xs400 help!

[Richardb]

Hi
I have an xs400, 1980 17k miles, (the one on this forum that previously had the blue smoke problem - thankfully fixed). Unfortunately, the starter went out, and I removed it in oreder to see if I could get it working again. It turned out to be a grounding issue. The big problem came when i replaced the starter and forgot to fish out the gear that turns the flywheel via a chain (REALLY stupid mistake, I don't need reminding!). On my way home, the gear became lodged in the flywheel locking up the entire engine, including the rear wheel (travelling about 35mph).

I pulled the cover off of the alternator and flywheel and managed to fish out and re-attach the gear and chain. Amazingly, after an oil change, the bike fired right up. It runs andshifts through all of the gears without any obvious issue, but I now have a rattle/knocking sound from what sounds like the right piston.

I have pulled the head cover and head. The cam chain/camshaft look ok, and there are no marks on the cylinders to indicate that a piston ring went bad. I pulled the valves to inspect them but don't really have any way to tell if they are bent. Is there a trick for this, or do I need a special machine?

Transmission and crankshaft seem ok, since the engine turns with almost no resistance now that there is nothing to compress. I didn't think to do a compression test before I pulled the head off, but when I turned the engine (with the valves closed, no rocker arms attached) I could hear the air leaking out. Should I hear that regardless of valve condition? Also, when I pulled the head off, I noticed that three of the valves were covered with black sediment, and one (exhaust on the cylinder that is suspect) was covered with white sediment. All in all, the compression chambers are VERY dirty, but I don't think that has anything to do woth the problem since it would have been that way before my little starter mishap.

Sorry for the essay, and thank you if you actually read this far! Any help at all would be appreciated!
Rich

[79XS11F]

With the valves in place and the cams out, turn the head over on the bench and make it LEVEL. Fill the combustion chambers to the top of the heads surface with alcohol. If the valves are fully seated and sealing as they should, the level of alcohol in the combustion chambers will not fall. If it does the valves are leaking but does not mean they are bent. They just may need a lapping but you can check for bent once their out for the lapping if a problem is discovered with the seal.
Rob

[petejw]

Just as Rob said, but i use petrol,
look at the valves in the combustion chamber
for seepage or leaks.

Do you have a workshop manual?
I found 1 i had lying around for the xs250/400.

[Richardb]

The valves are currently out of the bike, so I'll have to put them back in when I have time this weekend to do the leak test. Could a leak have been caused by the sudden stoppage of the engine? Is that likely to be the cause of the rattle?

I do have a shop manual, but it's in pdf form on the computer and not a very good one. Have ordered a haynes manual and desperately awaiting it's arrival!

Thanks for the input!
Rich

[soccer4m]

It could be the chain

Hey Richard,,,,Me and my son have had the same xs400,,,and the cause of the rattle could be that starter chain. It is loose and probably got stretched during the mishap. Unfortuneately, there is no way to tighten unless you take out a link and it could be too tight then. Anyway, I have had the rattle and it really doesnt cause any damage, its just annoying. Maybe take off the cover and check to see how much play in the chain there is, if its hitting anything. If its really stretched pop off a link. Good luck,,,,,Mike in S.Diego

[Richardb]

Ok, so here's the deal. Already had the valves out to check them but couldn't detect any kind of defect in any one in particular. When I put them back in, I filled the chambers with isopropyl alcohol (upside down, in the head) and found some leakage from both exhaust valves, but vwery little - after 25min, there was moisture detectable in the exhaust chambers (underneath the upturned valves) but not a signifiacant drop in the isopropyl level. Is this possibly the issue or is leakage of this kind negligible?

Re the starter chain, it seemed to be tight when I re-attached it, and also it was loose (not attached to anything) when the <mishap> occurred. I'm thinking it would have been bent or crushed if anything, but it seemed to be fine.

Rich

[soccer4m]

put it back together

hEY Richard,,,,,sounds like the bike should be ok,,,,put it all back together and be very careful to set the valve clearances on each side, exhaust and intake. Follow the manual. Take your time and set them a little snug,,,they will loosen up with heat. Clean the plugs or put in new ones, use fresh oil, hope you have an inline fuel filter, these carbs are very picky on having clean fuel. THE locking up shouldnt affect the pistons or connected parts. YOu can turn over the starter with the cover off and listen for any thing wierd from the chain or sprocket. Check for missing, broken teeth on the gears, sprocket. Also, make sure your wheel drive chain is adjusted a little loose, too tight and it will cause a lot of problems, an inch of play when its on the ground is good, do not adjust on the centerstand or it will be a problem when riding. Also, synch your carbs, easy to do with a vac gauge, it will really smooth out the engine. Good luck, Mike in S.Diego

[rpgoerlich]

Since you already have the valves out of the head, Why not get some lapping compound and the tool and lap them in. You'll at least get them to seat good if they will. If not you should see where the problem is on the back side of the valve, on or around the seat.

That stretched starter chain is very common. Plenty of noise from it.

Have you checked that cam tensioner ?

[Richardb]

Hi guys,
I know its been a while, took a little break from the bike and then put it all back together. I managed to get it going and it seems to run ok, but it starts a little harder than before. I think the ignition timing isn't quite right... also, I seem to be getting a whiny\possibly scraping noisefrom the top end. Sounds like it could be the rings, since I rehoned the cylinders while I had it apart. Other than that, it seems ok. Just gonna run it through a few tanks of gas.
, I figure it will either settle down or break down eventually! Thanks for all your help!

[jwhughes3]

why does adjusting on centerstand make a difference?

Also, make sure your wheel drive chain is adjusted a little loose, too tight and it will cause a lot of problems, an inch of play when its on the ground is good, do not adjust on the centerstand or it will be a problem when riding.

As long as there is play, I don't understand why not to do it on the stand when making the adjustment is much easier. I thought that was one reason for having the CS in the first place!

John