ATLAS RODS NOT CENTERED IN BORE

jms

jms

VIP MEMBER
Joined
Jul 26, 2005
Messages
300
Country flag
So here's a perplexing problem. Had the crank apart and ground .010 under. before I took it apart I indexed it relative which side went on what side of the flywheel. Came back from the machine shop assembled but with my "A" and" B " markings gone as they thoroughly cleaned the crank, so I'm not sure if it went back the way it came apart. When I took it apart there was ample sludge so I doubt it had been apart for some time. Now I've replaced the main bearings with FAG rollers, assembled a dry run and found that the rods are off center by 2MM. The rods are closer to the bore on the drive side and the crank end play is all of the way to the time side so essentially I can't get it centered. My only thought is too flip the crank journals from one side to the other and see what happens. I'm calling center of rod the oil hole in the top of the small end. Thoughts?
 
Normal. When they designed it they had to move the cylinders slightly away from the crank centreline. I believe to get enough meat around the studs.
Called the desaxe principle. Used for example in the Ford flathead V8. Some modern engines has it too,
 
So just read about this. The Atlas barrel design was moved back on the cases making it Desaxe. I’m not talking about front to back. My problem is side to side
 
jms said:
So here's a perplexing problem. Had the crank apart and ground .010 under. before I took it apart I indexed it relative which side went on what side of the flywheel. Came back from the machine shop assembled but with my "A" and" B " markings gone as they thoroughly cleaned the crank, so I'm not sure if it went back the way it came apart. When I took it apart there was ample sludge so I doubt it had been apart for some time. Now I've replaced the main bearings with FAG rollers, assembled a dry run and found that the rods are off center by 2MM. The rods are closer to the bore on the drive side and the crank end play is all of the way to the time side so essentially I can't get it centered. My only thought is too flip the crank journals from one side to the other and see what happens. I'm calling center of rod the oil hole in the top of the small end. Thoughts?
Click to expand...
When a crank is not marked, you can usually tell which way it goes together by the stains on the mating surfaces. PITA to take back apart, but I would.
 
The flywheel is the same thickness on the cheek flanges either way round so swapping the cheeks from one side of the flywheel to the other will not change the position of the journals relative to each other. Next time use a punch to make a unwashable mark but that is not the cause of you problem anyway.

Is the 2mm in the opposite direction of the crank shim, if so get rid of the shim or put it on the opposite side of the crank. Also the con rods have some sideways movement as there is a generous clearance, have you pushed the con rods over to reduce the 2mm. Are the bearing inners and outers full seated in their housings.
 
As komando says
It doesn't matter which way you flip the flywheel it's still the same thickness
Did you check the rods for centering in the bores before you stripped it?
It's likely to have been that way since built in my opinion
 
baz said:
As komando says
It doesn't matter which way you flip the flywheel it's still the same thickness
Did you check the rods for centering in the bores before you stripped it?
It's likely to have been that way since built in my opinion
Click to expand...
Got it. The engine was apart when i purchased the project
 
well I took it apart and checked everything over and I think what happened without realizing it was that the barrel wasn't all of the way down on one side. All good now the rod small ends are pretty much dead center of the bore and I've got .011 crank end play so I think I'm there.
 
Back
Top