850 Tri-Spark Problem

Status
Not open for further replies.

jcphilli

Joined
Aug 18, 2016
Messages
7
Country flag
Gents,

Running into an issue with a newly installed tri-spark set up on a ‘73 850 Commando. After a complete rebuild the bike looks great and runs well.... kind of. After setting the initial timing on the tri spark the bike will start relatively easy. However after I shut the bike down, the rotor (containing the magnets) drifts out of place from the taper fitting in the camshaft causing a loss of correct timing. I’ve cleaned the contact surfaces, torqued the bolt that provides the taper fit down pretty hard, tried to shim it... etc and no matter what the rotor still shifts out of time after shutting the bike down or extended idle period. Somewhat stumped and wondering if anyone has seen this issue before?

Thx,
-John
 
Mine did the same thing when I installed my Joe Hunt Maggie after the first few start ups the timing slipped even when the dummy shaft for the Maggie to cam was tightly done up, I put a bit of bearing blue on the taper and tighten it up as tight as I could then removed it to find the taper was only sitting at the end of the taper and not all the way on the taper, how I fixed mine was to freeze the taper dummy shaft for the Maggie then making sure where the shaft is right for the timing, gave the dummy shaft a wack in the right place for timing and did the bolt up tight, that was over 8 years go and hasn't slipped since as the taper is fully seated, I can remover the Maggie and timing cover without removing the dummy shaft for any maintenance, so your pick up might not be seating all the way on the taper use a bit of bearing blue to see where your taper of the pick up sits on the cam.

Ashley
 
Couple of things it could be:

As @ashman suggests, paint the end of the camshaft with some engineers blue, or even color it in with a sharpie, then push your Tri-Spark rotor onto the shaft and wind it around a couple of times.
When you remove it, the shaft should be shiny with no marker left at all.

If there are still signs of marker, I suggest you put some grinding paste on the shaft, and lap in your Tri-Spark rotor.
The rotor is aluminium, so you’ll do no damage to the camshaft.


The other thing that comes to mind is the bolt - it could be too long and is bottoming out in the camshaft before the head of the bolt is pulling the rotor all the way on to the taper. Or the threads in the camshaft are not deep enough.

It’s maybe worth doing the bolt up without the rotor on, and making sure it runs all the way in.

I don’t think you can pack the bolt out with washers, as it will rub on the back of the Tri-Spark stator plate, so you would have to shorten the bolt itself.
If you do saw off a couple of threads, make sure you put a decent lead on the bolt with a file so it starts nice and easy.
 
I may recall this incorrectly, but I seem to remember that the allen bolts were supplied in 2 different lengths due to "bottoming" out. If that isn't the case there were instances when the allen bolt was too long and needed shortening slightly.
 
Reggie said:
I may recall this incorrectly, but I seem to remember that the allen bolts were supplied in 2 different lengths due to "bottoming" out. If that isn't the case there were instances when the allen bolt was too long and needed shortening slightly.
Click to expand...

Two different threads (BSF and UNF), not different lengths.
" Install the Tri-Spark rotor using the correct socket head bolt for your engine. Two are provided (1/4 UNF and 1/4 BSF) for use with the earlier and later engine models. "
 
Status
Not open for further replies.
Back
Top