Enigne heat ... how hot can it get?

Hi all.

I have a 1977 KZ650B1 with 22,000 miles on the clock. Mild cafe modifications ... stock exhaust but pod filters, re-jetting on the motor. I've been running it for a few years with no mechanical issues after a thorough refurbish.

I noticed after getting home yesterday (after an extended blast at 60 - 80 mph) the engine seemed to really be radiating heat. Air temp at the time was 74 out with about 40% humidity. I took out a spray bottle and squirted the header pipes, engine cyliners and valve cover. The water mist instantly boiled off when it hit all three areas.

No big suprise on the headers, but would the cylinders and valve cover really get that hot? I don't have an oil temp gauge so I don't have an exact temp the oil was at.

The engine cooled fairly quickly after parking it, I checked all the plugs (good color) and the oil level and color through the sight glass (definitely full, definitely not burned). Am I being paranoid about this air-cooled beauty of mine? Or am I getting into a heating issue?

For the record, she ran fine the whole time and idled nicely before I shut her off at home.

You don't have to guess - these are really cheap. I've had my handheld Raytek for years and still use it to diagnose my 2-stroke tuning and operating temps, especially the triples where the center cylinder needs a little extra fuel to stay cool. The results I have found are interesting.

1) An old CB350 twin Honda with a hard, 6-7,000 rpm ride with me, a 240 lb rider will come home after an hour and read 230F at the cylinders and 255f at the head and plug areas. The carb intakes will read 190, and the exhaust just outboard of the head 500+. The oil temp will be in the 210-215f range.

2) Same for my CB500 Four and my TX650 Yamaha Twin.

3) My 1974 CB750 is equiped with a cooler and it keeps her oil a lot cooler - even with 10.5:1 compression, head porting, and 836cc. Her cylinder temps still go to 210~220 and the head areas will get up to 240~250 all the same, but even after 2-3 hours ride, the oil temp has never exceeded 190.

4) My modern, water-cooled bikes run 210f on the cylinders and the headwhile the cases show 170-190. I've got a ZRX and a 1500 Nomad - neither has ever shown a temp anywhere on the cyclinders or head above 210. The exhaust on the ZRX are the only "black" pipes I have measured and those are over 500 + degrees (the Raytek will not measure temps on chrome nor will it go above 499F).

Since water turns to vapor at 212f (boils), I am not at all surprised by the steam on an air-cooled bike - especially the exhaust where we know EGT is 1,100 degrees on a properly tuned engine and can reach 1,400 degrees on a lean one (pistons start igniting fuel at this point and detonation soon eats your bike's piston top, you lose ring lands, and this go sour real quick.

Here is the link to the tool you're going to buy for yourself - Regards,
Gordon

www.arizonatools.com/tools/temperature-g...i2zJMCFRLoxgodfiWVhg

Hey, I just noticed the new ones measure to 932 degrees and are $49. Mine goes to 499 and cost me $80 - I got a bad deal 5-6 years ago. Electronics and computers are definitely getting cheaper if gas and food prices aren't --

Go figure..

Gordon

Ilbikes wrote:

Hey, I just noticed the new ones measure to 932 degrees and are $49. Mine goes to 499 and cost me $80 - I got a bad deal 5-6 years ago. Electronics and computers are definitely getting cheaper if gas and food prices aren't --

Go figure..

Gordon

My sister used to work for Raytech. She gave me one for free.

This one goes to 1382 deg. F

Linky-Poo

I wouldnt worry about it, I rode my black motored GPZ750 across the desert my El Mirage dry Lake and it was 117 degrees. I put my hand behind the motor and could only leave it there for 2 seconds. I was thinking the whole motor should just melt into a pile of aluminum but it never fazed it. It did have an oil cooler on it. Ive seen harley dressers going thru the badlands running 85 , 2 up, pulling a trailer at 116 degrees too. Them bike motors are tough !

Synthetic oils can handle the heat much better than regular oil. No problems with my daily rider here in Texas in the summer for the past 15 years. Sitting at a stop light is much hotter than going down the road....chris3