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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).
Comparative tests between strap type and marine type connecting rods with whitemetal bearings for the Phantom III.

Identifier  ExFiles\Box 114\2\  scan0229
Date  27th November 1935
  
To E.{Mr Elliott - Chief Engineer}
c. to Wor.{Arthur Wormald - General Works Manager}
c. to By.{R.W. Bailey - Chief Engineer}

X1020

Hs{Lord Ernest Hives - Chair}/Swd1.14/KW.27.11.35.

Phantom III.

Comparative tests have been carried out on No. 1 unit between strap type and Marine type of connecting rods with whitemetal bearings, and run under identical conditions.

After 20 hours at 4,000 R.P.M., the big ends of the Marine rods shewed signs of the whitemetal cracking up and by their condition would not apparently have lasted much longer before a failure occurred. The top halves were in slightly worse condition than the lower halves, which indicates that the cracking up is more due to pressure than inertia loading. In this type of rod, the bearing is integral with the cap, the top half having a corresponding integral steel cradle.

In the case of the Strap type rod, No. 6 big end failed after 13 hours at 4,000 R.P.M., the metal running completely out of the shell. The remaining bearings appeared to be on the verge of running, but unlike the Marine rod bearings were free from cracks.

With this type of rod, the bearing is a shell and is clamped by separate strap caps. It is not such a solid job as the Marine rod bearing, and is more liable to distortion. Being a detachable shell, the heat conductivity is not so good, but on the other hand, the whitemetal appears to have better adhesion.

During the recent 10,000 miles test in France, the whitemetal big ends, as run in Strap type rods, failed after 7,000 miles.

If our endurance test be taken as a criterion, then Marine type rods and whitemetal bearings would last between 10,000 and 11,000 miles.
  
  


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