So, I took my newly built CB750 K2 out for a test ride and the engine seized up on me about a half mile out. And before I go crazy and start to take everything apart again, I’m looking for advice. Here is the breakdown of what happened (no pun intended).
During assembly of the engine, with the head cover off, I checked the oil pressure with a gage and observed oil reaching the heads. I don’t recall what the oil pressure was exactly, but it was fine. I was using the starter motor to crank the engine, and watched for oil to begin to seep up. Once I saw some oil, I stopped, buttoned up the head, and put the engine into the frame. The engine then sat for about nine months as I did not have the time to mess with the wiring; however, that changed with the COVID lock-down. I sorted the wire and a few other things one the bike to compete it.
The engine started fine. No unusual noise. I could start it with either the electric start or the kick start. At first I only ran the bike to sync the carbs and adjust the timing a bit. I would say it ran approximately 30 minutes on and off over the course of 2 or 3 days. There was some smoke coming off the headers, which I had wrapped, so did not think too much of this as it is likely just some trapped moisture or maybe some oil residue burning off. I also noticed an oil leak on the alternator side, but was not too worried about it either. I suspected the alternator wire plug was leaking a bit, and I would get to that later. I then took it for a few short spins around the parking lot up to third gear to make sure the gear box was fine. No problems.
I later took it down the street, listening for noise and running it through its gears. Just a short run, maybe half a mile. Still no problems. A few days later thinking of making a longer run, I checked the oil and saw that it was pretty low, so added more until it was mid-level on the dip stick assuming that the oil leak had depleted the oil that was present. Yep, I didn’t take into account that the oil will drain down into the sump. I took the bike out for a longer ride around the neighborhood – about 2 miles. The bike was smoking more than it was before. Around the head/headers, and when I opened the oil reservoir some smoke came out as well which concerned me (and of course, there was now too much oil as the pump circulated the oil that had drained down into the sump.
No sure about the smoking oil, I took a few days and looked over comments here on the forum and found that smoking engines are not a problem if they are new builds and to expect some smoke from the oil if the reservoir cap is opened. OK, great. I needed to get to that oil leak anyway, so I drained the oil and adjusted the alternator wire rubber grommet. The rubber is a bit hard, so after re-installing the cover, I added some silicone to the outside of the cover (not inside where the oil is) to shore up the rubber grommet/wires. New oil was added.
As this is a newly built bike it does not have a license plate and the DMV here is shut down for COVID, so I was not riding it. It sat for about a week. Last weekend I decided to take it for another longer test ride around the neighborhood – mostly to make sure the leak was fixed and that I had the proper amount of oil in it.
When I started it this time I heard a high-pitched squeaking that went in time with the engine rotation. I listened to it for about a minute as the bike warmed up and I got my helmet and gloves on. It concerned me, but I thought that maybe it is because I had drained the oil and refilled the reservoir, which now had drained to the sump, and it is likely that the pump was sending oil to the engine. So I took off, but was conscious that it had started making the sound. I could no longer hear it with my helmet on and the increase in RPMs as the engine worked. I got about a half mile away in third gear when heard the engine die, and I immediately grabbed the clutch, shifting down to neutral. Tired to restart and heard the starter engage the gears, but nothing. I checked the kicker. Locked. So, I pushed it back home to be sad.
I pulled the plugs to have a look at them – a little sooty, and looked down into the cylinders with an endoscope. Cylinders 1nd 4 were near the top, so I couldn’t see much there. 2 and 3 showed a little scoring, but nothing terrible – no pieces of rings or scorching. There was oil in the reservoir, so the pump at least returned the oil to it.
Last night, I went into the garage and just hit the starter to hear what it was doing. Surprisingly, the engine turned over. The plugs are still out and I had removed the gas tank. I checked the kick starter and it did not want to budge – I did not try to crank on it.
What are your thoughts? I can only assume lack of oil to the cylinders. Could there be a passage blocked to them, yet still return to the reservoir? Issues elsewhere? Not really looking forward to having to take this whole thing apart gain.
