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      JUST IN!   04/24/2018

      HOW TO: 4-STROKE PISTON REPLACEMENT DONE RIGHT!

drajasingam

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About drajasingam

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    Ireland
  1. Thanks guys! Here's one other pic (link below). Sorry, no pics of before restoration, which I regret bigtime. Trust me though, it was a complete piece of shit. It didn't really make financial sense. For one thing, I bought it thinking it was a 1996 model (that's what the seller said). I had to replace all suspension and steering bearings, re-sprayed the frame, reconditioned the brakes, and rebuilt the engine bottom end and transmission. I didn't keep a budget on the project, but paid GB£800 for the bike initially and spent around US$500 on the restoratin. I enjoyed it though, and learned a lot about these bikes in the process. I just have to get good at riding now! http://i109.photobucket.com/albums/n80/drajasingam/IMGP0808redcued.jpg
  2. Try this link, it seems to work now: http://i109.photobucket.com/albums/n80/drajasingam/886a8a46.jpg
  3. Hmm, the image is there for sure and the URL is correct. ???? http://i109.photobucket.com/albums/n...m/886a8a46.jpg
  4. My recently restored 1992 CR125R. (Don't be put off by the 1996 plastics!) BTW: Thanks to all those Thumpertalk members who helped me out with this project... greatly appreciated!
  5. I managed to find out definitively the year of this bike a while back. It turns out that off-road bikes in the UK were not given VIN numbers at that time (1992). Honda Customer Support were fairly useless, until they told me to send an email to their "technical team". I emailed them the frame number and engine number. They were able to tell me that the bike and engine were 1992, and that they were an original pair. Since I bought this bike on ebay.co.uk, I have been keeping an eye out for bikes advertised as later models than they really are. It's still going on, for example there is one right now (item 260005694631). This is advertised as a 1996 model, and, like mine, has fuel tank and plastics from 1996. A closer look reveals that it is older. For example, the colour of the frame, the crankcase, and the shape of the swingarm pivot bolt head, indicate late 80's.
  6. Here's a pic of the head. Regarding the cylinder, I should have mentioned that it does have a steel liner. I've only just realised that this liner is an aftermarket job and that these engines come with plated aluminium barrels. Am a bit relieved at this since if it is out of spec, I can just oversize bore again. When oversize boring, I imagine some grinding is needed on the exhaust valves to prevent them clacking the bigger piston??? Or else some kind of spacer can be made to prevent them from fully closing.
  7. So, I took off the top end today. I won't be able to measure anything properly until next week, but I did notice a few nasties anyway: 1. The combustion chamber roof, i.e. under the head, looks like it was sprayed with shrapnel in a previous life. This is in a ring pattern - the central, domed area is not affected. I'll post a pic in a while, but am guessing this was due to a shattered ring. Could nicks in the roof like these cause pre-ignition/detonation? Is it okay to continue using this head, or should it be scrapped? 2. There was a noticeable amount of rocking play between the conrod and piston. I guess the small end bearing needs to be replaced. Possibly the pin and piston also, but haven't yet taken any measurements on these. Visually, the piston, rings, and pin look good (i think they are fairly new). 3. The conrod bottom end had a noticeable rocking play also (as well as the normal end play). I doubt that this is normal. If this indicates a worn-out bottom end, is it cheaper/easier to buy an aftermarket crank assembly, or rebuild the existing one? 4. The cylinder has been oversize bored to nominally 55mm, and fitted with a 1.00mm oversized piston. There is no sign of the bore having been re-plated. If the piston-to-bore clearance is good, is it okay to run the engine like this (i.e. without plating), or will I have to re-sleeve, re-plate, or scrap the cylinder? I've seen aftermarket sleeves, e.g. by Wiseco - do these come plated allready? Can any 1992 - 1997 CR125 cylinder be interchaged with this one? NB: I don't even know what year this cylinder is since it isn't the original, but the rest of the engine is 1992. Does anyone know how to identify the year of the cylinder? As far as the engine noise is concerned, my guess is that it's due to the worn-out conrod bearings(top and/or bottom), or else its piston slap due to too much piston/cylinder clearance. I'll have to wait and measure everything to see if the piston could be slapping. I'm unsure at the minute whether I will totally repair this engine or just resort to damage limitation. I'm open to all advice and suggestions... and many thanks in advance.
  8. Ok, I made some progress today - but not a lot. I decided that before I take off the top end to check everything, I'd check the powervalve. I found a number of problems that I thought might be causing the rattling. First of all, the valve guides were not installed properly. The retaining plates were not slotted into the guides, but just holding them in flush with the housing instead. If the valves were allowed to fully close, then the right-side valve would have been able to clip the piston. I thought this is what the noise was. However, as I later discovered, the timing on the governor control linkage was wrong, and this wouldn't allow the valves to fully close. I had to take off the right-side crankcase cover to engage the governor properly with the control arm linkage. After doing this, cleaning the valve assembly, and adjusting them according to the manual, I was sure that I'd solved the problem. When I put it all back together and fired it up, the same clicking noise was there. Will have to take off the top end and check tomorrow. Seeing as how everything I inspect on this bike needs repairing, it may be a bad day.
  9. I'm pretty sure the standard pump gas here is 95 octane. the "super" stuff from the pump is usually 98 octane, but you have to look around for it. I'm using Silkolene Comp II lubricant at 32:1. Fuel probably isn't the problem, I'm going to tear off the top end and check everything next week. Thanks for the advice so far!
  10. Thanks, I guess it's safer to take the top off and check. BTW I'm using 32:1 premix, but with standard pump gas. Not sure if the low octane would cause this???
  11. maybe you mean motocross by mtx - if so then prob a CR125 ???
  12. Hi everyone, hoping for a bit of help here. I've just finished rebuilding a 1992 CR125, except I didn't touch the engine (the previous owner said it just had a top end rebuild). The motor fires on the first kick pretty much every time. But I noticed a clattering/clicking noise, which seems to be coming from the top end, but I'm not completely sure. I thougt it might be cold slap from the piston. I warmed it up a little and no sign of the noise going away. Is this kind of sound normal from this type of engine?- e.g. does the reed valve or exhaust port make noise? Will I need to take off the top end to check rings etc? Any help greatly appreciated. Thanks
  13. Is ATF recommended for most similar bikes, e.g. a 1992 CR125? Are there any benefits of this over a multigrade automotive engine oil? Is basic gear oil acceptable?
  14. The rear shock on my 125 is shot, and I've managed to find a free replacement from a 1989 CR250. This seems to work fine, but does anyone know what the manual recommends for the standard compression and rebound adjustments? Any help greatly appreciated. Thanks
  15. The rear shock on my 125 is shot, and I've managed to find a free replacement from a 1989 CR250. This seems to work fine, but does anyone know what the manual recommends for the standard compression and rebound adjustments? Any help greatly appreciated. Thanks