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View Full Version : Cam Timing--Lap, lead, etcetera



brian Rupnow
06-21-2014, 08:59 AM
I need to find some good literature on cam timing as it applies to small, single cylinder, low speed i.c. engines. Book that takes a practical, real world approach to lap, lead, etcetera. Any good suggestions?--Remember, I am in Canada, so probably an American publication would be more convenient to access.

A.K. Boomer
06-21-2014, 09:45 AM
Brian --- most of my knowledge is of the opposite as I used to build race engines --- but - it is directly the opposite for the most part so you just un-do what you do to go higher RPM's,
and in your case you might just start with a low RPM stock engine example and take it to the even lower range,,,


some basics that you probably already know,,, higher RPM's require the exhaust valve to be advanced and the intake retarded --- and an increase in the duration of the two... although not as much on the overlap period as the other,,, so you would want to do the opposite...

actually getting a scale of a typical sluggo engine and one that's set up more for performance will give you a rough draft of were to go for lower RPM's than the sluggo... as your building an ultra-slug...

keep these little tips in mind - the intake is by far the dominant valve, to some degree what goes in will come out,,, so if you end up with both lobes being solid fixed to a cam and you want to go for the biggest change the answer is to go with the change in cam timing that is best suited for the intake...

You really don't need a book - just some comparative values,,, nobodies going to be putting a "sniff tester" on your little baby (at least I don't think, I mean your not from cali are you :p)???

strokersix
06-21-2014, 10:48 AM
C. F. Taylor "The Internal Combustion Engine in Theory and Practice" volumes 1 and 2 are a great reference. Considered by many as a "bible" of sorts for engines.

dlsinak
06-21-2014, 12:00 PM
Brian, I suggest you do a search for Bruce Crower, Crower Cams. If you do a little looking, you will find his video on the 6 stroke diesel engine, pretty interesting. I don't know of any books he has published, but I think you will like what you see.
Dennis

Cuttings
06-21-2014, 12:45 PM
Brian, I did a bit of digging around on line.
There is a lot of information on camshafts & timing, most of which is related to performance cams.
I did find a couple of articles that may or may not help you.
<http://www.enginebasics.com/Engine%20Basics%20Root%20Folder/Basic%20Camshaft%20Understanding.html>
and a book " A practical approach to motor vehicle engineering & maint. by Allan Borrick & Derek Newbold
Some of the camshaft manufacturers have good information on their web sites.

MrSleepy
06-21-2014, 06:40 PM
John B Heywoods "Internal combustion engine fundamentals" isbn 0-07-100499-8 (http://www.amazon.co.uk/INTERNAL-COMBUSTION-ENGINE-John-Heywood/dp/0071004998/)

Its another fantastic book from the MIT Sloan auto labs staffers,as are the CF Taylor books.

It will probably have way more info than your currently needing , but its depth (and math) are staggering.
Rob

justanengineer
06-22-2014, 02:47 AM
+1 on the Heywood and Taylor books. I find the Taylor books more easily read and understood, but Im partial to Heywood bc Ive met the man and am hoping to take a class or two with him one day.

ammcoman2
06-22-2014, 09:53 AM
Another possibility is to check on "Gas engine design" in https://archive.org/details/texts

I downloaded the Parcell and Weed book and, while it is over a 100 years old, it is relevant to these type of engines.

Geoff

brian Rupnow
07-17-2014, 07:16 PM
I purchased the book "Miniature internal Combustion Engines" by Malcolm Stride published by Crowood Press in Wiltshire U.K. It is an excellent book on small engine design, with easy to understand articles covering all aspects of small internal combustion engines, including a great section on cam design. The book is a hardcover, of 175 pages, with many colour pictures and technical drawings. I highly recommend it to anyone interested in model i.c. engines. I believe I paid about $40 Canadian for it, including the shipping charges. You can contact Crowood Press at enquiries@crowood.com I purchased my copy through the Canadian book store Chapters-Indigo.---Brian

brian Rupnow
07-19-2014, 12:02 PM
I have just received and read through the second book I had ordered, "Model Four Cycle Gasoline Engines" by L.C. Mason. Although it is quite a good book, it doesn't give any more information than the book by Malcolm Stride, and doesn't have as many pages, illustrations, nor technical drawings, and was written in 1976, quite a lot earlier than Malcolm Stride's book, (although very little has changed in the world of small model engines since then.)---I really don't think it is worth anywhere's near the $200 Canadian that is asked for a new copy of it on Amazon.com So--a summary of what I have read/learned. I am quite sure I knew about 90% of the information contained in these two books. They have cleared up some of the mystery surrounding cam design, and a bit of the size relationships between various engine components. The rest of the stuff, I knew already----but then I should. I have worked as a mechanical design engineer for the past 49 years, been involved in hot-rod building and drag racing for almost as long, and have built 10 steam engines and seven i.c. engines. They will certainly be valuable reference books to add to my ever growing stack of "resource literature" about this marvelous hobby.---Brian

brian Rupnow
07-27-2014, 06:24 PM
So--After multiple readings of both books, I have began to comprehend the basics of cam design.I hope you are able to read the drawing posted here, because it will explain some of the theory/mystery behind the actual design of a cam itself. The timing of cams is a whole different issue, and all I will say about it here is that a relatively mild cam for a 4 cycle i.c. engine, running at relatively low rpm (500 to 2500 RPM) would begin to open the intake valve approximately 10 degrees before the piston reached top dead center on the exhaust stroke, stay open while the piston travels from top dead center to bottom dead center on the intake stroke , and remain open until it closes at about 50 degrees after the piston has started upwards on the compression stroke. I know that sounds like a lot , 240 degrees of total cam influence, but remember that when talking about piston movement in relationship to degrees of crankshaft rotation, the piston travels relatively short distances during the 30 degrees either side of top or bottom dead center, and travels most of its total distance to be covered during the 120 remaining degrees in half a crankshaft rotation. In the drawing, I picked the 3/8" shaft diameter. That is a somewhat arbitrary number, but must remain smaller than the "base circle diameter". The .080" of valve lift is a dimension that is calculated by determining that the volume of space between the face of the valve and the seat when the valve is fully open should be equal to the volume of a cross section taken through the intake runner leading to the valve. If anyone takes exception to the information I have given, or wants to ask a question, I will be glad to discuss it. Remember--Although I have been designing mechanical devices for 49 years now, this entire cam design thing is relatively new to me too.---Brian Rupnow.
http://i307.photobucket.com/albums/nn294/BrianRupnow/BrianRupnow016/CAM-RUPNOWENGINE-2_zps149b24ac.jpg (http://s307.photobucket.com/user/BrianRupnow/media/BrianRupnow016/CAM-RUPNOWENGINE-2_zps149b24ac.jpg.html)
I don't see any option for attaching a pdf. file of the drawing. If there is such an option, can someone please let me know.---Brian

Cuttings
07-27-2014, 06:46 PM
Very interesting information Brian.
I have a question that you may have come across the answer to in your reading.
How much does the diameter of the "tappet" or as we call it lifter come into play as to the start of valve opening and finish?
It looks to me like a larger diameter lifter would start to open sooner and stay open longer than a smaller diameter one.
As the cam rotates it would get to the point where it would start to lift the larger diameter lifter a little sooner.

brian Rupnow
07-27-2014, 07:38 PM
Good question, Larry. The tappet has to be large enough in diameter so that the cam, as it rotates, never contacts the edge of the tappet. If it does, there will be undue wear and early failure of either the cam or the tappet. Most tappets as in automobiles, are round, but there are also rectangular tappets. The rectangular tappet can be as narrow as the cam itself, but must be long enough, again, so that the cam never contacts the edge of it as it rotates,---And that of course means that the rectangular tappet must be restrained from rotating. Many round tappets are designed very slightly "of center" in relationship to the centerline of the cam so that the action of the cam causes the tappet to rotate a bit each time it is lifted. That way the wear pattern of the tappet in its guide is more evenly distributed, making the tappet and the guide last longer. So--to answer your question, if the tappet is designed to be large enough that the cam never touches the side of it when rotating, then any farther increase in diameter will have no effect on the valve timing.