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    • CommentAuthorkamran
    • CommentTimeJan 21st 2009
    Hello all,
    Any advantage or disadvantage of using timing belt and pulleys vs gears between the crankshaft and the camshaft?

    The way I have designed my engine, if I use gears, I need to use an idler gears in between. Also if I use pulleys with timing belt, I still need to use idler in between. I like to use pulleys but what do you think is best to use?

    Timing gears are easier if they will be enclosed, with access to lubrication, idler gear configurations can be found in some small engines, regardless of head design.

    Timing belts are excellent, they do not demand lubrication, can be exposed and are less noisy.

    in the gear case, idler will make camshaft and crankshaft rotate in the same direction, while in the belts design, you do not have an idler, you have a belt tensioner, therefore the rotation of crank and cam will be opossite.

    preventing you have enough space to build the belt tensioner, keep the desired ratio between cam and crank pulleys, I would tend to say it is easier to use timing belt.

    Great Answer Jaime, I agree in all your points.
    Kamran, have a look at Dale Detrich own design.... single over head cam. There are some great photos there. Very nice craftsmanship too!


    I wounder if anybody has a link to small time belts and their "gears".
    • CommentTimeJan 23rd 2009
    One little corection to Jaime's answer
    Gears with an ideler, a chain & sprockets, and timeing belt & pullys all turn the cam & crank in the same direction. The cam and crank turn in oppisent directions useing 2 gears with no ideler.
    • CommentAuthorkamran
    • CommentTimeJan 23rd 2009
    I got 3 options here, so I guess I need to make a decision as which way to go.

    Thanks all for the comments.
    1.User the pulleys with belt and idler (Based on Dale’s and Jaime’s comments they run very quite, but Dale mentioned oil could damage the belt
    2.use gears and house it inside the crankcase
    3.Use gears and house it outside of the crankcase with cover.

    Option 1 is tempting and you can see more things that are moving, while option 2 gives me more room outside of the engine for more stuff. Humm but option 3 gives it a little more complicated look with the gear cover which is not bad either.

    George thanks for the correction about rotation with time belt, both will move in the same direction, I tend to get this wrong most of the time, I need to get two shafts in front of me to get it right.

    If your design is an overhead camshaft, with over head valves, then you will need either very big gears (DP) to cover the distance or get more than one idler, this is what Westbury did in the Sealion. If your design is a side valve camshaft design, then gears with an idler can work, check also Westbury Seal major design.

    If you are going for overhead, I guess the easiest and cleanest approach may be timing belt.


    Yes that sliped right by me as well.... I understood what Jaime ment though... ha ha ha.
    Three gears.... same direction... always!

    • CommentAuthormiller
    • CommentTimeMar 10th 2010
    Do they make timing chains for miniature engines??
    • CommentAuthorgbritnell
    • CommentTimeMar 11th 2010
    First of all here's a link to a good supplier for miniature belts, pulleys and gears. I have used them many times.
    For overhead cams you can use belts for simplification if that's what you want. Most of the early automotive OHC engines had a gear train to drive the cams such as the Offenhauser because there weren't the synthetic materials available like today to make belts from. Most motorcycle engines use a metal chain to drive their cams but there is not much available of this type for modeling work.
    Hello All……I like this discussion between the gear or timing belt drive for the cam shaft…..On my four-cylinder engine I used three gears to drive the cam….first gear is the crank gear, then next is the idler gear, and then the cam gear….I had to use three gears because of the length between the crank, and the cam shaft…..Then I thought of a way to make the mesh of the gears easy for the builder….On my end plate for the engine, there is no certain way that the end plate has to be put on the engine…The end plate can be rotated 360 degrees….I made a idler gear mounting post, and the dimensions where to mount the post…..If you do not get a good mesh between the crank gear, and the idler, you can rotate the endplate and try again….After you have a good mesh between the crank / idler , you go ahead and mount the cam in it’s normal mounting….Now you rotate the endplate / idler gear into the cam gear to get a good mesh….Now you mark the endplate to the block , and now drill and use the mounting bolts to keep the endplate at the marked spot……The gears are lubricated by the engine oil, and I have had no problems……..If you take a look at the vert. single cylinder section, you can see that I used a timing belt and idler pulley for the cam drive….I needed a way for the timing belt to give me belt length and to also take up the extra belt when I change the compression of the engine….The timing belt drive is very quiet, and works well…..One of the show and tell things that I do at the shows, is to wrap a rag around the muffler and quiet the exhaust down to let you hear the engine running….The engine is very quiet , which is what you will get by using a timing belt…..With the gears, the smallest adjustment ( for cam timing ) is one tooth on the gear…..On the timing belt driven engine , you can see the three slots on the cam pulley…..The movement in the slots is longer that one tooth spacing on the belt…..This allows you to make very small cam timing adjustments…..I have had no oil problems with the timing belt……Both ways work fine, so it is up to you to make your choice…….Thanks…….Dale
    • CommentAuthorgbritnell
    • CommentTimeMar 12th 2010
    Hi Dale,
    Good explanation of your setups.