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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Engine failures due to stretched connecting rod bolts and instructions for overhaul.

Identifier  ExFiles\Box 10\4\  04-page12
Date  18th September 1936
  
CONNECTING RODS

We have had one or two instances recently of engine failures due to the connecting rod bolts having stretched and allowed the big end bearing to become slack in the rod.

The result of this is that the bearing housing in the connecting rod becomes badly hammered and the white metal of the bearing itself breaks up.

In all cases of failure which have been examined it has been found that the connecting rod bolts have stretched and that the nuts were slack. In one case the nuts had actually unscrewed themselves and were found in the sump.

The trouble does not seem to be confined to any one type of engine, but it is important that whenever an engine is down for overhaul, the connecting rod bolts should be carefully examined and if there is any sign of stretching they should be scrapped.

The thread on the bolts should be examined for any sign of having been "pulled".

In the past it has been the practice when overhauling engines to reduce the thickness of the big end bearing cap face by about .001" to ensure that the bearing is properly nipped when the cap is pulled down.

This practice must now cease, and on no account must the connecting rod or the cap be filed.

It is absolutely essential that the connecting rod bolts are tightened really hard.
  
  


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