Do you need a Tachometer for proper engine break in, or is it something I don't really need? I am going to place my order today, I think, and I am trying to sort out the crap I think I need and the crap I actually do need. lol.

I broke a few engines in before I ever bought a tach.. however, having the tach is really nice when experimenting with different prop profiles as well as the dia and pitch changes.. its been pretty handy when experimenting.. Idont think its a bad idea..

It's never a bad thing to have. And some people can't tune an engine without one (but then, some people can't tune an engine WITH one either).

Personally, I have one, but it is rarely ever used.

But NEEDED? Naaa.

Not saying I can tune an engine either way, but yes I do have a tach, but have used it only once that I can remember.

I have one, use it occasionally, but mostly when changing props, although most people can hear the differences in prop noises from what they originally had to what the new one does. But, if you go from 10,000 RPM to 15,000 RPM and you can't hear the difference, then I would say get a tach... [X(]

CGr

A tach takes the guesswork out of tuning. For break in, there's little benefit because it's easy to hear the transition point from slobbering rich to smooth operation. It does make it easy to get tuning right because you can find your peak rpm, richen up, then point the nose up and find it again. That will tell you how many rpm off peak you need to tune to never go lean, so setting your needle valves as the weather changes gets really simple.

Funny this came up now, I just came in and got a shower after breaking in my new SK .91. I did pull out my Tach but just to see what RPM I was pulling with the prop I have on. For most two strokes I don't bother using one unless there is a problem and I want to dial it in and know where I have the rpms at that setting and prop. Four strokes I almost always use one now, I run several YS engines and being older models you can't really hear the rpms rise and fall. Gas engines I use the tach too but not too often after they are set.
I have had several makes of tachs and most of them are junk. I broke down and spent the money on a TNC because I tune so many different engines I wanted a good one. I have tested other tachs against mine and found one taCH THAT HAS BEEN DEAD ON AND NOT SO MUCH MONEY. iT'S THE COMBO TACH AND VOLT METER SOLD BY hORIZON hOBBIES. My thinking on this is you need a volt meter so for the price you can get a good meter and tach all rolled into one. I could have saved myself a lot of money if I knew this was a good system but what the heck, you need a good tach to test the others against.

Tach Hmm, ya here is mine reads 7 to 17000its an OS too[8D]

That takes me back a ways

ha! looks like what I used to comb my hair with back in the early 70's!!!

You didn't have any hair in the 70's!!

If you're about to break in an OS, and have read and understood their recommended break in proceedure, no you don't need a tach.

And if you don't understand it, but can figure stuff out while following orders, no you still don't need a tach.

On the other hand, if you're about to break in a 4cycle, yes you need a tach. And will still need to figure out the break in instructions.

Still awake?

Beginners need to learn what "rich" means. "Lean" and "two cycle" isn't hard to hear. Once you get used to identifying when an engine goes into lean/rich, you pretty much don't need a tach. Unless you're planning to fly pylon or such.

But back to the original question but let's phrase it differently. Will a tach help you break in an engine? No, for a simple reason. Nobody publishes the rpm your engine will be turning when it is rich or the rpm when it breaks into a two cycle, or any of the other numbers.

Unfortunately, a tach won't help most experienced modelers break in any engines since the engine mfg's don't tell you numbers. They can't. The charts and graphs would fill a book bigger than the engine boxes. You're going to have to learn to identify "rich" and "2 cycle" by ear.

OK I could not resist sorry, I bought that tach in 1964 and it was made by OS you can see the name on the handle.

Yes back to Danks question: You are correct it is likely not needed at all and I say likely simply because I think we are talking about a typical two stroke. If that is the case I much prefer to teach the fellows to start learning just by ear and with a two stroke things are much more obvious than a four stroke -read easyier.

I teach everyone (with two strokes) to pinch tune on the high end but for now you are better off going by the factory recommendation and nope don,t need a tach.

That afro comb by OS I pictured is of course mainly for fun now freaking the boys out but like GB I also have an old analog by ace the is comprable to his TNC and these are remarkably accurate. When I was active in pylon a good tack is a must simply because even tho I still tuned to a pinch it is usefull for making decisions on props and changes to the engine itself.

I also have one of them red Glo Bee tachs that Tower sells and it works fine, Heck the red color matchs the red 18v battery under my starter It does not get as much use as I only really use it some times when their has been a climate change on my four strokes. Fortunately no one ever convinced me four strokes were some sort of a upgrade so got a whole bunch more of them peskey two strokes.

John

And to add to what DaRock said, what he said about "published RPM" makes a good point. That number will change with the prop, as already stated. The mixture richens out when there is a lot of fuel flowing that doesn't get burned.. it spits a lot of it out and sounds like a "four stroke" engine. But, the RPM that happens at will vary with the prop used. It's more of a sense of hearing the "four stroke" point than trying to measure it with a tach.

The same applies for leaning out the mixture. The engine will go to two stroke and increase RPM as the mixture leans out. But, if you are not careful, it will lean out to much and get very hot. Remember, that fuel not only provides the ignition source, but it also cools the engine down. Take to much away and it will get very hot very fast. So, it takes a "tuned ear" to know when it reaches that sweet spot between to lean and to rich... Aaaaahhhh, John, good stuff.. the good old pinch test. Yep, it works great. But, like many specifics about this hobby, it is an art and needs to be learned and perfected. But once you got it, you got it.

All this happens at full throttle, by the way.

If you use a specific prop to break the engine in, you will run it at some rich setting, again, at full throttle (check the manual) and richen the mixture till it blubbers.. spits out fuel. No one knows when that will happen for your given prop and that RPM will be fairly specific for your engine/prop combination. The same for leaning it out. The RPM will increase significantly and somewhat smoothly and the sound sill be very different as it loads up to the prop and settles to an RPM. What that RPM is, well, DaRock said it.. no one knows what that is.... it isn't published. An experience ear will know when all this happens.

You can use the tach once your engine has been fully broken in and is tuned properly, but a lot of things will vary that final RPM.. the temperature, humidity and atmospheric pressure will cause it to change from day today. That's why we all say that it has to be tuned each day before flying that day. Once set, it usually is ok for the whole day, but that too can change as weather conditions change. Quite frankly, I don't use one as often as some at the field do. I depend on tuning by ear using the "pinch method". If I use a tach, it's usually when I change props.

I'll bet you never thought you would get this much information from so many very helpful people.

More than likely, all of us will say that getting some help from some one that is experienced to help you get that first engine properly broken in and tuned properly will go a long way to getting you on your way. But I can also say that you won't get that experienced ear without doing it over and over again.

One important point that I've not read so far ( if I missed it, I apologize).... it is much better to run the engine slightly rich than it is to run it slightly lean. And don't shoot for the most RPM you can get out of your engine. Most engines that are off the shelf are made for the general sport flyer and will perform accordingly. Trying to get 16,000 RPM out of an OS 75 for instance just ain't gonna happen, or it will happen, but not many times. Keep it sane and you'll get many years of flying out of those engines.

CGr.

There are many factors involved with gaining maximum performance in an aircraft. Achieving the highest power to weight is necessary, but not the only consideration. For sport flying, your first consideration should be reliability.

While I don't find a tach necessary to set a 2C engine, I find that 4C engines are a different kettle of fish, one because you do not want to exceed rpm limits inherent with valve trains, and second because they are prone to back firing and throwing props if too lean. So use a tach to select a range of flying props and to richen up from peak rpm to avoid previous mentioned problems in the air.

2C engines are very flexible in operation. Changes in conditions (air pressure, temperature, and humidity) really effect the engine when you operate at the extremes, but have less effect for the normal sport engine. But understanding the basics of 2C engine tuning for the average sport flier can enhance the experience by eliminating unwanted dead-stick landings and poor throttle response.

So what tools does the 2C sport flier have at hand? Prop selection, fuel system, type of fuel, glow plug selection, and head shims go a long ways toward tailoring a power system that gives the performance you want. A tach is simply a tool to help evaluate changes, along with a critical eye during flight testing.

2st no tach, 4St better get yourself a tach

Well said. 2 stroke not needed. 4 stroke it's a gotta have.

Thanks for all of your help! It is greatly appreciated.

Like I said, some people can't tune without one. No one I know uses one to tune an engine - 2 or 4-stroke

So it's up to you. If you can buy a tach without it breaking the bank, got for it. It's always a handy item to have. If your trying to go light on the wallet, it's one of the last tools I'd ever buy

Amen. I can think of several other items in my field box that I prefer to have. Yep, I have one, but I rarely use it.

CGr

And I wouldn't buy it until I bought a 4stroke. Unless, like I said earlier, you plan to fly pylon racing.

Agreed on the tach for a 4-stroker. Was setting up a YS 63 this summer with a prop a bud recommended. Seemed pretty noisy, and found when we put the tach on it, it was near mfgr's redline (13K). In the air, would probably have floated the valves as the engine unloaded. Used a prop that dropped it by 3K, flew great. The tach probably saved me a repair bill.
Ed

To each their own, of course, but I use my tach every time I set up an engine. It is tough to tell 6500rpm from 6700rpm on a big gas engine or 10500rpm from 10900rpm on a glow model by ear in my opinion. Also, I find it nice to have a baseline in case one day your engine doesn't sound right you can tach it and see if it is just your ear or if you have a problem.

I use a TNC tach which is now distributed by Fromeco. The tach is regarded as one of the best in the industry and was designed by a no-BS engineer. Mine is a "tweaked" model as I knew TNC (Tony N. Criscimagna) very well. Check out a list of his other inventions below, how about the plasma screen!

http://www.patentgenius.com/invented...odstockNY.html

its not necessary but can be useful..i usually tune the high end by year.. i mainly use a tach to see how my engines are running... i compare the numbers from past and present, and sometimes used to compare RPM figures from other modelers, as well as hereon RCU. i especially like using them when i try a new prop on my gassers. i like to stay in a certain rpm range

Because of this thread, I pulled out my tach while breaking in an OS75AX just now.

Wearing really good earmuffs (competition shooting muffs purchased for highpower rifle matches) I had no problem telling the difference between rich, lean, and when the lean sagged. The tach showed the difference of course.

For one to help you set a new engine would of course require that you know ahead of time what rpm to expect, and that usually won't happen. So for you to discover anything with a tach requires you either had previous experience with the engine/fuel/prop before and know the numbers you want (so all you discover is if the new engine is like the old one) or you discover what the rpm is when you identify the way the engine is running (rich/lean/sag) by ear. As someone has already mentioned.......