Motor locked up on freeway

[NinjaFinch]

Hey all, long time lurker in need of help. Please don't hurt me.

So I have an '82 FT500 that I got last year with ~6k mi on it. It's completely stock mechanically, and I've been keeping up with maintenance. Until yesterday, it didn't really give me any major problems.

After a weekend of long-distance riding, I was heading home on a fairly straight stretch of highway at ~110 km/h. Then without any sort of noise or stuttering, the engine just stopped like someone hit the kill switch. It rolled for a bit and by the time I realized what was going on, it locked the back wheel (in 5th gear) at somewhere between 60-80 km/h. Luckily, being Saskatchewan, the highway was pretty empty when this happened. Got it off to the side of the road and despite my best efforts, I couldn't get it going again. Ended up going home on a wrecker.

One change of pants later, I tried to poke around a bit more with no luck. As it is, it still won't start. Changed the spark plug since it was due for that anyway, and it's getting both gas and spark. Air filter looks almost new. Despite the wheel locking up, the starter will engage the motor and the crankshaft turns normally. Oil was low, but still within the hash marks on the dipstick. All electrics beside the left turn signal (different issue) work normally. Gassed up about 20 mi prior, and tried the petcock in both on and reserve. Where should I look next?

[murdo]

Wow, I'll bet that got your attention. Lucky I've never had a high speed seize like that.
If the engine is turning over on the starter, does it have compression. Take the plug out and put a finger over the hole and engage the starter, it should blow your finger off the plug hole. If no compression then you will need to remove the cylinder head and see what has happened.

[NinjaFinch]

Yeah, first mechanical failure I've had to deal with on a bike. But if the fact that I could keep it righ side up isn't a testament to the value of the MSF course, I don't know what is.

Just tried the thumb-on-spark-plug-hole trick, and I could feel it motor pushing air past my finger. I'm guessing that says there's some compression? But if everything else is good, it's probably not enough.

I checked the valves on the exhaust side. One was perfect, the other was a bit tight (>0.05mm). No idea about the intake side yet, I'll have to tackle it after lunch. Just hoping it's not permanently knackered.

[firecaptp7]

According to what you’ve written …

You’re riding down the road when suddenly the engine stops running as if the kill switch was turned off. But you’re still moving forward? Did you immediately pull in the clutch lever? And the rear wheel was still locked up?

First question? Why did the rear wheel lock up? When you pulled in the clutch lever did it roll free?  Or is it still locked up? If so that’s a separate issue from the starting problem.

Second question - You now have fuel, spark and compression but the engine won’t start?

Trying to understand.

[NinjaFinch]

I didn't pull the clutch until after it came to a stop. It was when I was trying to get it off the side of the highway that I pulled it and it rolled no problem. For the second question, I have fuel for sure, some compression (gauge doesn't fit, so I can't tell how much, or if it's even enough), and spark.

Thinking about it now, the spark colour is dramatically different from what it used to be. But for every argument I can find that says 'weak spark' is a thing, I find another in all caps saying it isn't. I don't know who to believe anymore, but I'm testing the ignition system later today. Hopefully that yields something.

Edit: According to the ignition pinpoint test that's elsewhere on this site, my CDI is putting ~6V to the coil vs the expected 36-42V. Ignition Pulse Generator is ~493Ω vs the expected 500-570V, which is out of limits but also doesn't seem too far off. Still need to test the alternator, but I feel like one or both of the two might do it.

[scottly]

What do you mean the spark plug is dramatically different?? Can you post a pic?
You may have "soft seized" the motor. What can happen is the piston expands from heat enough to lock against the cylinder, then after cooling off, it frees up. This happened to a friend of mine, and was due to low oil level, while pulling a long grade at 65+ MPH. He was able to add some oil and make it the remaining 40-50 miles to home, but ended up needing a re-bore and new over-size piston.
You should do a proper compression test before messing with the ignition system.

[triguyracer]

Sure sounds like it seized up ,once the motor cools some,then many times it will turn over and you are abile to restart it,once it gets some heat it will seize again if that was the problem in the first place.If you can pull the clutch in and it disengages the rear wheel you can almost be sure it was some kind of seizure ,the piston or some thing in the gearbox,your best bet is to get a acurett compression reading that will tell you a lot,am I reading this right when you said it locked up did you skid off the road before you pulled in the clutch ?

[scottly]

We seem to think alike, triguy.

[triguyracer]

Yes you nailed it just what I thought too, seized up way to many motors in my time racing ,thankfully only cost money and not any broken bones and such lol

[NinjaFinch]

What do you mean the spark plug is dramatically different?? Can you post a pic?

I'll try, but I also won't have a before pic for comparison FWIW.

Edit to answer the question: I remember testing it last month when I took it out of storage, and it was more of a bright violet colour. It's a dull orange if I test it now.

when you said it locked up did you skid off the road before you pulled in the clutch ?

Sort of. I didn't think to pull the clutch in before I came to a stop. It was while I was trying to get it to the side of the road that I pulled the clutch in and it rolled fine.

You should do a proper compression test before messing with the ignition system.

For sure, it's going to get done regardless. But since it's not going anywhere while I track down an adapter, I figured I might as well tackle the ignition while I wait. Two birds, one stone, right?

Actually on that note, I did the full pinpoint test late yesterday and here's what I've found:

Spark plug - brand new, gapped correctly, produced dull orange spark when cranking

Coil/Wire - tested primary coil at 0.8Ω (nominal 0.2-0.8Ω) and secondary coil at 10.5kΩ (nominal 8-15kΩ)

CDI box - produced a 6V signal to the coil (nominal voltage is 36-42V, according to J6G1Z's test thread), box was grounded properly

Pulse generator - tested at 498Ω (nominal 513-567Ω), out of limits but not sure to what effect

Alternator - tested white stator wire at 299Ω (nominal 259-351Ω), tested blue stator wire at 386Ω (nominal 73-99Ω), did not test the yellow terminals

Regardless of whether I have compression or not, I feel like a bad ignition stator isn't helping. More to follow when I can get a proper reading.