The OP is 54 years old and in his first post referred to rebuilding engines in the 70's, both in cars and in an old Norton. I'm guessing he's mechanically inclined and knows his way around an engine. I'd also make the assumption that he knows how to ride and doesn't cause unintentional damage by over-revving his 426. I started road-racing before I'd ever owned an MX bike and knew what was good/bad for an engine.
If a noob (not referring to the OP here) has rebuilt the same engine 3 times and it blows up again, it's either time for a new bike.. or a new hobby.
As another posted mentioned, I probably should have cut my loses but I'm stubborn like that. I had a desire to win this war. It's kind of like Kevin Costner in the movie "Tin Cup" where everyone tells him to lay up on one of the holes but he pulls out the "big dog" and tries to drive the green only to put it in the water. He hits another ball instead of taking the drop and does the same thing, again and again and again. If nothing else, he was persistent and consistent.
As the above poster mentioned (thanks for pointing out what others failed to read), I know my way around engines as I've built and road raced big bore bikes for many years and I currently have 4 old classic, late '60's early 70's, Honda
's and 1 Suzuki
that I've rebuilt/restored and many others in the past. This is the first big single that I've owned and my intent on posting the pictures was to add data to an already data rich website. Since I try to never stop learning, maybe someone reading my sad tale of woe would have some advice on an admitted neophyte big single mechanic. But, I digress even more.
I got the motor back together easy enough but after messing around it for quite a few days, but it failed to start. A week or so ago I took it with me to Texas World Speedway to watch the road races for the first time in a few years and figured I'd tap some of my very smart racing friends about ideas on why it won't start. They quizzed me on this and that and most of the items I'd already checked and re-checked, but nothing new came up. Lots of young guys who race motards kicked and kicked but other than the occassional "pop" nothing was working.
In my world when it "pops" it's usually a timing issue. Since these bikes don't have adjustable ignition timing it must be something else. I had drained the carb before storing it so I took the pump apart, cleaned it and shot some carb cleaner through the jets and passages. I didn't check it before, but when I was done, the pump was shooting fuel just fine. Still no joy getting it started.
So, lets think about this. The plug is firing and at the correct time. The carb is putting fuel where it needs to go, so that leaves compression.
New piston, new rings, new cylinder and new gaskets. I had checked the valve seating with some acetone and they were tight. When I removed the head I never even pulled the buckets off the valve springs so that should have been fine.
I'm using an '03 decomp cam so doing a compression check didn't make a lot of sense and I had checked cam timing numerous times. In a final attempt, I decided to check the valve clearances even though there was no reason they should have been off.
To my surprise, the left and center intake valves were so tight I couldn't get a .0015" feeler guage in there. The right intake was fine at .25mm and the exhaust
valves were fine.
I removed the intake valve buckets and shims for inspection/measurement and they looked fine. On a whim, I reinstalled the shim and bucket and torqued the cam cap in place. Surprisingly, the valve clearance was now in spec at .25mm. Well, isn't that just peachy.
The only thing I can figure is that when moving the head around it might have gotten jarred or turned on it's side and those two shims got cocked in the valve retainer and didn't allow bucket to seat properly. Regardless, it was fine now.
I quickly put it all back together and it fired on the 3rd kick.
Excellent, now there is nothing left to do but finish up the details and go riding again. I'm having a problem removing the countershaft sprocket nut from the old output shaft that is still in the old crankcase. Even with my 1/2" drive impact wrench and 150 psi I can't get the nut to budge. I suppose I'll have to take it to the local shop and let them have a go with it. My impact wrench is almost as old as I am and was passed down from my dad who was an auto mechanic. Like me, it's probably gotten weak with age.
Thanks for listening.