Wrapping an exhaust holds heat inside the pipe a lot, but that heat is moving through the inside of the exhaust. The heat your dealing with is the glowing outside heat outside the exhaust, which is much lower, but too close to the engine. High quality Hose camps, passed through aluminum roof flashing, doubled up (by making a slot you could pass the tab through two slots, in, then over the aluminum, then back out towards the exhaust) then run the clamp around the exhaust pipe, a clamp at each end of the heat shield, which you want only wide enough to shield the engine, but not so much that it blocks the air when the bike is moving. I think doubling up on the flashing will give you the rigidity you need, and allow for one sheet to absorb the bulk of the heat, and the second one to absorbe the rest. I would not make the sheet much widder than the exhaust, it would have a radius, I'd think 1/4 inch away from the exhaust, and the heat shield strip should be maybe 1/4 inch wider than the pipe. An aluminum block could act as a spacer. This would tell you if this concept would work. If it does, then you make one a little bit more finished off.

 

No thermostats in the KX450F, surprisingly. The metal sheet is a good idea. They have a heat shield like that for the drivers leg outside, yet the engineers let the 625F heat within 2 inches of the radiator and the cylinder head, it just cant keep the heat out. The fan seems like a must. It would be nice to have a bolt on aftermarket exhaust header section that had the heat shields already welded in place. I can add it, just a bit of fabrication. The heat is way too close to vital areas that need to be warm. The left side of the engine runs at like 100F ish. The exhaust side 220F, its surely the exhaust adding heat to the motor. A Fan and a Shield would work well. The cloth - fiberglass does not look like it lasts a while - yet people say it reduces the temperature big time for other bikes.

 

I would definitely do that fan. If I remember correctly, you put new thermostats in. The radiator will be hotter in places where the hot water first comes in and cooler where it exists, that's normal. It's important to make sure there are no leaks as fluid boils under a higher temperature when under pressure, so it will overheat less when no leak is present. It's also normal for the radiator temperature to rise when stopped as there is nothing pumping fluid through the radiator. Catch the over flow, eentually any excess will be pushed out. If you put a sheet of aluminum between the exhaust and the radiator, the would shield the radiator better than tape would. You don't need thick aluminum either, something you could hose clamp ontoo the exhaust would work, if you really feel you need to do that. Wrapping an exhaust takes the hea of the combustion and helps hold that heat it, and makes the bike run more efficiently. Wrapping wouldn't hurt. I've worked on many British cars that were known for vapor lock, and a small sheet of metal was all that was needed to stop the heat causing it.

 

Update: Was able to idle the bike for 7 min 45 seconds, then a few drips off coolant on overflow came out. Killed the engine. I watched the temperature rise with infrared thermometer. Right side of engine is hotter than left side probably due to the exhaust so close - going to wrap the exhaust. The radiator gets to about 170-180F in places, just incrementally rises in time. Then it overflows, granted a full radiator and leaning to the left on the stand probably helped the coolant overflow a bit easier. Perhaps I am over filling the radiator fluid. Will double check the specs to be sure to put in only the required amount to see if filling it up is okay. Maybe its different than a car, not sure. Likely will still add a battery and fan in time. Motor oil is clear, no leaks either. Just going to tell my son to keep it moving and not idle for more than a few minutes until we get a fan on it.

 

Sounds like you are heading for a happy ending. Fingers crossed.

 

Update: Purchased a piston kit from RevZilla , part was fine. The gasket to the crank case did not fit, the previous one was fine just added some gasket seal to it black - oil resistant. Checked the valve clearance - in spec. Cranked right up. Did the break in procedure. Checked compression it is now 110PSI after 5 cranks. Had to adjust the TPS sensor to the middle of the spec as it was too rich from my prior increase in richness, now its fine just a faint bit of black smoke occasional throttle probably could be a little leaner but I will leave it for now. So far no overheats during riding. No overheat with a garage blower/fan on it. What I did notice is that the oil filter goes on a certain way, black gromet/seal to the outside of the filter housing. Changing the oil a few times as coolant got into the crank case and first go was a bit milky. I will change the oil after 2 runs each time until it is cleared up. Not sure how to really flush 100% of the old oil out just on a drain with the oil filter out. Hope it clears up and no other issue. The other issue ran into was oil seeped out of the weep hole, which forums stated was either 1) overfill or 2) the spark plug gasket seal on the valve cover - which I just re-used and then had to go back in and clean up and add black sealant - no leak now. The other lesson learned was the compression tester adapter, is now in the cylinder head since I forgot to really tighten it before inserting into the cylinder - my fault. Added red thread lock to it and will take it out tomorrow. Not a fan of the adapters, would rather have the set where adapters are not possible to leave behind when removing the hose/compression gauge. So far so good. Will update when I leave it running at idle now that it is broken in and can take being a bit hot. My guess is it should be fine and not overheat.

 

Okay, that explains it; it's a high compression motor that provides some de-comp relief to allow you to move the kickstarter.

 

A battery is a really good idea. It will store any extra energy, and when the fans kick in, it will be just long enough to cool the engine down, and relay to shut off the fan tased on the thermostat a must. the battery will regenerate, and you have made a great modification.

 

As the article notes, the author recommends a one minute (or less) warm up and then ride gently.

Since an MX bike is designed to run at high speeds which forces a lot of air through the radiator, I expect they skimped a bit on the cooling aspect. The fan idea is interesting as is your testing ideas. Keep us posted.

 

There are so many of these kits, you really have to decide on what size you need first, then shop for that, and you will find a kit.

 

Search google for Universal Fan Kit for dirtbike - many are available. For example: https://www.amazon.com/Tusk-Digital-Radiator-Fan-Universal/dp/B08Y5GBV5D
Anywhere from $100-200

You are probably correct on the design for motocross. This article form cyclenews mentions modern 4 strokes warming up for 5 minutes is excessive. So, I would imagine idle for 3 minutes should be tolerated.

How to warm up your motorcycle

How to warm up your motorcycle: It may be different than what you think.

www.cyclenews.com

" “There is a need to allow an engine to warm up,” says Danny Massie of Maxima Racing Oils. “There is a multitude of reasons behind warming up a motorcycle, including allowing the metal parts to grow in size in a controlled manner (due to heat) and to allow for proper oil migration. It isn’t necessary to idle your motorcycle excessively (e.g., five minutes) during the warm-up period because this poses a separate set of issues related to overheating because there is no air flowing through the radiators, cylinders and heads. A good warm-up protocol is starting the motorcycle and allowing a minute of idle, then riding the motorcycle in an easy manner to allow time for the engine to come up to temperature. Good examples of this would be a sight lap, riding to the trailhead or easing the bike out of your neighborhood before blasting the open road. "

I am going to compare the head temperature and exhaust temperature on the 250 vs the 450. The 250 never has an issue, interestingly the compression is 110psi, which is higher than the 70psi the 450 has.
In addition, will time the overheating on the 450 to see how long it can actually idle before overflow.
My guess is after riding it, it took maybe 1-2 minutes before coolant overflow. Starting from a cool engine it was probably 4 minutes.

Will be looking into retro fitting a battery onto the bike, then I will be able to run lights and the fan.
Hopefully the stock stator / rectifier system charges the 12V battery fine.

 

Interesting, do you have any links you can provide for these fan kits?

I would agree that the engineers probably should have built a bit more cooling capacity into these bikes, but we don't know if these problems existed when the bikes were brand new. Perhaps the problem arises over time as parts wear or carbon builds up etc.

However, I maintain that if used only for motocross racing which is what they were designed for, the bikes would likely not overheat.

 

They sell universal electric fans that attach to the radiator. They include a temp sensor to add to the radiator shroud to then be able to set thresholds to turn on the fan. In addition, there is an LCD display of current temperature which also allows to program the thresholds. Seems this is a common issue with overheating if aftermarket not only sells these fan kits, the overflow tanks and higher pressure radiator caps. Some engineer messed up their calculations at the manufacturer for the aftermarket to fix. A bike should be able to idle for 4-6 minutes in my opinion before overheating. Many reports of riders in hot climates running long distance overheating and doing all the above mods. Factory should reconsider the design.

 

Good plan. Very methodical. I will be very interested in the results.

I am very picky and overly scientific for things like this and I would likely find a way to monitor the temperature in real time. You can buy a digital cooking thermometer with very slender probes for very little money. The only trick is finding a way to get it into the coolant stream somewhere without causing a big leak.

Mounting the display up on the bars would allow the rider to keep a constant eye on the temperature.

 

We topped off the oil and put it back together. Will ride it this weekend and never leave it idle to see what happens. I ordered the Top End Kit and will get that back in spec. My other KX250F is at 110 PSI compression at 5 kicks, so this KX450F is low at 70PSI. I looked at some of the fans available, this bike does not have a battery/electric start. Perhaps there is a mod to make it a batter/electric start to tie into the electrical system. Did also see others altering the cooling system with an overflow tank as well as a different cap with higher pressure levels, seems the 1.6 works for many and the 1.8 just is too much pressure. I would expect an idle 450 to overheat in 90 degree temp after like 15-30 minutes, not 3 minutes after going on the easy run. I will post an update after the top end job. The pressure test on the radiator was well over 20PSI, which shows fine for the head gasket. A possibility with 70psi on a 110psi top end is that the gases are going somewhere and increasing the heat.

 

Lots of stuff to check. Adding a fan would be a last option. It's better to make sure everything else is on the up and up. It gives you the best baseline to work with.

 

Adding a fan is an interesting idea. I just wonder if the stator and regulator which were not designed for anything other than ignition and fuel pump are up to the task. Need specs. But also it would require two fans due to two radiators.
Worth looking into though IMHO.

In the meantime here is what the Owner's Manual has to say about overheating:

 

-recenet New Plug gapped - ( need to re-test to see if this changed anything in overheating, would be surprised if this resolved the issue )
-ECU - Not sure
-Throttle body cleaned and tighten up

• Cleaned and sealed Air Filter
• ( carbon build up, a possibility - rebuilding top end and will change the valves if not seated well and worn )
• Oil is spec.
• Clutch slipping - interesting - need to look into this. I adjusted to be sure the cable does not move the clutch lever any at stand still. Maybe it needs a clutch?
• New chain ordered, drive chain is clean and fine.
• Coolant is new. Some say some brand of ice something. Its all ehtylene glycol it seems and its a matter of ratio 50/50 or 60/40 coolant/water. Higher coolant, higher temps tolerated before boil.
• Radiator - tested the flow with an open hose and it was fast moving water.

-Water pump. same test above showed fast moving water.

Next changes. 1) Top end refresh to get compression to 110PSI. 2) Radiator Cap to 1.6 3) coolant overflow tank addition 4) fans addition.

I will add one at a time and document the results.

 

Why not install a fan on it? It would be easy to do, and make a aluminum shroud to keep the air going through the radiator? Also, there's is a chemical to test if exhaust or gas from a blown head gasket is present in the coolant.

Link = https://www.amazon.com/Block-Tester-BT-500-Combustion-Leak/dp/B06VVBSFTF

 

Yes there are all kinds of articles and some of them point out that this is a motocross racing bike and not a trail or dirt bike. It is meant for short, fast rides on a race track.

If the intended use is a trail or dirt bike, then you may want to look at selling the KX450 and getting something that was designed for that purpose.

 

"In fact if you Google it, you will find overheating to be a known issue on the KX450"
like this one: 450 overheating prevention

 

Since we are running out of things to try, I am going to throw this out there.
Next time it "boils over" measure the temperature of the coolant to ensure that it is in fact at or near boiling temperature.

If it is boiling, then perhaps we need to acknowledge that on this high performance motor with a non-fan radiator, it cannot tolerate idling for anything more than a few minutes. I know this is a bit of a long shot, but overheating when idling has happened on other models. My GPz900 will overheat when idling in hot weather and stuck in traffic. This was due to a design flaw that did not turn on the fan soon enough, but yours do not even have a fan.

In fact if you Google it, you will find overheating to be a known issue on the KX450. Some people will run a 1.6 radiator cap, or a 1.8 radiator cap (instead of the stock 1.1).

 

Thanks Robert.

Conclusion: Compression is fine.

The reason Kawasaki uses a "partial" compression test and the reason the numbers don't match the traditional comp test
readings is the use of de-comp weights on the exhaust cam, opening the exhaust valve each time you turn over the engine.

Okay, that explains it; it's a high compression motor that provides some de-comp relief to allow you to move the kickstarter.

 

Sorry Robert, I'm not trying to give you a hard time, it's just that I've been working on internal combustion engines for over 40 years, and this is the first time anyone suggested that those numbers were okay as compression readings, just sayin' Perhaps the "book" is suggesting a partial comp test where you only turn the engine a few revolutions, then record the reading, but the way I was taught was to open the throttle wide open, and crank the engine until the gauge no longer advanced, then record that reading. Which book are you looking at? Does "at 5 times" mean kick through 5 times?

 

Cylinder Head Cylinder Compression (Usable Range) 420 ∼ 698 kPa (4.28 ∼ 7.12 kgf/cm², 60.9 ∼ 101 psi) at 5 times ––– Cylinder Head Warp ––– 0.05 mm (0.002 in.)

Which converts to 60-100psi

 

Okay. You are in the best position to make decisions about going ahead with the rebuild of the top end.

I just always have the nightmare that I finish a full rebuild, and it still does it!
That's why it might be worth your time and effort to continue troubleshooting a bit more, before teardown.
That said, I'm not sure what else to check? I assume you were pretty careful about purging every bit of air from the system; that's about the only thing I can think of that causes such "boiling".
Do you want to pressurize the cooling system with engine hot and run it beyond 20 lbs, it's a little risky so be careful, but is there the possibility of a porous casting or crack somewhere in the cylinder head? With the head off, you can visual check any cylinder head surface near the combustion chamber but a porous casting can be hell to discover.

Didn't know about the thermostat, sorry.
They call the thermostat housing a "Fitting" and the gasket is titled "Gasket, Thermostat", then they put a washer where the thermostat
would have been, wow! Someone makes a kit to install a thermostat, available online. Wouldn't affect your problem though.

Still confused about compression, but no big deal. Are you sure the gauge is well seated, some engines have a raised area with a cut for water drain, and that can interfere with proper seating of comp gauge? Curious: which book says: "...60-100 is operable." Since "Bike has tons of power, wheelie no issues" I would expect readings closer to 160 psi, just sayin'