Export thread

WHY WORRY HOW HOT Air cooled heads do not remain at sump oil temperatures. According to experts their heat can rapidly increase and surpass the oil temp when doing hard work (power demand, high ambient temp, lean mixture -and/or combos). Oil coolers do not alleviate this inherent weakness. (There is discussion of oil spray-jets on AC tractor piston bottoms, but seems unlikely IMO due to cost). Most head heat unloads from the head(s) so knowing the danger zone is important, and an idiot lite or reliable index to that heat is key.

IMO the danger zone is 325F to 350F for AC tractor heads. That is based upon "creep" temperature of 390F (Alloy A 242 ) , where head metal starts softening , moving, and cracking-releasing valve guides and seats. AC tractors seem especially vulnerable . They cannot dive/coast (aircraft), or descend/coast (motorcycles) to cool, and lack significant external airblast.

So can the alert owner reduce this temp? IMO he can if he sees it. To see it accurately may be possible with the K thermocouple. Once known, some operational clues (e.g. 80-85F bagging damp grass on hills) or better an accurate warning light , or even stopping for another K couple reading , may avoid problems. Would you rather pull over in shade or tear down your tractor?

Hmm
For the last 6 weeks here in So Cal it has been well over 100 degrees every day. My clients run all their equipment in the heat of their 8 hour day, 6 days a week, but never had "any" over heating on either the air cooled, or the water pumpers. If a mixture is lean, or oil is too low or contaminated, "that" could cause overheating.

motoman said:

IMO the danger zone is 325F to 350F for AC tractor heads. That is based upon "creep" temperature of 390F (Alloy A 242 ) , where head metal starts softening , moving, and cracking-releasing valve guides and seats.

Click to expand...

Where did you get these temperature values. I don't mean to challenge these numbers but I saw a wide range of numbers on the net. For example, this 1970's NASA paper seems to give a much higher allowable temperature for Aluminum heads. On page 3, "the recommended maximum temperature measured at the spark plug base being about 230' to 260' C (446' to 500' F)"
http://www.google.com/url?sa=t&rct=...jrY4Xmv0CMyAmSnCw&sig2=mbpUykU9evhratSsVf1QZg

Panabiker, Yes I am aware there are some big variations in critical temp from my reading. For instance aircraft engine data is anywhere from 300F to 500F and I could not penetrate the variation. I decided to plunge ahead based upon the Alloy data I found . I had to assume it is A242 because of...marcusfarkus.com, pg 12. I could not find any thing more definitive. Also take a look at afsinc.org, pg 1 , and wikipedia refractory metals, pg 2. You must understand I do not hold out as a mechanical engineer. Something is going on with some of these AC tractors. Perhaps the "systems" guys are not packaging the engines properly , or perhaps the low end (big box stuff) units are truly going out doomed to short life. This "creep" thing appears to be a cumulative problem. The engineering guys who put this stuff together could probably clarify this in short order, perhaps at pain
of job termination. A "fly on the wall" at some of these companier would be fun.

By the way, since I'm preparing for some kind of warning light I did select the "critical temp" as a set back from (let's say) 400F. If the head is at 400F it's already too late. The 325F-350F zone provides a buffer against upward heat soak and time to cool off. Also this thread is not about water cooled aluminum heads

motoman said:

Also this thread is not about water cooled aluminum heads

Click to expand...

LOL I hope not! At "those" temps you might discover the awesome untapped energy of steam. LOL

chance123 said:

LOL I hope not! At "those" temps you might discover the awesome untapped energy of steam. LOL

Click to expand...

This exercise is just that, an excercise. I am merely a curious private party who has only owned one powered lawnmower in this lifetime. My findings, even if surprisingly "hot," are only one finding. What I hope is that others use this simple, accurate equipment , and report. This excercise will not complete until I get some data. That cannot be now until spring-summer. I realize there are many professionals and entrepreneurs who contribute to this forum. But facts (if found) will stand up.

With regard to 100F ambient...yes that's hot. Are your clients' tasks many short duration mows
such as yards or are they 8 hours mowing acreage? Are they carrying 120 lbs of grass in bagger systems? Are they working hills? These questions are not to needle , but to emphasize the need of a systematic approach for this to make sense. Maybe there is something to branding. :smile:

HOT HEADS...BUY IF YOU WANT

Below is tractor with K termocouple from the head connected to the hand held thermometer (cold engine). Although this is DIY thread I will describe the "purchase" approach.

The K thermocouple CHT cnnector is simply a spark plug gasket replacement with the 2 lead K wires attached. At the other end is a K male connector. I do not pitch vendor sources or sites. The DIY gasket is a little tricky to make. Ebay stores show turnkey setups cheap. There's a catch- these are ordered direct from China. The same stateside setup are $35-$75. Handheld thermometers stateside seem to start at $29.

motoman said:

With regard to 100F ambient...yes that's hot. Are your clients' tasks many short duration mows
such as yards or are they 8 hours mowing acreage? Are they carrying 120 lbs of grass in bagger systems? Are they working hills? These questions are not to needle , but to emphasize the need of a systematic approach for this to make sense. Maybe there is something to branding. :smile:

Click to expand...

Yes, to all of the above. They work 10 hour days averaging 8 hrs of mowing time. Everyone has hour meters on their machines. Very few residential and mostly large fields, parks, college campases etc with all the hills, slopes associated with it. The machines only stop for (2) 15 minute breaks and 30 minute lunch breaks, and to refill their fuel tanks. The equipment includes air cooled and liquid cooled. 4 stroke & 2 stroke. Push mowers and riders as well as line trimmers, blowers, hedge clippers, and edgers. To be honest, in my whole life the only time I've "ever" seen an air cooled engine over heat was an Ariel square four motorcycle. The back 2 cyl ex pipes used to turn deep purple and even glow if allowed to run too long while not moving.

HOT HEADS DIY... K THERMOCOUPLE WIRE

Experience is with the solid 30 gauge and the bundled flex cable. Only about 36" was required for tractor. That includes some service loop (slack) so the connector end can be pulled in and out of the cowl. Experience here is that unless you buy bulk wire/cable it is necessay to buy terminated K wire which always seems to be solid wire (china). Advantage: " balled" connection for spark plug gasket is already done. This solid wire is not flexible, but may work well on tractor with careful routing.

The cable used here (brown jacket) is from an online surplus store, $.25/ft. It Is jacketed with foil shield, clear mylar filler, drain wires and finally the two K wires. Not know if the electronic shielding is necessary on tractors. (Long story short: tiny current signals self generated by K wires may be susceptible to external signals) Use what you can find. K wire usually good up to 2000F , always (I think) to 400F.

chance123 said:

Yes, to all of the above. They work 10 hour days averaging 8 hrs of mowing time. Everyone has hour meters on their machines. Very few residential and mostly large fields, parks, college campases etc with all the hills, slopes associated with it. The machines only stop for (2) 15 minute breaks and 30 minute lunch breaks, and to refill their fuel tanks. The equipment includes air cooled and liquid cooled. 4 stroke & 2 stroke. Push mowers and riders as well as line trimmers, blowers, hedge clippers, and edgers. To be honest, in my whole life the only time I've "ever" seen an air cooled engine over heat was an Ariel square four motorcycle. The back 2 cyl ex pipes used to turn deep purple and even glow if allowed to run too long while not moving.

Click to expand...

Chance,That's very compelling and I am glad you are contributing. However, what do you mean by "I have ever seen overheat?" What kind of repairs do you make? (As an aside I remember the Ariel because they could not keep the cranks coupled. The patina color purple on an exhaust pipe may not be significant as we're concerned upstsream in the guide aea. I have a Nissan with purple headers-great color!) motoman

HOT HEAD DIY...K WIRE JOINT TERMINATION

Apparently the manufacturers join the K wires "hot end" with an electric weld. Not tried ,but you may read about hooking up car batteries to produce the "ball." Sounds risky. The metal of the two K wires is slightly different versions of nickel alloy ; one is magnetic (-). Termination techniques vary from twist (seems weak), peening, crimping, and gas weld. The ball is the instant temp pickup contact, and can be configured for surface, gas or fluid measurements. Tin/lead solder may work , but may loosen due to reflow temps at head. Silver solder and braze should work, but fluxes must be removed.

HOT HEAD DIY...SPARK PLUG CONNECTOR

Cut off your plug sealing washer. What follows is Intek 24 , my only ref. Measurements for this effort: (1) washer seat .830" OD, width .165" NOTE: the washer seat is counter-bored with a ridge at .831" (2) Plug thread OD .548", plug washer thickness .059". (3) K washer material (here) plain or stainless steel . Pictures online look like copper.

A note on the pics below which may confuse. First attempt was wire rivet butt- brazed to washer. This did not work out. Too weak. The picture series is included because it contains other useful views. (pics lost in cyberspace and reappeared). Tractor has gas weld version.

Start with a washer OD large enough for a 1/8" by 1/4" grip pop rivet hole at the outer radius (1/8" drill). The washer is drilled for the pop rivet as a wire barrel. Blue (marker pens work) and scribe the desired OD and barrel tab. Then reduce the OD to .830" except for the tab. Drill tab.

More clarification: In third pic a solid ("chinese") K wire setup is shown Two wires inside the white jacket. As you may know I did not use this style, rather the cable with stranded wire. But this shows how the "purchased" solid wire comes to you with a male K connector. The balled end is not shown. As noted someone should try this style to see if it can take the vibration and (possible) external noise interference. Geeze what a patchwork I created.

HOT HEAD DIY...GAS WELD, CRIMP, ROUTE

Used big oxy/acetylene torch. Smallest tip with 3 psi oxy-acetylene. Flame tiny, just enough so it does not "pop out." Make the K wire ball contact now if you need to. (either stranded wire or solid), and the barrel to washer weld. Did not fuse weld. Grind down a 1/16" steel rod end to a small diameter. A little dab will do 'ya. Get in and get out asap both tasks. I used a vise to just expose the wire ends for the ball contact. ( A jeweler's torch is perfect here).

Your washer must seal the plug. Blue it and torque lightly (12 ft lbs) . Read contact both sides. Improve it if necessay. RE blue .Retorque full (15-20 ft lbs) read , correct if necessary. The wire barrel may be bent away slightly to clear boot. No leakage permitted at seal!! FIRE hazard and lost power. Slide heat shrink onto wire above crimp. Crimp the balled K wire into the wire barrel. If you route wire from plug to cowl thru a SMALL HOLE you must connect the K connector from the tractor seat. With solid wire should be no problem. With stranded wire this is difficult. The left pic does not show K wire, just mock up.

Again and to answer panabiker question about wire shown on head pic below. Sorry , folks, bad choice for DIY. That wire is NOT K wire. The K wire is shown in other pics as red/yellow and welded ball. Panabiker is right about extending K wire- regular copper apparently can be used , but only to "cold" end which is thermometer. Sometimes long runs require this e.g., VW bus. Not on our stubby tractors. OK?

From the picture on the left, did you just make the K junction from two regular, plastic shield copper wires? My understanding is that you have to use the special K thermocouple wires to form the junction.

panabiker said:

From the picture on the left, did you just make the K junction from two regular, plastic shield copper wires? My understanding is that you have to use the special K thermocouple wires to form the junction.

Click to expand...

Please see edited correction above.

OK, Initial 3-temp readings with the installed Bedee oil temp gauge (sump), sump K, and head K.

Ambient 78F
Bedee, Sump K, Head K, Activity
195F 176F 215F lite haul
225F 208F 268F cut weeds out chute
230F 216F 260F dry leaves bagged

T HEADS DIY...MISCELLANEOUS

CONDUIT Brake line should work as a conduit for the white, solid K wire. This line may also work for (electronic) shielding. The ends would require foil or ? It is easily formed for routing.

CHT GAUGES Reality check. Why go K thermocouple and not the kits for $80-$100? Latter are resistive type, non linear and may be wildly inaccurate. Classic bench tests show error of up to 60 F.

DUAL INPUT Want to look at two areas at once, like both cylinders? Two channel thermometers are available at low cost..

KITCHEN CALIBRATION Check accuracy of your set up with ice water (32F) or boiling water (212F)

PLUG RING CARE When the spark plug is tightened or loosened hold the ring in place, square, during swivel action. Should not follow plug around. If it hangs up open the ID slightly.

READING Curious about the effect of 300 F plus on the head (s)? Try:

aagaskets.com; liquidcooledairpower.com; enginehistory.org; sut.ac.th;
en.wikipedia.org/wiki/refractory_metals; afsinc.org;

motoman said:

...
CHT GAUGES Reality check. Why go K thermocouple and not the kits for $80-$100? Latter are resistive type, non linear and may be wildly inaccurate. Classic bench tests show error of up to 60 F.
...

Click to expand...

I thought most CHTs do use thermocouples, either K type or slightly more expensive J type. The problem may be that the meter they sell in the kits lack the ambient temperature compensation circuitry to display the hot junction temperature accurately.

Very interesting and very relevent.
Since you have collected, and have the technology to collect data, it seems to that determining the effect of ambient temp on engine temp is something we could all use.
Can you graf the effects of engine temp rise as it relates to ambient temperature rise????

panabiker said:

I thought most CHTs do use thermocouples, either K type or slightly more expensive J type. The problem may be that the meter they sell in the kits lack the ambient temperature compensation circuitry to display the hot junction temperature accurately.

Click to expand...

I am not an expert, but I have spent a lot time on line. The motorcycle sensors must be resistive as their sensor heads resemble coolant sensors (brass tubes) and there is no talk of K or or temp compensating features ( the digital K thermometers have a Tc button to push which adjusts the cold end to ambient rather than some estimate like 72F ambient. I guess some aircraft ( at least some, maybe all) use the K . What is a little confusing is that a lot of the $280-$3000 units show 28v, but that could be back lighting. I have seen that resistor sensors can be very accurate, but very expensive. Amusing and impressive is the widespread use of the K on the new wave of scooters and of course the go cart guys have used the K for years.

RobertBrown said:

Very interesting and very relevent.
Since you have collected, and have the technology to collect data, it seems to that determining the effect of ambient temp on engine temp is something we could all use.
Can you graf the effects of engine temp rise as it relates to ambient temperature rise????

Click to expand...

I have only started comparing the Bedee oil temp gauge to the K probe, but there is disagreement already. See above . The resistor sensors are known to be non linear. My Bedee gauge is reading high on 3 tries. What is important is that it get accurate out around 280F and up. I'm still getting use to the K dipstick probe.

I have my old Intek head that pushed the guide and started all this. Plus I have a brand new head. Today I found local test lab that will run a Brinell test on both for $45. I don't know...I'm thinking about it.

My gut feeling is that the head temperature versus the ambient temperature will have a constant differential. In other words, if the ambient goes up by 20 degrees, so will the head temperature go up by roughly 20 degrees, under the same condition (loading, wind, etc.).