Perplexed

MacMcMacmac

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I finally had enough with the rattly motor. Convinced it was a cam chain guide gone the way of the dodo, I pulled the motor and found the following:

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It sure is easy to push now!

I really can't find anything wrong. When my old Seca turbo cracked it's front cam chain guide, I knew right away when I pulled the cam cover that the chain had been buzzing away at the top because of the fresh rub marks, but there is no evidence whatsoever that the chain has been rubbing anywhere. The front guide looks ok (I will replace it anyway) and the back guide has some light tracking, but no real signs of distress. Kind of bummed, but at least I know nothing major is failing, and the motor really needed painting anyway, so I'll order up the new gaskets and button her back up. Rotten outcome after 4 hours work in the heat and rain. Notice my lovely work surface. Ah well...
 
Pretty dark looking oil coating going on in there.
Might want to check the rings & cylinders.
If you go that far, check the rods.
Then, there's always the rattly clutch basket springs...
 
have you checked that the back of the clutch basket is not rubbing on the crankcase ??
its quite common.
The Yamaha manuals clutch assembly diagram had a shim washer missing but 35 years wear will also increase tolerances and clearance.
If you need to pack the space behind the clutch basket to gain more clearance then the shim washers you need are M25 x 35 and they are available in various thicknesses and are a generic part not Yamaha.. you can stack them of course to get the thickness you want ie 3x 0.5mm thick washers to get 1.5 .

My video recommends at least 1mm clearance but it really needs a 2mm clearance as mine is rubbing again after just 1000 miles grrrrr

 
Pretty dark looking oil coating going on in there.
Might want to check the rings & cylinders.
If you go that far, check the rods.
Then, there's always the rattly clutch basket springs...

Factory, black head LOL

Kind of late now, but watching crank ends while spinning it over can be instructive. This can still be done.... some ideas to pursue here.

http://www.xs650.com/forum/showthread.php?t=38420

http://www.xs650.com/forum/showthread.php?t=23162&highlight=crank+wobble&page=3 post 149

Note at least put a down a sheet of plywood, motor teardown in a grass yard, what could go wrong? Reminds me of a forlorn Triumph I saw sitting head off along a very dusty gravel road in Northern Idaho decades ago.
 
Solved.........

Turns out the el-cheapo Mike's re-pop gas tank cap is resonating loudly at certain rpm.....

After putting it all back together, I was non-plussed to find the rattling as bad as ever. I was at a loss as to the cause and resigned myself to the fact that is was probably piston slap. Today I took it behind the shop to try and tune out a bit more by adjusting the cam chain only to find the rattle was not coming from the motor but higher up. I looked for an obvious cause and put my hand on the gas cap while revving the motor.

Silence...

Don't know if I was relieved or pissed considering the labour that went into the whole motor pull and inspection, but at least I know my engine is in good shape and I finally gave it a lustrous Black Pearl Metallic VHT paint job, so it was worth it in the end ( I keep telling myself...)

I tried to remedy the rattle by pulling the undersized split pin that attaches the cap to the innards. It is a very loose fit. In fact, the whole cap is a shite design, lightly built and a sloppy fit. The rubber seal is already splitting after only 3 years. It is a hair different from the much better built Yamaha OEM cap that is off by just enough that you can't reuse it on the re-pop.

I tapped the screw-on mounting hinge for 8-32 and reinstalled it with stainless hex head bolts and some red Loctite to keep them in place. It still rattles. I think the actual lock mechanism is vibrating around in the cap. Damn annoying and not simple to remedy. I can bring on the rattle at exactly 3000 rpm and damp it out by touching the key hole disc lightly with my finger. It's a loud bugger and easily passes for cam chain noise.

I might put a sleeve over the pin that the latch snaps over. That will take a bit more slop out of the assembly. I wish there was a screw on cap that would work with this neck. I have little confidence in it now after seeing how thin the parts are.
 
Flog mikes. Send them the labor bill tearing it apart and putting it back together. Not that it would do any good though. Glad it was something stupid easy. Until u find an original xs gas tank, just deal with it. Maybe find another rubber gasket to help hold it tight? Wedge a something inther to keep the ringing down?
 
After looking at the underside a bit more, I could see that the part was removable with two screws. I took it all apart and shoved an oring around the lock tumbler assembly and put it back together. A nice long ride revealed no rattles , at last! Nice to hear only the motor and the nice bark from those Commando pipes.
 
Hi Mac,
coulda been worse, coulda spent a mort of money on new parts before finding that the gas cap was buzzing.
But about your alfresco work area. An 8' x 4' sheet of builders plywood will improve the venue and a 2" x 2" wooden strip all round the edge will help stop those little parts that get dropped from burying themselves in the gravel.
 
Ooh...Tell me more about the o-ring you used, and where you put it. I have a rattle at the key slot at certain RPM's and I've resigned to live with it, but would love a simple solution if there is one. This is an OEM cap fyi.
 
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