Top End Temperatures

[Bill2001]

This Hodie is my first contact with 2-strokes since I was kid (child of the '60's). We puttered with them, but not seriously.

One thing I am learning about 2-strokes is that they prone to run hot with catastrophic results. My guess is that without lubricating oil missing on the backside of the piston, there is little to remove excess heat. And there aren't that many signs of running hot until a piston seizes or melts a hole.

With current sensor technology available, I wonder if it might be possible to keep tabs on the critical internal temperatures by monitoring the cylinder head temperature, or the temperature around the exhaust port, or even the exhaust gas temperature. This could give an early warning before failure. It could save the Walk of Shame back home... ;

[Bullfrog]

Cylinder head temps change so slowly due to the thermal masses involved that a seizure can happen long before cylinder head temp tells you something is wrong. EGT (Exhaust Gas Temp) sensors are often used on dynos in order to "see" dangerous situations developing. That being said, even if you have an EGT read-out on your scooter, you will have to assure yourself that the ignition timing is correct, and the jetting is correct - along with a host of other things (compression, combustion chamber shape, exhaust system, intake system, fuel, etc) in order to achieve a situation where you won't have to ride with one eye on the EGT read-out at all times. So, get all things tuned and operating correctly and you are good to go.

Of course it IS fun to have a bunch of instrumentation on the machine . . . and you can learn a lot . . . so I don't mean to discourage the installation of an EGT gauge.
Ed

[Bruce Young]

IF I may suggest, go to your local or near sno-mobile shop they have lots of info on use of EGT,s on hot spots, exhaust systems and engines, along with gauges w/warning lites so you can see what is going on. Like Ed said, things happen in the engine long before you could react. Better to watch you oil ratio,s and jetting. Good luck Bruce Young

[Bill2001]

Good info, Ed. Like I said, 2-strokes can be Creatures of Mystery and even though you think you have the mixture dialed in, it may not be the next day, or the next phase of the Moon. Look at the current "spudman" thread where he thinks he has it dialed in. Or my situation where the mixture seemed good and the sparkplug looked good and the piston seized anyway (though I suspect an earlier seizure, which made tis one inevitable). At lest with EGT readings a norml baseline can be established for the engine under certain conditions and that parameter can be monitored. And you may be able to have a setpoint trigger for a certain temperature and set an idiot light a-squawking so you don't have to watch a gauge readout. I have a friend who races dragbikes and is very good with instrumentation. And as Bruce says, EGT gauges are available for snomobiles, so it's not rocket science.

[Bullfrog]

I'm all for fun and education! Go for it!
Ed

[Bill2001]

Oh yes, education _is_ fun.

Progress report: EGT gauges are readily available, and one good source of gauges and expertise is within the snowmobiling community. The installation and interpretation of gauges is a frequent topic of duscussion in snowmobiling forums, where I've started lurking. As I guessed, the EGT gauge modules can be compact digital units with adjustable setpoints and loud warning buzzers. Cost is in the $100-200 range, within the cost of one top-end replacement.

More as I dig into it.

[DGardner]

Bill

Check out the Kart racing forum's and shops that sell racing Kart parts. There is a lot of info out there on just this subject.....DG

[Bill2001]

Karts--good idea, DG. Adds to the selection and knowledge base.

One snag is tbat most any EGT meter runs on 12v vehicle power, and of course the Hodie is old-school 6v. Of course I could assemble a 12v NiCad/NiMH rechargable pack. Or Karts, being pull-start and magneto might have battery powered EGT gauges, so we'll see what is available.

One thing I've read is that on 2-strokes some of the unburned charge is passed out of the exhaust port into the exh manifold, only to be pushed back into the cylinder by the reflected pulse of the tuned pioe, so the reading close to the exh port is lower than the exhaust gas proper. The EGT probe needs to be put closer to the cone of the tuned pipe.

Little Sunday AM techno-trivia.

[Modracer70]

I run my Diagatron EGT/Tach on my 125, you run it off the lighting coils if you didn't know, works fine.

Dave

[Bullfrog]

I run a standard after-market solid state 12V voltage regulator for the enduro lighting system on my Hodie 125, so a 12V system is do-able.
Ed

[Bill2001]

The Koso EGT should be here by Wednesday. I've gotten the weld-on fitting for the temperature probe on the exhaust pipe. Where should I place it to minimize possible damage by debris? I'm thinking that the rear-facing and upper quadrant would be the safest, with some protection from the feame downtubes and clutch cable.

The batteries for power are going to brmore difficult-- the company I used togettcustom pacls from is defunct, and I'll have to hunt up the NiCad cells, shrink wrap, etc and build my own.

[Bullfrog]

Hmmm, a previous reply seems to have disappeared into the ethers.

I've used rechargeable AA (NiMH) cells for my digital camera for years. An original purchase of 8 cells and a charger has allowed 1)carrying spare batteries 2)"rotating" the cells to even out the "aging" of the cells 3) pretty economical operation compared to disposable batteries 4) no noticeable problems like those often seen with NiCad "memory".

What about a truly light weight and compact . . . and rechargeable lithium battery pack?
Ed

[Bill2001]

Great comments, Ed. And very true. From my viewpoint as an amateur photographer and RCelectric aircraft flyer:
I've used NiMh rechargables in my digital cameras and my film flashnunits for years. They have worked well. In my RC electric aircraft, we started with NiCad, then NiMh, then Lipo (Lithium polymer) batteries, all with more power and lighter weight. And more tempermental. We still use NiCads in our low-current radio transmitter packs. The weight and current (amperage) output is still good and the batteries are reliable. The Big Plus with NiCads is low self-discharge. Charhe them and the battery willbe ready next year. NiMh will self-discharge more quickly, and Lipos need to be stored at 50% storage charge. I envision having a spare Nicad pack in the toolkit that I cn swap out when the working battery gets low. And, depending on the current draw of the EGT meter, I can get several hours, or several days, use from one charge. Tht being said, for the initial setup and testing of the EGT gauge I'll probably use a 2200 mAh 3-cell Lipo, which is a standard flight pack for many if my planes.

Confused? I babble.

[Bullfrog]

OK! It is clear that you have the knowledge to select the proper battery for the purpose. It is also clear that when I have a question along those lines, I should contact you for input!
Ed

[Bill2001]

Here is an article on evaluating exhaust gas temps in a 2-stroke Ultralight aircraft engine:

http://www.challengers101.com/ExhaustGasTemp.html

[Bill2001]

Koso EGT gauge installed on Wombat 94 using custom bracket. Battery pack is 12v 700 mAh NiMh.

[racerclam]

Knowing how to red plugs is fail safe , the plug tells the story .

Rich

[Bill2001]

True, reading the plug and noting the piston wash is standard practice, but monitoring the EGT for your engine keeps a running check on the piston.