After some sleep, I am significantly more upbeat about the situation. It sucks that it happened and pushes back when I'll actually be riding again, but its okay, and job #1 is to figure out what happened. I know I was quick to blame my head builder, but he is a very experienced technician, if a bit rusty on the SuperHawk. I'm sure something I assembled is the cause of this, or at very least, something that I just didn't foresee.
First off, the motor was reassembled with some NOS Kenig 10.5:1 race pistons. Since these are NOS and were last on a shelf in the 70's, I have no way of knowing what parts were sold with them-- like adjustable cam sprockets and the like. I am tossing the plan to use them. I just thought it would be an interesting touch to use them but are just one extra variable to worry about.
I really have no idea what happened first, but here are the pictures of the carnage:
The right-side piston, unscathed. Those swirls are not from some weird valve impact, they are from my rag that I wiped all the dirty gasoline off with.
The left-side piston.... not so lucky! It has the entire dome blown away clear to the rod pin. This is a big impact.
The valves on the left side are destroyed. I haven't gone all CSI: San Francisco yet to figure out how the valve was hit initially and if it damaged the head, but I'll let you all know. It looks like I might have gotten lucky and the exhaust might have just hit the intake valve without knocking into any aluminum. I'm not optimistic about that, though.
So here's my story, I'll include everything I've noticed about this engine in the last 2 days after reassembly with the cam / points cam issue.
I break in engines the race car way. 10-15 minutes of high idle, followed by slow sweeps to maybe 2000rpm. Once that's done, just a bit harder sweeps to the same or just higher rpm but never over that. After that's done, it needs some miles with load to set the rings. I had finished my first 10 minutes and had let it warm up to start giving it some harder sweeps from idle to low rpm. I had noticed there was some clean oil sitting on the cooling fins on the front of the motor right around the exhaust exit and again a little around the mating point of the head to the block the morning after the first time I started the engine. I had no idea how long that had been there. It worried me, so I cleaned it off before starting it the second time and was planning on watching it carefully to see if any of it forms again. I was fairly confident that I hadn't blocked any oil passages and also noted that there was, indeed, oil reaching the head, and escaping back to the sump. Upon starting it the second time, I saw that there were some wisps of oil smoke from the exhaust port before the retaining ring. I didn't think much of it because I had only quickly put these on to start the engine with the thoughts that letting exhaust valves feel the cool air directly on their rear faces is a very bad thing. I didn't put a super sufficient torque on the bolts yet but was confident that they were tight enough for their current purpose.
The engine idles fine, once again, at maybe 1000-1500rpm. I did a couple slow revs not much above that point and started increasing in amplitude from there, going off ear, as to not rev too high. As soon as it revved up a bit (probably not even to 2500rpm) it made and odd shudder. I did the same thing again, and the bike instantly seized. A small wisp of smoke poured from the inlet of the left side carb and I knew what had happened.
I tossed the frame off the thing and pulled the breather plate. The cam chain was dead tight on the tensioner side, and quite loose on the front, past the sprocket. The cam tensioner itself, once removed, was very free-spinning but it should be noted that I spent a lot of time making sure it was going to be that way. It was from a junk block pile at my neighbor's house since the block I was using needed the larger style that I didn't have. When it was all cleaned up, it was very hard to spin, so I spent a lot of time oiling and greasing and tugging on the edges to ensure it can freewheel. All the valve springs (which happen to be higher rate "racing springs") were intact. The right cylinder is very carboned up. I knew the bike would run a bit rich as I have larger jets than I think it will ultimately need. I went bigger on these due to different air filters and those high-compression pistons. Error rich better than lean, I figured.
Here are a few things I feel could have happened:
1) The chain somehow slipped. My neighbor said that the proper way to tension it is to install the tensioner, release the bolt holding the rod in so that it presses against the chain with no more than the spring's force, and re-tighten. The chain itself was the original one, but it seemed to be in very good condition. A motorcycle mechanic actually took a look at it next to a brand new one and said that he can't see any thing indicating need for its replacement.
2) The valve came unseated and impacted the piston. I don't know how this happens. Any insight would be appreciated. Could the smoke out of the exhaust be due to some compression leaking into the head somehow or oil leaking out into the cylinder? Again, I have no idea how this thing is assembled at the valves since I didn't do the assembly!
3) The piston hit the valve due to mis-timing. I am very sure I had the cam timing itself dead-on to spec. This doesn't mean it was correct for these pistons. I turned this motor over countless times and idled it for a total of 20 minutes before it collapsed upon itself. This leads me to believe that as long as the springs were doing what they're made to, there shouldn't ever be contact between the valves and piston, regardless of RPM, if not at idle.
Here is the motor idling on the stand the first time. This was 1 day before it popped.
http://www.youtube.com/watch?v=k8wwSL3A1aA
I have no tachometer, but didn't feel I was revving it high enough to cause any pre-break-in damage. I am very prudent with my fresh engines and try to take care of them properly. I've seen this kind of damage on race car engines that have been overreved or lose a valve, but never at 2000-3000rpm!
As I said, I need to pull this thing apart and really take a good look at what happened. I'll be going back to stock-style pistons but keeping the valve springs and valves. Since I'll need some new sleeves, I'll probably go back to the block (and tensioner) that this bike came to me running on just for continuity.
Any help is appreciated in solving this issue!!!
