I have a 2010 Suzuki Thunder 125 that I bought second hand and abused. I managed to make it run in the past but as usual, life happened.
The bike was left at the farm exposed to the elements for about two years.
No I finally have the time (and more especially funds to buy parts) so I went back to fixing it. #realmechanic
Disclaimer: I am not a mechanic nor do I claim to be. Everything I do on my bike is a combination of hearsay on forums, YouTube tutorials, and advice from my good old friends ChatGPT and Claude.
I checked for spark. Initially there was none but I managed to fix the wiring and replaced the CDI which went bad so...
- Spark (electricals) ✅
- Fuel (tank + carb + air-fuel mixture)
- Compression
Next up, was fuel. I removed the carb and disassembled it, cleaned it, and reassembled it. I've done this multiple times in the past so I'm confident that fuel is going into the combustion chamber now.
- Spark (electricals) ✅
- Fuel (tank + carb + air-fuel mixture) ✅
- Compression
Unfortunately, when I checked compression, I had a reading of 50psi. Which is too low for this motorcycle. It should be at least 120psi. And that's still bad as it is the lower range.
One of the first things I check for low compression is valve clearance. The rocker arms could be pushing the valves open thus compression becomes impossible.
The first problem came from removing the crank shaft access cover bolt. It was exposed to elements so badly it welded itself onto the left crank case cover.
I tried everything. The hex/allen key that's originally designed for the cover bolt just rounded the hole. I tried a slightly oversized torx key. Same thing.
Finally I tried a bolt remover. Initially it didn't work, it just made the hole larger. But when I used a size bigger than what did it, it finally cracked the head of the bolt allowing me to turn it and take it out.
I was finally able to access the nut/bolt thingy that will turn the crank shaft.
Note: Specs and tutorials always said 17mm for this, but the actual size for my bike is 14mm. Weird but okay. If you encounter inserting a socket wrench key in there and nothing fits, try 14mm.
I turned the crankshaft so that the piston is at the TDC position and adjusted the valve clearances against the rocker arms. The intake valve didn't have any space at all and I ran out of adjustment screw. I had a bad feeling about it but I still continued and closed everything up.
But, I still had no compression. I can still easily push the kick starter by hand. I didn't even bother taking out the compression testing tool as it was too soft.
- Spark (electricals) ✅
- Fuel (tank + carb + air-fuel mixture) ✅
- Compression ❌
I was sad but I got to move on. Tomorrow I'll pour some engine oil and gasoline into the spark plug hole to remove any carbon build up and give the piston rings a bit of lubrication and filler for any gaps in one go.
If this doesn't work, I might have to do a top overhaul which I have never done before.