Advantage in drilled cam gears ET157/1 ?

[highbury731]

Is there a technical advantage in having drilled cam gears? Besides looking fancy, they save a lttle weight (how much?), but is it an advantage? Does it alter flywheel effects in the gear train?

 

[TouringComet]

Yes, I believe for the go fast racer types, it is both a slight weight savings, plus it helps the engine rev up quicker.

 

[chankly bore]

P.E.I. was once shown a lightened gear at a Section meeting.He made a disparaging remark to the effect of "it took me hours to design that correctly." As a percentage of the rotating mass of the flywheels it is negligible, and you shouldn't sacrifice strength and rigidity. In my non-engineer opinion probably your time will be better spent elsewhere. When you think on, there is not much "flywheel effect" on the cam pinions, more thrust and pressure I would have thought.Wiser men may differ!

 

[davidd]

Is there a technical advantage in having drilled cam gears? Besides looking fancy, they save a lttle weight (how much?), but is it an advantage? Does it alter flywheel effects in the gear train?

It is like asking a marathon runner if lighter running shoes will give him or her an advantage. The answer will be yes, but will the same shoes give you the same advantage?--and the answer is almost certainly "no". If you are building a race engine and you need more power, there are lots of mods that you can do to make more power, say changing the compression ratio or the cam. As you make these mods, it is always a question of: how much bang for the buck am I getting and second, how does it affect the reliability. Titanium valves, for example, might need to be serviced every race and replaced every few, but they may get the number two rider closer to the number one rider. The marathon runner may use new running shoes every race or every few. This too may keep him competitive.

When you see lightened timing gears the question should be: "What are the one hundred and twenty mods that were previously made to the engine that caused the builder to decide he needed to lighten the timing gear." This would be like asking the runner what were the hundred and twenty training techniques that were used to get him to the point where the expensive running shoes made a difference. Most often we just slip on the shoes and hope everyone else will mistake us as a top runner.

To answer a little more directly, I have used lightened gears in several engines because I had them. They were lightened and thinned. In the last engine I used stock gears and it just happens to make more power than the earlier engines with exactly the same components, but carefully built. I have nothing against the lighter gears, but with good horsepower at 7000 plus RPM it is difficult to get too excited about the gears. Then again, sometimes you just want to wear the sneakers.

Maughan will make them for you, but you will most likely have to wait as they do them in batches when they have enough names on the list.

David

 

[dave g6xnc]

In Tuning for speed the great man, whilst refering to polishing inlet ports to a high shine said it might impress chance beholders but not much else (or words to that effect. Same would apply I think to lightened cam wheels, the The Prof would be the man to ask.

 

[clevtrev]

P.E.I. was once shown a lightened gear at a Section meeting.He made a disparaging remark to the effect of "it took me hours to design that correctly." As a percentage of the rotating mass of the flywheels it is negligible, and you shouldn't sacrifice strength and rigidity. In my non-engineer opinion probably your time will be better spent elsewhere. When you think on, there is not much "flywheel effect" on the cam pinions, more thrust and pressure I would have thought.Wiser men may differ!

So I wonder why the factory made the large idler lighter when it went from bronze to aluminium ?

 

[dave g6xnc]

Cost, they were up against it all the time, and I think they said it was quieter.

 

[vibrac]

forget rotating weight
look at it this way if you were racing would you leave a 1/2 diameter steel rod 1-1/2 inches long attached to your your timing case?

 

[Big Sid]

Most got this right , it's the many other licks that together help to build more power . My drag racer used std. Cam gears but other tricks added overall , like those two blow through ports behind the cams in the wall were enlarged to help reduce base pressure beneath the descending pistons , less pumping losses . And lightened followers and rockers to lessen valve float , less work for the valve springs to control , turn higher revs . So many other licks all resulted in better quarter mile times .
The alloy idler ran quieter , it expanded to follow the cases growth as they heated . The weakness was that the cam pinion teeth in many cases had sharp teeth edges and sliced off tiny slivers which ran through the entire motor . Loaded up the filter element and the bottom of the oil tank . Where the pinion teeth were less sharp the alloy idler lasted in many motors for huge mileage .
Best of all is the Lightnings steel idler , lasts forever , nicely adjusted at the half time gear and up against the cam gears its very quiet running too. Sid .

 

[Big Sid]

Also they were easier and quicker to hob out , led to fewer replacements making them , less costly than bronze I'd guess , the original material .
The redesigned and upgraded components found necessary developing the Picador drone motor to acheve reliability at sustained high power points the way to whats necessary for a very long lived and powerful road machine . That plus a good friction reducing oil nearly eliminates internal wear . One having the ZDDP package protects all high friction sliding surfaces . Sid .