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Post by littlered50 on Feb 7, 2009 18:05:37 GMT -5
Through a friend I have access to a fully equipped workshop and pretty much any part for chainsaws and cut-off saw there is (my friend works with developing and testing them). And so we have been discussing for some time how to improve the _rotten_ CVT cooling capacity of a 139QMB engine. A number of ideas where discarded, first idea was to use a electric blower fan to force more air into the CVT case (would most likely have worked) but eventually we decided to try and swap out the existing cooling fan. Here is what the original looks like. The fan blades are 10 to 6mm high, not very impressive:  The original CVT cooling sucks the air in from the perimeter of the fan through a hole in the side of the case, a very in-effective solution. This type of fan should suck the air in at the center, the centrifugal force then "flings" it outward inside the case. Now, the CVT case is full of what we deemed to be non-essential stuff such as kick-start gears and various badly designed baffles that limits the already mediocre air flow. Here is the original:  And here is the new CVT case, from the same angle after some work in the milling machine:  Much better! To replace the fan we started out with a cooling fan for a cut-off saw, and then modified it. Here is the unmodified original:  Other side  After a lot of work with lathe, drill and milling machines we ended up with this:  The back of the fan is shaped exactly to the same angle as the belt drive wheel, to get it as close as possible to it. It will also help cool the actual wheel via heat transfer. The ramp angle is 15 degrees on a standard 139QMB drive wheel, as measured by us.  Here is the final result, mounted on my scoot:  Closeup. The starter does not hit the fan, even tough it looks like it might:  And here is a closeup showing how the fan fits against the drive wheel once everything has been tightened down:  What remains to be done is to weld shut the old air intake and kick start holes on the CVT case, and mill out the new air intake. More pictures will follow once this has been done... /Otto (And a big THANKS to Marcus for all the help. I owe you one. At least.) |
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Post by medman1952 on Feb 8, 2009 1:39:50 GMT -5
Looks like some quality work you did there. Were you having a heating problem?
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Post by erictheviking666 on Feb 8, 2009 3:44:51 GMT -5
That looks really cool! But, won't that bigger, thicker, heavier fan draw to much horsepower just too spin it? Unless thats some super light material it looks like it weighs considerably more than the original.
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Post by littlered50 on Feb 8, 2009 9:00:38 GMT -5
Thanks guys!
I was not having more of a heating problem than everyone else with a modified engine I suppose, the smell of hot rubber from the belt was almost always there when stoping after driving for a while.
I wanted to make the CVT a little more reliable and make the belt last a little longer. And it was a fun mod to do anyway, this being the season when I can't ride very much ;D
The new fan is cast aluminum, and I estimate it weights about 3-4 times as much as the original plastic fan. Not that we are talking about a lot of weight though; about 50 grams or something. The drive wheel actually weights more than the new fan...
I am quite certain it will not have any impact at all on the engine's performance. We went to considerable lengths to ensure the thing is well balanced too, we think it might actually lessen the vibrations of the engine.
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Post by tortoise on Feb 8, 2009 12:57:34 GMT -5
not having more of a heating problem than everyone else with a modified engine I suppose, the smell of hot rubber from the belt was almost always there when stoping after driving for a while. Any actual before and after comparative references, such as engine oil temperature or CVT cover infrared temperature readings? This thread does document another downside example of 139QMB engine "enhancement" modifications. |
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Post by Enviromoto on Feb 8, 2009 14:18:37 GMT -5
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Post by littlered50 on Feb 8, 2009 14:53:40 GMT -5
Unfortunately no, Tortoise.
I do not have any temp readings from the case before the mod. All I know is that it got too hot to touch with my bare hand after long rides. That would place the temperature at more than 50C, from my experience.
Once I have everything back together I will post a follow-up with some temp readings.
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Post by kliff on Feb 8, 2009 18:08:33 GMT -5
The new fan is cast aluminum, and I estimate it weights about 3-4 times as much as the original plastic fan. Not that we are talking about a lot of weight though; about 50 grams or something. The drive wheel actually weights more than the new fan... I am quite certain it will not have any impact at all on the engine's performance. We went to considerable lengths to ensure the thing is well balanced too, we think it might actually lessen the vibrations of the engine. I hate to burst your bubble, but a mod in one area, ALWAYS affects another. Any engine.... Add to the flywheel weight, and you reduce crankshaft acceleration...or throttle response, as well as absorb some HP to move the additional weight. Add parasitic drag, in this case, moving more air...requires horsepower. That engine must work to move the additional air. These are tried and true facts in the HP world. You may end up with a cooler running CVT, and I'm sure you will, but don't be surprised if you notice a 10-15% performance loss. And lastly, by adding these factors up, your engine may well run hotter in an effort to cool the CVT... Nothings free when it comes to engine and drivetrain performance, and every step forward, can quite often lead to 2 back steps.... |
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Post by littlered50 on Feb 9, 2009 15:00:43 GMT -5
Interesting points, Kliff. Some I had already considered but not all of them.
That the crankshaft acceleration will be reduced I am aware of, but I don't consider it to be a problem. Perhaps it would have been if the engine had been an unmodified 49.5cc, but mine isn't.
I find it unlikely that the fan drag would demand as much as 10-15% of the engine's output. But then again you might have had experience with this type of mod before?
If the engine ends up running a little hotter than before I don't see a problem with that; I have an high-performance cooling fan and an airscoop on it so cooling is taken care of.
Also, considering that some of the engine heat is taken up by the swingarm acting as a heatsink, and that it now has a much increased cooling capacity I imagine that too will help cooling the engine.
Possibly I could end up with a scoot that has a little less performance I know, but I don't mind at all if it does 75km/h rather than 80km/h. If the belt lasts a little longer and the scoot is a little more reliable I am satisfied.
I suppose we just have to wait and see; it will be a few weeks before I can test the new setup.
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Post by kliff on Feb 9, 2009 17:31:54 GMT -5
Keep us posted, and I do hope my figures are wrong.
BTW....BEAUTIFUL machine work and execution!
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Post by medman1952 on Feb 9, 2009 17:36:53 GMT -5
Ditto on the machine work, good job.
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Post by rapidjim on Feb 10, 2009 9:43:45 GMT -5
Great machine work ! Excellant pictures also. Nice to see pictures with the word picture.
Good Luck
Jim/Owner
Rapid Repair
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Post by Scootless Wonder on Feb 12, 2009 11:35:25 GMT -5
Interesting ideas. Truthfully the first thing I would have thought of doing would have been welding that side hole shut and putting the hole where it SHOULD have been in the first place.
Another thing to think about is possibly machining the blades on your new fan to about 1/2 their current height. From the pics, the new fan blades look to be at least 6 times the height of the original stock ones. I know you're going for a better cooling system and whatnot but there's a point in which the cooling isn't going to help the system any more than it already is and it turns into just more useless metal leeching power and performance.
The other consideration is an exhaust hole. You have an intake for the air to come in but where is all of it going to go? I may be wrong and there may be plenty of places for it to go since I'm not outside looking at my setup at the moment (I'll go look in a little bit).
The only other thing is the kick start. Personally I would prefer to have that present. What happens when your battery falls on it's face, you're at a shop or a buddy's house and you go to head home and the starter just goes click click click? You're now stranded because you have NO way to start your scooter until you get a new battery and a charger to pump it up.
Just my $0.02 on the ideas. I think it's great that you're looking for a viable alternative to the horrid cooling setup but on the other hand I spent 5 years in the service on a submarine and we ALWAYS had a backup system for EVERYTHING that could possibly go wrong. I just don't feel safe without having backups in my everyday life now.
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Post by medman1952 on Feb 12, 2009 14:06:37 GMT -5
If the fan causes too much drag, I'm sure he will let us know, he already stated the weight was not very much more than the stock part. The vent hole for the air to exit by is still there. As for the kick start, my rebel didn't even come with one from the factory, I could push start it if I needed to but that is no fun. Jump starts are not too hard.
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Post by littlered50 on Feb 15, 2009 15:33:04 GMT -5
Ok, an update: I have put it all back together now, and was able to make some short test runs today. There is no loss of throttle response at all as far as I can determine, the engine runs just as before but with a little less vibration which is nice. I can feel a good, strong flow of air from the air exhaust at the back of the CVT even at idle. The only change I have noticed is the engine noise, I am hearing a distinct whining sound from the cooling fan low speed :-). At higher speeds my not-so-very-standard exhaust system drowns out any noise. I was not able to take any temperature measurements or make any high-speed runs to determine if I have lost any top end performance. It is too cold and icy here for me to ride right now. For now, all I can say is that the mod works as expected so far. More info will follow. Here is a pic of the end result. The grille up front on the CVT is the new air intake I milled out. I am going to chrome it all once I am satisfied with the performance and have stopped tweaking it.  Retrorider, some comments on your post: It is impossible to move the air intake to the proper location without completely removing the kickstart gear and milling or grinding away all the supports and whatnot that holds it. See the 2nd picture in my first post above. As for the air exhaust, I have milled away a lot of metal that was preventing the air flow. The exhaust hole is much larger now and has no obstructions. See below:  And regarding your concerns about removing the kickstart I see your point, but I have never ever had to use it. Since this mod is impossible to do without removing it I will just have to live with having no kickstart, and take proper care of my battery instead. |
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Post by littlered50 on Feb 22, 2009 11:14:43 GMT -5
Update:
A thaw today made it possible for me to make some test runs at WOT.
The conclusion is that I seem to have lost about 5km/h (3mph) top end and that acceleration and throttle response appears completely un-affected.
The CVT cover was lukewarm after 1hour of riding, and the engine was also much cooler than before. I could actually put my hand on the crank-case after the test runs, something I would not have dared to do before this mod was made.
Outside temperature today is 5C (41F). It will be interesting to see how well the new cooling holds out in the summer.
All things considered, I am satisfied with the mod.
Anyone looking to do the same mod on their scoot should know that machining the fan was the hardest part.
However, anyone with an angle grinder and some determination could modify the CVT cover the way I did, and gain an increase in the air flow with the stock fan. At the expense of the kick-start of course.
I would not recommend a Dremel or similar tool though, unless one is prepared to spend an awful lot of time on the job (and a lot of cutting wheels). It is simply too much metal to remove...
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Post by medman1952 on Feb 22, 2009 12:41:12 GMT -5
Since you started this thread I have seen a very similar looking cooling fan on a clutch for a 150cc scooter. I agree about not using a dremel to do this to your cover, anybody that wants to can purchase a 4 1/2 inch angle grinder from harbor freight for about $18.00 (US) and it will make quick work of this, I have one I've used for years it is a great little tool. They go on sale at the stores for about $15.00. www.harborfreight.com/cpi/ctaf/Category.taf?CategoryID=104&pricetype= |
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Post by kliff on Feb 26, 2009 20:13:50 GMT -5
Update: A thaw today made it possible for me to make some test runs at WOT. The conclusion is that I seem to have lost about 5km/h (3mph) top end and that acceleration and throttle response appears completely un-affected. The CVT cover was lukewarm after 1hour of riding, and the engine was also much cooler than before. I could actually put my hand on the crank-case after the test runs, something I would not have dared to do before this mod was made. Outside temperature today is 5C (41F). It will be interesting to see how well the new cooling holds out in the summer. All things considered, I am satisfied with the mod. Anyone looking to do the same mod on their scoot should know that machining the fan was the hardest part. However, anyone with an angle grinder and some determination could modify the CVT cover the way I did, and gain an increase in the air flow with the stock fan. At the expense of the kick-start of course. I would not recommend a Dremel or similar tool though, unless one is prepared to spend an awful lot of time on the job (and a lot of cutting wheels). It is simply too much metal to remove... Sweeeeeeet! Looks like I was wrong on all counts....GREAT! I hate to see anyone put out an effort like yours and have bad results. I am glad I was mistaken. Here's wishing you some warm, clear weather to get out and ride that scoot. Again, well done.  |
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Post by littlered50 on Mar 6, 2009 15:53:53 GMT -5
;D Thanks Kliff!
I borrowed a tach the other day, and took some RPM measurements. I have also installed a bike speedo, and found that my speed figures was completely off... Max speed is 60km/h, not 75km/h as the Chinese speedo says. I suppose I should have known better than to trust it...
Anyway, here are the RPMs. Looks OK as far as I can tell, except for the idle with choke engaged which is a little high.
Max RPM at takeoff: 7300
RPM at max speed (60km/h): 6700
Cruise RPM (50Km/h): ~6400
Idle with choke engaged: 2500
Idle, hot engine and no choke: 1200
Now, I am wondering if I should change my roller weights to something heavier, seems 60km/h (37mph) is a little less than everyone else is reporting? The RPMs seem OK though, at least for a stock engine. I have what is supposed to be a performance cam on mine, so the max HP may be higher up in the RPM range I suppose.
/Otto
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Post by Enviromoto on Mar 6, 2009 20:45:27 GMT -5
I wouldnt go any lighter than 6g, I like the 6.5g Dr. Pulley sliders on a stock scoot.
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