The effect of clearance between tappet insert and camlobe on the tribological and tribochemical performance of cam/follower surfaces. (September 2020)

• Record Type: Journal Article
• Authors: Al-Jeboori, Yasir; Kosarieh, Shahriar; Ofune, MacDonald; Neville, Anne; Morina, Ardian
• Is Part Of: Tribology international. Volume 149(2020)
• Publication Date: 2020-09
• Subjects: Tappet insert clearance -- Valvetrain -- MoDTC -- ZDDP; Tribology -- Periodicals; 621.89
• DOI: 10.1016/j.triboint.2018.09.021
• Languages: English
• ISSNs: 0301-679X

Abstract

Abstract: This paper examines the effect of tappet insert clearance on the tribological and tribochemical performance of the camlobe/follower tribopair when lubricated in a fully-formulated oil containing 1 wt% of Molybdenum Dialkyl Dithiocarbamate (MoDTC). Tests were performed on a Single Cam Rig (SCR), taken from 1.25 l FORD Zetec (SE) engine. White Light Interferometry and Talysurf contact profilometry were used to characterise the wear scar on the tappet inserts and camlobes respectively. In addition, Scanning Electron Microscopy (SEM) was used on both (i.e. camlobes and tappet inserts) for wear mechanisms assessment as well as to access the durability of coatings used on tappet inserts. Energy-Dispersive X-ray (EDX) and Raman spectroscopy analyses were also used to understand the tribochemical interactions between oil additives and the cam/follower interface. Results show that the chemistry of the tribofilm derived on camlobes and tappet inserts vary as a function of tappet insert clearance and cam profile. Also, regardless of the type of coating, the smaller clearance of tappet inserts exhibited higher friction and wear. Therefore, based on this work, the use of the thicker tappet insert would be inadvisable as this possibly can cause higher fuel consumption and inefficient performance of the intake/exhaust valves of the engine. Highlight: The effect of tappet insert clearance on the tribological and tribochemical performance of the camlobe/follower tribopair has been investigated. The chemistry of the tribofilmderived from camlobes and tappet inserts was understood to be varied as a function of tappet insert clearance and cam profile. Regardless of the type of coating, tappet inserts with small clearance showed high friction and wear. In terms of camlobes wear, the cam nose was considered to be a region of significant wear, especially toward the edges.