Yam_Tech314's official build thread

...The wrist pin clip looked like it was also in wrong, in school (if I remember correctly) the opening in the ring clip is supposed to be riding in the top or bottom of that piston, not the side. (Perhaps they move over time?)

Good catch.
Yes, our oldschool shop practice was to install clips with the opening up or down. Prevents their potential closing and ejection at high rpms.

Your homework.

http://www.xs650.com/threads/used-cam-chain-for-rebuild.54079/#post-581362
 
when referring to "degree" of timing retardation, is that measuring from one set point on the actual cam itself, and then turning the cam til its tight in the other direction, and measuring the degrees that the cam turns given the slack of the cam chain? if so, that ship has sailed. I took a grinder to it... :)
 
Those pistons don't look too bad. I'm sure the correct 'engineering' answer is measure the pistons, measure the bores and see whether it's all within tolerance. Then possibly hone the bores and rebuild with the old pistons cleaned up and new piston rings.

But as said, you have decided to rebuild with new pistons and that will give the best basis to work from.

From the close up picture I really don't like the positioning of that cirlip. As you said, the end gap needs to be well away from the notch on the piston casting - top or bottom. Wonder if whoever put the piston on had trouble getting the circlip in?
 
I agree, your pistons don't look too bad. That's just what you normally find. The connecting rods push and pull on the pistons at a slight angle as they move them up and down. This tries to rock the piston fore and aft in the bore. When new with tight clearances, that doesn't happen, but it begins to more and more as the parts wear and more clearance develops.

Something else you'll need to carefully inspect is your front cam chain guide. That's one of this engine's weak spots. It's not that it's a particularly bad part, it's just that they're so old now, many are failing. The rubber strip glued to the aluminum base is coming loose, the glue is failing.
 
I agree. Pistons and bores both look pretty good. A feeler gauge would give you a good check on skirt clearance. If it's within limits, I'd go with 'em.

I lost count of the times ive gotten oil, and parts cleaner in my eyes... Ill learn soon.
Here's hoping you learn before you permanently damage an eye... :yikes:
 
Yes, my pistons and bores looked similar to yours and all I did was re-ring it. It's given me a good 12 years of trouble-free service but it is getting near time to go back in there now. This time it will get bored. A big consideration for me at the time was cost. The low cost pistons from CruizinImage weren't around yet so oversize pistons and a bore job would have added near $400 to the rebuild cost. Today I can do it for about half that.
 
Determine the wear, the piston to cylinder clearance you now have, and that will tell you if you can re-use them. New clearance spec is about .002", the wear limit is about .004". You can do a rough check with a feeler gauge between the piston and bore as Jim mentioned. If you can jam a .005" or .006" feeler gauge in there then you're over the wear limit.

But your parts don't look too bad. There is hardly any brown discoloration below the rings on the pistons. That indicates the rings were sealing well. Reach in the bores and see if you can actually feel any of the scratch lines present with a finger tip or finger nail. If you can't, that's another good sign.
 
And, if you compare the discoloration on the pistons to the head I’ll bet you can convince yourself as to which is which. Usually twin cylinder engines give clues with carbon build up and discoloration..
 
Oh, and did you find the tach drive rod shim washer when you pulled the right cover?

I did. I had to pull the gear out of the side cover, and it was tucked in behind that. Getting that locator pin back in was kinda tricky, but All's well that ends well. got the side cover properly reassembled, and I learned my lesson. gonna clean and polish that up in some downtime when I find some.
 
When I got my bike, that shim washer was M.I.A., lol. I have no idea what happened to it and found no evidence of it anywhere. I found a suitable replacement. You really need that washer in there. Besides shimming the excess up-down play out of the rod, it keeps it from grinding it's way into the bottom of the case.
 
Besides shimming the excess up-down play out of the rod, it keeps it from grinding it's way into the bottom of the case.

Good call. I definitely have it in correctly. I tested hands free operation to make sure. Made sure to put the outer sheathe on and reinstall the bolt that keeps it in place so that when I spin the gear it stays positioned properly.

Speaking of shims... Do the advance arms get shimmed? I pulled 7 small washers from the assembly and couldnt find an 8th washer. I could only guess that they're shims of some kind. Perhaps to make sure they're riding on the center of the governor shaft? (Or whatever the manual calls the shaft that runs through the camshaft.)
 
Are you talking about the arms on the advance unit with the springs? The ones that fling outward as the unit spins? There is usually one combination shim/spring washer under each arm, nothing above it but the e-clip. As far as the advance rod that runs through the cam goes, I've never found any shim washers on any of them, but some could use them. The one on my '78 had quite a bit of in-out play, more than I was happy with. I added my own shim washers to it to reduce it's end play.
 
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