A few questions about top end rebuild


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Hello there, first post.
I just picked up a 79 Yamaha XS 400. It had a blown head gasket, so I've spent the past few days tearing everything down. I changed the gasket and started to put her back together, and realized i was missing a washer for one of the acorn nuts. If it's fallen into where the cam chain goes, is there anyway to check from the bottom of the motor so I don't have to pull the whole motor apart again?

Also I'm kind of confused with the cam chain tensioner. I reinstalled it and the chain seems to be pretty tight, I can't really even wiggle it. I'm ready to throw the valve cover back on, just hope I did everything right =/ My first time ever tearing any kind of engine apart.


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I have not done that type of rebuild yet, However, I think you might have gotten lucky. If I remember anatomy right, Straight down from that hole, is the big oil screen behind the 6 bolt panel, underneath the engine. meaning a new gasket, New Oil/recycle oil if you just put it in there.

good luck, Lucky
You can get a long magnetic pick-up from most auto parts stores. It helps to know for certain something is in there before you go fishing.

You can check one of the other washers to see if they are magnetic.
Just rebuilding my motor. Sorry no good news. Washers under acorn nuts are copper. Magnet will not work. At the bottom of the timing chain tunnel is the crankshaft. There is a windage tray under the crank so the washer will not drop to the bottom. The oil should keep it (hopfully) from moving to far. Cross your fingers get a flashlight and a long pice of wire and go hunting.
Hope it works out.
One of those long, thin pick-up tools might work; often they are used in plumbing, but I also see them at auto parts stores. It isn't going to be easy getting that thing out!
Are you sure you dropped it in the engine or are you just missing it? I remember that I had a hard time getting mine off of the head having been torqued in place for all those years. Have a second look. maybe it is still on the head.
I found it. No worries.. Only thing now is I don't I put the cam back in right or something.. I tried putting the cam cover back on and I can't manually crank it once it's tightened down.. My dumbass also snapped one of the bolts on the timing chain tensioner.. doh
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For the chain tensioner, you need to reset the ratchet mechanism as you seat it. I didn't do this the first time and ended up needing new bolts.
Thanks, I got it. Now it just seems like the cam cover won't fit on top. The cam cant move, it's like i did something wrong. If I can I'll take a picture.
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When I bolted it down it would get stuck at a certain point. So I took off the bolts and just laid the cover on there and rotated it until it popped up. Does it look like I did anything wrong? Is there anything I should be doing? Thanks.


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Are you tightening the bolts gradually and in a diagonal/star-like pattern (just like lug nuts on a car)?

It is normal for the cam cover to be cocked up on one side like the first photo when it is laid on. The lobes on the cam push on the rocker arms which push on the valves. As the cover is tightened, the valves become depressed; there will always be some resistance during the process. It should not be difficult, however, or require any strength.

How are you turning over the engine?

Are the points and advance unit on for some reason at this point? I remember having them off until the cam cover was installed. The same goes for the cam oil seal. I am a little concerned it could be pinched by the cover as it is tightened, but this may not happen.

Also, just to double-check. You did set the cam chain timing correctly, right?

Other things; the cam might not be seated properly.

Did you lube the cam and bearings and fill the troughs with oil?
Well, my cousin had one of his mechanic buddies stop over, and it turns out I had cam guide and chain tensioner blades in backwards :banghead: But still when I put the cam cover back on she won't turn over. Valves are moving, and bike ran good before head gasket went loose, so don't know if it needs any adjustments. Oh well.. Gonna take another crack at it tomorrow.
I did not set the timing correctly at first, but I had a mechanic help me line it up.
When I tightened up the bolts I did it evenly in a diagonal pattern.. umm..
I tried turning it over by pushing the kick start with my hand, and by the bolt.
And the oil seal is on the left side that sits in that little groove snug? It's in place.
We loosened the right rear lobe? and then the motor was able to turn over more freely but we back it off a whole turn so there was a lot of play in the rocker arms..
Page 46 shows how to set the cam chain timing.

The blade orientation can be seen clearly here:

The only other thing you can do wrong is lay the cam in improperly.

It is normal for it to be difficult to turn the engine over by hand with the kick start; use the bolt on the stator side under the round cover (17mm).

You shouldn't need to adjust valve clearance for the engine to turn over; even if they're way off the engine should feel about the same when turning it over.

Make sure the transmission is in neutral (lol).
Hmm.. Bike is in neutral, even turning the 17mm bolt though it wouldn't spin. Laid the cam in the right way, found timing marks, got everything lined up, and blades are in correctly, there's no play in the chain.. so I really don't know what it could be. I'm gonna check it out tomorrow in the day light and hopefully be able to put it back together..