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Heads and Cylinders All about your porting, compression, rings, cylinder and piston modifications to your bicycles engine

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  #11  
Old 03-20-2010, 09:48 AM
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BarelyAWake BarelyAWake is offline
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Default re: The Basics, Port & Polish and Port Matching

Yarp - good call on that distinction and thanks, I r just tryin' to "keep it simple" if ya know what I mean - the castings on these HT's so sloppy something must be done heh

I've messed with the intake and exhaust on these things, there's not much meat fer opening them up any more than what you see in the pic (still need a face fer the gasket to seat ofc), there's been nothing but good to come of that small amount larger (about 1/8" overall).

I've not had a chance to warn anyone to not alter the actual shape as I've not gotten there yet lol - but still, good info man!
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  #12  
Old 03-20-2010, 01:34 PM
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Default re: The Basics, Port & Polish and Port Matching

Just my .02
Intake ports are best left as a satin finish to promote atomization of the incoming intake charge. They will still flow plenty fast.
Exhaust ports are best left as a mirror polished finish to promote fast flow and reduce the chance of carbon build up.

The above is what I was taught by pros in the know.
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  #13  
Old 03-20-2010, 01:43 PM
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2door 2door is offline
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Default re: The Basics, Port & Polish and Port Matching

John the Great is absolutely correct in his advice to leave the walls of the intake ports slightly rough. The marks left by the grinding stone or burr is enough. Do not polish to a mirror finish. Doing so will have the opposite effect that one might assume. Proper fuel atomization can not occure across an extremely smooth surface. This is not my opinion but was proven years ago in drag racing and other motor sports.
That being said, port matching can be beneficial but I believe it might be wise to inform the great unwashed who might try it that they should not expect great performance increases. The expectations of noticible power increases, given the amount of work involved, will not be what some assume. Agreed that anything you can do to 'help' these little engines will be good but I just don't want to see some poor inexperienced dude tear into his otherwise good running engine with the assumption that he's going to set land speed records when he's finished. I think it might be wise to stress that in most cases the benefits will be engine longivity and smoothness as opposed to huge or even noticible power increases. One other item we might want to pass along to newbies contemplating these modifications is the fact that many engine suppliers will not honor the warranty if they suspect that an engine has been disassembled. That could be a problem for someone on a limited budget. Just my thoughts. Otherwise, good thread and should reveal some of those deep dark mysteries regarding so-called porting issues.
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Last edited by 2door; 03-20-2010 at 06:11 PM.
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  #14  
Old 03-20-2010, 03:56 PM
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Default re: The Basics, Port & Polish and Port Matching

per wikipedia, under cylinder head porting and myths


The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past which develops a velocity profile (or gradient) across the duct. In order for surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this.
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  #15  
Old 03-21-2010, 01:12 AM
Creative Engineering Creative Engineering is offline
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Default re: The Basics, Port & Polish and Port Matching

It is, what's known as, the rate of diminishing returns. In other words...a lot of work for very little gain.

A finely polished port will offer a 3-5% power increase at a cost of much labor. It must be done 100%...there is a fine break point between "good enough", and realizing the 3-5% increase.

For general purpose use, (even in race circles), most consider it not worth the effort.

Jim

Last edited by Creative Engineering; 03-21-2010 at 09:20 AM.
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  #16  
Old 03-21-2010, 01:28 AM
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Default re: The Basics, Port & Polish and Port Matching

To clarify;

Polishing a port to a high gloss may not be as effective as a matte, a port & polish won't make yer bike go noticeably faster...

But gettin' them scabby chunks out sure does help it run smoother
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  #17  
Old 03-21-2010, 10:40 PM
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Default re: The Basics, Port & Polish and Port Matching

perfect^^^^^
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  #18  
Old 03-23-2010, 06:53 AM
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Default re: The Basics, Port & Polish and Port Matching

k - sorry 'bout the delay folks, that pesky RL thang keeps intruding heh


Anyhoo - as I recall yer sittin' there with yer engine all apart and perhaps wonderin' if it was such a good idea. Never fear - trust me when I say there's few engine projects simpler than portin' one of these lil happy time 2smokers FTW

If you've never shaped aluminum with a Dremel before - I heartily recommend practicing on something you don't care about first, preferably something with a hole not dissimilar to a port as that's the project yer interested in, but anything will do. Dremels are great tools but they have lil quirks like spinning the "wrong" way and spitting bits and sparks into yer face heh, safety glasses are ossum.

Lets start with the slightly easier exhaust port, all these engines are jus' a lil different so I've no way of telling how bad the castings may be on yours, but the general procedure is the same. The Dremel comes equipped with two different sized sanding drums, grab the lil one and see how it fits in the "corners" of the oval port - it should be smaller than the curve of the port - allowing you to get down into the "corner" without changing the port's shape or galling the sides. If it's too big and hits the sides without touching the inside of the corner - don't use it, you'll hafta do the detail work by hand.

It's important to start with the hard stuff first, the hard to reach places and corners. That way it's simple enough to match the rest of it to the work you've already done, if you were to do the large flatish sections first - you may well distort the shape when you try to get the corners to match... that's a pretty good rule of thumb with just about any project by the way - be it porting or painting heh

With such caution in mind, we'll experiment with a milder grit (like 120gt) small sanding drum and setting yer Dremel to a medium speed. You'll want to use as much of the drum's surface as possible by always keeping it parallel to the port - don't tip the Dremel to use just the edge of the drum as you'll dig into the aluminum and leave gouges that will be hard to make flush later. ALWAYS keep the tool moving for this same reason, back and forth, up and down, whatever it takes - just dont grind away at any one place too much... think like brushing your teeth, just slower ofc.

With nice smooth lateral motions (side to side) clean all four "corners" of the exhaust port till they're smooth but not necessarily perfect, paying careful attention to always keep the sanding drum flush against the port - particularly near the edges as you do NOT want to bevel them even a little. Resist the urge to do the easier "in and out" motion as you'll leave a deep trench, not to mention when hand sanding later - that motion is about all you can do, so lets use the power tool to do the more difficult method first. If the tool just isn't taking enough off - you can increase Dremel speed and/or switch to a coarser grit, but always remember to let the tool do the cutting - don't press hard or "scrub" with it, all that will do is generate heat, load up the drum with galled aluminum, and put deep and irregular scars in the surface that you'll hafta clean up later and defeating the purpose.

All four "corners" done and lookin' good? Sweet - now switch to the large sanding drum with 120gt and get the "flat" areas, same method as above except this time with more "side to side" movement, again - always keep it moving, even in lil circular patterns as this will help provide a smooth uniform surface, spend even a lil time in one place and you'll get a wavy, irregular face. The larger the drum, the easier it is to get a smooth flat surface, the lil drum just for the hard to reach stuff.

Don't worry if you've got a deep pit or two - odds are it was just a bubble in the casting and if you try and chase all of those down you'll end up with nothing but a pile of dust for your troubles. There's no "perfect" with these things - if the port is simply clean and smooth that's beautiful and all we're tryin' for.

Assuming that you cleaned up your mess with no coarser a drum than 120gt - now we finish sand by hand, 320gt works well (400+gt ifn yer crazy), if you've got particularly deep swirls and scratches you may need to start with 220gt or so. Always use a popsicle stick, round pen, or something similar as a sanding block and same as the Dremel - keep it flush with the work surface as not to bevel the edges. Keep a close eye on any "extra" sandpaper as even a lil bit scraping the edge when yer not lookin' will round that edge.

You'll notice that despite how much you tried to avoid it - the Dremel left lateral scratches simply because of the way it spins. So while your hand sanding try and keep it to "in and out" opposite of the lateral scratching and circular motions - convenient as this is pretty much all you can do with the space yer in.

I bet that exhaust port is lookin' pretty hawt now - nice and smooth without alla scabs and bumps it usta have... guess what? The intake port is exactly the same job except as I remember the "corners" are too tight to get even the little Dremel sanding drum in there, so sadly - you'll hafta do those by hand using a pen or a sharpie as a sanding block *shrug* I hate not being able to use power tools... but that's just the way it rolls sometimes heh

Remember - don't press hard and let the tool do the cutting, keep it flush with the surface at all times, and always keep it moving in circular/oval motions whenever possible. Smooth uniformity is what we're after so that's what ya need to get there




As I've now got 10 minutes to get ready fer work, "To be Continued" yet again lol
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  #19  
Old 03-23-2010, 07:38 AM
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Default re: The Basics, Port & Polish and Port Matching

Barely,
Thanks again for teaching us. I'm developing a real game plan and feeling more confident about what to do and how.
SB
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  #20  
Old 03-23-2010, 10:19 AM
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TerrontheSnake TerrontheSnake is offline
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Default re: The Basics, Port & Polish and Port Matching

Hey has anyone ever tried a "Vortex" fin inside their intake? a small fin or blade inside the intake tube, this has proven effective in large motors, but I have no idea what it could do for a small 2 smoke
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