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Antique Gas Engine Discussion

Engine Speed.......

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Old 03-28-2005, 11:41:56 AM
midpw midpw is offline
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Question Engine Speed.......

I'm tired of not knowing the speed that my engines are running. I've been looking around at tachometers.

Tell me, what do you guys use? What do you like? (What should I buy?)

I work on a lot of different engines and it seems that I want my hit 'n misses to run just as slow as possible when displaying them. And yet when I have them belted to an implement I want them at or near rated speed.

So what do ya think?
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Old 03-29-2005, 12:21:24 AM
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Jim Young Jim Young is offline
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Default Re: Engine Speed.......

I use a Stewart-Warner hand tach. It has a rubber tip that "couples" to the dimple in the end of the crankshaft. Reads right or left hand revolutions, seems reasonably close, though I wonder about the accuracy below a hundred RPM or so. At "working speed" of 500 or 600 revs, it's probably pretty accurate. It came in a bright yellow and red can with instructions and an alternate tip.

There are hand held accumulating rev counters where you would engage it for a fixed time, like 10 seconds, then read the total indicated turns and multiply by 10. That would give RPM's too.

For a really slow runner, you can just count 'em.

Jim Young
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Old 03-29-2005, 07:58:10 AM
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Doug Kimball Doug Kimball is offline
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Default Re: Engine Speed.......

Stewart-Warner or AC are options in a single range hand tach but as Jim said accuracy may suffer at slow speed. The AC's are available 0-2500 or 0-4000 rpmonly, I think. There is a counter type, Starrett being the most common but requires the counter & a watch to count revs over a certain time period to give an average speed. Also Jones, Herman Sticht, etc. with a round dial & attachments to read rpm or surface speed per minute. These can be single or up to four ranges & typically read from 0 to 10,000 with good accuracy. This type will show the peak speed reached shortly after it "hits" and the lowest speed just before the next "hit". These usually come with a handy case for tach & accessories and is one I prefer. Also some digital electronic ones which I know little about. All can usually be found on Ebay by searching for hand tach & range in price from $25 to $75.
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Old 03-29-2005, 11:33:06 AM
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Elden DuRand Elden DuRand is offline
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Photo Re: Engine Speed.......

I've been using this gizmo for years to measure shaft speed.

You put one of the rubber tips on the shaft of the instrument. There's a 100:1 worm drive inside the case. The output is the center dial.

To measure shaft speed, use a fingertip to loosen the screw in the middle of the dial and move the dial so the little bump is opposite "0" then tighten the screw.

Grasp the instrument so your thumb is where you can feel the bump as it passes zero. Look at a clock and, at a handy moment, press the tip to the end of the shaft. Count the bumps for whatever interval you want. At the end of the interval, remove the tip.

Add what the dial says (0 to 100) to the number of bumps times 100 and multiply that figure by what part of a minute you ticked off (10 seconds is times six, 15 seconds is times 4, etc.). That is your shaft speed.

This is good for something whose speed isn't constant because it gives an average speed.

Take care - Elden
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Old 03-29-2005, 12:09:29 PM
Joe Morris Joe Morris is offline
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Default Re: Engine Speed.......

Since most all these old engines only run 500 t0 600 RPM s at top speed and the bigger the engine the slower the rpms,its easier and cheaper to simply count the number of times the pushrod moves in 60 seconds and multiply them by two. This gives the total number of times the engine crankshaft revolves in one minute which is the answer you are seeking. Remember, R P M means total Rounds Per minute. regardless of the type engine whether it be hit and miss or throttled. Joe Morris
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Old 03-30-2005, 02:12:25 AM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Engine Speed.......

There was quite a large thread a few months ago on engine speed. Some engines can be idled down quite sucsessfully (Hercules for one) and for others, it could lead to catastrophic failure - metal fatigue. The Woodpecker 1 1/2 HP is a prime example of an engine that WILL self destruct at low speeds. The crankshaft cam side throw will break due to torsional stress if run at low speeds constantly. I have seen half a dozzen wrecked due to this reason, the most recent - actually witnessed the breakage! John Smith (the wood-pecker man) and I were having a conversation at the Jacktown show. He was considering buying a 1 1/2 HP Woodpecker engine that was on display there. I had seen the engine earlier, and it was running real slow - the flywheels almost stopped, as it was running. I told the owner, that running the engine that slow was a sure way to break the crank. I was politely told where to go, and how to get there, as well. Several hours later, John looked me up, and asked me if I could give him an opinion on an engine he wanted to purchase. It was making a strange noise, and neither he nor the owner could find where it was coming from. We went over to the poor old woodpecker that was now making a weird noise when it fired. I watched the engine for a few cycles, and told John, "It's Done!", and started to walk away. The Owner and John asked "what do you mean Mack". I told them to watch the left side flywheel. When the engine fired, the wheel developed a distinct wobble, and the engine labored to get back up to speed. Once the engine was up to speed, it coasted easily! John stopped the engine, and re-started it. It labored like the timing was retarded, but once it reached idle, it coasted fine! I told John "stop the engine, and push the top and bottom of the flywheel in and out alternately". This was done - no movement. "Now do it front to back" I said. This time the flywheel moved about 1/4" What the H--l" John said! "Crank's broke" says I. Sure enough, the crank has developed a spiral stress fracture, under the cam drive gear - extending to inside the crank bearing shell. When coasting, the cam drive dear on the crank kept everything in relative alignment. When the engine fired, the left flywheel lags a split second behind the right side wheel and the crank throw, due to the crank break. the spiral fracture was acting like an expander to the internal length of the crank, between the journals, and in fact the left side journal was being shaved to pieces every time the engine fired!. John later told me that he had seen over 20 broken cranks on woodpecker engines, all due to stress fractures - because of slowed engines. This one was a first, he said, as it was the first one he had seen run after breaking the crank! I told him "I don't believe the guy is going to continue to run the engine - if the cam drive gear breaks, that flywheel is coming off! I don't care if the engine is doing 600 RPM, or if it's doing 60 - if that wheel comes off the engine, there is going to be h--l to pay, if that sucker gets into the crowd!" John ended up buying it for a much reduced price, but not before the broken crank nearly completely gutted the crank bearing, and cracked the timing gear. Another 5 minutes, and that flywheel was history! John was looking into having new steel replacement cranks made to fit the woodpecker engines, but I don't know if he followed up on it before he died.
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