'Knocking' in second gear.

jthiessen

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Before I put the bike away for winter I noticed a new and strange sound.
It was most defined when I downshift to 2nd and decelerate. That is, in fact, the only time I hear it.
It can also be somewhat felt in my boots.
It disappears with clutch...

I have a fear that the oil may have run too low...
How can I diagnose this?

'79
 
Bump!
Sun is out. I'm getting antsy!

A friend said to check the clutch and see if the steels are discolored from heat and friction plates have some meat on them.
Does this sound logical? How would i do this...?
 
Could be jet the gear worn. Hard to tell without riding the bike or opening it up to inspect parts. Check you sump screen and filter for metal. I run magnetic drain plugs on all my bikes. It helps me keep an eye on any potential issues.
 
Well, did an oil change.
Not really what i wanted to find, but might answer some questions...
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It would appear to be a gear tooth.
 
I did a few oil flushes (cycling fresh oil through the bike) and I didn't find any shavings or additional pieces. I think that is a good thing.

A friend suggested I remove the clutch cover and check the basket to see if there is anything that doesn't look right. Does this sound right?
 
Gear fragment. Have you been shifting without using the clutch? It looks like a clean break, replace it and be good. Id think foreign matter would do more damage than a just gear tooth. The gear could be cracked now, a grenade waiting to happen. 70s Sportsters had a similar problem with 2nd gear shattering which usually results in the case splitting wide open.
 
You need to split the cases. I would inspect all internal parts. You might be better of finding a replacement motor. 77-80 xs400 will fit. The 81-82 sohc had different lower rear mounting holes. You would need to make some mods to make it fit.
 
You might be better of finding a replacement motor.

Yikes. I'm at a point where I need this project to be over... If I can get this fixed I'll either ride it, or sell it running, otherwise sell it as a parts bike...

To split he cases, I have to take it out of frame and basically follow this? Without going up to the cylinders, correct?
 
Remove the foot pegs and foot controls. Removed gas tank and coils. Removed H-pipe and carbs. Disconnect the 2 connectors coming from the engine. Once you removed the engine mounts and mount bolts, you should be able to pull the engine out of the left side with relative ease. I sit on the bike and grab the bottom of the engine and walk it out of the frame. Takes about an hour to remove. Youll want to drain the oil first obviously.

Splitting the case is just as your link describes. Dont touch the rotating assembly, dont remove the connecting rods. You should be able to pull the bottom half right off using a gentle flat-head screwdriver and a rubber mallet, a block of wood would work probably.

This could be done in a day or two if you have all the parts you need already. Assembly will be much easier and faster.
 
It would be a good time to replace the oil seals. They are supposed to only be installed when the case halves are joined together. You can find an oil seal kit here: https://www.ebay.com/itm/Yamaha-XS4...778690?hash=item548216b382:g:fm4AAMXQQJBQ4zg3

I would pull the clutch pushrod out and clean it and remove any burrs you feel. This will prevent the new seal from tearing. I use normal sandpaper or emery cloth. The rod should be checked for straightness also. Yamabond is the stuff to use for sealing the case. I use mineral spirits for cleaning and then a final clean with denatured alcohol on gasket surfaces.

Obviously you can skip out on most of that, reuse and take the risk of having to take it all apart again. A gasket kit and oil seal kit arent that cheap and youll only need some of whats provided. Its good to have a stock of parts on hand especially the "high traffic" gaskets like the timing unit cover or oil filter seals and side cover for the timing marks.
 
It would be a good time to replace the oil seals...

I would pull the clutch pushrod out and clean it and remove any burrs you feel.

A gasket kit and oil seal kit arent that cheap and youll only need some of whats provided.

I already have a gasket kit, and I replace many of the seals just externally. I was going to check the clutch wear, thats kinda the piece I thought might need maintenance. How often do the clutches need to be maintained or refreshed?

I was thumbing through the manual. Are there any special tools I will need? One tool that stood out was a Sprocket Puller or Extractor?
 
Clutch doesnt need maintenance, only cable adjustment.

Clutch cables wear out and can stick and cause a hard pull. They stretch out and you might run out of adjustment eventually. A new cable makes a huge difference. If you still slip after adjustment, youre either not doing the adjustment the right way or the clutch is in fact worn out.

The clutch springs can be measured for length and the plates checked for thickness. Unless you are slipping, I wouldnt bother. Many problems come from improper cable adjustment.
 
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