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 4V flat tappet improvement?

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hipower
Carlotto
Carlotto
hipower

Posts : 37
Join date : 2020-06-06

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PostSubject: 4V flat tappet improvement?   4V flat tappet improvement? Icon_minitime1Sun Jul 26, 2020 8:17 pm

On my last thread I wanted to share my inspection of my 2010 GRiSO's flat tappet.

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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.

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Pete Roper
GRiSO Capo
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Pete Roper

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Join date : 2013-05-29
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PostSubject: Re: 4V flat tappet improvement?   4V flat tappet improvement? Icon_minitime1Sun Jul 26, 2020 9:02 pm

Nah, won't save it. Believe me, I've done a lot of research into the problem and it isn't so much the DLC as the cam profile and valve spring design.

Cutting slots in the bearing surfaces will simply make it impossible for the oil to form a wedge properly. Contrary to your belief as well there is an absolute abundance of oil up there. A shortage off lubricant is not the problem and in their efforts to effect a cure the engineers did redesign the weirs to be deeper at one point. It didn't help.
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hipower
Carlotto
Carlotto
hipower

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PostSubject: Re: 4V flat tappet improvement?   4V flat tappet improvement? Icon_minitime1Sun Jul 26, 2020 9:31 pm

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circles mark the spots

I was thinking of cutting a small slot, .020 x .020, with a jewlers saw or something similar
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hipower
Carlotto
Carlotto
hipower

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PostSubject: Re: 4V flat tappet improvement?   4V flat tappet improvement? Icon_minitime1Sun Jul 26, 2020 9:46 pm

Pete,
 
So if oil isn't the problem, then MG made the cam profile too aggressive. Maybe the marketing VP wanted too much power and wasn't willing to back off. Comparing this engine to the BMW R1100 can be helpful. The beemer had a little less displacement and was about 20 hp less. Maybe 80 hp if I remember correct.
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Pete Roper
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Pete Roper

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PostSubject: Re: 4V flat tappet improvement?   4V flat tappet improvement? Icon_minitime1Sun Jul 26, 2020 10:33 pm

If you do a search on this subject I've covered it several times before in considerable depth.

At certain speeds the valve springs allow the tappets to leave the opening flank of the cam and they then crash down on the nose circle of the cam. The coating being only microns thick and very frangible, crazes and then gets wiped off by the cam lobe. The variance in wear comes down mainly to individual spring specs and the mass of the valves in conjunction with the way the machine is used.
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Pete Roper
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Pete Roper

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PostSubject: Re: 4V flat tappet improvement?   4V flat tappet improvement? Icon_minitime1Sun Jul 26, 2020 11:25 pm

hipower wrote:
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circles mark the spots

I was thinking of cutting a small slot, .020 x .020, with a jewlers saw or something similar

This is a really good photo showing what looks like tempering marks on the nose circle of the cam. The reason it looks like a tempering mark is because that's exactly what it is, caused by the hammering of the tappet face.

If you examine the surface of your tappets under an electron microscope you would see the damage and, shortly, the DLC lifting.
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