Alyn, Thanks for your interest, curiously enough the tappet adjuster seemed to shear whist still within the thread of the rocker, it sheared at the weakest point, where the pushrod socket leaves the surrounding metal at its thinest, Reassuringly enough the two threaded parts fit back together perfectly without any loss of material, no obvious fragments missing, of course the material abraded from the pushrod must have gone somewhere, but I am not intending to pull the motor down to check, time will tell on that one. With time on my hands and nowhere to go I might pop off the timing chest cover in the next few days.
E: Engine Exhaust Tappet
- Thread starter Peter Holmes
- Start date
Looking at the failed adjuster I get my doubts about oil supply from the rocker bearings - and along these lines about oiling the cams via pushrods and oil hole in follower. I can imagine all oil is flung off the rocker before it gets to the rocker end to lubricate the adjuster cup and in fact most of it runs down along the pushrod shrouds possibly. So I do not bet on cam oiling from pushrods and instead care for oil through cam spindles and their needle bearings. With same logic I lasered the follower oil hole shut .
One thing all Vincenteers should watch is unusual adjuster settings way off the initial looks with time : This is a great tell-tale of something going on in the valve train, either low down in the box of troubles or in the top end. So really this defect could have been found before dramatic failure.
I think the cups in the adjusters and in the followers as well are way too deep machined: All you need is a depth like the radius of the ball ends, anything more is of no use , in fact bad as it limits the deflection between pushrod and rocker or follower, critical for high lift cams. So I ground off one mm from the Neal Videan adjusters and the followers too, no use anything deeper. On some pushrods the waisting below the ball end seems a bit minimal so another detail to rectify. Bent pushrods and defects like above are the consequence of hitting the edge of the deep cup on deflection.
In my photo to compare sizes the top pushrod is Horex 400 alu, below BMW /5 or /6 series stainless steel, later changed to alu 10 mm 2mm wall thickness, like on my own on bottom place. See the BMW adjuster with cup depth same like radius of ball end,no need for more depth, even with that length of rod which is safe to standard 7000 rpm, in fact more than 8000 rpm. The shortened Videan adjuster on my alu rod got all that deflection you see in the photo while still sitting in the cup.
The 10 mm alu pushrods in the B-Rapides required some mods : The countersinks in the engine case for the rod shrouds and their seals don´t line up with the cups in the followers from design and were never rectified I guess ? So for extra clearance I made offset alu seal adapters and shortened the shrouds for offsetting the pushrods. Works to my likings but needs a little attention when assembling the head and pushrods. All alu engines , cylinders and heads should go with alu pushrods for keeping valve clearances, steel is not desirable here.
One thing all Vincenteers should watch is unusual adjuster settings way off the initial looks with time : This is a great tell-tale of something going on in the valve train, either low down in the box of troubles or in the top end. So really this defect could have been found before dramatic failure.
I think the cups in the adjusters and in the followers as well are way too deep machined: All you need is a depth like the radius of the ball ends, anything more is of no use , in fact bad as it limits the deflection between pushrod and rocker or follower, critical for high lift cams. So I ground off one mm from the Neal Videan adjusters and the followers too, no use anything deeper. On some pushrods the waisting below the ball end seems a bit minimal so another detail to rectify. Bent pushrods and defects like above are the consequence of hitting the edge of the deep cup on deflection.
In my photo to compare sizes the top pushrod is Horex 400 alu, below BMW /5 or /6 series stainless steel, later changed to alu 10 mm 2mm wall thickness, like on my own on bottom place. See the BMW adjuster with cup depth same like radius of ball end,no need for more depth, even with that length of rod which is safe to standard 7000 rpm, in fact more than 8000 rpm. The shortened Videan adjuster on my alu rod got all that deflection you see in the photo while still sitting in the cup.
The 10 mm alu pushrods in the B-Rapides required some mods : The countersinks in the engine case for the rod shrouds and their seals don´t line up with the cups in the followers from design and were never rectified I guess ? So for extra clearance I made offset alu seal adapters and shortened the shrouds for offsetting the pushrods. Works to my likings but needs a little attention when assembling the head and pushrods. All alu engines , cylinders and heads should go with alu pushrods for keeping valve clearances, steel is not desirable here.
I have a decent magnifying glass, the two broken pieces fit back together perfectly, when held together it is almost impossible to see the break, it would appear that the seat of the fracture started in the valley of the thread, there is no sign whatsoever of the pushrod hitting the edge of the cup.
Reply to to oexing, I have replaced the damaged pushrod with a spare I had in my under the seat toolbox, must replace it some point, the new adjuster I have fitted is a Neal Videan product, I have fitted as supplied from Neal without modification, it seemed to be a very good fit with my spare (but not new) pushrod, I did lubricate the socket with MOLYFORT MP, the lubrication of this part does concern me, but it never had done before in the last 54 years, if that tells us something.
I have been using Neal's adjusters with VOCS rods. How do your rods differ in ball radius, length and type of metal. Just asking as a Chemist because I adjust my pushrods every 5,000 miles. I have had a pushrod failure once in 40 years. Hind leg of a donkey is what it was.
You and me both Alyn, first time I have had this type of failure in 54 years, but most of that time on a twin, only owned the Comet for 10 years approx, I thought I had seen everything, starting with gear change bevel gear failure in the very early days, 1965, always something waiting to surprise you.
I will probably pop off the timing chest cover and take a peek inside, what is the view on replacement gaskets, can I purchase a Cometic gasket in the UK, is it a good idea, would I have source thicker rubber washer seals for the cam wheel spindles to compensate for the thicker gasket, does anyone sell thicker washers for this purpose, last time I had a timing cover off I felt that the new rubber washers that were supplied were a bit thin anyway.
