Performance mod - Polished Head???

Discussion in 'Performance Mods' started by SuperDave, Feb 9, 2013.

  1. SuperDave

    SuperDave New Member

    I've been toying with this idea of polishing the combustion chamber to a mirror finish to enhance performance. My reason for thinking is thus: a semi-smooth or textured surface allows carbon to deposit, becoming a heat sink & lends to pre-detonation - knock & ping. If it were mirror smooth, it would
    A) Reflect the heat back into the cylinder, aiding the expansion of the gasses and push down on the piston a little bit harder,
    B) Discourage carbon buildup which might lead to pre-detonation,
    C) Run cooler - the heat isn't absorbed as much into the head but goes out the exhaust.

    I've looked around on the forums but haven't found much on this subject. I'm wondering if anyone has tried this, or if anyone has justification as to why I SHOULDN'T do this. Polishing the piston face might also be help too. I figured I could do this when I remove the head & jug to lap (sandpaper taped to glass) the mating surfaces for better seal (already blown 1 head gasket already) & maybe a wee bit of a compression increase.

  2. jaguar

    jaguar Well-Known Member

    Still the carbon will build up on it, maybe at just a slower rate though. Go ahead and do it but be prepared to have to repolish it often if you feel it helps and you want the continued benefit.
    These low rpm engines don't have a problem with detonation though.
    I always thought that carbon buildup acted as a slight insulation. ... I just looked it up and carbon has only .8% the thermal conductivity that aluminum has. So my advice would be to leave the piston top and head surface "dirty" unless the buildup is causing too much of a compression increase.
  3. Fabian

    Fabian Well-Known Member

    Polishing the combustion chamber to a mirror finish to enhance performance is like trying to polish a piece of bread and hoping it won't turn black when you throw it on a raging fire, as well as being more edible than a nicely toasted slice that's made golden brown.

    The moment you run fuel through the engine and send combusted waste product out the exhaust port, the mirror finish you so carefully made mirror shiny by spending countless hours of your life polishing it to perfection will instantly become black with nothing more than an oily filth made out of pure carbon.

    I'm fairly confident it will have "zero effect" on performance enhancement.
  4. Purple Haze

    Purple Haze Active Member

    On my first engine, I polished the combustion chamber, piston top, and all ports. After riding about 100 miles, pulled head and guess what? Carbon buildup on both chamber and piston top. My advice? Don't bother. Also, I didn't feel any increase in performance or see any gains in fuel economy. Spend your time on mods that will make a difference.
  5. So you guys are saying port & polishing the intake & exhaust combustion chamber will do nothing in performance?
  6. Fabian

    Fabian Well-Known Member

    It will do absolutely nothing for performance - it's a complete waste of time.
  7. It wont hurt anyt5hing will it?I gutted my ports some and sanded them down smooth thinking I could force more air in and out..I also raised the pin on the needle was that a bad idea?I run 90 with no ethanol and 1 container of lucus smokeless oil to a gallon..New to these engines is that a good fuel source
  8. Fabian

    Fabian Well-Known Member

    What i can say is that you "did not" do any research on this issue, despite the massive amounts of information on the internet and this website.

    I spent a full 3 weeks researching everything about motorized bicycles and the available technology options; then hitting the credit card and purchasing components for my build.
  9. No I did not Fabian,I just started researching last night my PC was down..Iv ordered another combustion chamber I take it ill have problems in the long run..
  10. Fabian

    Fabian Well-Known Member

    If you do the research and choose the right components and make the necessary modifications, the engine will be surprisingly reliable.
    Typically i get 4,000 kilometers (2,500 miles) out of a cylinder and my previous bottom end lasted 10,000 kilometers (6,000 miles) with a Jaguar CDI, which is seriously good mileage for $30 and $60 replacement items respectively.
  11. geebt48cc

    geebt48cc Member

    Fabian, that motor that you are referring to that was surprisingly reliable, did you replace any bearings? Or where they also all original?

  12. Fabian

    Fabian Well-Known Member

    Nope, i never replaced any bearings. These days the engine manufacturers have mostly changed to the crowded needle roller connecting rod bearing method, which is very reliable, though it doesn't like excessively high rpm.
    If you stay under 5,000 rpm, (4,800 being a nice figure for max rpm) the engine will give good reliability.
    Florida_Trail_Rider likes this.
  13. geebt48cc

    geebt48cc Member

    Wow Fabian, that's great to hear. I just replaced the needle bearing, but nothing down below. You hear of so much stuff that can really cause the domino affect on these little engines. Yeah, I'm sure that I run this engine well over 5000 RPM, but I really keep it down 85% of the time. Fabian, I know that it's much easier to keep thoughs RPM's lower with the shift kit.

    Fabian, I found with a lot of time, a great needle bearing I put on. It's made in Japan, and rated at 50,000 RPM's. DA"".......Found out that the stock needle bearing is 10X14X13, so the one everybody was pointing to is 10X14X15.

    Ok, put it on, and the engine really seems much tighter. It kills 95%l of the free play mounting piston to push arm.

    CU, Glen

    Attached Files:

  14. Fabian

    Fabian Well-Known Member

    I have never had a small end needle bearing fail, "ever", so i've never had to replace a failed needle bearing; in fact i've reused one small end needle bearing a total of four times which works out to around 15,000 kilometers, and that same needle bearing is in my current engine.

    I'm curious as to how long it will last before it tears itself to pieces.

    Having said that, i have a SickBikeParts shift kit and keep the rpms around 3,800. I don't push the engine over 4,800 rpm if i have to hold a gear longer than i want to.
    Once you go over the 5,000 rpm mark, vibration seems to increase with exponential force, and it would be a logical conclusion that this mechanical stress would impact on engine longevity and reliability.

    At the end of the day, it's a cheap Chinese bicycle engine, not designed to take racing engine rpms.
    Sure the engine will do 7,000 rpm and higher, but for a limited time frame.
  15. geebt48cc

    geebt48cc Member

    Yeah, Fabian I believe you may be right considering. The needle bearing I took out was like new & stock?!~ That's after 800 miles.............(So go figure?)

    The only reason I felt that it was a must, was because that's all I hear is to first replace stock needle bearing?
  16. Fabian

    Fabian Well-Known Member

    I hear lots of things on this forum, but the results of pushing an engine too hard for what it was designed for is always going to be component failure; that and running to lean an oil/fuel ratio and an excessively lean air/fuel ratio, which cooks the piston and radiates excessive heat into the small end of the connecting rod and connecting rod bearing.
  17. roughrider

    roughrider Member

    Hmmm... I am routinely running my engine at just above 5,000 rpms to drive a 27 inch tire by means of a 48 tooth sprocket. At that rpm range, it goes 19-21 mph, and I consider this my cruising mode. The vibrations are minimal. The engine and drive train sound and feel like they like this speed.

    I wonder how long it will last.
  18. geebt48cc

    geebt48cc Member

    Yes, I would say that it might fool you as long as you keep it in that sweet range. Around here I have so much stop and go, that's hard to be able to hold a good cruising speed for any length of time. Uno, doing that does worry me a bit more, because it's harder on these bikes. It makes total sense when you weigh a bit more than average Joe.?

    Whenever I pull from dead stop, I'm thinking ouch for the spokes....................(because most areas I'm doing that are on some type of incline............Anyway, I know................GET A SHIFT KIT!
    Last edited: Mar 8, 2013
  19. Fabian

    Fabian Well-Known Member

    Like all engines, it will last as long as it doesn't make any strange rattling noises, but you can rest assured that when it does, there will be someone who advises running a smaller jet will fix the horrible clatter or that running a leaner oil/fuel ratio will fix the horrible clatter or that throwing banana peels into the engine will fix the horrible clatter, but on the other hand there will be an equal number of people who tell you to do the exact opposite, mentioning that banana peels have caused irreparable damage and a mixture of apple and orange peel should have been used instead.
    Florida_Trail_Rider likes this.
  20. roughrider

    roughrider Member

    Mwaa-Ha-Hah! <-- That's me, belly laughing.

    But yeah, I am listening closely all the time. I did buy a spare engine, and my design mods are now in the direction of more lower end torque and a smaller rear sprocket...

    Even so, my engineering sense says a lightly loaded hi revver should last a long as a hard loaded low revver. (Within rather close limits, mind you.)