Flat tappets vs roller tappets, I'm dumb on this stuff, whats the diff?

[bad Chad]

I believe the tappets lift the valves open and closed.   Over the last year there has been lots of talk about roller tappets replacing flat tappets on later 8vs, and I get rollers are better, at least for some applications. 

I would like to see a diagram that could illustrate how these tappets work, and how roller are alike, and unlike flat tappets.  Don't just tell me, I need to see it to get anywhere!  Can someone help a poor yellow hammer out?

[Chuck in Indiana]

Yes, you are, Chad.  ;D :BEER:
Uh... think about a wheel compared to a board.
<running and ducking> Chad's a really big guy..

[youcanrunnaked]

Here you go:

https://www.youtube.com/watch?v=GV9eLZrRbgA

https://www.youtube.com/watch?v=y8J43AbENXA





More information than you asked for:  http://what-when-how.com/automobile/intake-and-exhaust-valves-and-mechanisms-automobile/

[Vasco DG]

I'll see if I can find some diagrams I can post of the 8V top end.

One thing that I think is often misunderstood is the difference between roller ROCKERS and roller TAPPETS.

A lot of people refer to setting the valve clearances as 'Adjusting the tappets' and this I think has led to some confusion as well. The TAPPET is actually the device or component that contacts the cam lobe and changes the rotary motion of the lobe into a linear motion. When one is settings he valve tash there is no 'Adustment' of the tappet, the tappet is just a component. What is being done is setting a clearance that in theory can be measured anywhere in the valvetrain so that when the engine is at operating temperature the tappet still has enough clearance so that it doesn't ride the cam on the base circle which allows oil to get between the tappet and lobe and lubricate and cool. It also means that the valve won't be held off its seat and get burnt. It also means that there isn't so much clearance that as the tappet comes off the base circle to start opening the valve it bypasses the gently opening ramps at the beginning of the lift and slams into the opening flank creating much higher shock loadings and more noise.

A roller tappet, is essentially a wheel rather than a flat plate that rolls up and down the cam lobe rather than sliding.

As I said. I'll try and find some pics. I have several sets of rollers on the bench at the moment but I don't want to disassemble a cambox unless I have to as they are a bit of an embuggerance to reassemble, even with the correct tools.

Pete

[Aaron D.]

The diagram illustrates why not to use a roller profiled cam in a flat tappet engine. Normal cam profiles aren't shaped that way.

Personally I think it best to have the parts in front of you. Too much misinformation on this issue. But I think I have photos of cams and tappets from an engine I repaired a while back. I'll see if they are on my Flickr. A classic worn cam/lifter case.

[youcanrunnaked]

The diagram illustrates why not to use a roller profiled cam in a flat tappet engine. Normal cam profiles aren't shaped that way.

Thanks.  Fixed it.

[flip]

Stupid question time. Are there roller kits for 2 valve per cylinder Guzzi engines?

[rodekyll]

A little fact about adjusting tappets:

This comes from the flathead/sidevalve generation.  Flathead valves live in the block, not the head.  They extended downward from the top of the block to either ride directly on the camshaft, or on a cam follower between the two.  To adjust, you opened a plate in the side of the engine and stuck the feeler gauge between the valve stem and the cam follower.  There wasn't any other linkage, so adjusting the tappets was a correct term then that made it into common (although technically incorrect) use over time.

Looking at the roller tappet v flat hat, I don't see how they could modify a flat one to go roller.  Roller tappets depend on a precise axial angle for the roller to work.  In the pics you can see that the roller tappet holds that angle by virtue of its shape -- it's oval, not round.  So it can't spin in it's bore and affect alignment.  A flat tappet is designed to spin in its bore a little at every valve cycle so's not to wear unevenly.  It seems to me that at some point of rotation, the roller in that design would be enough off-axis that it would drag instead of roll.

But maybe they have a workaround by now . . .

[Vasco DG]

Stupid question time. Are there roller kits for 2 valve per cylinder Guzzi engines?

Nope, not unless you're looking at some of the Rossopuro offerings.

Pete

[Aaron D.]

I've seen roller-tipped rocker kits in pictures, at least. I bet a clever fellow could make some roller cam followers if they really thought they needed it.

[guzzisteve]

Not to be confused w/roller rockers.
Figure that one out Chad w/o pics.

Hope I didn't pee in your snowbank.

Aaron beat me to the punch.

[rodekyll]

But a rocker only rocks this way and that.  It doesn't spin.  So you can easily put a roller in a rocker and rock-n-roll.

[Chuck in Indiana]

Ok, Chad.. it's all clear now, right?

[kevdog3019]

Where's Rocker when you need him to police things.   :+=copcar 
I guess Rocker is rolling with this one.   ::)

[lucky phil]

A little fact about adjusting tappets:

This comes from the flathead/sidevalve generation.  Flathead valves live in the block, not the head.  They extended downward from the top of the block to either ride directly on the camshaft, or on a cam follower between the two.  To adjust, you opened a plate in the side of the engine and stuck the feeler gauge between the valve stem and the cam follower.  There wasn't any other linkage, so adjusting the tappets was a correct term then that made it into common (although technically incorrect) use over time.

Looking at the roller tappet v flat hat, I don't see how they could modify a flat one to go roller.  Roller tappets depend on a precise axial angle for the roller to work.  In the pics you can see that the roller tappet holds that angle by virtue of its shape -- it's oval, not round.  So it can't spin in it's bore and affect alignment.  A flat tappet is designed to spin in its bore a little at every valve cycle so's not to wear unevenly.  It seems to me that at some point of rotation, the roller in that design would be enough off-axis that it would drag instead of roll.

But maybe they have a workaround by now . . .

Sorry but no, roller lifters aren't oval. that's what the linkage is for in this particular photo and case, to stop the rotation of the lifter and keep the roller in the correct orientation with the lobe.
Chev Gen 3 engines use a lifter tray for the purpose and the newer Guzzi engines with the roller lifters use a locating peg that engages a slot on the lifter carrier.
I much prefer the term "lifter" myself over "tappet" as you can likely tell.

Ciao  

[roofus]

There is lot of useful information posted above. It seems that roller tappets are superior to flat tappets.

I have 2 questions:

1. Have there been any problems with Guzzi's with flat tappets? I have a 2012 Norge which probably has flat tappets, because I understand MG switched to roller tappets during that production year?
2. Since roller tappets have more moving parts, is there a greater chance of something failing in a roller tappet despite is superior design?

[pressureangle]

There is lot of useful information posted above. It seems that roller tappets are superior to flat tappets.

I have 2 questions:

1. Have there been any problems with Guzzi's with flat tappets? I have a 2012 Norge which probably has flat tappets, because I understand MG switched to roller tappets during that production year?
2. Since roller tappets have more moving parts, is there a greater chance of something failing in a roller tappet despite is superior design?

The only trouble with flat tappets is Oil. Engine oils used to have a lot of additives targeted towards lubricating sliding surfaces like flat tappet cams and lifters. The EPA has mandated most of those additives out of engine oil, because over time they damage catalytic converters. Use a Motorcycle-specific oil and verify the ZDDP content. Read this;

http://www.enginebuildermag.com/2014/08/preventing-flat-tappet-cam-failures

Roller lifters have been standard in almost every pushrod-operated automotive engine since 1988. They are completely trouble-free *when the camshaft is relatively mild* as in most street engines. Roller race cams are of course more prone to failure; Retrofitting roller lifters into an engine not designed for them, like Guzzi, is probably not a good return on investment. I spent a lot of time researching Guzzi cams and found that considering the archaic design of the engine and the length of time cam grinders have had to work with it that even if you engineered a roller setup for it you wouldn't find a lot more power. You might, if the cam was mild, find some longevity; but since the flat tappet cams can already go a few hundred thousand miles, you may not find any more there either.

Here's what I'm currently up to, re cams and lifters etc.

http://wildguzzi.com/forum/index.php?topic=74056.0