tappets

[TINTIN]

Hi all, here is another Norwegian Guzzi racer. Very nice to find a dedicated forum for Guzzi racing!

I have a question about tappets. I'm building a new race engine for next season. I have collected various parts from ebay and by a mistake I bought a California 03 crank case as I forgot that this model had hydraulic tappets. These tappets are of mushroom type with a 15mm shaft (and 22mm head) so the tappet bores are 15mm as opposed to the normal 22mm.

The intriguing thing is that the hydraulic plunger (is that the term?) drops right out of the tappet and can be substituted by a small receptor for a normal pushrod (a little brick with a spheric grove of own manufacture). The big (?) advantage would be a weight saving of 22 gr on each tappet.

What I'm unsure of though, is weather these tappets will be strong enough run in a race engine.

Another unknown is that these Cali tappets don't have the usual radius but are ground flat. However it does work on the Cali, doesn't it?

Does anyone of you have any experience with these tappets or any opinion? Why did Guzzi change the tappet design in the first place instead of just fitting hydraulic plungers in the normal 22mm tappets?

 

[ed]

The weight savings might be tempting, but consider that those Cali tappets were not exactly engineered for high stress or "performance". Also consider that those tappets wont rotate as well if they aren't radiused, which can lead to pitting and fatigue issues...a noted problem that Dr John had with one of his bikes. High valve spring tension, high lifts or radical racing cam ramps will certainly exacerbate these issues.

Ed Milich

 

[Penis Rotor]

Errr. What Ed said. But I'd also add that as long as there isn't an issue with the oilways to the tappet holes why not just bore the tappet guides in the block out to accept the 'Solid Lifter' tappets? That would seem the easiest way of addressing the problem.

As for weight savings? if you're really getting that serious how about Ti. pushrods?

Pete

 

[TINTIN]

Thanks for the answers, both of you. And yes, I tend to agree with you, why run these tappets as an unknown when there isn't much gain in doing it and it would be relatively easy to avoid it by boring the block or just getting another solid lifter block.

But that said, I'm still curios about the whole lifter issue on a general level. I feel that the lifters are one of the bottlenecks in extracting real power from a 2V big block Guzzi engine as they are too small for a real high lift cam.

Fitting bigger lifters raises some questions.

- what are the pros and cons on mushroom lifters versus cylindrical lifters. Going for the mushroom type would be easier as it could be done by sleeving down the lifter bores rather than boring them. Also I guess the mushroom type in general could be made lighter than the cylindrical type.

I observe that Guzzi are using mushroom lifters in both the new and old 4V motors as well as in the small blocks but not in the big block 2V except for those hydraulic Cali's. Why did they those one type over the other in those designs?

- How does different material in the lifters work? The normal lifters seems to be made from some kind of cast iron which I would imagine are rather brittle and thus needs to be made thicker. The hydra Cali lifters on the other hand seems to made of normal hardened and ground steel and have much less wall thickness. Of course the critical place is the working face against the cam lobe and the requirements here will largely determine the choice of material. It's just interesting that steel lifters seems to work in the Cali.

- Then there are the question of the radius on the lifter face. I just don't understand how and why this radius work. In order to make the lifter rotate the main thing must be the off sett of the cam lobe relative the center of the lifter. This done, the radius-ing of the lifter face would just move the point of contact between lifter and lobe back into the very center of the lifter and thereby not create any rotation? Obviously there are something I haven't understood as the lifters in fact do rotate! And the reason they do, is NOT because the cams are ground with a tapper. I have measured this on 4 different cams: an 1100 sport, a Breva 1100, the Hydra Cali and a German after marked cam from HTMoto. Non of them had any tapper. The myth of the tapper might stem from the fact that the lobe will wear to a tapper due to the radius-ed follower. But that takes a long time. The cams I measured had somewhere in the region of 10-15K miles on them and didn't tapper across the lob more than 1/100mm


I would much appreciate any coments or view points on these questions. Also of course, I would love to hear about any practical experience with bigger/non original lifters. Are there anyone who have tried that?

 

[Chris R]

- what are the pros and cons on mushroom lifters versus cylindrical lifters. Going for the mushroom type would be easier as it could be done by sleeving down the lifter bores rather than boring them. Also I guess the mushroom type in general could be made lighter than the cylindrical typ

Basically it boils down to what the engine design's geometry allows. With a flat lifter the limitation is the lifter digging into the side of the cam. There is no real advantage to one type over the other except that a cylindrical lifter has less stress raisers and more bearing surface and a mushroom lifter, if available, is easier to fit as you don't have to bore out the lifter bores.

If you want more more acceleration the only solution is to go to a roller lifter - there are probably some harley cam people who could help as the motor is similar in geometry and they are used to get serious power out of a seriously old design.

Weight does not really have much effect in this part of the valve train - if revability is an issue look at pneumatic valve springs and titanium valves. Do not bother lightening lifters - strength and fatigue resistance is critical here.

- How does different material in the lifters work? The normal lifters seems to be made from some kind of cast iron which I would imagine are rather brittle and thus needs to be made thicker. The hydra Cali lifters on the other hand seems to made of normal hardened and ground steel and have much less wall thickness. Of course the critical place is the working face against the cam lobe and the requirements here will largely determine the choice of material. It's just interesting that steel lifters seems to work in the Cali.

Chilled or quenched cast iron is the standard material as it has good self-lubricating qualities and the appropriate hardness. Most hydraulic lifters are made this way as well - don't know about guzzi's. I guess these days steel and things like DLC coatings are becoming more widely used - again talk to the cam people.

- Then there are the question of the radius on the lifter face. I just don't understand how and why this radius work. In order to make the lifter rotate the main thing must be the off set of the cam lobe relative the center of the lifter. This done, the radius-ing of the lifter face would just move the point of contact between lifter and lobe back into the very center of the lifter and thereby not create any rotation? Obviously there are something I haven't understood as the lifters in fact do rotate!

I have never heard of cams being ground with a taper so don't know where your myth came from.

Why do the tappets rotate? Good question and I don't have a simple answer except to say that they certainly do and I suspect it is due to machining intolerances, end play on the camshaft and maybe some other things. Remember also that they go from floating to being highly loaded from full open to full closed. The same applies to piston rings - I have no idea why they rotate except it seems in their nature to do so!

The radius is critical though and if you grind the tappets flat and install them the cam will never break in and will self-destruct. Basically the radius is there so that there is always a single point of contact with the cam.

Chris R

 

[Chris R]

Oh and I should add that the real geometry problem is valve to valve interference which is the main problem with a hemi. You can sink the valves to some degree - this may help or hinder flow, you really need a flowbench to sort it out. Which is why a roller cam may be the only real option as you can get much greater accelerations.

Again there is lots of cam development software out there that will let you figure out what will work without cutting metal.

Ta,

Chris

 

[TINTIN]

Hi Chris,

just want to say thanks for your comments. During Christmas I have dived deeper into the actual metal of the art and mystery of Guzzi tuning and I am beginning to realize and appreciate the fact that there isn't any one easy fix to liberate all the horses. It's all subtle and interconnected. It's a fascinating dive though and I'm learning a lot about balancing conflicting interests, striking the right compromises.

It's fun and new to me to really enter the mindset of the engine world as I so far in my racing effort always have been more drawn toward the chassis side of the equation. The engines were mere means to propel those chassis'. But last season, having tasted the sweetness of a really powerful Guzzi engine built by HTMoto in Germany, got me hooked. And then, when that engine blew up, I wanted to look into the secrets myself.....and here I am.