Why to use max lift for cam degreeing

[idunno]

Cam companies typically recommend the max lift method. Here's the best reason. The specs given for the cam duration are generally as the lobe was designed on paper. There is usually some variances from as designed to what finally gets put onto the cam. Also the same lobe will vary its durations due to differences in the base cir. diameter on roller stuff. Typically around 1 degree per .040 of base cir. difference from the spec base size. When you use the max lift method you eliminate all of those and gets striaght to "phasing " the cam timing in. Also Some designs are so asymetrical that you have to measure very close to max lift. I check mine now at .002 before and after max lift,yes 2 thousanth's not twenty thousanths.

[OldSStroker]

Good points, but "paper" went out a long time ago. I suggest that the better cam grinding hardware compensates for base circle diameter. The newest CNC grinders probably do this.

Cam durations are quoted in degrees, and usually even numbers, but if you "Doctor" them or get a chance to look at the actual design numbers, they may be in an odd degree or fraction of a degree.

Wildly asymetical lobes are probably symetrical +/- a few degrees from max lift. So what do you do with a lift rule lobe that has dwell at max lift point?

[SStrokerAce]

FWIW.... max lift is about the only accurate way to figure it all out....

You seemed to answer your own question though?

Bret

[idunno]

All lobes dwell at max lift. But I know the designs you are talking about,the ones that look square. Check them closer to tdc. Try checking your next one at .002 from tdc ,you will be surprised how many degrees of crank rotation there will be. I posted this topic by mistake,it was actually supposed to be a reply to the degreeing in the cam post and I hit the wrong button DUH...It was easier to just post as a new topic than to have to re-type all that stuff. I actually work for a Cam company and I know that alot of our Masters were made on a milling machine by hand (the old fashon way). We are having all masters remade by a CNC machine but we have to do only so many at a time due to cost. Alot of cam companies are in the same boat but will not be so honest about it.

[OldSStroker]

All lobes dwell at max lift. But I know the designs you are talking about,the ones that look square. Check them closer to tdc. Try checking your next one at .002 from tdc ,you will be surprised how many degrees of crank rotation there will be. I posted this topic by mistake,it was actually supposed to be a reply to the degreeing in the cam post and I hit the wrong button DUH...It was easier to just post as a new topic than to have to re-type all that stuff. I actually work for a Cam company and I know that alot of our Masters were made on a milling machine by hand (the old fashon way). We are having all masters remade by a CNC machine but we have to do only so many at a time due to cost. Alot of cam companies are in the same boat but will not be so honest about it.

idunno, I like your screen name. All evidence to the contrary.

My understanding is that with machines like the Okuma CNC cam grinders lift numbers are directly input from the design software. Floor-to-floor time on a cam with lobe design stored digitally is in the 12 minute or less range, I hear. That includes changing from one design core to another.

IMO, I still think a VERY good mechanical grinder using near perfect masters might be able to generate a lobe surface with fewer imperfections than a CNC grinder. Perhaps the only real need for that might be in the very upper end of racng like Cup. I might be too old fashioned and conservative about this, however. For those Cup teams who grind their own lobes, are they using CNC?

Do you guys have trouble getting billet roller cores? My guess is that most cam companies don't make their own cores, but keep the "core guys" busy.

[idunno]

Cores are a concern. The Cores are coming from Crane, EPC, Cam Machine and Andrews. There are other companies that make alot of what they sell like Cam Motion. I have seen some of the mass produced CNC'd cams with lobes that did not clear and some with pitting, I guess the human eyes was watching something else when it was prepped and shipped.To error is human but to really foul things up get a Computer.

[Trev]

Guys
If the accuracy of the cam can be out on the base circle, whats the promise that its not out on the ramps and the lobe.

I would have thought that it would probably be better (if you want to) to check at 2 or 3 different locations

lift at TDC
degrees of inlet opening
degrees of exhaust opening

This is for carl, these modern machines companies like yours have, can you produce ( say a cam for instance ) accuracy to within a thou cam after cam.

Trev

[Jay Allen]

I *Doctor* most everything these days. I give the customer opening and closing events at .006, .020, .050, & .200.

However I have found that the lift at TDC I furnish them works out best. I have many customers that own a degree wheel yet I am not sure that they even know how to install it. Yet a dial indicator and a given lift at TDC and they are on their way.

.......Now just as long as TDC is REALLY TDC.......

[SStrokerAce]

.......Now just as long as TDC is REALLY TDC.......

Yeah that's the first problem.... and your right most people don't know what a degree wheel is used for. They don't understand that degreeing a cam is checking to make sure it's installed correctly not setting it at a proper advance.

Bret

[Adger Smith]

Why do you think the Top Fool guys hate to change complete engines or short blocks between rounds?
They can have a handle on all variables except Cams.. they know that no two cams are ground identical so the cyl pressure & air flow will change when they swap cams, Even with same grind cams. It even changes Cyl to Cyl. Cyl pressure changes play havoc with a Fuel tuneup.
That is one reason I have invested in cam profile equipment & software.
I had a twin engine boat bite me, quite a few years ago. Everything supposed to be identical. They had 30 hp difference. (made for some unique throttle settings) Turned out to be a difference in the Cnc'd heads air flow & the cam profiles. I use two different methods of cam installation. lift @ the valve @ TDC & the Max lift @ the cam I C/L. Always after running a profile check.