How do you port and polish

Discussion in 'Motorized Bicycle General Discussion' started by Joshua, Jun 16, 2008.

  1. Joshua

    Joshua New Member

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    So what exactly do you do when you port and polish your exhaust, I'm still waiting on my throttle and fuel line that wasn't packed in the box before shipping so I have time to do a few things before I get it going. This site is great and I'm glad I found it and joined up.
     
  2. Ghost0

    Ghost0 New Member

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    Porting and polishing loosely refers to ensuring that your exhaust port, exhaust gasket and exhaust manifold all are of the correct shape and size and are very smooth. Here is a quick how to. Take your exhaust gasket and place it up to your exhaust port on your cylinder. Do they match? Probably not. Take a dremel tool or knife and make the exhaust gasket match the exhaust port. Now that your exhaust gasket matches the port. Use it as a template to start machining the exhaust header on your pipe to match the gasket. Once that is done you have now ported your exhaust. Now you can polish the exhaust manifold and exhaust port to make them very smooth. You can repeat the process for the intake but skip the polishing part. Intakes work better when they are slightly rough, it helps atomize the fuel air mixture. Hope this helps.
     
  3. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    I'm no expert, but I can tell you the initial stages are pretty darn easy - it doesn't even require cutting on the head:

    1) Match exhaust port to "exhaust manifold" and gasket. Ideally this should be a header pipe for an expansion chamber pipe, but the stock pipe will benefit as well. The actual engine port is much larger than the exhaust header pipe flange (exhaust manifold) - put the factory gasket on alone and see what I mean. First make a gasket out of Mr. Gasket HD gasket exhaust gasket material (do it with heavy card stock first to practice). This will be your template. Now match this up to the header pipe and mark the metal you need to remove with a Sharpie. Using a Dremel tool and small size 80 grit drum start grinding, you'll need 3 or 4 drums. When the metal is gone you have achieved a perfect transition. Switch to a 120 grit drum and make it really smooth. It's actually a bit easier with the pipe kits because you can install the little header and feel inside with your pinkie. If you feel a step, take more material off. Make it baby but smooth when you are done.

    2) Repeat the basic step above for the intake tube manifold, plus grind all the weld lumps out at the inside upper end bend and where the flange is welded to the tube. This one you can make a gasket from regular gasket material and I smear blue RTV on both sides for a good seal on the final install.

    3) Make sure you do the sanding/grinding well away from your work area and clean the parts really well be bolting them on.

    I'm sure I forgot some things but the other guys will jump in……it's really quite easy.
     
  4. nitroscope8

    nitroscope8 New Member

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    For those who have matched their exhaust/intakes/gaskets, do you notice an improvement? If you are on the boarder of saying yes, then it's a mental thing and no improvement was noted...so anything? On paper you should notice a difference, but is it real?
     
  5. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    I can tell you, it makes a difference. Combined with a new pipe, a HUGE difference. The stock parts are really made for the 49cc engine, so they choke the 67cc.
     
  6. Joshua

    Joshua New Member

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    Thank you that is way easier then I thought it would be, I think I'll go start on it now. Learning more every time I check in.
     
  7. misteright1_99

    misteright1_99 New Member

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    It does make a difference. Just look at your bike. My muffler flange covered the exhaust port by at least 25%. Just think about it the faster and smoother the exhaust can leave the engine the faster and smoother new air/fuel can enter...
     
  8. nitroscope8

    nitroscope8 New Member

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    Alright, ill give it a shot and see what happens. I use this thing almost every day, so ill be able to tell quickly if it makes a difference.
     
  9. Joshua

    Joshua New Member

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    1.) Another question, well I guess I'm looking for some tips. I got my motor mounted up and it was a little tight inside the frame on my mountain bike. well the thing is I'm going to have a really hard time getting my plug out with a socket and I'm not sure I can get a box end wrench between the cooling fins. I could just cut the plug off with a cut off wheel, but then getting the new one back in is the same problem. any Ideas?

    2.) Also I was taking the nuts off of the head studs and the whole stud came out, well not thinking when I put it back in I added an extra washer and well there wasn't enough threads catching and I pulled the first three threads out of the engine(great haven't even started it yet). Well I got the capped nut off of the stud and put a bb in it and tightened it on the stud and then worked the stud back in past the stripped threads. I got about 1/4 - 1/2 inch in before the nut and washer touched the head, it tightened down fine, will I have any problems down the road. Kinda long post, sorry.
     
  10. FileStyle

    FileStyle New Member

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    what kinda mb do you have? replace all your studs with 1/4-20
     
  11. Ghost0

    Ghost0 New Member

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    You should be able to remove your plug with an open end wrench, I have done it on mine. You can replace your stock plug with a champion L78C, I believe it is shorter.

    Good save on the cylinder studs, just make sure they are torqued to about 15 ft/lbs.

    I don't recommend replacing your engine mounting and intake and exhaust studs with 1/4-20's but I would recommend replacing your stock ones with good quality 6mm ones. That goes for all of the nuts too. If you can't find 6mm studs you can get 6mm bolts and cut the heads off. Just make sure you get the correct length.
     
  12. Joshua

    Joshua New Member

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    thank you guys for your help. The bike is a cheap wal-mart roadmaster, starter bike.
     
  13. FileStyle

    FileStyle New Member

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    hi Ghost0
    why would you not use 1/4-20 studs? the stock rear mounting studs have both broken and I replaced them both with 1/4-20 S.S studs and seems to be fine now!
     
  14. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    I'm obviously not the studly and hairsute Ghost0, but I did stay at a Holiday Inn and I play a lawyer on TV: Whilst a 1/4 is 6.35mm - so it is an upgrade from 6mm, it's pretty easy to find treated or even generic USA 6mm stud material which will do fine.

    Also Ghost0 and I have found the nut threads strip out way before the studs go 90% of the time, so just getting new 6mm nuts can be an upgrade. With the jackshaft kit we don't even use studs on the rear mount any more.

    Of course this is moot if you have actually pulled the threads from the block, then 1/4-20 makes sense.

    Just curious - why SS? Certainly will help with corrosion, but is not stronger than treated HS steel. (But SS is plenty strong enough for the Chengine)
     
  15. Ghost0

    Ghost0 New Member

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    To reiterate what Pablo said. The 1/4-20 will work if you correctly re-drill and re-tap the hole. All I was saying is that for most people it is much easier to just replace the low quality stock hardware with good hardware and not have to re-drill and re-tap. If the quality of the hardware is good you will not have any failures using the stock sizes.
     
  16. MrLarkins

    MrLarkins HS Math Teacher

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    is it a good idea to port the stock muffler by modifing the opening and not enlarging the tubing? or is a new, larger porter muffler REQUIRED?
     
  17. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    It can't hurt. The port match is horrible.
     
  18. nitroscope8

    nitroscope8 New Member

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    So I decided to port and gasket match my intake and exhaust. I was a non believer before, but now i'm sold. The intake was pretty close already, but the exhaust was about 20% blocked. I matched the pipe as best I could and took it out for a test ride. First, this thing runs smoother. Second, it accelerates MUCH faster now to top speed. Top speed is the same, but the time to get there is reduced. Not too shabby.
     
  19. blckwlfny1

    blckwlfny1 New Member

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    Been reading quite a bit. I have a very clear sense of what porting is. And how to do it. I'm just a little unclear on how much material to take off with regard to the piston sleeve. It seems to me that the ports in the sleeve are considerably smaller than the ones in the outside housing, so I'd probably want to open them up to match the outside.
    But won't opening the ports in the sleeve alter the port timing?
    So how much material do you take off of where?
     
    #19 blckwlfny1, Mar 30, 2011
    Last edited: Mar 30, 2011
  20. DaveC

    DaveC Member

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    Lowering or raising the port changes the timing. If you don't want to deal with that then widening the port is good just for more flow. Up to 2 mm from each side of the port really helps the flow. Now, I've seen some porting jobs that just make me cringe. They some how make it look like the port twists around several times on the way to the port opening. Be very careful with a Dremel. They spin so fast you are in trouble before you know it. I like useing the sanding rolls ment for a compressed air-powered die grinder. They are longer so you are less likely to overgrind a spot causing a dip. I use a pressure regulator to slow the grinder. The whole idea is a smooth transition from carb to intake pipe to port or exhaust port to header pipe.

    What your looking for is a port that's as wide as possible and still be as straight and smooth as you can get it. Best is a straight line from one end to the other. If there's a taper then it needs to be a straight taper from port to port.

    I first started porting when I was 17 or so with a set of mid-60's Pontiac cast iron heads. I used up two of my grandfather's old electric drills learning how to do porting on all 16 ports ;)
     

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