Checking engine timing with a protractor

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    Dean McGinnes

    John Loribecki (sp?) “volunteered” to explain it all to us. I have my own idea but having never done it, probably it is wrong. Help us John.


    OK, since I opened my big mouth….

    You will need a 360 degree protractor, and engine stand, and a piece of music wire- .032 or so, and possibly a small flash light…

    In this instance, we will only be looking at the liner timing. Crank timing is a bit more complicated as you need to tell when the engine is at top dead center. For intake and exhaust timing, all you need is a set of eyes…

    Mount the engine to the stand. Mount the protractor to the crankshaft. The music wire will be a pointer. Mount it to one of the lugs of the engine or engine stand. It should point to the edge of the protractor. You are now ready to look at some numbers.

    To make things easier, remove the head. However, you must make sure that the liner does not move. You can take a head screw with a washer and screw it in place to hold the liner in place.

    Take the flashlight and shine it thru the top of the liner. Look thru the exhaust port and rotate the crank and piston until the light is no longer visible thru the exhaust. Carefully rotate the protractor until the pointer points at zero. Rotate the crank the opposite direction (going towards the bottom of the stroke (BDC)) and continue to rotate until the piston is now approaching the upper edge of the port. slow down and continue until the light is no longer visible. Note the number.

    The number you end up with should be somewhere in the 150-170 degree range. I like to do this a few times to verify the numbers. Note that non-piped engines will be the lower numbers- Also, if the engine is a lower performance engine, these numbers will be smaller. If you happen to have a piped engine, this number could be as big as 180 degrees.

    Use the same technique for the intake- Sometimes I will shine the light thru the backplate. The numbers here should end up in the 125-140 degree range…If a schnuerle ported engine is checked, it is very common that the boost port and the intakes will be at different durations.

    Now, if you want to check shaft timing, you will need either a dial indicator or possible a depth micrometer. Rotate the piston to top dead center (TDC). The best way to find TDC is to rotate the engine to the top and set the protractor to zero degrees. Rotate the engine until it is .050″ down the bore. Note the number on the indicator. Now rotate the engine the opposite direction and continue to .050″ down the other way. Note the number on the protractor. Add these together and divide by two. If it comes out to zero, then the protractor is set at TDC. If not, then move the protractor or pointer the difference noted by the number.

    Once TDC is determined, we will look at closing and opening timing. Rotate the engine in its normal direction. Shine a light thru the shaft hole and continue until the light is no longer visible thru the venturi. This number will normally be between 40 and 65 degrees ATDC (after top dead center).

    Then, reset the indicator to the bottom of the stroke. This is because the numbers seen here are normally referred to as After Bottom Dead Center. Use the same tricks to determine an accurate bottom dead center. Rotate the crank (again in the normal direction) until the light is just barely seen thru the venturi. Read the number and this will be the degrees ABDC…

    I have found that normally the closing number is critical- For instance, most of the modern day engines will close somewhere close to 62 degrees.

    Once you do this once or twice, it takes very little time to do. Questions??


    Very interesting stuff John, thanks!

    I have been wondering about shaft valve timing – in particular I was trying to figure why the Irvine 15R was such a disappointment in Open Exhaust mode, where it was a superb F2A Speed engine.

    I was thinking that part of the reason was that the shaft valve opened a little too early. At the bottom of the stroke there is very little piston movement for quite a lot of shaft rotation. Little suction is developed until the piston gets moving a bit. On the Irvine the valve opens at 25 degs ABDC. On the Rossi it is 30+ degrees (I have no Nelsons to compare to). My Dad thought 30 degs was the magic number for open exhaust, and I have a number of bits and pieces he made for disc valve engines that gave variable timing – so he proved it, I guess.

    With a pipe (I reasoned) that the low pressure pulse above the piston from the pipe would advance through the engine and add to the piston induced suction, so an early opening shaft valve could be an advantage when using a tuned pipe.

    Any thoughts on that?

    John Buskell


    I would agree with that somewhat- As stated, in most instances I have found that the opening of the crank (or rotor) typically doesn’t have as to do with engine performance changes as does the closing. From what I remember, your opening number of about 30- 35 degrees ABDC is about right with the Rossi- the exhaust timing on the piped version was about 175-180 degrees. If the Irvine was trying to be run with that much exhaust timing off the pipe, it would surely be a dog- just way too much exhaust scavenging and blow down.

    The pipe is a truly wonderful device when ran to its maximum- such as FAI speed. To take something that is blurbling and not making any power to one that is run at 40,000 rpm (at least I know that the 1/2A stuff is running that- seems that I heard something about 42,000). Wish we could play with them on our stuff- this is one reason why I would like to make a late 60’s early 70’s FAI model- just to put a pipe on her and play…


    Hello John’s

    Nice work – i used to re work Rossi Blackheads for Dad and i plus a couple of other F1C mates, 360deg’ protractor worked very well for me, i used to set, (dremil) shaft induction back to 32deg’ opening, fit an Irvine .15n ABC piston/sleeve, but drop the sleeve so that the exhaust gave 158deg’ opening. I called this method blue printing as the timings came from the Rossi Bro’s spec’ for the Rossi 3′. I figured the engine designer knows best, (people talked about all sorts of crazy tuning ideas). These blue printed Rossi’s were very strong runners and matched the original Nelson SE’s for rpm’s and volume on my test prop’ – i now have hearing damage!
    I would love to build a Koster’s original ‘Cream’ – spitfire wing tips, with a piped .15 – just for fun.

    Regards Andy


    The Irvine 15R and the Irvine-based Halman Special used in F2A are very different engines. The Halman Special has a 14mm crank with tungsten counteweights, the case is designed for front mounting lugs and a single rear lug to use the speed pan as a stuctural member to stiffen the system. The piston/liner is completely different as well. The 15R is a good engine – MUCH better suited for FF use. THie only “problem” was the the last few poduction runs had very soft crankshafts.

    Ron Bennett


    Just so that we’re clear here, the Irvine I have is not a Halman Special, it is a normally timed 15R. I have a pipe timed Irvine 15R piston/sleeve, too, and it is appreciably different.

    I’ve only come across one good Irvine 15R F1C motor. It belongs to my Old Bristol and West clubmate Mike Wills (in the UK), and it is a George Aldrich tuned version. I have no hesitation in saying that it is a top notch f/f motor. Other than that, they seemed to cause widespread disappointment in f/f circles (at least in the UK) – perhaps I’m wrong, but it’s telling that the likes of Screen, Watson, Faux etc didn’t put them in models. My dad didn’t either, and he knew a bit about engines, although he’d kind of lost a bit of his interest in F1C by the late 80’s.

    The engine I have belongs to John Thompson – there is a bit of history in Buskells having Thompson motors, but that’s for another time. I’m in the process of stripping and cleaning it.

    It sure looks like it should go.



    John B,
    I understood the Halman special to be the speed/ pipe timed version. I have a stock version for F/F, sounds like what you have to. I could not get it to rev hard, the only good thing that came out if it was the ABC set for one of the Cordes Rossi’s. A great shame, they look like a power house to me.


    Question for Ron- How much exhaust timing are guys now running with the pipes? Also, have they played any with intake/boost port timing as well as crank timing? If so, do you have any actual numbers? Here again I am thinking mostly of .15’s….



    Hi John,

    We run about 178-182 degees on F2A engines and just a bit below that on .29s. The boat guys run 188-195!! But, and this is a BIG BUT, they have almost no mass/load when starting. Starting and high timed piped engine gets harder the higher the timing.

    The Russian/Ukranians in the early 90s had engines that flew faster than any of todays F2A fliers, but, they rairly were a factor since they almost never could get a run in because thier engines were so had to start.

    There has not been much change in intake timing for front intakes but most have to greater duration with quarter segment rear intakes. There is a trend back to front intake for .40 and .65 engines because we feel that we are just not getting engouh air to rear intake engines (.65 cu. in. at 500 times a second is 32.5 cu. feet of air!).
    We (Scott, myslef and Phil McGee) are working on .65 with a 7/8 inch crank right now.

    Best wishes,
    Ron Bennett

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