Question about Tappets?

simtech

simtech

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Simtech
So...tappets are nothing more than a lifter? Why am I just learning about this...Is there a physical difference in them from a typical lifter?
 
normally lifters have rollers on the bottom, where as a tappet is normally flat.

Tom would know, but I have to assume that newer model engines have roller lifters now.
 
Ah...I was going to ask if roller lifters..er..tappets are the norm now in newer engines.

I just learned of tappets when a buddy of mines tappet came from together in flight. Never heard of tappet and Ive built many car engines...
 
simtech said:
roller on the bottom and concaved on top to accommodate pushrod.
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You must only work on late model car stuff if that's what you first think of. Summit Racing even calls solid lifters "flat tappet" on their website. :)

I'm making broad generalizations here, but Lycoming and the smaller Continental engines commonly use a "T" or "mushroom" shaped tappet with a separate hydraulic unit that sits inside the cavity in the tappet. Something shaped like this:

https://www.summitracing.com/parts/cca-2931-16/overview/

The big Continentals typically use more of what I would call an "automotive style" hydraulic lifter shaped something like this:

https://www.summitracing.com/parts/lun-70992-16/overview/
 
Tappet is a generic term for something that imparts motion (typically linear)
A lifter is somewhat more specific in that it commonly refers to something that "lifts" a valve.

Either term can be used to apply to either smooth or roller cam following device which can also be called a cam follower.

Now, your Lycomtinental manual may be specific in referring to some particular part by one name or the other, but that does not make the use of that term universal.
 
tappet with lifter inside....
fig2.jpg
Lycoming-O-360-Tappets.jpg
fig4a_big.jpg
 
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mondtster said:
You must only work on late model car stuff if that's what you first think of.
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You got it! hahaha I do remember back in high school not having flat bottom lifters. Just never heard of tappet until now.

Id much prefer roller lifters anyway, smooth operation and less surface area to rub.
 
I always heard the terms as interchangeable. A Lifter is a tappet/follower, etc
 
lifters are removable without splitting the crank case.....tappets are not.
 
mondtster said:
What do you consider a typical lifter?
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That's the problem right there. The word "typical" is highly loaded because it is application and period specific.
As somebody who's converted flat-tappet blocks to rollers, I can't even decide what I'd consider "typical".

Now to take the conversation into even deeper woods, would you say that a "typical" lifer is hydraulic? ;)
 
BigBadLou said:
Now to take the conversation into even deeper woods, would you say that a "typical" lifer is hydraulic? ;)
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I would, considering most of my work is on my 2004 chevy that had the bad casting castech heads which I have had to replace and the new aftermarket head cracked and hydro locked my engine resulting in a bent connecting rod.... Do I sound bitter..yup Chevy you can eat it on this one! The only saving grace is the FAA aint in on this one and I was able to repair it myself in my garage.

I see what your saying though typical is kind of in the eye of the beholder. If you never see a hydraulic lifter then its not typical to you and vise versa. Ive dealt with 70's to 80's era chevy 350's in the past. Ive build them bad and ive build them good...to this day though my mind goes to hydraulic lifters in modern day vehicles...or at least in my Silverado.
 
midcap said:
normally lifters have rollers on the bottom, where as a tappet is normally flat.

Tom would know, but I have to assume that newer model engines have roller lifters now.
Click to expand...
The difference would be in the engine you talk about and even then, they vary from model to model.
Roller lifters are still lifters. there are roller, domed, flat, some are hydraulic adjusted and some are mechanical adjusted.
some are called tappets because when the normal was mechanically adjusted they would tap, tap,tap until you adjusted them to the proper clearance. hydraulic eliminated that requirement, and so they became known as 0 lash lifters because they hydraulically run with no clearance between the filter and the cam.
 
nah its more fun backing them off until they clatter then tighten them to shut them up.hahaha
 
simtech said:
I'd much prefer roller lifters anyway, smooth operation and less surface area to rub.
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All they do is wear in a different manner, as many racers have found out.
 
The Lycoming tappet paper is most intriguing to me, but I have trouble with the author's statement that the gallery oil pressure is less on one side vs the other side of the engine. Yes, there would be a measureable difference but I'd bet it is less than a few percent since the port sizes in the crankcase are generous compared to the minor bleedoffs of the bearings etc.

Personally I think a lot of the problems of right-side Lycoming cylinders are related to startup and the tangential oil spray pattern from the main and rod bearing shells combined with the high location of the camshaft.

The authors obviously know a lot about hydraulics etc & it would be fun to split a 6 pack with them some afternoon. I gotta study it some more.
 
nrpetersen said:
Personally I think a lot of the problems of right-side Lycoming cylinders are related to startup and the tangential oil spray pattern from the main and rod bearing shells combined with the high location of the camshaft.
Click to expand...

Sorry for nitpicking, but I believe the correct term is "splash" lubrication. Spray lubrication is used in some engines but generally not as described.
 
nrpetersen said:
The Lycoming tappet paper is most intriguing to me, but I have trouble with the author's statement that the gallery oil pressure is less on one side vs the other side of the engine. Yes, there would be a measureable difference but I'd bet it is less than a few percent since the port sizes in the crankcase are generous compared to the minor bleedoffs of the bearings etc.

Personally I think a lot of the problems of right-side Lycoming cylinders are related to startup and the tangential oil spray pattern from the main and rod bearing shells combined with the high location of the camshaft.

The authors obviously know a lot about hydraulics etc & it would be fun to split a 6 pack with them some afternoon. I gotta study it some more.
Click to expand...
The pressure applied to the lifter is less significant than the pumping pressure the lifter develops.
 
Yes they pump - note the ball check valve in them. Actually it is a pair of them if you assume the action of the push rod on the piston is also somewhat like a check valve.
 
simtech said:
So...tappets are nothing more than a lifter? Why am I just learning about this...Is there a physical difference in them from a typical lifter?
Click to expand...
Tappets, Lifters; tomato, tomaato. They both do the same job, and the terms are used interchangeably.
 
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