ky

i work at an engine shop but i get nervous when my boss asks me questions about motors. like the difference between a flat tappet, roller, hydraulic, solid lifter, etc. can someone explain the differences in all the kinds of cams?

i know a roller has roller lifter and a wider lobe cam. and a hydraulic has hydraulic lifters. primarily whats the difference between a hydraulic and a flat tappet?

Starfury

A hydraulic lifter is one that uses oil pressure to take up the slack in the valvetrain. There's a small plunger inside the lifter that gets pumped up with oil pressure until all of the slackin the valvetrain is removed. Most cams in OHV enginesuse hydraulic lifters, be they flat tappet or roller,to reduce noise and valvetrain wear. The downside is that they generally cannot be used in very high-rpm applications.What happens is that as rpm increases, the lifters don't get a chance to bleed down before they get pumped up again with more oil, which can cause them to expand past their design limit and break.

Mechanical lifters are the counterpart. They're a solid lifter with no internal hydraulic components. The use of a mechanical cam/lifter setup requires constant adjusting of the valve lash (free play in the valvetrain), but allow much higher rpm operation. K code motors and Boss 302's use mechanical lifters toallow the engines to achieve 7k+ rpm without risking engine damage.

Flat-tappet cams use lifters with flat bottoms that ride on the cam lobes. Both the lifters and the cam are made of machined cast iron in order to properly wear into eachother.

Roller cams use rollers on the bottoms of the lifters that ride ona machined steel camshaft. This design reduces friction and wear and is much more durable than a flat-tappet design. The other added benefit is the ability to machine a much more aggressive lift into the cam lobes, since there is no sharp edge on the lifter for the lobe to catch on. This allows a wider duration at maximum lift without added valve overlap, resulting in more power across the rpm range without sacrificing low-end driveability.

JBradley500

how possible would it be to run roller lifters on a flat tappet? does the lobe have too aggressive of a peak shape on it to run a roller lifter or is it possible?

ky

ok so flat tappet and roller are alike, right? both dont have moving parts in the lifter, like the hydraulic? which has a plunger.

so then i was correct in my head. thanks tad.

and jbradey, no you cant run a roller lifter on a hydraulic cam.

Starfury

No, that's not correct, and no, you can't run roller lifters on a flat tappet cam.

Hydraulic and mechanical refer to the internal workings of the lifter, not the external. The vast majority of OHV engines use hydraulic lifters. You can have a hydraulic roller or flat tappet, just like you can have a mechanical roller or flat tappet. The mechanical portion just means that it's a solid lifter and has no internal plunger.

Most people are going to be fine with hydraulic lifters, be they flat tappet or roller. You only need to start looking at mechanical lifters when you start looking at cams that rev up past 6500 or so.

ky

ok thanks. i guess the more im around them the more ill understand.

Starfury

Well, tell me what you don't understand and I'll explain

ky

so i guess my question was, whats the defference between a hydraulic and a flat tappet.

but im assuming the only difference is the lifter. the cam is the same. the hyd lifter has a plunger and the flat tappet has a solid lifter with no plunger so its capable of going beyond 7k rpm.

Starfury

The problem is that you're comparing apples to oranges. Like I said, hydraulic and mechanical refer to the internaldesign of the lifter, not the external. A flat tappet design has nothing to do with whether or not the lifter is a hydraulic design. It can be mechanical (solid)or hydraulic. Flat tappet just means that the bottom of the lifter is flat. Roller means that it has a roller on the bottom.

67mustang302

There's 4 general lifter types, hydraulic flat tappet, hydraulic roller, solid(mechanical) flat tappet and solid roller. A hydraulic cam can be either flat or roller, and a solid cam can be either flat or roller.

One other problem with hydraulic lifters, is the newer types of anti pump up lifters prevent the pump up issues associated with hydraulic lifters, but at high rpm have the opposite problem, the increased valvetrain force at high rpm can cause the plunger to depress down into the lifter rather than transfering the force to the valve. The end result is an effective decrease in cam lift/duration at high rpm, causing a loss of power. And hydraulic lifters tend to be heavier than their solid counterparts, increasing the liklihood of valve float at high rpm.