Top end work, 1100 Sport

[luhbo]

... they are definitely convex. Do you believe that is an urban myth?....

 

I've no problem to believe you. If you hold them together as you did it, how large would you say the resulting gap is?

 

Hubert

[Guest ratchethack]

Why not bring those rockers to a shop and ask them to grind nice little convex surfaces on them If you tell them how important these are to keep the valves spinning they'll do their very best probably.

 

. . .One can read every now and then of such convex surfaces, but all followers I've seen so far (mostly old stuff ) don't show this feature. FIAT ones neither, nor was it implemented on the ones I bought from Stucchi once (the long and light ones). I could see no avantage of such a shape, but the downsides are obvious: only a very small contact area between cam and follower, short line if not even point only.

No one other than yourself (and one other) has posted anything about spinning valves, Hubert. Several (myself included) have mentioned spinning (rotating) tappets (aka lifters, aka followers).

 

Though routinely called "flat tappets" to distinguish them from rollers, all advanced "flat" tappets are actually ground to a convex or "crowned" shape, to match a specific cam lobe taper grind. A convex tappet design is a far more sophisticated design than true flat tappets. Convex ground tappets provide a broad, curving "swipe" of contact between cam face and tappet with each pass of the cam lobe, that rotates the tappet a few degrees with each pass, thereby spreading the wear across a relatively large surface area of the tappet face. The design contacts the full working breadth of the cam face. There IS NEVER either a "short line" or "point" of contact. This is a far superior design to true flat tappets, and has been well established with pushrod motor builders (and builders of other kinds of motors) for well over a century.

 

TAPPET CROWN:

 

A small amount of spherical crown ground on the faces of most nominally “flat” tappets, to prevent the edge of the tappet from riding off the edge of a tapered cam lobe. The amount of crown is determined by the amount of lobe taper, both being set by the engine manufacturer. Normal tappet wear occurs as a “donut” partway off-centered on the face. Wear near the edge indicates a tappet with too little crown for that cam. Loss of specified tappet crown indicates a worn cam.

 

TAPPET ROTATION:

 

Flat tappets must rotate in their bores, to continually present a fresh part of their face against a rotating cam, and thus equalize and minimize wear. (In contrast, roller tappets must NOT rotate at all.) Rotation is driven by offsetting the lifter bore from the center of the lobe face, lobe taper in the same direction as lifter offset, and lifter crown to match lobe taper. Before installing tappets, check that each lifter is free to rotate in its bore, and apply only engine oil (not sticky “cam lube’) on the sides of lifters. If a flat tappet does not rotate sufficiently, or at all, that lifter and cam lobe will wear out prematurely, perhaps as soon as break-in.

 

LOBE TAPER:

 

The small amount by which one side of a flat-tappet lobe is larger than the other, even though both follow the same profile. Cams carry taper left or taper right and zero to .003” taper, depending on the engine. The direction and amount of taper is measured best across the diameter of the base circle. Hold the front of the cam to your left (as a cam-grinding machine does). If the forward (left) side of the lobe is larger, that is taper-left (TL). If the rearward (right) side of the lobe is larger, that is taper-right (TR). All lobes should measure with the same amount of taper, but not necessarily the same direction. TR pushes cams into the block, off the angled pressure from tappets. Engines with TL, mixed tapers, or roller tappets (with no taper) require a cam thrust plate. Lobe taper works with tappet crown and tappet bores offset from lobes bores to drive flat tappets into rotation. See: “Tappet Crown, Tappet Rotation.”

 

 

SOURCE: Elgin Cams CAM GLOSSARY

 

http://www.elgincams.com/glossary.html

[raz]

If you hold them together as you did it, how large would you say the resulting gap is?

Pushing one side together so I double the gap, I can fit a 0.10 mm gauge but not a 0.15.

 

I thought they were not actually convex but rather just tapered from center, as in "cone shaped" and when I hold them together I can't see any spherical shape, just an angle. Hard to tell though.

[luhbo]

.10 is a lot of wood as I would call it talking about it

 

I took pictures of two old ones, out of the scrap box (they're coming from a totaly worn LM1 engine):

 

 

 

 

Measuring the gaps would mean a major task even for a professional I guess. Anyway, something like a convex or even biconvex shape seems recognisable.

 

Here are two others, possibly showing the ring where the ruler in the above pictures was laying on:

 

 

On second sight it could as well be that the ruler lay upon the least unworn areas. In the center material is missing, and at the peripheral regions material is lost. Then, how could they've been looking once when they were new?

 

 

Hubert

[Guest ratchethack]

I took pictures of two old ones, out of the scrap box (they're coming from a totaly worn LM1 engine):

TAPPET CROWN:

Loss of specified tappet crown indicates a worn cam.

 

SOURCE: Elgin Cams CAM GLOSSARY

 

http://www.elgincams.com/glossary.html

 

FWIW, here's wot a tappet looks like when both tappet (and cam) are well beyond thoroughly roached (upper left).

 

This one has worn right past true flat, and went concave. Once the case hardening was gone, it quickly wore all the way through.

 

 

For comparison, moderately worn crowned (convex) flat tappet, with correct, characteristically smooth "donut" wear pattern clearly visible (lower right).

[Greg Field]

 

On a new Guzzi cam of this era, both front lobes taper toward the front, and both rear lobes taper toward the rear. The taper is not much, 0.002 inch or so. (FWIW, Guzzi's use of tapered lobes started, I'm pretty sure, with the Sport 1100; earlier Guzzi cams feature flat-top lobes, or so I have been told by one of their engineers.)

 

If you look at the sides of your cam's lobes, you can see this manifested in the worn (high point of the taper) and unworn (low point of the taper) areas. On a new or good Guzzi cam, the unworn area would extend up and over the tip of each lobe and would be as much as half the fore-aft width of the lobe. As the cam and tappets wear, the fore-aft width of the wear pattern will move forward on the front lobes and rearward on the rear lobes until eventually it marches off the front or rear or the lobe. Once this has happened wear accelerates. Pretty soon, the wear stretches across most of the side of the lobe, too, leaving just a crescent unworn on the upper third of the lobe, and circular spin marks near the center of the side lobe. Things are still spinning but wearing fast.

 

This is exactly where your camshaft is at. Look at the exhaust lobes, especially the front (for RH cylinder) one. The crescent is there and growing smaller. Can you yet catch a fingernail on the edge of the crescent? Soon, you will be able to. One day, one of the lifters will cease spinning, and then you'll soon hear nasty noises. Replace the cam or have it re-ground.

 

Use new tappets or good re-grinds. As said in the other similar thread, they must not be flat on the bottom. They are ground on the bottom surface to the shape of a very low cone, such that there is a point in the center, to mimic a "radius."

 

Commit to using good oil that contains API SG levels of zinc and phosphorous (1200+ ppm of both).

[gstallons]

Raz,

I hope you will take some good advice.

1. See if there is someone close that regrinds camshafts and price their labor vs the cost of a new cam.You might have to research to get the original specs.

2. Install new lifters or have these reconditioned by a firm that knows how much convex surface theses lifters need.The surface has to be angled so the center of the lifter contacts the center of the cam lobe.

3. The naked eye or a bunch of friends will not be able to tell you how much wear is on these parts.

[raz]

Thanks a lot, Greg and Gene. This is becoming expensive

[motoguzznix]

Thanks a lot, Greg and Gene. This is becoming expensive

But there are advantages too:

 

If you use a reground cam, the base circle has a tighter radius. When you mill off the head and shorten the cylinder barrels to get a working squish arera, the reground cam helps you to cope with the stock pushrod length. Otherwise the pushrods shoud be shortened to keep the valve train geometry when the cylinder/head length gets shorter.

[raz]

But there are advantages too:

 

If you use a reground cam, the base circle has a tighter radius. When you mill off the head and shorten the cylinder barrels to get a working squish arera, the reground cam helps you to cope with the stock pushrod length. Otherwise the pushrods shoud be shortened to keep the valve train geometry when the cylinder/head length gets shorter.

That's a thought. Pistons already seemed level with barrels (unless my new base gaskets differs from the old ones) so I guess I'd just take a mm off the heads. I would keep the stock pistons but replace the rings and maybe I can sell the unused FBF pistons for €200, which is what I paid for them... that route would hurt my wallet less, thanks for reminding me.

 

It seems a new cam from Guzzi is 310 €. The only one available is 05053331 "Breva, Griso, Norge, Cal. Vint.", I wonder if that has the same specs as my old one?

[Greg Field]

That's a thought. Pistons already seemed level with barrels (unless my new base gaskets differs from the old ones) so I guess I'd just take a mm off the heads. I would keep the stock pistons but replace the rings and maybe I can sell the unused FBF pistons for €200, which is what I paid for them... that route would hurt my wallet less, thanks for reminding me.

 

It seems a new cam from Guzzi is 310 €. The only one available is 05053331 "Breva, Griso, Norge, Cal. Vint.", I wonder if that has the same specs as my old one?

 

 

Similar specs but not exactly the same. We have fitted them to 4-5 Sports. They work just fine and are a drop-in. You could also go with a Megacycle cam or nay of several other offerings that are common in Europe (Scola, etc.)

[raz]

So I found a reputable guy who can regrind my cam and it seems it will end up around €100 with hardening. Pondering Motoguzznix' comments I wonder what if I don't mill the heads or barrels? The pushrods will be a tad short, how much of a problem is that? I guess I'll refresh my rocker faces too but tappets will be replaced with new ones.

 

If this really makes an incentive to mill the heads and ditch the FBF pistons, I'll go for that. Otherwise I like the idea of trying the FBF ones out and not touching the heads. For now.

[gstallons]

Ask the man doing the work how much he will remove from the cam lobe. Then ask him if you have any worries. He will tell you that is what the lash adjustment screw is for.

[motoguzznix]

By design the stock pistons seem to me the stouter items.

Maybe you can use the lighter pins in the pistons if the length is the same.

Concerning the combustion chamber design the stock pistons combined with milled heads is the better solution. You will get squish and a more compact chamber with less surface area. Both keep the engine away from pinging. CR will go slightly above 10:1 (mine started at 9.15 from the factory) which makes no need for a twin spark.

 

When the pushrod length is not correkt (being too long or short) the valve lift curve géts asymmetric. You can observe this when you look at the connection where the pushrod meets the valve lash adjustment screw at the rocker: At closed valve there is an angle to the one side, at full open valve the angle is to the other side. This angle should be the same left/right. If this is the case, rocker adjustment screw and pushrod are exactly in line when the valve is at half lift.

If the pushrod length is incorrect or the valve seats get deeper after reworking, this symmetry is disturbed. This means the angle pushrod/rocker gets tighter to one side thus increasing the valve train wear. Additionnally the maximum possible valve lift of the cam will not be reached.

 

Keeping in mind this I think it becomes clear what direction to go. Just my

[CFB]

My sympathies... Yep, Sports do wear that way...