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MG MGB Technical - Play in Rods after new bearing install

I picked up a parts car that had a bad lower end knock so I went and replaced the connecting rod bearings. The engine had been rebuilt in the past and the bearing shells were .010. I replaced the bearings and find that when each rod is at full bottom of it's throw I can wiggle the rod side to side slightly, The play disappears when the rods start their trun upwards. #4 at first was the only one I noticed play in as it's bearing was in the worst condition upon removal and was going to remove it(rod) to have it machined. I assume this play is not normal? Should I have all the rods checked. Was only trying to get this engine to run so I can test a OD unit it has and do a proper rebuild later but?
Thanks for any imput.
Mike
MK Mike K

Mike - You need to measure the rod journals on the crankshaft. Someone may have put 0.010" undersized bearings on the rods when they should have gone to 0.020" undersized bearings. If I were doing things, would pull the crank shaft and measure all the journals and have the big ends of the rods checked for proper size. Cheers - Dave
David DuBois

Hi Mike

Assuming the head is off? Turn the engine so the pistons are after tdc on their way down again then press down on the top (center) of the piston if the piston moves down you may be in trouble....side to side sliding of the rod is how things should be up and down play is not good, maybe a couple of thou in the little end is ok.

Peter
peter burgess

Mike,

There SHOULD be between 8 and 12 thou end float (ie side to side) on each big end, insert a feeler gauge between the big end cap and the crank web to measure it.

There should be no vertical movement apparent if the bearing has oil, without oil you may have 1 to 2.7 thou clearance in the bearing.
Chris at Octarine Services

What's sideways? Along the line of the journal i.e. end-float, or across the block i.e. bearing clearance? Did you Plastigauge them?
Paul Hunt 2010

No, it's end float I have since found out with help from you guys. I have some up and down movement on the rod/bearing. Rod needs to be checked and cleaned up. No small end movement. Just hope the machinest will be able to get the press fit piston off ok.
MK Mike K

"The play disappears when the rods start their run upwards" Sounds like you have oval journals. Get the mike out!
Art Pearse

Art-
An ovaled journal would not allow up and down motion of a connecting rod. However, an ovaled big end on the connecting rod sure would. When the big end of a connecting rod goes oval, it's almost always along the axis of the length of the rod, hence the up-and down play. At the least, new big end caps are in order, because that's where the deformation takes place.
Stephen Strange

Stephen, why would an oval rod journal not allow up/down motion, if the minor diameter was in that direction? And Mike has already put in new bearing shells.
Art Pearse

Art-
If the widest part of a ovaled journal will not permit movement, it will do so regardless of the orientation of the connecting rod. This is, of course, presuming that the big end of the connecting rod is not also ovaled.
Stephen Strange

This thread was discussed between 06/04/2010 and 11/04/2010

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