Cam Calculations

[ChrisHParticipant @chrish]

Does anyone have a link to a cam calculation programme for calculating the cam profiles for an I.C. engine? Thinking, design your own engine here.

The modelenginenews website used to have a programme, but it does not seem to be working since we turned the New Year.

Chris

[ChrisHParticipant @chrish]

[Roderick JenkinsParticipant @roderickjenkins93242]

Chris,

If you have Excel then my cam spreadsheet can be copied from my Drop box here

Change any of the entries in the blue boxes on the data entry sheet (no.1) to get the cam profile. If the cam drawing goes wonky then the figures entered do not give a solution. PM me if you need further advice.

HTH,

Rod

[ChrisHParticipant @chrish]

Thanks Rod, have sent you a PM.

Chris

[Tim StevensParticipant @timstevens64731]

There are really two problems to solve – both of which can be complex.

I think the OP wants to know how to draw, or to make a cam which meets given criteria – probably both draw and then make.

The more important question which bothers the designer is 'What are the correct criteria for this engine?' Not merely the opening and closing angles, but the lift, the accelerations and decelerations that the various bits will stand at peak revs, and so on. Much of this can be left to a million dollar computer and a flock of geeks, but there is always a good chance that when they have done their best, someone with fifty years of dirty fingernails will tweak another few revs, or Watts, out of it all.

In my limited experience, a ploy that works reasonably well is to design what theory tells you will give the dwell and lift (etc) you know the mechanicals will stand, and make test cams with a vernier fitting to the shaft giving options no more than 2 degrees apart.. Then you can play with openings and overlap, etc, knowing that the basic mechanicals are Ok, and you are 'only' altering the pneumatics.

Some of my experience was gained at the bench at BSA while they were not making Tiger Cubs …

Cheers, Tim

[steveteeParticipant @stevetee]

Following on from Tims comments, if I may , the shape of the cam follower is also vitally important , flat or radiused and the radius of the follower all affect the rate of opening( and closing), but not the overall lift. If I can remember a flat cam follower will give an aggressive rate of opening wheras a radiused follower is more gentle.

[Phil PParticipant @philp]

I used this method to produce my cams,

http://www.modelenginenews.org/techniques/meek_cams.html

Phil

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by stevetee on 27/01/2017 00:41:47:

Following on from Tims comments, if I may , the shape of the cam follower is also vitally important , flat or radiused and the radius of the follower all affect the rate of opening( and closing), but not the overall lift. If I can remember a flat cam follower will give an aggressive rate of opening wheras a radiused follower is more gentle.

These "Harmonic cam" programs let you fiddle around with the design of the cam to get valve opening to be as gentle or as aggressive as you wish. The cam is made of 3 components, the base radius, flank radius and nose radius and a gentle transition from one to the other is ensured by making the transition point share the same radius i.e. the tangents are the same. All this, of course, with a flat follower. The problem that then arises is trying to fit the cam design into the space available in the engine and, particularly, having a round follower that is of sufficient diameter such that the edge of the follower does not ride on the cam (even though some commercial engines including, as I understand it the 1600cc engine in the Maestro, suffered from this "problem" without apparent ill effect). I guess that having a curved follower can help to alleviate this problem. Having some knowledge of the acceleration profile spat out by the cam calc program can help to put the size of spring required to keep follower in contact with the cam in the right ball park. There are, of course, loads of other issues to contend with such as tappet clearances but the programs do give you a good starting point if you are designing the engine from scratch. If you are just trying to make an engine just goes then these considerations are unnecessary but beyond that some calculation can provide a little help.

Cheers,

Rod

[CorRadParticipant @corrad]

A cam Calc spreadsheet is precise what I need right now. Unfortunately, the spreadsheet on Dropbox is not available anymore. Would it please be possible to drop it again.

Thank you

Cor

[Roderick JenkinsParticipant @roderickjenkins93242]

Sorry, had to clear out my dropbox – too full.

Here's a new link **LINK**

PM if you have any problems.

Rod

[Wayne WardParticipant @wayneward51978]

Cam design is a really complex job if you are going to look into all aspects of the problem. I can recommend the book by Rothbart "Cams: Design, Dynamics and Accuracy" if you like maths. It's available second-hand and the price has fallen in recent years, presumably because a lot of old boys are retiring and the young pups just rely on incredibly expensive programs to do the calculation for them.

It depends what you are doing. A new engine where you can leave yourself lots of space, where performance is not an issue and where speeds are modest is easier than designing a cam for a racing engine which runs at high speed and where maintaining valve to piston clearances and control of the valve and spring are significant problems.

I wrote a huge spreadsheet in excel many years ago for flat-faced followers where you played with the shape of the acceleration profile until you got an acceptable maximum opening angular velocity (which dictates the size of the follower you need), sufficient oil film thickness between cam and follower, sufficiently low contact stresses between cam and follower (always at the nose at the lowest engine speed), sufficient spring force to maintain a safety margin at max lift / max engine speed etc, all whilst having tangency in the acceleration curve. It took many weeks of work, but it played a significant part in landing me a couple of good jobs.

Curved followers, finger followers, pushrods etc all make the problem more difficult.

To top it all off, every bit of the system is elastic: the camshaft twists and bends, the valve compresses and stretches etc. Designing a desired valve lift profile is one thing, but making the valve do what you expect it to do in a high-speed engine is quite another. Thankfully most people are blissfully ignorant that their valves are not following the designed profile until they get on a valvetrain rig where valve position can be measured with a laser at high speed.

None of this is meant to put you off, just to point out some of the things that you might need to consider.

[CorRadParticipant @corrad]

Hi Rod, thank you very much for the spreadsheet. It works perfectly for my purposes. Regards.Cor

[DollyDiggerParticipant @dollydigger]

Is there any chance this spreadsheet is still hanging around somewhere?

thank you

[JasonBModerator @jasonb]

Try this link Rod posted last week

Edited By JasonB on 24/08/2020 19:31:25

[DollyDiggerParticipant @dollydigger]

hi jason that looks like a motor

cheers

[JasonBModerator @jasonb]

Should be correct now and take you to Rod's Dropbox

[DollyDiggerParticipant @dollydigger]

Posted by JasonB on 24/08/2020 19:31:55:

Should be correct now and take you to Rod's Dropbox

Thats brilliant, many thanks

[Josh LewisParticipant @joshlewis91024]

hi does anyone have a working link to the cam excel file as I can't seem to access it and would like to have a look as it would help with my uni degree thanks !

josh

[JasonBModerator @jasonb]

The one Rod posted in this thread works OK

[Author]

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