't!

User avatar
Waterthunder
Site Supporter - VIII
Site Supporter - VIII
Posts: 8166
Joined: Fri Jan 21, 2005 3:16 pm
Location: Melbourne
Contact:

Re: 406 rear main bearing issues

Postby Waterthunder » Mon Dec 14, 2015 5:53 pm

I have seen this cause problems many many times especially on 400SBC blocks with the rear #5 thrust bearing. The oil passage hole in the upper main bearing does not line up with the oil passage in the block. This starves the bearing surface for oil. All you need to do is get a small jewelers file and file the bearing until the holes align perfectly. This may not be your problem but it can be there are a ton of things you need to check.

ALSO ITS VERY COMMON FOR The Eagle cranks to have a ton of tapper on the journals (major problem) also what was your bearing clearance. If you mic a Eagle in the middle of the journal you will see it get larger as you go to the end of the journal. I have seen over .0007 variance that's almost a thousandths of an inch. In China when they cut the cranks with a stone they are not dressing the stone often enough to maximize production. So after cutting 3,5,10 a 100 cranks the end of the stone is worn more and smaller, so the end of the journal is not cut as much as the center. This has been going on for years. I will try and find some pics and a post on this from the past! When we mic each journal we usually see .0001 yep that is one tenth of one thousandth. Also we try and keep all journal dia within 1/10th.

Common misalignment

Image


after fileing the bearing
Image
THE PROOF IS IN THE PROP!

"If you copy someone you will only achieve what has already been done."

http://waterthunder.com/
321-508-5316


Return to “Automotive Power Only”

Who is online

Users browsing this forum: No registered users and 5 guests