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  #1  
Old 9 Aug 2009
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Air cooled engine is for limited use?

Hello

I have a bike (Honda XR 250) but I don't know so much about technical stuff
yet so I thought to ask the more experienced people here.

I am confused about air cooled engines versus water cooled engines. People
tell me different things about them. I hear that an air cooled engine on a
motocross like mine will become so warm if you take it out on the motorway
for hours and hours of touring, and that this will wear the engine faster and
shorten it's lifespan. This is because it is only made for working during shorter
time intervals on a motocross track.

Thus one has to have water cooling for touring on the motorway.

Others tell me that a motocross like mine on the motorway will cool itself fine
and not to worry.

I would like to take my Honda out on the motorway with average speed of
100 km/h for several hours at a time if it is advisable.
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  #2  
Old 10 Aug 2009
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You can run an aircooled engine on the motorway without any problems.
Think about it this way: When doing offroad work you usually have pretty high revs and comparativly low speeds, meaning little cooling of the engine.

On the motorway you also have high revs but lots and lots of cooling, so no worries there.

If you're really worried about that, there's also oil temperature gauges that replace for the normal cap of the oil tank, so you can have a look at the temperature while riding.

See ya!
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  #3  
Old 10 Aug 2009
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Think about it this way, there are a lot of BMW's, Triumphs, Harleys and bikes going back to the earliest times that were not water cooled. They cruised highways just fine.

There are actually three types of cooling, water, air and oil. A water cooled engine is designed with tighter tolerances on the basis that if something is a bit tight and the extra power from the same capacity makes it run a bit hotter the water will get rid of that heat in a much more controlled way. A pure air cooled engine (like a Enfield) is designed for the optimum temperatures, the tolerances close up to make better fits as it warms up, then get a bit too tight causing wear if you run it too hard for too long. This I'm guessing is the sort of motor people are telling you about. A Bullet motor with it's 1950's materials and ancient lubrication circuit won't run for tank after tank at motorway speeds without wearing faster than it should. The oil cooled version simply has an oil cooler in the circuit so the oil mimics some aspects of a watercooling circuit. It's nice and simple without extra pumps, pipes and other bits that can fail, but isn't quite as efficient.

My air-oil cooled Triumph which uses modern materials will cruise at 90 mph all day. My aircooled Bullet didn't like more than an hour at a time at a constant 55 mph. I don't know where the XR falls in terms of technology, but I suspect it's much more like the Triumph.

I'm sceptical about gauges. To me they only cause worry when the air is a little drier or hotter and are horribly innacurate (my last one measured drinkable tea at 110 degrees C!), but if you want something for comparison, they work for some people.

Andy
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  #4  
Old 10 Aug 2009
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I hired xr250's in Thailand for a couple of weeks and they were fine for road use (no motorways, though) and awesome for tracks/trails etc - as you'd expect. This was with a 90kg load (me) and about 12/14kg luggage (a large Ortlieb and a full daysack). It was ok running at 80/90kph but i wouldn't ask for more... that's where the 650's come in! Aircooled is fine for highway running as long as the airflow is cooling the engine, but use a good oil and change it regularly.
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  #5  
Old 10 Aug 2009
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Your XR250 is an enduro/trail bike, not a motocross bike.

One reason that the engine is not ideal for long distance touring is that it has a small oil capacity, probably 2 litres max? This means that the oil has a hard life as it's circulated through the engine twice as often as an engine with double the oil capacity. This is one reason why offroad bikes in general require more maintenance than your average road bike.

Being a 250, you'll also be working the engine at higher revs to make decent progress, especially if loaded with luggage and/or pillion.

As others have said, there have been plenty of aircooled bikes that make great tourers, it's just that they tend to have bigger oil capacities and larger engines that don't need to be worked so hard.

There's nothing to stop you doing anything on your XR250, just remember its limitations and service it accordingly.
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  #6  
Old 14 Aug 2009
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Many hubbers have done rtw trips with smaller bikes like 125cc. Perhaps you just need to take it a bit easier and try average a bit less speed. Good luck.
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  #7  
Old 14 Aug 2009
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I have owned a Dominator 650, a XBR 500 and now a XR 400. All were air-cooled, and all have run well on longer cruising spped jaunts.

The only disadvantage with the XR is the smaller oil capacity and hence the very frequent oil changes the factory manual requires of it's XR owners.

If you are happy about that and about the "faster then normal" wear on your posterior courtesy of the XR Geneva-convention-infringing saddle, then you should be fine...
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  #8  
Old 14 Aug 2009
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Quote:
Originally Posted by Threewheelbonnie View Post

A pure air cooled engine (like a Enfield) is designed for the optimum temperatures, the tolerances close up to make better fits as it warms up, then get a bit too tight causing wear if you run it too hard for too long. This I'm guessing is the sort of motor people are telling you about. A Bullet motor with it's 1950's materials and ancient lubrication circuit won't run for tank after tank at motorway speeds without wearing faster than it should.

Andy
You appraisal of the Enfield is so out of date I am surprised you did not warn him about the girder forks and solid rear suspension equipped with cross ply tyres .

Truth is since 2004 they have been running a modern AVL designed engine which has nicasil barrel ( they usually do over 200K in BMW's). There have been some problems with exhaust valves sticking, mainly due to people removing the PAV which in the Enfields case directs the cool air onto the exhaust valve. Remove the PAV and you remove its cooling.
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  #9  
Old 15 Aug 2009
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Quote:
Originally Posted by oldbmw View Post
You appraisal of the Enfield is so out of date I am surprised you did not warn him about the girder forks and solid rear suspension equipped with cross ply tyres .

.
They also run lean which makes them hotter. To date, with my own eyes I've seen one siezed and one bottom end failure on Bullet Sixty-fives that the owners ran on UK motorways for extended periods. One was a 2004, the other (I think) 2007.

Nikasil in this case is a bit of a red herring, it's a hardening process. A cast iron bore had to be made under size to allow for the wear. The engine started with a tight bore, was run in then lost compresion over the cylinders life. It always ran hot either due to friction or working harder to make the same power with the worn components. The nikasil bore is made the correct size (hopefully) and then keeps it for longer. This helps in that the fits are correct, so only the required amount of heat is produced, but it doesn't help an engine run at full power with no way to get rid of the heat except convention past the fins.

Yes there have been serious changes (in the oil circuit too), but are you saying the Electra/AVL will run 250 miles in under 4 hours day after day? No one seems to be able to give me a straight answer on that one as I can't find anyone using the newer Bullets except as weekend toys, running them just like the cast iron engines.

Yamaha XT's burn oil when used on the motorway, another pure aircooled design that simply can't get rid of the heat, it isn't restricted to the Enfield. BMW's, Harleys and Triumphs don't do it because you are only taking 25 HP out of a motor designed for 50-60 HP while the singles run full tilt. A Harley's biggest issue is cooling the rear cylinder at idle, hence the newer ones idle on the front cylinder only, again they simply can't get enough air to flow past where the heat is.

Apologies if I somehow denegrated your personal choice of bike, but there are designs much better suited to the motorway.

Andy
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  #10  
Old 15 Aug 2009
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Your XT will be fine !!!

Its aircooled but designed as such.. Massive cooking heatsinks surrounding the bore's sucking heat away, the motorway is the BEST place to be !!

The engines are pretty low tuned too to what they could be if they were water cooled..

Like said, replace the filler cap with an temperature guage cap and keep an eye on it..

Your oil probably isnt even going to get to 100c when cruising on a hot day. The hottest my oil got was 130c in Brazil in thick slow traffic and it still looked and smelled good 3000 miles later. (XT600E).

Modern synthetic and semi synthetic oils can take high temperates very well !! Just make sure you always use good quality oils and change when you're meant to.

Stop worrying !!!!!!!!!!
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  #11  
Old 15 Aug 2009
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Quote:
Originally Posted by Horses View Post
Others tell me that a motocross like mine on the motorway will cool itself fine
and not to worry.

I would like to take my Honda out on the motorway with average speed of
100 km/h for several hours at a time if it is advisable.

As others have also pointed out, your XR should be fine, provided the oil is of the right type, right level and in good condition..... and remember to change out of first gear!

However, I re-read your post and saw the above bit.

My XR has both SM (Super-moto) and standard wheels. The standard wheels run with standard gearing on the rear cog. However, my Supermoto wheels run a smaller cog meaning less acceleration but more speed.

Based on riding around with both these set-ups and on a bike that has 60% bigger capacity (my own 400), I would say that 100 KPH on the 250 might not be so wise.

Even if gearing is the same and not higher than the 400, your engine will be revving relatively high. On the 400 I tend to do 80-90 KPH and I would advise the same for you. A bit frustrating at first but you get used to it!
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  #12  
Old 16 Aug 2009
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Thanks people

Thank you all for your answers.

There was a lot of simple logics put into this.

Of course my motor will be less hot on the highway than on a forest track.
I should have been able to figure that out by myself.

Will be checking the oil and do so with sufficient frequency. I will use synthetic.
My engine has only 2 liters, yes I think it was that.

And I will keep it at 90 km/h.

Enduro… I never knew that was distinctive from motocross.
So now I know I have enduro.

Hmmm… starting to think about a 650 now…
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  #13  
Old 16 Aug 2009
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Quote:
Originally Posted by Horses View Post
Hmmm… starting to think about a 650 now…
Try before you buy IMHO. We are all looking for the bike that rides like an XT225 on the trail then transforms into a Goldwing or Fireblade at the flick of a switch when you hit the highway. As no such bike exists (or ever will until they start hovering), we all blow lots of time and cash looking for the right compromise. A 650 will do most things for most people but it's a different enough beast for some people to prefer the smaller bike, especially if you ride serious trails nine times out of ten.

Keep looking and enjoy it though

Andy
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  #14  
Old 16 Aug 2009
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Quote:
Originally Posted by Threewheelbonnie View Post
They also run lean which makes them hotter. To date, with my own eyes I've seen one siezed and one bottom end failure on Bullet Sixty-fives that the owners ran on UK motorways for extended periods. One was a 2004, the other (I think) 2007.
Andy
The sixty fives use the old 1938 engine, not the AVL, but they do have the five speed gearbox
The AVL does run hot, I advise you wait some considerble time before putting naked hands anywhere near the exhaust system


Quote:
Originally Posted by Threewheelbonnie View Post

Nikasil in this case is a bit of a red herring, it's a hardening process. The nikasil bore is made the correct size (hopefully) and then keeps it for longer. This helps in that the fits are correct, so only the required amount of heat is produced, but it doesn't help an engine run at full power with no way to get rid of the heat except convention past the fins.
Andy
The AVL motor has an aluminium barrel nicasil plated, same as the BMW's and they seem to cruise well enough on motorways. My old one did. ( I think, but am not sure that the barrels (nicasil) for both BMW and Enfield are made in the same factory in India, as are the pistons and conrods for mercedes, porche and MAC trucks, among others.

Quote:
Originally Posted by Threewheelbonnie View Post

Yes there have been serious changes (in the oil circuit too), but are you saying the Electra/AVL will run 250 miles in under 4 hours day after day?

Apologies if I somehow denegrated your personal choice of bike, but there are designs much better suited to the motorway.

Andy
It is too soon for me to answer that one as I have not yet done 2,000 miles with it. However I did run it to/fro the UK . left here in 35c after about 150 miles around Rennes I ran into bad weather. It ran that without any problems. Also on the way back was rain until Rennes then 30+c sunshine. This meant I did 150 miles in rain and 150 in warmer weather ie 300 mile seach way to the ferry port..
Yes I bought it to poodle about locally with the odd camping trip. I have to say I am a little shocked by how much they have optimised this build for motorways, to the point I will be undoing some of them. It likes 55-60 and really dislikes running below 50mph and at a constant throttle for that speed, it will slow going up hills and speed up considerably going down. I do cruise slightly slower on it than the BMW, but this is because it is naked, and not fully faired. My times from place to place are pretty similar, but then I do not habitually ride fast. Your 250 mile trip on the Enfield will not need a fuel stop, as over the 900 miles of my trip it averaged 94mpg. So had a greater range with its 14.5 liter tank than my BMW had with 20+.
At some point I will invest £160+VAT and get myself an 18 litre tank. This will give me aound 350 mile range to reserve.
You are right, this bikes forte is not the motorway, and there are many ( probably most) that are better. But it will cope. I prefer to use quieter roads, but there are times and places where the only sensible option is to use motorways and by-passes, the enfield will do it.
I would say my BMW was better on the motorway, apart from frequent fuel stops, but worse every where else. The fuel stops equalises the transit times between points. Getting off the ferry, I was able to do a U turn across the width of a single car, so made my exit some considerable time before any of the other 20 or so bikes there could. Only one of them later passed me at bout 40-50 miles on.

You did not denigrate my choice of bike, as you were talking about the 1949 model. It is just that this advice is not entirely correct now. You need to separate the old bike, the Electra X ( now no longer exported) and the new efi unit construction Enfield, of which I have very little knowledge or interest, as it cannot easily be converted to RH gear shift.

UPDATE: Today I discovered that my bike is fitted with a one tooth larger gearbox sprocket. This makes sense because it feels overgeared. You now need to change all the speeds downwards by 5.5%.

Last edited by oldbmw; 17 Aug 2009 at 20:17.
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  #15  
Old 22 Aug 2009
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Morning Horses,

well my trusty Yamaha XT250 Serow's covered over 67,000 miles, in 3.5 years worth of riding and gets plenty of distant Motorway type use. I find that if I keep the speed to 90kph, that the economy remains OK but, if I stretch it to 100, then she feels a little stressed and drinks more fuel.

The oil capacity's only 1.2 litres. so I perform oil only changes every 1,500km, followed by oil and filter changes every 3,000km.
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