Ironhead Cylinder Head Temp. How hot is too hot?

[billeuze]

Whats the max safe Cylinder head temp? I overheated once last summer, don't know how hot but blew the rear rocker cover gasket and then with the heads out found I needed all new valve guides too.

So this year I installed a Cylinder Heat Temperature Gauge so I could observe temps. Then went on a road trip. I was quite surprised at the temps much hotter than I expected. I was only monitoring the rear cylinder. What i found was:
@60mph: 400-450 deg F
@65-70mph: 425-475 deg F (with short bursts up to 500 deg)
Going up long steep climbs increases CHT by 20-30 deg.
Down hills decrease CHT by 20-30 deg.

Ambient air temp made practically no difference. on the first day out air temp was 97 deg F. My 3rd day on the way home was soooo cooold there was actually snow on the the road (and cars in the ditch) on the highest mountain pass. But my CHT readings were practically the same as the hot day.

One myth that I disproved (with my bike anyway) is what I hear often that being stopped at idle is the worst for raising CHT especially when just coming into town from freeway speeds. Not so. I could be buzzing along at a steady 70mph 450 deg F and come to a standstill bumper to bumper 1 mph traffic jam and my CHT almost instantly goes down to 400 and stays there.

I know that iron doesn't dissipate heat as well as aluminum but I didn't know ironheads get that hot. Now that I know I am switching to redline oil (the only one stable to over 500 deg F, made from poly ester base) and I'll install an oil cooler too. Any recommendations on a good oil cooler?

If anyone's looking for a CHT gauge, they are cheaper from the airplane suppliers than from motorcycle suppliers. I used http://www.aircraftspruce.com/menus/in/chtgauges.html (Canadians, just change the .com to .ca for Canadian pricing). The micro-1000 is the only one in the cheap the lines that uses the "E" type thermocoupler - more accurate than common "J" type and is not affected by changes in ambient air temp. Note that for this model you have to buy a 7' long cable and find someplace to hide it on your bike -the guage is calibrated for 7 feet of cable length resistance, don't cut it short. Probes for these gauges at http://www.aircraftspruce.com/menus/...nders_cht.html

[IronMick]

Last year I purchased on eBay an NOS OEM Harley Davidson Cyl Hd Temp gauge part number 75000-69A. Hottest i have seen it is just over 350`. Most of the time on the hiway it is reading quite low, about 250`. The hotter temps are in city riding. Hottest reading was when my electronic ignition was failing.

[fdny37]

I'm not saying that your gauge is wrong but that seems kind of hot. Have you tried checking the temp with an inferred thermometer gun against your gauge to see if there is a difference in temp readings? I have never had readings anywhere near that hot on the cylinder heads of my engine. I would double check with the inferred just to be sure.

[IronMick]

Originally Posted by IronMick

Last year I purchased on eBay an NOS OEM Harley Davidson Cyl Hd Temp gauge part number 75000-69A. Hottest i have seen it is just over 350`. Most of the time on the hiway it is reading quite low, about 250`. The hotter temps are in city riding. Hottest reading was when my electronic ignition was failing.

I should add in here that mine is connected to the front cyl not the rear so perhaps it would read cooler? The sensor goes into the fins right next to and in front of the spark plug.

[billeuze]

Originally Posted by fdny37

I'm not saying that your gauge is wrong but that seems kind of hot. Have you tried checking the temp with an inferred thermometer gun against your gauge to see if there is a difference in temp readings? I have never had readings anywhere near that hot on the cylinder heads of my engine. I would double check with the inferred just to be sure.

No I haven't tried but that is something I want to do. Does anyone have an infrared gun they could send me? i'd only have to use it once to get a reference reading, then I'd send it right back.

I thought too my gauge readings were too high. at least I know it is working though(going up and down with tempeerature) All I need is an independent reference reading to calibrate.

[Shadowdog500]

They are only $39.00 at HF. Ive been using mine for several years, works great.

Chris

[billeuze]

Originally Posted by Shadowdog500

They are only $39.00 at HF. Ive been using mine for several years, works great.

Chris

Wow. what they can make for cheap in China is amazing. I haven't seen any sub $1,000 sportster clones yet but look out, they may be on the way.

[billeuze]

OK, I went over to town today. Found an infrared temp gun for $70. bought it, used it, returned it. Anyway according to that gun my CHT gauge is reading correctly in the 325 - 375 deg F range. I would expect then that it is also reading correctly in the over 400 deg range (but I'm not going to hang over the side of my bike aiming the gun at the head going 70 mph to confirm).

I also went up the highway a ways while I was over there. same temperature readings as before - high (well a little lower than on my road trip but that may be because I didn't go over any mountains today). I did though do a stretch at 80mph - the temp of the rear head was between 475 and 500 deg F the whole time. So I'll still be looking for an oil cooler.

By the way, while I had the gun "on loan" I found that there was about a 30 deg difference between front head and rear head temp.

I'm wondering now about making some kind of wind deflector to direct air over the rear cylinder. Anyone ever done that?

[MDT]

IR readings can be tricky. Also trying to find 2 IR guns that read the same temp on the same surface at the same time can be even more tricky.
But that being said, my 61XLCH, my 74 Shovel, and my buddy's 63 Panhead all read 375 and pretty much stay there. If I point that sucker at my flat black pipes, I get temps around 675.

[marioserafica]

Many years ago I asked to HD Co about head temperature and they underlined that usually front cylinder runs hotter than rear, because front fender and wheel inder air flow to it. Ciao Mario
68xlch