TR6 TR6 Flat Tappet

[vettedog72]

What is a flat tappet; all the tappets I've seen appear flat except for roller lifters on roller cams. How do my TR6 lifters differ fom any late model push rod motor?

 

[startech47]

A flat tappet is a lifter that is not hydraulic. Also called solid lifters. Phil

 

[Alan_Myers]

Hi,

There are two other types of tappets now more commonly in use.

First, your TR6 has flat-faced, solid (one-piece) cam followers (aka "tappets" or "lifters"). One way to tell is simply to notice that the valve clearance needs to be manually adjusted every so often.

Most modern production cars now use a hydraulic lifter that is essentially self-adjusting. It does the same job, following the cam, but uses some engine oil trapped within it's multi-piece assembly to "pump" up and take up clearance space. This is basically self-adjusting and most cars with hydraulic lifters have no means of manually adjusting clearances. Hydraulic lifters will often run quieter, too.

There are also roller tappets. These are more likely to be found in high performance engines. They have an actual roller on the end that rides against the cam lobe. The idea is less friction and wear, along with more accurate tracking on more radical camshaft lobes spinning at very high rpms. This type lifter is set up in pairs, with a guide bar in between to prevent them from rotating within their bores, to keep the roller aligned with the face of the cam lobe. The camshaft itself has to be specially designed to work with roller lifters and is usually called a "roller cam".

One other thing, in the older 4-cyl. TRs the flat, solid tappets weren't designed to rotate in their bores, although I would guess that they do a little. I'm not sure about TR6. But, for a while some solid tappets were intentionally designed to rotate in hope of reducing wear and tear on both the lifter face and the cam lobe it rubs against. The rotating type are not completely flat, but have a very slight dome shape on their faces. I think the cam lobe is slightly different, too.

Flat, solid tappets and the cam lobes they come up against need to both be in very good condition. Any flaws in the face of either one will act like a milling machine on the other. Keep in mind that there is a lot of spring pressure always bearing down on them and the engine spins the cam rubbing it against the faces of the tappets.

When they are manufacutured, tappets are hardened and so is the cam lode face. Both will "work harden" from running against each other, but the first 10 or 20 minutes of running can and will ruin one or the other or both, if not pre-hardened to a certain degree. There have been a lot of poorer quality tappets sold in recent years, that simply weren't hard enough initially and did damage. Also, when a camshaft is reground it needs to be rehardened, because the grinding process used to reshape the lobes removes the .010" thick layer of hardness from their faces. The same would be true if tappets were refaced, but most often they are simply replaced, hopefully with good quality ones that are adequately hardened. Also, the entire tappet might be made of harder steel to begine with (unlike the more complex casting of the camshaft).

There are a couple different types of hardening done. Some need to be polished afterward, while others don't. I imagine both roller and hydraulic cam followers and their respective camshafts also need hardening for all the same reasons.

/ubbthreads/images/graemlins/cheers.gif

 

[Guest]

Hence "The Tappet Brothers" on Car Talk at National Public Radio.

 

[startech47]

The cam lobes are ground at a slight angle from front to back. This moves the point of contact from the center of the lifter from the center towards the edge,thus imparting the froce to rotate the lifter. Phil

 

[Bob Claffie]

Flat tappet is a mis-nomer. Flat tappets are any non roller tappets regardless of "flat" surface or "dished" surface. Flat tappets (lifters) can be either solid (mechanical) or hydraulic. Mechanical lifters, in theory, allow higher revs at the expense of a slightly nosier engine. As mentioned above, dished lifters, either mechanical or hydraulic induce rotation, flat ones may or may not depending on the design of the camshaft. All other info above is correct, for all practical purposes. Bob

 

[Don Elliott]

Alan - I thought that the engine in my TR3A had flat bottom tappets (cam followers or lifters). In 1988 when I rebuilt my engine I could easily see that the bottoms were flat and which ones were rotating because there were spiral marks on the flat end. A few had not been turning, so I lapped them on a flat piece for thick glass, onto which I had placed some fine emery cloth to level these out. This was with over 80,000 miles from new on the tappets. I put these same tappets into the engine because I had heard bad stories about "soft" tappets from suppliers. These original tappets in my engine have now done me fine for over 174,000 miles.

I also was led to understand that the tappets rotate in our 4-cylinder engines because the bore in the block for the tappets is off-center from the center of the cam lobe. It seems that this geometry makes the tappets rotate. I also heard that on the TR5, TR250 and the TR6, this might not apply, but I can't confirm this.

 

[YankeeTR]

Man...this topic has any many different opinions as a discussion about motor oil! Here's MY two cents.

Flat tappets can be either solid or hydraulic.

Flat tappets, in ANY post 1930's engine that I know of, are not really flat or dished. They are precisely machined with a very slight "crown" which is what causes the rotation that has been discussed. There are several cam manufacturers (like Elgin) that regrind lifters for a nominal charge.

Cam break-in is CRITICAL...use plenty of moly cam break-in lube and run the engine for 20 minutes at 2000 rpm to properly break-in the cam. I've done this probably one hundred times in street and race engines without one camshaft failure.

Most of you have always heard that you MUST always keep your lifters in order because they develop a wear pattern that matches each individual cam lobe. Good advice, to be sure. But if you mix up one or two don't despair. I've seen engines that had ALL of their lifters tossed into can and replaced in the engine in no particular order. These engines ran fine and gave thousands of miles of service for their owners. The key is there was no abnormal wear on any of the components that would cause one part to wear unevenly.

Solid lifters allow a higher RPM because they will not "pump up" which causes the valve to stay open and results in a loss of power and, often, valve to piston clearances issues. Anti-pump-up and Rhodes-style lifters address this problem by providing a "bleed-off" port that won't allow it to "pump up"...some lifters also accomplish this by loose tolerances built into the lifter that allow oil to escape during high RPM operation. (most OHV engines are designed so the valve lifter "plunger" is centered in the lifter... high RPM's don't allow enough oil to leave the lifter fast enough causing the lifter to "pump up").

 

[LastDeadLast]

While we're on the subject... I've always heard that the roller tappets (lifters) usually offer a substantial advantage over the older styles. Has anyone heard of some enterprising fellow (or gal) that experimented with rollers on a TR engine?

 

[jerrybny]

Thanks for the education Alan. I am now a little smarter.

 

[Simon TR4a]

When I changed the cam in my TR4a a few years back I purchased new, lighter weight tappets, and kept one of the old ones. (It is now on the top of my memo spike on my desk.)

There is a small witness mark from wear on the flat face of the tappet and marks on the sides from rubbing, but worst by far is a small amount of what looks like acid etching in the flat surface. I think I changed the cam in 1989, the engine was rebuilt by a previous owner in 1973, but I do not know if the tappets were replaced. The car had done about 80,000 miles at that point which would represent several million openings of each valve, so the tiny amount of wear seemed remarkable.

I have also read that tappets are domed a tiny amount, but cannot tell with the naked eye, and it does not seem to rock at all when placed on a sheet of glass, though this may not be flat enough to tell.

Simon.

 

[trfourtune]

yup,
all true. exception is-you can get ceramic lifters if you have $400. i am told there is NO BREAK-IN and you will never wear them out and can even swap cams with the same lifters without break-in procedure. they save cams as well so it's a win-win except the cash, but it starts to look better when you consider the benefits. schubeck makes them.
not legal in some racing rules (too much advantage and cost).
regrinding lifters with camshaft is best way to go otherwise because you will have a matched set. otherwise you should supply your new lifters to your cam grinder for best results.
rob

 

[YankeeTR]

[ QUOTE ]
While we're on the subject... I've always heard that the roller tappets (lifters) usually offer a substantial advantage over the older styles. Has anyone heard of some enterprising fellow (or gal) that experimented with rollers on a TR engine?

[/ QUOTE ]

Rollers offer more performance because the cams can have a higher rate of lift on the lobe...and they have more 'meat' so they can grind a better profile.

Roller lifters on any flat tappet cam would have no advantage..and might hurt performance.