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CHT
Jun 14, 2011 11:23:21 GMT -5
Post by Rebel on Jun 14, 2011 11:23:21 GMT -5
OK, tell me about what a cht is.
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jmkjr72
contributing staff
Commander 132nd Northern Cav. Division
Posts: 2,779
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CHT
Jun 14, 2011 11:40:25 GMT -5
Post by jmkjr72 on Jun 14, 2011 11:40:25 GMT -5
cyl head temp the most common is an inductive loop ring that goes between the plug and the head and it tells you the temp of your head i dont know what the safe temps on a 4 stroke would be i try to keep cast at 350 f or less and al at 450 f or less
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CHT
Jun 14, 2011 12:05:59 GMT -5
Post by Rebel on Jun 14, 2011 12:05:59 GMT -5
Duh, I was trying to think of the name of a instrument. My mind was a terrible thing to loose.
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jmkjr72
contributing staff
Commander 132nd Northern Cav. Division
Posts: 2,779
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CHT
Jun 14, 2011 20:24:31 GMT -5
Post by jmkjr72 on Jun 14, 2011 20:24:31 GMT -5
where are you looking for cht i got one ring terminal fromt tto for 30 bucks and there are lots others out there like that also try looking on pages like stella speed there are a lot of guys there with them in fact i run an ultra light set up on my stella and there are is lots of info on chts for 2 strokes in dirt bikes and on the shifty scoots infact even over on zuma forums there are guys running chts trailtech.net/tto_temperature.htmllooks like the direct price from tto has gone up some but you can find them on amazon and ebay egts on the other hand are a small fortune to tune with and are more in the price range that you are talking about just sounds like you didnt look very hard for a cht and the set up that brent had will work but isnt as accurate as a ring terminal as you are starting to cool when you are way out on the fin
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noday
Non-Com
"Sparky" Electronics Research and Development Officer
Posts: 90
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CHT
Jun 14, 2011 20:37:13 GMT -5
Post by noday on Jun 14, 2011 20:37:13 GMT -5
re: temp gauges
I do have both a non-contact laser and a digital probe type that I use in AC repair work. the shroud gets in the way & ....well just say, I am too old to turn upside down to read a digital probe in the dipstick hole while going WOT.
accuracy v precision of a gauge. a temp gauge does not have to be always true in it's reading, as long as the reading is consistent for the same conditions & can be translated to safe v unsafe.
the trouble I have is finding data as to what are normal operating temps v too hot.
there are a few threads, here and there, on 2t forums but one has no idea if temps and sensor position can be/are usable on a 4t engine.
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jmkjr72
contributing staff
Commander 132nd Northern Cav. Division
Posts: 2,779
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CHT
Jun 14, 2011 21:01:27 GMT -5
Post by jmkjr72 on Jun 14, 2011 21:01:27 GMT -5
honestly for 4 stroke data i would start looking at vw forums and harley forums (harley used to offer a cht for there bikes) this would give some idea of temp ranges
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CHT
Jun 15, 2011 1:04:13 GMT -5
Post by Rebel on Jun 15, 2011 1:04:13 GMT -5
Joe, That Trailtech looks pretty slick. I like the ring under the spark plug, but have you ever seen one make it not seat well?
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CHT
Jun 15, 2011 1:52:05 GMT -5
Post by theswede on Jun 15, 2011 1:52:05 GMT -5
jmkjr72, thank you for posting that link. I knew such instruments are available as I have seen them before but I could not find them. Google was not my friend this time. A quick search on eBay and Amazon seems to indicate that they cost around $36 no matter where you buy them. I think I am going to order one, seems like a cheap insurance.
/Otto
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jmkjr72
contributing staff
Commander 132nd Northern Cav. Division
Posts: 2,779
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CHT
Jun 15, 2011 17:12:54 GMT -5
Post by jmkjr72 on Jun 15, 2011 17:12:54 GMT -5
no i have never seen a plug not seal with that ring in place
on the 2 strokes people have issues with the wires going to the ring busting when they chenge plugs
what i have done on the 2 strokes is run it thru the fins and get it in place with a plug and then back by the fins use some jb weld (the runny stuff not the putty) to hold the ring and wire where it belongs so you can get the plug in and out with out messing with the sensor
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noday
Non-Com
"Sparky" Electronics Research and Development Officer
Posts: 90
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CHT
Jun 15, 2011 17:31:25 GMT -5
Post by noday on Jun 15, 2011 17:31:25 GMT -5
well this is what I condense from numerous HD related threads and airplane engine web pages.
a 4T air cooled aluminum engine usually operates in the 350F to 400F range.
maximal CHT is obtained when the A/F ratio is 14.7 to 1. mixes below and above stoichiometric produce lower CHTs.
CHTs above 400F can lead to knock/detonation with a lean mix. a rich mix at the same high CHTs prevents knock.
The best power production is with a slightly rich mix.
EGT (exhaust gas temp) increases more with a lean mix.
Oil temps. normal is in the 200F to 250F range. oil temps under full load and with increased ambient temps are often in the 250F to 300F range.
At one time, HD fitted their bikes with CHT gauges from the factory. Apparently this was discontinued because of excessive calls from concerned owners about the high CHTs too high ( more a rumor than any fact I can find). no information concerning any incread incidence of top end failures due to the high gauge readings.
so the questions come:
did theswede's top end fail because of a high CHT due to an optimal (for burning) A/F ratio, rather than a slightly rich ratio ? does this EFI need to be calibrated more for power than for fuel consumption ?
(edit) if the CHT is highest at 14.7 to 1 how will monitoring CHT help in preventing top end failure ?
or was the A/F ratio too lean and the EGT too high, rather than the CHT ?
was this a case of the injector being unable to deliver the fuel or is there an error in the Algorithm used to calculate fuel delivery ?
was knock involved ?
when we get top end failure due to a lean mix is this caused by temperature alone (metal related ) ?
is it a combination of lube failure ( 2nd to a high oil temp and breakdown) causing excessive ring wear at high load and high RPMs ?
I wonder if inspection of the head, piston, rings and bore can shed any light on the failure mechanism ?
all in all, more questions than answers.
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CHT
Jun 16, 2011 9:03:00 GMT -5
Post by theswede on Jun 16, 2011 9:03:00 GMT -5
Noday, thanks for pulling all that info together. Are you sure CHT is at its highest at 14.7 to 1 (lambda 1.00)? I have always had the impression that if you lean the mixture out, CHT goes up. But I may be completely wrong of course, or maybe I confused it with EGT. To answer your questions: On my setup, the 38g injector can't supply enough fuel at RPMs above ~6000 or so. I end up running lean, with a lambda of 1.250, and I have lost quite a lot of power because of this (about 10mph in top speed) Ecotrons is sending me a new 60g injector that will solve this. As I wrote in my build thread, typical oil temperature on my engine is 90C (194F). But after a long run a little more than a week ago, when I went WOT for some 30-40 minutes on a very hilly road I had an oil temp of 120C (248F) when I checked the gauge after stopping. I believe this is when the engine got damaged. I did not hear any knocking, but I have a pretty loud exhaust so it may have been there, not sure. If I had a CHT gauge on the dash, I would hopefully have learnt about the issue before anything got damaged. I will be posting some pictures of the head, cylinder and piston when I tear it down. Hope to have the parts early next week. I expect to see the exact same damage on the piston as I did last fall, when I overheated the engine due to a too constricted exhaust. See this thread: scooterrebels.proboards.com/index.cgi?action=display&board=50ccscooters&thread=1290&page=1
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jmkjr72
contributing staff
Commander 132nd Northern Cav. Division
Posts: 2,779
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CHT
Jun 16, 2011 12:06:08 GMT -5
Post by jmkjr72 on Jun 16, 2011 12:06:08 GMT -5
wow you only had a 38 gph injector my small injector is 80 gph
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noday
Non-Com
"Sparky" Electronics Research and Development Officer
Posts: 90
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CHT
Jun 16, 2011 20:48:33 GMT -5
Post by noday on Jun 16, 2011 20:48:33 GMT -5
I looked back again at theswede's older thread about failure and did not see anything on the piston photos other than "normal" wear. no real evidence of heat caused seizure (usually longitudinal vertical striations) perhaps I am missing something ? if that was a pure heat failure there should be visible signs of piston seizure One reference is: www.boosttown.com/engine/piston_damage.pdfIt has excellent descriptions & discussions about different types of piston damage. if any scenario fits it would be page 20 or 80 ( loss of lubrication from fuel flooding ) the statement about maximal CHT with a 14.7/1 A/F ratio applies to a static or constant load & rpm. it does not preclude a higher CHT at higher rpms or load with a leaner mix. . lean mixes at high temps are more likely to knock and pre ignite. pre ignition causes an almost exponential very rapid increase in cylinder temp and pressure that causes top end failure. I look forward to photos of the top end at tear down.
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CHT
Jun 17, 2011 20:31:42 GMT -5
Post by bagga on Jun 17, 2011 20:31:42 GMT -5
i have a cht on my 85 hd. alum. heads and the gauge is always in the 350 degree range. it's mounted between the sparker and the head.
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noday
Non-Com
"Sparky" Electronics Research and Development Officer
Posts: 90
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CHT
Jun 18, 2011 3:42:46 GMT -5
Post by noday on Jun 18, 2011 3:42:46 GMT -5
thanks bagga. there is not a lot of data from scoot owners about actual observed CHT of these GY6 engines
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