Chinese new parts or used OEM parts

Discussion in 'Tech Area' started by MonkeyBikerCanada, Apr 4, 2018.

  1. MonkeyBikerCanada

    MonkeyBikerCanada New Member

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    Hello
    Recently I had to open the engine of my Honda 1970 ct70 because it burned oil and I discovered that I had to replace the cylinder by a new one, but the question that I ask myself is that I have an aftermarket head that must be used with a flat top piston, but I also have the original head that I repair and no longer lose oil in my opinion because I changed the exhaust valve seal and I have improved the valve seat with a special paste. So, I would like to know if I should buy a new cylinder with a Chinese flat top piston to put on the Chinese head or buy a cylinder with a piston dome and install it with the original head. Could I reuse my original piston (ART) which is in a good condition with new rings and a new cylinder? What are the differences that there will be with a flat head piston and a head that has a cam that raises the valves higher?
    Thanks for your advice
     
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  3. cjpayne

    cjpayne Well-Known Member

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    Usable used OEM is still much higher quality than China.
     
  4. Tripod

    Tripod Active Member

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    OEM is the least amount of hassle. Get burned on a few China parts and that's all it takes.
     
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  5. MonkeyBikerCanada

    MonkeyBikerCanada New Member

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    Thanks for your reply Guys i undertsand well than the OEM parts are better because its Honda parts but im not sure at 100℅ if my head doesnt lost oil in the combustion chamber. So, if I decide to keep the head honda, I would like to know if you know of a place where good quality aftermarket cylinders are sold and also I would like to know if I could reuse my original piston which is in good condition. state and only buy rings for the piston or it would be better to change the piston for a new one
     
  6. Tripod

    Tripod Active Member

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    Since you seem to be in Canada, PhatMX is a good source.
    CHP, DrATV, NEVC, Tbolt, Trailbuddy, and Partzilla are the big ones. No one site has everything, and some parts are unavailable. For that you have Ebay or hit up your local classifieds for donor bikes.
     
  7. MonkeyBikerCanada

    MonkeyBikerCanada New Member

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    Ok thank you for the parts sales website, indeed there was some that I knew among them. Finally, I would like to know if I could keep my original piston (ART) which is in good condition and only buy a new cylinder and rings
     
  8. cjpayne

    cjpayne Well-Known Member

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    I've reused pistons before, but they need CLOSE inspection and cleaning. If the new rings fit tightly too, I've reused them. Pay attention to rod play. If there's any, replace the assembly as a whole. Snap rings, everything and have the crank rod inspected too. The piston pin should also be checked for scoring,ect. That piston pin should be removable, but very tight.
     
    #7 cjpayne, Apr 4, 2018
    Last edited: Apr 4, 2018
  9. MonkeyBikerCanada

    MonkeyBikerCanada New Member

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    Thanks a lot for the information cjpayne i will check that because I think the rod is a bit worn
     
  10. cjpayne

    cjpayne Well-Known Member

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    While the head and jug are off, I think you can get a feeler gauge in the block to check the side clearances on the rod to crank assembly. Check that and reply here what you found. I cant remember what the tolerances are right off hand. Also check the rod for end play. There should be none at all or it will knock.
     
  11. racerx

    racerx Administrator
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    The rod should be checked at both ends. With the piston on the crank, check for slop; if you can feel any lateral movement, or the pin is not a tight fit, the rod is toast. At the big (crank) end, I believe the radial runout limit is 0.006" (going from memory, which ain't what it used to was:confused:. Lateral (side) clearance wear limit is 0.031"...way too generous, imho. Once they reach 0.018", you're just about guaranteed to hear rattling. 0.014", or less, is what you want. New, side clearances range from ~0.008-0.012".

    As long as you have the proper piston (6v compression height, exact size for the bore, "old" 6v dome to fit your head) and it's in tiptop condition, it should be reusable. Have the cylinder deglazed and use new rings. It might be easier for you to just source a new cylinder & piston...maybe an 88cc/52mm bore-up kit. Have the valve seat cut, install new valves and have them lapped. New seals and gaskets...that goes without saying.
     
  12. MonkeyBikerCanada

    MonkeyBikerCanada New Member

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    I inquired about an 88cc TB cylinder and it seemed like an interesting solution but I wondered if it would not bring premature wear to some parts of the engine for example, the clutch that is not made to receive more torque and also the crank. Am I going to have to buy a high flow oil pump? Do I change the jet of my carb or would it be better to buy a new one? Do you know a website where he explains how to do timming with an 88cc cylinder?
     
  13. racerx

    racerx Administrator
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    I would go with the HV oil pump & a dipstick thermometer. That ought to keep things safe & happy. HD clutch springs wouldn't hurt, either. The torque increase isn't going to be huge, by any means. FYI, Honda took the 49cc lower end out to 90cc. The C90 was never sold in North America but was highly sought-after, especially the 12v/4-speed version. You may need/want to go one size larger on the main jet, then again, it might not be necessary. Adjusting the jet needle height might be all that's necessary.

    One thing you may consider is a hotter cam. Raising the hp peak by ~1000rpm should be good for 4-5mph at the top. You'll also want to go with a 16t countershaft sprocket, to take advantage of the added torque.
     
  14. MonkeyBikerCanada

    MonkeyBikerCanada New Member

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    Thanks a lot racerx, I will think about that to decide if i put a big bore cylinder or just a stock cylinder
     
  15. preventec47

    preventec47 Member

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    To be fair, China has a population roughly ten times greater than USA and I would guess that per capita they sell a lot more motorcycles. What I am getting at is China probably sells fifty or more times smallish motorcycles to their population
    than the USA market consumes. It would stand to reason that some of the companies stand out as word spreads re
    reputation etc. Also consider there are several European, "Japanese" and American companies using China
    sourced motors in their motorcycles. We just have to figure out who the "quality" players are in their own
    market and then shop for that brand here in the USA. I have a clone 124cc engine that I just giggle about cuz
    it was so cheap and runs so well. ( thanks admittedly to original Japanese engineering and design ) $Motor DSC_5406 LG.jpg $Motor DSC_5415.JPG $Motor DSC_5450.JPG $Motor DSC_5450.JPG
     

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