An amazing story of unfortunate events (GT250)
Posted: Thu Sep 05, 2019 7:47 pm
Hey guys,
I recently posted a question about my oil pump arm not returning correctly. viewtopic.php?f=9&t=14013&p=173500#p173500
Here's the full story. Two years ago, I was riding my restored GT250 back from work (a short, 7 mile commute with stop signs, stop lights, etc). At this time, I had about 600 miles on the restored bike - all the kinks ironed out.
So, about 1/2 way home, I noticed the bike was getting a bit fussy...it didn't seem to idle right at stops. One of the cylinders wasn't firing quite right. So I held the throttle open a bit (that seemed to help). I got a few blocks from my house, and now one cylinder was basically dead. I had to ride on the side of the road because I couldn't get going fast enough for the 35 mph traffic.
I chalked it up to a carb float getting stuck. I parked it in the garage, thinking I'd take a look at it whenever (this was fall in MN).
The next year I picked up a 74 Kaw 750. Totally my focus. The GT250 sat.
This year, I found an amazing deal on a hold-over (non-sold) 2015 CB100R (like, almost 1/2 off sticker price). I had to have it! The wife said, "you can buy it, but you need to sell one of your bikes." Done!
The GT250 was the gal. After the CB1000R was sitting in my garage, I pulled out the GT250. Remember, I thought a carb was just being stubborn. I fired it up - and I could clearly see it was the right cylinder not firing. I shut her down. Cool, I'll just pull the right carb off. As I was removing the two nuts on the carb, I happened to look down and noticed the oil pump cable looked a bit off. I grabbed it, and it was loose! F!
I quickly removed the oil pump cover, and to my horror, the cable was completely detached from the oil pump arm.
My mind raced. This was the reason the right cylinder stopped firing! I thought, while riding home, the cable was detached, and I burned up the rings enough that compression was lost. And I thought, thankfully I didn't lock up the engine - I surmised that my synthetic two-stroke oil had saved the engine.
I hooked up my compression tester. The left (good cylinder) read 120 psi. The right (bad cylinder) read 90 psi. I checked the spark on the right cylinder - she was lighting up. Not good, as 90 psi is not strong enough compression. I sprayed WD-40 into the right cylinder, tried it again, then it got to about 120 psi. This was my first mistake. I should've trusted that value.
However, with the oil pump cable loose, and my first reading of the right cylinder, I was certain that the right side rings and/or cylinder was compromised. I even did some crude micrometer measurements - and they all came back as "marginal" in respect to the hayne's manual.
So, I popped off both cylinders, searched (and found) a couple of 0.5 oversized pistons (and rings), and brought the cylinders/pistons/rings to a great machine shop near me (bill bune).
Sunday, 9/1/2019, I installed everything (new gaskets, the whole deal). Started the old gal up, same problem! Seriously? I just did all of this, and the right cylinder was DEAD. I threw some gas into the right spark plug hole, nothing.
I sat there, in my garage, 6pm, defeated. So I did the old 3 point test in my head. I have gas, I certainly now have compression, and I thought I had spark (I did).
I was just about to go back into the home and have a beer. Then I thought, why not take off the left-side ignition cover? I did. Then I started the bike (firing on the left cylinder). I looked down, and saw the right-side points firing like lighting bolts. I looked back to my hayne's manual, and it basically said if you see this, your condenser is bad.
The next day (labor day), I dug out my old right-side condenser from the rebuild (I save everything). Installed it, and sure enough, the gal was running perfectly!
So, in the end, I spent $250 on new pistons, rings, gaskets, and a bore for each cylinder...when it just needed a $10 condenser.
The oil pump cable was probably disconnected when I was fussing around with the throttle when the bike was not running (after the ride home).
So, as promised, a story of a bunch of ill-timed unfortunate events that lead me to believe something that wasn't correct. It still torques me that I had my GT250 bored from original to .5 over (it's only got 4200 miles on the clock).
At any rate, I had to share this story with folks that would appreciate it!
I recently posted a question about my oil pump arm not returning correctly. viewtopic.php?f=9&t=14013&p=173500#p173500
Here's the full story. Two years ago, I was riding my restored GT250 back from work (a short, 7 mile commute with stop signs, stop lights, etc). At this time, I had about 600 miles on the restored bike - all the kinks ironed out.
So, about 1/2 way home, I noticed the bike was getting a bit fussy...it didn't seem to idle right at stops. One of the cylinders wasn't firing quite right. So I held the throttle open a bit (that seemed to help). I got a few blocks from my house, and now one cylinder was basically dead. I had to ride on the side of the road because I couldn't get going fast enough for the 35 mph traffic.
I chalked it up to a carb float getting stuck. I parked it in the garage, thinking I'd take a look at it whenever (this was fall in MN).
The next year I picked up a 74 Kaw 750. Totally my focus. The GT250 sat.
This year, I found an amazing deal on a hold-over (non-sold) 2015 CB100R (like, almost 1/2 off sticker price). I had to have it! The wife said, "you can buy it, but you need to sell one of your bikes." Done!
The GT250 was the gal. After the CB1000R was sitting in my garage, I pulled out the GT250. Remember, I thought a carb was just being stubborn. I fired it up - and I could clearly see it was the right cylinder not firing. I shut her down. Cool, I'll just pull the right carb off. As I was removing the two nuts on the carb, I happened to look down and noticed the oil pump cable looked a bit off. I grabbed it, and it was loose! F!
I quickly removed the oil pump cover, and to my horror, the cable was completely detached from the oil pump arm.
My mind raced. This was the reason the right cylinder stopped firing! I thought, while riding home, the cable was detached, and I burned up the rings enough that compression was lost. And I thought, thankfully I didn't lock up the engine - I surmised that my synthetic two-stroke oil had saved the engine.
I hooked up my compression tester. The left (good cylinder) read 120 psi. The right (bad cylinder) read 90 psi. I checked the spark on the right cylinder - she was lighting up. Not good, as 90 psi is not strong enough compression. I sprayed WD-40 into the right cylinder, tried it again, then it got to about 120 psi. This was my first mistake. I should've trusted that value.
However, with the oil pump cable loose, and my first reading of the right cylinder, I was certain that the right side rings and/or cylinder was compromised. I even did some crude micrometer measurements - and they all came back as "marginal" in respect to the hayne's manual.
So, I popped off both cylinders, searched (and found) a couple of 0.5 oversized pistons (and rings), and brought the cylinders/pistons/rings to a great machine shop near me (bill bune).
Sunday, 9/1/2019, I installed everything (new gaskets, the whole deal). Started the old gal up, same problem! Seriously? I just did all of this, and the right cylinder was DEAD. I threw some gas into the right spark plug hole, nothing.
I sat there, in my garage, 6pm, defeated. So I did the old 3 point test in my head. I have gas, I certainly now have compression, and I thought I had spark (I did).
I was just about to go back into the home and have a beer. Then I thought, why not take off the left-side ignition cover? I did. Then I started the bike (firing on the left cylinder). I looked down, and saw the right-side points firing like lighting bolts. I looked back to my hayne's manual, and it basically said if you see this, your condenser is bad.
The next day (labor day), I dug out my old right-side condenser from the rebuild (I save everything). Installed it, and sure enough, the gal was running perfectly!
So, in the end, I spent $250 on new pistons, rings, gaskets, and a bore for each cylinder...when it just needed a $10 condenser.
The oil pump cable was probably disconnected when I was fussing around with the throttle when the bike was not running (after the ride home).
So, as promised, a story of a bunch of ill-timed unfortunate events that lead me to believe something that wasn't correct. It still torques me that I had my GT250 bored from original to .5 over (it's only got 4200 miles on the clock).
At any rate, I had to share this story with folks that would appreciate it!