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 performance of bottom tappets and issues with valve bounce, comparing a Chevrolet type to an existing design.
| Identifier | ExFiles\Box 6\6\ 06-page229 | |
| Date | 22th June 1937 | |
| - 3 - Rm{William Robotham - Chief Engineer}/Swd1.1/V8.22.6.37. Bottom Tappets (Continued). (7) Rotary movement of Chevrolet type tappet is better than our type with push rod at the top. This is believed to be due to the fact that with the push rod housed at the base there is less side thrust on the tappet than when the push rod is housed at the top. (8) In conjunction with the conical face of these Chevrolet type tappets, we are boring the guides at the same angle as the cone (45°) on the 15,000 miles unit. This, according to Taub., increases the moment of rotational force and in line with Chevrolet practice. (9) The second Wraith is running on a mixture of 10% lard oil and 90% F.4. (mineral oil), this being a recommendation from Vauxhall, and is the usual American practice on this type of tappet. (10) By inserting a feeler in the valve clearance, thus bringing the bottom tappet in continuous contact with the camshaft, the rotational speed of the tappet is increased. It is interesting to note that Chevrolet use bottom tappet springs, which does the same thing. It would be equally interesting to know whether they are for the purpose of inducing rotational speed to the tappet, or to supplement the valve spring against bounce. (11) The doubtful point about adapting the Chevrolet type of tappet in our engine is that in releasing the oil from the tappet on to the camshaft, we rob the oil feed to the camshaft bearing. Continued running on the bed will determine whether the bearings are starved of oil. Valve Bounce. By the time we were doing valve bounce tests the camshaft was possibly damaged by the tappet "scuffing" so that the results obtained may not be absolutely correct. We give the figures, however, and will confirm on our next unit. continued. | ||