On my last thread I wanted to share my inspection of my 2010 GRiSO's flat tappet.[You must be registered and logged in to see this link.]
I bought a C kit but haven't installed it yet. The kit is a little more complicated than I expected but I'll get to it eventually. Its just too hot to ride right now and I have other things to do.
I've been pondering why these lifters are failing and what was the reason MG decided to go with flat lifters with a DLC coating. It seems they may have just coated the lifters with chocolate and would have had the same result. Except the DLC got them out of the warranty, which is smart in a Machialvellian way.
Since I already bought a roller kit, this is just a mental exercise. Can the flat lifter system be saved? Why have zillions of Chevys, Fords, Porsches and Volkswagons been built with flat tappets and are still on the road.
My first thoughts on the cause of the failure is lack of lubrication and/or too much pressure between the cam lobe and the lifter. I think the DLC was a band-aid to a lifter failure problem but it turned out to be just a temporary fix, sort of like plugging a flat tire. I'm talking about when MG was testing the 4V engine prior to putting it in production. I speculating here. They found failing lifters late into their testing program and decided to slap some black goo on the lifters so they could meet their schedule.
There isn't a lot of oil up where the valves are. The pushrod engines have a single cam either above or below the crank and it has a constant bath of oil coming off the crank. The MG 4V cams are splash lubricated from the oil coming out of the cam bearing journals.
One idea I had was to cut a very small slot on the inner cam journals to provide a path for more oil to get to the lifters. A second idea is to fit a piece of sheet metal to partially block the hole where the oil leaves the cam block. Maybe just reduce the hole by 50%. The problem here is we want oil to flow up to the head, lubricate the valve train and carry heat back to the sump to be removed by the oil cooler.