HOT HEADS CAUSE TROUBLE-KNOW WHEN TO COOL IT: K thermocple DIY

[motoman]

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?

 

[chance123]

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.

 

[panabiker]

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.

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

 

[motoman]

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

 

[chance123]

Also this thread is not about water cooled aluminum heads

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

 

[motoman]

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

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:

 

[motoman]

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.

 

[chance123]

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:

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.

 

[motoman]

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.

 

[motoman]

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.

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