My Seca 750 is making some awful noises

My starter button does nothing if the engine is running. It sounds like yours engaged the starter which stopped the rotation of the motor and is still engaged, keeping the motor from starting even with a bump start. Could this be possible?

 

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Before you remove the alternator rotor can you use a socket on the rotor nut and try and turn the rotor anticlockwise to see if it locks because the starter clutch dowels should be jamming in the narrow end of the clutch hub ramp? I know it might have to spin faster to catch but it is worth a try. It should turn clockwise easier if it is not driving the starter motor I think although I could be wrong.

 

This a case where bolts backed out of the starter clutch causing it to lock up:

https://www.xjbikes.com/forums/threads/starter-motor-issues.67016/page-2

 

I don't think so. The starter switch and solenoid should be active when the bike is running in neutral, as mine was. But a freely spinning starter clutch should, I think, prevent any interaction if the starter is triggered while the engine is running. I think this is just more evidence that my starter clutch is not releasing correctly.

I think it's more because of a different design, but my daughter managed to break her starter gear and tear up the stator in the alternator on her Ninja 250... by the same method of pressing the Start button while the engine was running.

 

I'll give that a try after I've pulled the starter. I know what the behavior should be for the idler gear. I'll see whether it's locked to the crank, and whether turning the alternator can make any difference there.

 

I don't think the starter clutch is releasing correctly either.

 

I pulled the starter. It seems OK. The idler gear is not idling. It's stuck solid. Even if I put it in gear and rotate the rear wheel, the idler will not move. In some way the idler, and the starter clutch, are stuck pretty solidly.

 

Here's what I can see after pulling the rotor and the alternator shaft.

I was pleased to find that the center bolt from the alternator puller I'd bought for my daughter's Ninja 250 was a perfect fit for the XJ rotor.

On the other hand, I'm now left thinking: really?! they couldn't make the alternator bearing plate big enough to allow replacement of the starter clutch?!

Once the alternator shaft was out, the idler gear spins easily. I'm not sure yet what part was grabbing. It was not the starter, as, with the starter out, the crank was still tough to turn... but it seems to move more easily with the alternator shaft out.

 

This evening's progress.

I was a bit annoyed to have to remove the dental tube for the oil cooler / spin-on adapter. On the one hand I had bought some longer ones because I thought an extra 5mm would be good. On the other, the Loctite Red really was doing a great job of holding the existing one in place. But, I couldn't get it to clear the front engine mounts without removing the valve cover, and it seemed like a better idea to remove the dental tube.

 

The culprit

 

Great progress. That's what the noise was all along. Are you going to replace the chain guide too?

 

That is so weird that after 40 years the bolts backed out. That looks to be the same as what happened to TheCrazyGnat

 

Yep, major engineering oversight.

 

I think I will probably replace the guide while I'm in there. Most everything looks quite good and clean, other than the starter clutch, of course.

I am worried about one of the half-circle shims for one of the transmission gear sets. When I lifted it out, I dropped one, and it basically disappeared. I hope it didn't drop through the timing chain tunnel...

 

Might be able to find it with a small pick up magnet if it's in the case.

 

Here's what the parts look like. Is there a bearing that the central gear runs on?

Nevermind. While looking for the shim/clip (which I still haven't found), I found the "collar" that the gear runs on.

 

While I'm waiting for parts, I think I will also tackle the steering head bearings. Might as well combine all the downtime into one.

 

Looks like I didn't actually lose one of those clips. There is only one per bearing. I thought the part I had removed had two and that I had lost one.

I reassembled the clutch hub today. I used Loctite red, and tightened the bolts to 22 lb feet. I think they'll stay put this time.

 

By the way, my crank counterweight also shows the same discoloration as was seen in that other starter clutch hub backed out screws thread. I wonder if the two bikes were made around the same time. Mine was 10/81.

 

Got my dental tubes in on Friday. Yesterday I welded one to the oil cooler center bolt to make the proper center bolt for my setup. Today I finished putting the bike back together and it's running again. Need to do some more tuning, or checking, initial idle stabilizer position seems too open. But, aside from that, sounds good. Normal cranking, no whining, etc.