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@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
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I just saw this video by White One Racing, a couple of Italian guys who do some interesting stuff.

https://youtu.be/tpXrjCJ_Swo

This is a subject that has popped up from time to time - namely the fin design of most Piaggio and third party heads actively restricts flow to the outer fins. This is partially due to the design of the cylinder cowl. Air flows into the channel from the flywheel and arrives at the head, where it "sees" maybe 5 or 6 fins. The air flows over these and out.
The side (shorter) fins are more or less excluded from this process, and I'm guessing only really cool by transferring heat to the centre fins.

I like the idea but wondered if it might be easier to alter the cylinder cowl instead of the head itself - he does mention in the video that you shouldn't cut too much or risk making the cooling worse through lack of area.

I haven't had any luck with plastic welding, but maybe all it needs is heating and shaping to make the channels rather than adding any material.
Forum member supplied image with no explanatory text
Forum member supplied image with no explanatory text
The tape is on the fins that are visible when fitted into the cowl
The tape is on the fins that are visible when fitted into the cowl
@philos avatar
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UTC quote
Interesting topic. Especially for those who like to push the limits.

Unfortunately my Italian isn't up to scratch so I couldn't watch the youTube vid.

It'd be interesting to know what the actual temp variations are on the head. I thought of something like these temp indicating stickers which I've used on other engines..

http://temperature-indicators.co.uk/acatalog/Thermax_Label_TDS.pdf

Not sure how these would work TBH, but something that could give you definitive information on temp variation would be very helpful. Maybe they could be stuck on the inside of the plastic cowl?

Or even thermal probes somewhere, somehow?

One trick we used to have up our sleeve with jet engines was to wrap various components in aluminium foil to detect temps beyond what we were after. The foil melts at a given temp so you have a rough idea on what's gong on. Maybe that kind of idea could be employed? I dunno.. line the inside of the cylinder cowl with alfoil and see what happens? It might show some hot spots. Then again it might just blow straight out lol? Wouldn't do any damage if you were careful.

Another thought is.. to maximise the efficiency of what you've already got in the cooling system. More efficient fans? Sealing air leaks and smoothing flow path would be a good start. I've seen somewhere a deflector tab which was added into the flow path just before the air reached the head. Again it'd be great to be able to actually measure how effective that was.

What about looking at the loss of air between the fan cowl and the fan to improve efficiency? I bet there's huge losses there. Might be able to sculpt the metal fan cowl a bit to bring it closer to the fan?

Just some ideas.
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@ginch avatar
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Veni, Vidi, Posti
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@ginch avatar
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UTC quote
I like the idea of the thermal indicator stickers, sounds very useful!

If you want to watch with subtitles, first turn on subtitles via the settings icon in the bottom right corner. Click on Italian (auto-generated). Then click on it again and choose Auto translate. That will bring up a list, and you can then choose English. It's a bit hit and miss but you'll get the idea a lot better than guessing from the pictures!

I had thought about closing up the gap near the edges of the fan somehow but not sure how that would work, or how you would test if it was working.

And I still haven't tried the deflector tab yet - which was Rolf's idea btw.
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the smallframe shroud solves this problem

External inline image provided by member with no explanatory text

no reason this could not be formed into the large frame one.

Heating, forming, welding the plastic is not that hard.
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here's a picture of a patch I made closing up the plug hole and drilling a new one. done with a scrap from an old shroud and soldering iron.

I think you could shape the largeframe one without the need to weld or patch it.
Forum member supplied image with no explanatory text
@philos avatar
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UTC quote
Ginch wrote:
I had thought about closing up the gap near the edges of the fan somehow but not sure how that would work, or how you would test if it was working.

And I still haven't tried the deflector tab yet - which was Rolf's idea btw.
Francesco is the man! Definitely a bit hit or miss on the translation. At one stage it was hard to tell if he'd just ordered a pizza with extra toppings or talking about the head he was holding? But I think I got the idea of what he was on about.. very interesting and makes a ton of sense to customise the shroud to the particular head... and sort out the airflow so it reaches all the fins. It's a wonder the kit manufacturers haven't cottoned onto that. Anyway, Franco's got it under control...

Yeah, Rolf's tab sounds interesting.

Cut and shut the fan shroud/cover might be something to try. And a little panel beating..
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@ginch avatar
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@ginch avatar
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I don't know what I'm doing wrong then, I simply couldn't get any of the plastic to stick. I used an offcut of the same material to try to fill as well.

I'll have a go at shaping the LF one, I guess I need something solid with a channel-sized gap to press it out into I imagine.

That's good about the SF one. Because we have the long rod on the Zuera 144 and therefore an 8mm thick spacer under the cylinder, I thought that we would have a hard time getting the stock cowl on. And after reading this - https://www.germanscooterforum.de/topic/339711-zylinderhaube-f%C3%BCr-k%C3%B6pfe-mit-zentralkerze/ we got T5 cowls. But now I re-read it a bit closer I see it's actually a central plug cowl from a PX/Cosa 150. Damn. But may have one kicking around the shed somewhere...
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UTC quote
Ginch wrote:
I don't know what I'm doing wrong then, I simply couldn't get any of the plastic to stick. I used an offcut of the same material to try to fill as well.
Have you tried using acetone?
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@ginch avatar
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UTC quote
What, to clean it first?
@philos avatar
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UTC quote
Stretching the memory a bit here but... in a nutshell, there're 2 types of plastic - thermoplastic and thermosetting plastic. Thermosetting plastic is set and unworkable. Thermoplastic can be reworked and reformed using heat or solvents.

I'm pretty sure the plastic cowl material is thermoplastic and re-workable.

I just found a video which demonstrates the solvent welding method.. it saves me rattling on.

You can always try on a sample piece if you have any lying around. Basically the acetone melts the plastic and then evaporates off leaving only the original plastic at the same strength. It bonds to other pieces of the same material incredibly well and probably better than using heat to melt it.
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Molto Verboso
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Does the part have a marking to indicate the type of plastic? Assuming it's ABS, you might also want to consider ABS primer and then adhesive. These are commonly sold in home repair stores in the plumbing section. The adhesive is a mix of solvent (MEK, which work similar to the acetone described by Philos) and dissolved ABS to improve the bonding.

I've used this a couple of times now on an LX:
A repair for broken glove box hinge mounts
https://modernvespa.com/forum/post2281537#2281537
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@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Location: Victoria, Australia
 
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@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Location: Victoria, Australia
UTC quote
berto wrote:
Does the part have a marking to indicate the type of plastic? Assuming it's ABS, you might also want to consider ABS primer and then adhesive. These are commonly sold in home repair stores in the plumbing section. The adhesive is a mix of solvent (MEK, which work similar to the acetone described by Philos) and dissolved ABS to improve the bonding.

I've used this a couple of times now on an LX:
A repair for broken glove box hinge mounts
https://modernvespa.com/forum/post2281537#2281537
Thanks for the info Berto. No it's definitely not the same as your glovebox, it's softer and more flexible. You couldn't possibly snap it.

The 5 (if that is the identifying number) would mean it's Polypropylene. I put a bit in some water and it floated which is meant to be one step in identifying it.
Forum member supplied image with no explanatory text
@berto avatar
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Molto Verboso
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UTC quote
Ginch wrote:
Thanks for the info Berto. No it's definitely not the same as your glovebox, it's softer and more flexible. You couldn't possibly snap it.

The 5 (if that is the identifying number) would mean it's Polypropylene. I put a bit in some water and it floated which is meant to be one step in identifying it.
OK, you might be back to plastic welding then. Acetone won't dissolve PP plastic either. (Rubbing a drop of acetone on it to see if any of the plastic dissolves / rubs off is probably a more reliable way to evaluate ABS vs PP).
@subetherbass avatar
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1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
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Im happy to use the trusty "blowtorch & hammer" option when the time comes. I can also get hold of a mini oxy kit, then we can simply melt the fins
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While I've had good luck welding PP, it can be really difficult and refuse to stick due to small batch to batch differences.

For the cooling modification I'd try and just heat/shape the existing material. If you do need to weld, I try and get a mechanical interface going first. my soldering gun has a flat blade that I use to cut from the patch to the main part and then back again, so it drags material across the two parts and gives them an interlocking fit. Then I go over it filler material and use the flat side of the blade to melt it in.

YMMV
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