Engine Rebuilding : Spun Bearing, Is The Rod Oos ?

[Pierre_b 4]

Hello,

 

I am wondering if I can put rod back in an XU5 engine that has a spun bearing. The bearing has turned 90° in the rod.

I have tried to change just the bearings, but the engine start to make noise few minutes after starting.

I have put the engine to pieces, and the rod seems visually fine (the crosshatch marks are still ok). My machinist checked the big end internal diameter and said they are ok. I have changed the cranck for a used one, and with new bearing, the clearance checks with plastigage are just below 0.003".

The issue is on french forums, people says that a rod that has a spun bearing is dead, but is unable to say why. I would like to know if the rod is really destroyed, and if yes, why and how I can check that?

 

Thanks,

Pierre

[B1ack_Mi16 67]

Hello,

 

I am wondering if I can put rod back in an XU5 engine that has a spun bearing. The bearing has turned 90° in the rod.

I have tried to change just the bearings, but the engine start to make noise few minutes after starting.

I have put the engine to pieces, and the rod seems visually fine (the crosshatch marks are still ok). My machinist checked the big end internal diameter and said they are ok. I have changed the cranck for a used one, and with new bearing, the clearance checks with plastigage are just below 0.003".

The issue is on french forums, people says that a rod that has a spun bearing is dead, but is unable to say why. I would like to know if the rod is really destroyed, and if yes, why and how I can check that?

 

Thanks,

Pierre

 

You can have the big end rebored and hooned, then it shall be fine, but really depends on the condition of the big end.

 

I had this done to a T16 rod that spun a bearing, and it's like new.

[Beastie 1]

If the shell spins then there is a very good chance that the rod will have been damaged. But it would be foolish to condemn a rod without checking it! If you are confident that your machinist is skilled and knowlegeable then accept his judgment! If you can still see the cross hatching then it sounds as though the rod has not been abraded by the O.D. of the spinning shell so perhaps it has been distorted? Does the cap still fit nicely on the rod? Are the butt faces in good order and do they fit together by hand so that no daylight shows between them when held up to the light? Do the butt faces of cap and rod still have a nice even matt finish or do they have a tarnished, uneven finish where dirt has accumulated in areas where there is a mis fit? Are the butt faces slightly shiny and smooth where they have been hammering due to movement between cap and rod? If all this is correct try a trial fit of the bearing shells in the rod (without the crank). Tighten the rod bolts with your fingers until the cap is starting to tighten the shells and then tighten one bolt only down with a spanner (hand tight only) Is there a "nip" of about 3 thou holding the shells into the rod and measured between the faces of rod and cap with a feeler gauge?

 

If all this checks okay then maybe your machinist is correct! Just to put things in perspective the definition of a scrap rod depends on how common the rod is. I recently purchased a set of rods for a 1962 Aston which had been very nicely reclaimed: The faces of rod and cap had been machined and the parent bore had been accurately honed back to the correct round diameter. The rods had been straightened and then fitted with new small end bushes before they were delapina honed in line to the big ends. I expect the labour bill for those rods would have been breathtaking to a lot of people - but no one is likely to find another set to use instead

[Pierre_b 4]

Hello,

 

Thanks for yours answers. The issue is that they are pressed fit pin rod (stock XU5). So if I need to bore the big end, I'm afraid that the machinist has to pull the pin out, and apparently it destroy the piston. So, new pistons, new sleeves.... Not the same price...

 

Beastie : For your control ideas, I'll check this week end. I didnt quite understand the part with the bearing nip (my english is not so good ). You mean I tight one side of the big end, and check the clearance between the two part of the rod?

 

Pierre

[nick 3]

If your machinist can't remove a piston pin without destroying the piston try another machinist.

 

Nick

[pug_ham 245 3 Cars]

If your machinist can't remove a gudgeon pin without destroying the piston he is in the wrong trade.

 

I'd suggest a career change.

 

I've removed them with a bush in a vice without damaging the pistons before.

 

Graham.