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Guichaoui |
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Guichaoui L Plate Warrior
Joined: 10 Apr 2024 Karma :
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Posted: 15:11 - 10 Apr 2024 Post subject: Honda CG 125cc to 150cc conversion problem |
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I have a honda 125 cc engine that's driving me crazy, the engine has 2000 miles on it, relatively new with no problems whatsoever and runs great. I got a 150cc kit for it (piston, cylinder, head,) the whole top end, the installation went smoothly without any problems, it has great compression and top range performance, the problem is, when i started it the first time i noticed a clunking sound coming from the top end, when rotating the engine, you hear the sound when the piston is at TDC and BDC, the sound is louder with the spark plug off,and even louder when the bike is running, the sound disappears above 4000 rpm, after disassembling it again, i noticed no signs of valves hitting the piston, no piston play, even with the old head it gives the same sound. When i installed the old cylinder with the new head, no weird sounds and it ran greatly, so one would say the problem is in the cylinder, after comparing the new and old cylinders, the only difference i could notice is the 150 cylinder is 2mm longer on the bottom, but its not touching the crank, and the new piston is relatively tighter when entering it into the cylinder, even with no rings.
Notes:
No rod play up and down, slight play left and right
Piston pin fits perfectly in the top rod bearing with no play
Piston fits snuggly in the bore, no play front to back, slight play left and right
Valves adjusted to spec
Any ideas would help, thank you. |
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WD Forte |
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WD Forte World Chat Champion
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stinkwheel |
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stinkwheel Bovine Proctologist
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Guichaoui |
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Guichaoui L Plate Warrior
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stinkwheel |
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stinkwheel Bovine Proctologist
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virus |
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virus World Chat Champion
Joined: 17 Aug 2006 Karma :
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Nobby the Bastard |
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Nobby the Bastard Harley Gaydar
Joined: 16 Aug 2013 Karma :
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Guichaoui |
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Guichaoui L Plate Warrior
Joined: 10 Apr 2024 Karma :
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A100man |
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A100man World Chat Champion
Joined: 19 Aug 2013 Karma :
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Posted: 22:10 - 10 Apr 2024 Post subject: |
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Guichaoui wrote: | Solved actually it turned out somehow the piston is too snug in the bore, i tried it even without rings and it moved with difficulty as if the rings are installed, i just sanded down the skirts of the piston until it moved smoothly in the bore then installed the rings and put back and everything ran without a sound. |
Meh, ghetto fix works for me. if you still have decent compression and no noise why not run it a while and see. I would run it in for a couple of hundred miles still though.
Edit - better check ring end gap while you're in there. too tight and it may seize ____________________ Now: A100, GT250A, XJ598, FZ750
Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600 |
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stinkwheel |
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stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
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Guichaoui |
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Guichaoui L Plate Warrior
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jeffyjeff |
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jeffyjeff World Chat Champion
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Bhud |
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Bhud World Chat Champion
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P. |
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P. Red Rocket
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virus |
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virus World Chat Champion
Joined: 17 Aug 2006 Karma :
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MarJay |
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MarJay But it's British!
Joined: 15 Sep 2003 Karma :
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Posted: 18:22 - 11 Apr 2024 Post subject: |
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https://i.gifer.com/embedded/download/Ywqm.gif ____________________ British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another. |
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stinkwheel |
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stinkwheel Bovine Proctologist
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virus |
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virus World Chat Champion
Joined: 17 Aug 2006 Karma :
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Posted: 19:31 - 11 Apr 2024 Post subject: |
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stinkwheel wrote: | virus wrote: |
That was the nathans that played with big bore CGs back in the day. Funilly enough my CG125 engine was of of few bikes I've owned that I never blew up, I also never badly fitted a 150 kit by sanding pistons and blocking the oil jet for the piston. Maybe its a coincidence? |
Oh, I thought you blew one up at a freeze-up in the snow when we burned that huge mining vehicle tyre. Maybe it was someone else... or someone elses? |
That was naths. I may have been the last person to ride it before the clutch fibre plates had a rapid unexpected disassembly. ____________________ own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance. |
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Guichaoui |
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Guichaoui L Plate Warrior
Joined: 10 Apr 2024 Karma :
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MCN |
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MCN Super Spammer
Joined: 22 Jul 2015 Karma :
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Posted: 01:49 - 12 Apr 2024 Post subject: |
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The CG125 doesn't really suffer from lack of powah. It is absolutely fine for its task.
The secret to using small engines is learning about energy conservation.
Don't upgrade the engine.
Downgrade the brakes.
Slowing down is the worst thing you can do on a 125. ____________________ Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN. |
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A100man |
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A100man World Chat Champion
Joined: 19 Aug 2013 Karma :
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Posted: 09:56 - 12 Apr 2024 Post subject: |
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Guichaoui wrote: | UPDATE:
..the parts for the 125cc top end are inexistent in my country, you couldn't even find a gasket set for it. |
Blimey.. where's that? ____________________ Now: A100, GT250A, XJ598, FZ750
Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600 |
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lingeringstin... |
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lingeringstin... Spanner Monkey
Joined: 01 May 2014 Karma :
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Guichaoui |
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Guichaoui L Plate Warrior
Joined: 10 Apr 2024 Karma :
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Posted: 20:23 - 19 Apr 2024 Post subject: |
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UPDATE:
Got 500 km on the bike today, changed oil, checked valvee clearance, the sound was getting quieter throughout this week but its still there.
Here is what it sounds like:
https://youtube.com/shorts/iP_0VJd5gF8?si=8ZIZ06_MpSJ_uI_I
The video is taken when the bike is at operating temp, been driven for 15 minutes, when its cold its the same.
Any help is greatly appreciated. |
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A100man |
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A100man World Chat Champion
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Guichaoui |
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Guichaoui L Plate Warrior
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