Con-Rod Services

Call us for expert advice and a quotation for your engine machining requirements.

Connecting Rod Services

H T Howard offer a wide range of services to check, repair and remanufacture connecting rods.

Straightness Check

Connecting rods are critical components within an engine which control the movement of the piston within the bore as it moves up and down its stroke.  If a connecting rod is either bent or twisted the piston may be forced against the bore resulting in tightness within the engine.  At best, this will sap power and at worst could cause friction which can in turn lead to piston damage and even seizure.

Connecting rods can be checked for straightness using a dedicated jig.  A mandrel registers in the big end housing diameter and the con-rod is locked in a vertical position.  With the wrist pin in place, a height gauge is used to check the relative position of the pin.  Any discrepancy between the positions of the pin from one side of the rod to the other will mean that the connecting rod is bent or twisted.

Big End Housing Re-Sizing

Following a big end failure where a crankshaft, shell bearings and con rods have suffered lack of lubrication it is a common occurrence for the bearings to rotate within the connecting rod big end housing itself.  When this happens the steel backing of the shell bearings will wear away the housing diameter within the connecting rod causing it to become oversize, oval or distorted.  If this situation is not rectified during the rebuild in conjunction with a crankshaft regrind, the additional clearance between the back of the shell bearing and the rod housing will eventually cause the shell to distort.  This in turn creates an excessive clearance between the shell and the crankshaft which will cause premature failure of the big end.  To avoid this, whenever an engine is rebuilt following a shell bearing failure the crankshaft and con rods should both be machined prior to fitting the new shell bearings.

As an alternative to replacing the connecting rods H T Howard can re-size any existing damaged ones.  Providing the damage is not too severe, the mating surfaces of the rods are machined which creates an ovality within the diameter of the bearing housing.  Removing material from the parting surfaces has the effect of closing the original circle diameter along the length of the rod in the top to bottom plane.  The con rod can then be machined, (either bored or honed depending on the severity of the damage), to remove some material from both the upper part of the rod and lower part of the cap which in turn restores the housing to its original size.

This machining operation is not suitable for connecting rods with “cracked” cold fractured or serrated jointing faces.

Small End Bush Replacement

More frequently found in older engines and diesel engines, small end bushes are prone to wear because most do not benefit from a pressurised oil supply.  Worn small end bushes can be replaced and at H T Howard we have all the necessary equipment to remanufacture connecting rods with small end bushes fitted.

Usually, small end bushes are available as a spare part which H T Howard can supply but in cases where these are not available, we are able to manufacture replacement bushes from suitable materials.

Small end bushes are removed from their connecting rods using a hydraulic press in conjunction with special dollies and punches.  Replacement bushes are also fitted using the press and frequently oil holes in the bushes need to be drilled.  Small end bushes are supplied un-finished which means that they need machining to their final size once they are installed.  At H T Howard we carry out this operation using our honing machine which gives a far superior and more accurate result than using a reamer which is often the solution used in less well equipped workshops.


Connecting rods are originally produced in sets which are usually matched for weight.

However, manufacturer’s tolerances in this respect are often not as accurate as they could be and balancing to more accurate tolerances can help any engine to run smoother.  Engines which have balanced components will endure less internal stress which can result in better efficiency and longer service life.  At H T Howard connecting rods can be balanced not just for overall weight but also using the “end for end” method for even higher degrees of accuracy.

Call us for expert advice and a quotation for your engine machining requirements.