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).
The overhaul and performance testing of a B-7 unit, detailing issues with gear backlash and adjustments to valve timing.
| Identifier | ExFiles\Box 82\2\ scan0197 | |
| Date | 27th September 1934 | |
| x4553a COPY. 27.9.34. B-7 UNIT. This unit has been overhauled since being removed from 4-B-IV chassis after completing 10,000 miles test, and refitted with new Textolite gears having ground metal gears to suit. The original Aerolite Pistons have been removed and a new set in A.122 alloy having the latest skirt dimensions fitted, these pistons are registered for reference as E.1. The cylinder block fitted was the block that ran the 10,000 miles test and had standard bore dimensions except that half way down the bore the diameters were .0005 oversize. When first run the engine gears whined very badly and when thoroughly hot there was a distinct rattle, the cam wheel fitted had .004 backlash and was turned down for this reason, it being useless to try and stop gears rattling with this amount of backlash. The experience gained on B-3 unit with Textolite showed that we could not have more than .002 backlash if we wished to avoid rattle; in fact we can definitely say that .002 is the absolute maximum of backlash that we can permit. Our first Power Curve (1) shows a maximum power of 113.5 B.H.P. and a maximum B.M.E.P. of 122.4 at 2000 r.p.m. This power was rather lower than expected considering that the unit had a high compression ratio cylinder head of 6.95:1 with 1.500 dia. inlet valves and 1.200 exhaust valves. The valve timing (timing "A") was rather on the early side which of course would reduce our maximum power at high speeds but at the same time increase our low speed M.E.P. Our next test consisted of making the valve timing later, we could not get a normal timing so we adopted valve timing "B", which as will be seen from the timing diagram on the attached curve is about 4° later than the normal timing; in all other respects the conditions of the test were the same as for the previous test. | ||