Conrod bolts, LM2...

[Dukedesmo]

As part of my rebuild (due to valve to piston interface) I removed the conrods to check for straightness and replace a loose small end bush.
So on the rebuild I'm replacing the conrod bolts, nuts and big end shells as a precautionary measure - originals look fine but are (probably) 35 years old and I wouldn't want to have one fail in a couple of months time.

Got all new parts but the bolts are a tight fit in the rod - as in they won't go in, at least not by pushing. I've not tried heat/cold, hammer or vice yet as I'm wondering if this is something that is well known and I don't want to bugger it up.


Basically it's the (9mm) thick part in the middle that won't go in, the part that will sit between the two halves of the rod; the originals are a good, precise fit but the new bolts are 001" larger than the old (I only have an imperial micrometer).


Normal or wrong? 


Here's a pic;





Original bolt is the silver one, new is black and slightly different design.

[blackcat]

Hmmm....doesn't sound right. When I rebuilt my CX engine the new bolts just slid right into place.

[nc43bsa]

How does the middle part of the bolt fit into the rod cap?

Keep in mind absent a dowel, that part of the bolt should precisely locate the cap to the rod.

The race car rods I dealt with were a press fit into the rod and a tight push fit into the cap.

[NCAmother]

How does the middle part of the bolt fit into the rod cap?

Keep in mind absent a dowel, that part of the bolt should precisely locate the cap to the rod.

The race car rods I dealt with were a press fit into the rod and a tight push fit into the cap.

my experience with car motors has been alway to press fit the bolt, I wonder if the upgraded motor of the LeMans, they are pressed.

[Dukedesmo]

I assume that it needs to be tight because there is nothing else to hold the 2 pieces from moving sideways but how tight is right?

[Offcamber1]

Where did you source the replacement bolts from?  Do you know the history on the motor; who was into it before?  Have you considered just having the old bolts crack tested?

Something not right with the new ones...

[ailgev]

Had A Similar Problem With 1100 Sport Rod Bolts. I Had To Get Them Ground Down To The Correct Thickness.

[Dukedesmo]

So I've fitted them now, managed to get one in as it was, the other three I ran them in the drill with some 600 grit emery and oil - didn't take much and all were a 'snug' fit but I reckon that's better than being loose, I reckon maybe the black coating was maybe a bit rough?
 
Got them from a reputable supplier and I'm told they're genuine Guzzi parts but they're not as nicely made as the originals.

Anyway, rods back in now with new bolts, nuts & shells and everything looks/feels fine.