Rabbi Mike

At the risk of inviting stinking piles of ridicule from all the modders here, I have to ask:

What are direct-acting mechanical buckets? Do they have to do with the camshafts or valves?

I'm sure that I'm supposed to be happy about this, but I have no idea why.

Ltngdrvr

3.7 V6 DAMB are buckets that sit on top of the valve/spring assembly and the cam lobe sits directly on them to open the valves instead of having cam followers like the V8 motors.

Gene K

Think about a small bucket. Now set it upside down over the valve/lock/retainer and spring. Now set the cam on top of the bucket. Thats your entire valvetrain. No follower (OHC version of a rocker). Its like the valvetrain on a 14,000+ RPM Superbike.

Ltngdrvr

Seems like I provided about the same explanation...

Ford is touting it like it is something new. Overhead cams have run on direct acting buckets from the very first OHC motor ever built.

The OHC motors with cam followers are the ones that are not the norm.

cdynaco

Right. My Lotus 907 4V had the cup/bucket style cam followers. But without the fancy DAMB name. The lobe acted directly on the 'upside down' cup. Underneath the cup sat a shim about the size of a dime which sat directly on the valve stem. No hydraulic 'lifters'/followers. The clearance was adjusted by the shims. It was a tricky job and even trickier reassembling! LOL A labor of love for sure for 15 years.

Ford's 4.6 3V was the first I personally saw using finger followers that reach out from the cam lobe to the hydraulic lash adjuster (lifter in a push rod engine) that sits on the valve stem. Its sort of a rocker arm (similar to a push rod engine).

The 5.0 really utilized the extended reach of the finger follower and allowed them to play with cam placement and port placement. No more having to have the cam directly over the valve bank/stems like back in the day.

hawkeye18

The original SHO engine uses buckets and shims. The SHO engine came out in 1989, a full 21 years ago. Though to be fair it was incredibly advanced for its time. Much like this mustang engine is now. Might be why I'm getting one.

cdynaco

Yeah my Lotus was a 1974. Thought it was incredibly advanced too!

FivePointO

So I have to ask... Whats better the mechanical buckets or roller finger followers for high rpm? I would guess the mechanical buckets do to not having adjusters.

Gene K

Buckets are better. I think the difference is the finish Ford is putting on the buckets.

Ltngdrvr

The fewer parts the better generally but there are pros and cons to both.

cdynaco

Yeah I doubt high rev F1 engines use finger followers - nor Top Fuel.

Ltngdrvr

No, Top Fuel uses shaft mounted rocker arms, real old school stuff there...

hawkeye18

The advantage to buckets is that the fewer times energy changes direction, the more is kept through it all. This is the same concept that results in a SRA using less drivetrain power than CV axles. So, the camshaft pushes directly on the valve; all of the energy is transmitted to the valve. Also, the less moving metal you have, the less inertia you have to deal with.

The reason Ford used followers for the GT was for physical cam placement, IIRC. They wanted the cams as far outboard on the heads as possible for port placement. This usually results in a lower possible red line, but Ford seems to have done ok at 7k rpm. FWIW that was the redline of the original SHO motor as well (although that was just so the dang alternator wouldn't blow up).

cdynaco

Oh. right. duh. not enough coffee in the tank!

Gene K

And I dont think F1 even has steel springs. Im thinking their valvetrain is pneumatic.
Some correct me if Im wrong?

cdynaco

Really? Well that shows my age. Not the same as back in the day with the Lotus John Player Special streaking through downtown Long Beach. Course back then they actually had to shift too.

Mario Andretti and Niki Lauda...

Rabbi Mike

So . . . the upside-down bucket contains the shim, which pushes on the valve-stem?

If so, why is this better than just having the cam lobe push directly on the valve-stem?

Thanks for everyone's info!

cdynaco

You need a way to adjust the 'tappet' clearance. The shims are mic'd to the thousandth. The clearance changes based on different engine temps - all the moreso with aluminum heads - and of course miles on the engine.

On my Lotus (all aluminum even back in '74) they went out of adjustment between 7-10k miles. The valve wears deeper in the seat over time and the top of the valve stem can wear from the constant action pushing it down - both of which affect clearance between the top of the valve stem and the inside of the cam cup/bucket (we simply called them cam followers back then). If the clearance was too tight the valve wouldn't close all the way. The resulting gases seeping past on the combustion cycle would in time burn/warp the valves, which would prevent complete closure and affect performance (the combustion chamber is leaking). If the clearance was too great, the valve wasn't opening completely (again robbing performance because you weren't flowing at full capacity).

Different thickness shims are used to get the clearance to spec. Cold spec exhaust valve clearance was .010 - .012, the intake valve clearance was .005 - .007. I was always taught that a little rattle (tappet noise) was better than none. Your micrometer and feeler guage were your friend. Keep in mind those clearances narrow when the engine is up to temp and/or really hot from hard driving. If the cold clearance was too narrow, you'd use a thinner shim. If it was too great, you'd use a thicker shim. AND you'd have to allow .004 in your calculation for the liquid gasket material between the cam tower and the head itself, lay down a bead just right, and then torque everything to spec. (Whereas the 4.6 3V & 5.0 4V have the cam tower incorporated into the head mold itself.)

The cold spec clearance process was the same with pushrod motors back in the day with solid lifters. Although they didn't use shims, there was a stem adjuster with a lock nut on the rocker arm.

Whereas in the case of hydraulic lifters (push rod) and hydraulic lash adjusters (OHC), the hydraulic action of the oil takes up the slack. No more shims and such.

In the case of the new 3.7 and the DAMB, I assume this is a hydraulic lash adjuster of some sort between the lobe and the top of the valve stem. Hence the "dynamic actuated" (hydraulic) mechanical bucket. Just a hunch. I haven't read up on it.

Ltngdrvr

The bucket spreads the load out across the cam lobe just like a lifter does on a cam lobe in a OHV motor. A cam lobe acting directly on the valve stem would wear a groove in the cam and wear the top of the valve stem down pretty quickly.

Ltngdrvr

And D.A.M.B. stands for Direct Acting Mechanical Bucket which sounds to me as if it is a solid unit, no hydraulics to it.