Flat Tappets, old motors and ZDDP
- Thread starter Tire Shredder
- Start date
Yes it is...if you want more ZDDP in your oil, use diesel oil. There are also additives available. For a Supra, the ZDDP levels are not as critical.
The only thing similar is the shim surface is flat...that's it. Unless you would like to educate me on how the 7M valve train set-up is similar to the way flat tappets work in a SBC 
And I'd like to see a set of 7M, 1J or 2 J cams with excessive wear on the lobes.
And I'd like to see a set of 7M, 1J or 2 J cams with excessive wear on the lobes.
my 84 5m has excessive cam lobe wear. They use automatic hydraulic lasdh adjusters with a rocker assembly. However, is is due to a lack of oil supply to the top of the motor... so much so it was a TSB and revised in 85. some more ZDDP may have helped.
7ms seem to be ok, but I do see a lot of similarities in their design compared to a flat tappet motor.
7ms seem to be ok, but I do see a lot of similarities in their design compared to a flat tappet motor.
Lack of oil supply is the cause...no amount of ZDDP is going to help that (hence the TSB).
I'm still waiting on the explanation of these "similarities" between the valve train in a flat tappet engine and the 7M. Sorry...just don't see it.
Like I said, if you want more ZDDP run a diesel oil or use one of the additives available.
I'm still waiting on the explanation of these "similarities" between the valve train in a flat tappet engine and the 7M. Sorry...just don't see it.
Like I said, if you want more ZDDP run a diesel oil or use one of the additives available.
well, the 7m has direct oil splashing from the cam journals onto the shims/caps that are directly on the valves. A flat surface (non-rolling) ontop of the valve actuates it...like a flat tappet motor.
Flat tappet V-8s are basically the same idea, just using a push rod, being upside down and having a rocker arm...increasing the amount of force on the cams. I don't know how the V-8s get oil supply to their cam lobes.
Flat tappet V-8s are basically the same idea, just using a push rod, being upside down and having a rocker arm...increasing the amount of force on the cams. I don't know how the V-8s get oil supply to their cam lobes.
You're leaving a couple minor things out...like the spring pressures.
On a 7M spring pressures range:
Stock - 35 lbs
Comp Cams - 55 lbs
BC - 60 lbs
Ferrea - 67 lbs (std dual spring)
On a SBC the pressures range from 85 lbs stock to 130 lbs on a built motor...this greatly increases the pressure between the tappet surface and the cam lobe. That is why the cam profile for a flat tappet motor is less aggressive than what's possible with roller cams.
Plus (like you said), the rocker assembly is what the tappet pushes against, changing the force required to open the valves...on a 7M, 1J, and 2J the pressure is exerted directly against the shim/bucket (technically this is also a tappet). The valves in a flat tappet motor are bigger and heavier as well, requiring even more force. The design of the flat tappet motors in question is nowhere close to the design of the 7M. Like I said, the only similarity is the cam lobe is pushing against the flat surface of the shim. Other than that, you're comparing an apple to an orange.
The issue with flat tappets is not only due to what's happened to oil formulation. A lot of inferior tappets (Chinese) have entered the market and budget minded builders are using them. This design (very old) was not the best to begin with and guys pushed it to the limits. The Chinese tappets are not holding up very well.
On a 7M spring pressures range:
Stock - 35 lbs
Comp Cams - 55 lbs
BC - 60 lbs
Ferrea - 67 lbs (std dual spring)
On a SBC the pressures range from 85 lbs stock to 130 lbs on a built motor...this greatly increases the pressure between the tappet surface and the cam lobe. That is why the cam profile for a flat tappet motor is less aggressive than what's possible with roller cams.
Plus (like you said), the rocker assembly is what the tappet pushes against, changing the force required to open the valves...on a 7M, 1J, and 2J the pressure is exerted directly against the shim/bucket (technically this is also a tappet). The valves in a flat tappet motor are bigger and heavier as well, requiring even more force. The design of the flat tappet motors in question is nowhere close to the design of the 7M. Like I said, the only similarity is the cam lobe is pushing against the flat surface of the shim. Other than that, you're comparing an apple to an orange.
The issue with flat tappets is not only due to what's happened to oil formulation. A lot of inferior tappets (Chinese) have entered the market and budget minded builders are using them. This design (very old) was not the best to begin with and guys pushed it to the limits. The Chinese tappets are not holding up very well.
the rocker arm ratio plays into it a lot as well...
Our stock cams aren't very agressive either, at least from the standpoint of some of the cams I've seen from a SBC.
Our stock cams aren't very agressive either, at least from the standpoint of some of the cams I've seen from a SBC.
I guess I have a different mindset. Similar to seeing the glass as half full or half empty.
Rather than seeing the only similarity as being the flat surface...I see the only difference being the force exerted between the tappet and cam. When only considering how the valve train interacts with the cam at the contact point, they're exactly the same...same principle.
but I guess this reduced pressure is below the threshold of damage...as you suggested, I can't think of any excessively worn 7m cams (aside from reading a few build threads where they were slightly out).
Rather than seeing the only similarity as being the flat surface...I see the only difference being the force exerted between the tappet and cam. When only considering how the valve train interacts with the cam at the contact point, they're exactly the same...same principle.
but I guess this reduced pressure is below the threshold of damage...as you suggested, I can't think of any excessively worn 7m cams (aside from reading a few build threads where they were slightly out).
I guess is the difference is that the buckets on the shims dont spin like the the flat lifters on a pushrod engine. I guess that the small contact patch on the flat tappet leads to more concentrated wear.
That's my whole point Shredder...the forces exerted against a flat tappet is far more due to the design. The rocker arm, seat pressures, and valve size/weight make a huge impact. If you look at it in a very narrow way, the cam lobe pushing against a flat shim on a 7M is the only comparison. The thing is you have to look at how the two valve train designs work in the big picture to understand why flat tappet motors experience this problem. It really doesn't matter seeing it half full or half empty...it's seeing it as a system and how the parts interact.
Jman - the tappets spin to provide lubrication. The pic you posted is not entirely correct...the tappets have a slight concave shape on the surface that contacts the cam. This provides the spin and it does tend to concentrate the wear on the tappet. The material used for the tappets is critical...the best quality use specific alloys and are nitrated. The Chinese versions are crap IMO and have gone a long way causing this problem happening with such frequency.
Jman - the tappets spin to provide lubrication. The pic you posted is not entirely correct...the tappets have a slight concave shape on the surface that contacts the cam. This provides the spin and it does tend to concentrate the wear on the tappet. The material used for the tappets is critical...the best quality use specific alloys and are nitrated. The Chinese versions are crap IMO and have gone a long way causing this problem happening with such frequency.
Or the 1J or 2J motors...and the amount of ZDDP in modern oils have little to no impact as to why there's no issue in these motors
jdub;991511 said:Or the 1J or 2J motors...and the amount of ZDDP in modern oils have little to no impact as to why there's no issue in these motors
They are also designed a lot better...
jdub;991487 said:
How is a concave shape going to make it spin?
Edit: The tappets are concave, and the cam has a taper. I guess thats so you dont have to run as much taper on the cam. For the sake of argument, my diagram was sufficient, though.
The head design on the 7m isnt that far behind the JZ motors. Mechanically, they are very similar. And the main reason that its behind on airflow is because it has to be mated to 40 year-old block architecture thats very undersquare, which limits valve size, among other things.CryoSlash;991543 said:
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