'79 XS400F - bent valve(s)?

[mixelpix]

Anyone know where I can get a decent and affordable set of valve spring compressors?

Recently triple cleaned, balanced & synched the carbs after notcing some backfire while decellerating and what seemed to be a lean condition in the mix. Did the cleaning for good measure - to set a baseline for the fuel delivery. It's been a while since i've set the pilot screws properly and have been futzing regularly with the throttle adjust screw and balancing screw to ear and eyeball things into place.

First I thought the backfiring and stumbling idle was the timing. The gasket between the air boot and cylinder head had blown apart from carb farts... Timing checkd out fine (statically - gonna set the advance dynamically tonight). Then I thought it must be the valve clearances. While adjusting the clearances (which were all within spec and pretty even w/one another) I found a sticky spot in the rotation of the crank. I am now suspecting a bent valve.

I have heard that top end overheating is fairly common with these motors and am wondering how likely it might be that the cylinder head is warped instead of, or, in addition to the valve(s)? I do have a replacement set of valves, so I guess it would be easy enough to evaluate the head (also have a couple replacement heads... don't ask!)

I've never replaced valves before, just wondering what kind of fun I can expect? While I am taking off the head I figure it would be a good time to decoke? Any other things I should do while I am down in there? Also planning on attempting to fix the slipping sprag clutch on the starter - when it engages though the bike does fire right up.

And it no longer dies while idling at stop lights...

Gotta love the colortune plugs and the carbtune tool!

Thanks!
-Patrick Kennedy

[Pat Kelly]

Easiest way to remove valve spring keepers is to put a socket (14mm or so) on top of the spring and smack it with a hammer. If the head is off I put a wadded-up rag under the valves (in the combustion chamber area) to support them. The quick compression of the spring allows the keepers to fall out. This can be hazardous but I've never been hurt doing this (over 30 years).

My cheap way to reinstall the keepers takes 2 people (though I've done it alone before). Support the valves like when removing them. Using my body weight and a brake keeper tool (anything round and open so you can reach inside it) I pressed down on the valve spring and install the keepers. Sometimes they will fall into place, sometimes a helper can hold them in place as you SLOWLY release pressure on the spring. Make sure both keepers seat into the groove.
I've done this on bikes and cars. A valve spring compressor is easier but this way is possible, and cheap.

[mixelpix]

aaarg!

just did a prelim dynamic strobe test of the timing and the static and dynamic don't add up. Maybe there is more at work. . . The idle seemed to be extra advanced and the advance a little retarded. Hmm...

Anyone recall which way turning the timing plate - clock or counter-clockwise - retards/advances the timing? Easy enough to test, but I would rather avoid monkeying around too much on it.

Thanks!!

[John]

Generally, turning it against the direction of rotation will advance it.

[mixelpix]

aren't the archives awesome?

<http://www.xs11.com/forum/showthread...=&threadid=148>

Thanks for the tip on timing advance retard with the contact plate. The alternator spins counter clockwise on the 400 so I think you are right.
-pdk

[xs1100yam]

Hi,

Before to remove head, did you check compression ? it's sometime a good indication...

While the head is off, it's a good idea to :
- decoke
- lap valves
- check valves guides
- replace the 4 valves gaskets
- check head / gasket surface.

the special tool (valve spring compressor) is very usefull to work alone, but a bit more expensive

Depending of milage, check and replace if necessary the cam chain, check pistons and rings. then you're quiet for years !... when head is off, it's not difficult to remove cylinder

I did it on my XS 250 and 360 (engine is quite similar to 400)

Have a good WE

Patrick

[mixelpix]

So Much To Do...

Originally posted by xs1100yam Before removing the head, did you check compression? it's sometime a good indication... While the head is off, it's a good idea to decoke, lap valves, check valves guides, replace the 4 valves gaskets, check head / gasket surface. Depending on mileage, check and replace if necessary the cam chain, check pistons and rings.

Hi, thanks for the info. Just curious about replacing the rings. What all is implied by the different ring standards?
These are currently available on eBay:
<http://cgi.ebay.com/ebaymotors/ws/eB...MakeTrack=true>
But I dunno what "This set is a 1st over or 0.25" means. I assume that these wouldn't work with standard stock pistons? Are each of the size increases for the larger pistons you would use after reboring? I presume there's no way to tell except to measure?

Otherwise the compression was 150psi in both cylinders last I checked, w/& w/o oil, so I think the rings and valves are okay. Any idea how to do a leak down test, or if it would help in this case? Bike is close to 25k, hasn't been too horribly abused...

Recently replaced valve cover gaskets (you mean the ones over the valve adjusts, no?) as well as a new cam chain tensioner. Maybe a good time to replace the timing chain while I am in there... I do have four replacement valves, and I think one of them is just ever so slightly kinked - prolly happened sometime around when I disintegrated the cam chain tensioner - has been running a little rougher since then. Got the soft bits out, have triple cleaned and timed and run a lot of rotella through the block. Hopefully this is it. I love this lil' gal, but am sick of fine tuning her - hell, you could eat off the crankcase cover or bottom I've gone over the thing so many times! We'll see how she lookes whe I get the head off..
Thanks!
-Patrick

[John]

Pat, I too bought a set of .025 oversize rings. They will fit the stock pistons I believe. You will probably need to have the cylinders bored to accept the oversize ring. It seems that is all that is available for these things. I have a 78 E engine that I may freshen up ...just in case. I have the ring, main bearings, and I'm looking on Ebay for the con rod bearings. You really wanted that belt buckle, huh?

[xs1100yam]

Hi,

Bike is close to 25k, hasn't been too horribly abused...

the compression was 150psi in both cylinders last I checked, w/& w/o oil, so I think the rings and valves are okay.

Well, you have 95 % chances the rings are OK.

Anyway, you can't use oversized rings with standard stock pistons ! A set of pistons, rings, cylinder shuould perfectly match !!!
If the cylinder walls show vertical scratches or excessive wear, then you must rebore cylinder and use 1st oversize pistons and rings.
Standard cylinder and pistons are available in two sizes, having the mark A or B on. when replacing cylinder or piston, it is necessary to replace with new ones having identical mark.

"A" piston size (in mm)is: 69 - 0.020 or less, 69 - 0.031 or more.
"B" piston size is: 69 - 0.030 or less, 69 - 0.040 or more.

"A" cylinder size is: 69 + 0.020 or less, 69 + 0.011 or more.
"B" cylinder size is: 69 + 0.010 or less, 69 + 0.000 or more.

1st oversize piston is 69.25 mm
2nd oversize is 69.50 mm
3rd oversize is 69.75 mm.
4th oversize is 70 mm.
clearance between piston and cylinder should be 0.030 to 0.050 mm.

You need a micrometer to measure the outside diameter of the piston skirt.
Measurement should be made 6mm above the bottom edge of the piston by placing the micrometer in parallel to, and at right angle to the piston pin.

Easy to check if you have standard or oversized rings: the oversize top and middle ring sizes are stamped on top of the ring (if genuine Yamaha ).
To measure a ring: push this ring into the bore (with the help of an inverted piston to make sure it is not cocked) and check gap clearance between the ring ends.
Top and 2nd rings gap is 0.2 to 0.4 mm. limit is 0.7 then rings should be replaced.
the 2 oil control are 0.2 to 0.9 mm ( spacer can't be measured...)
However, when it's not possible to found the right rings, it's possible to get oversized ones and grid the rings ends with a Dremel to get the right gap. ...but it is a delicate operation that need great care

valve cover gaskets (you mean the ones over the valve adjusts, no?)

NO ! (I'm sorry: I used a wrong word cause in french, we use same word for both "gasket" and "seal")
I was talking about "valve stem seal " .
This seal slip down over the valve stem to prevent excessive amount of oil from passing down stem and into the combustion chamber (blue smoke at exhaust ).
As they are 20 or 25 years old, suffer of combustion chamber heat and are "peanuts priced", it a good idea to replace them
More: when you pull the valve out, the stem tip or retainer lock groove edges will probably damage the seal rubber lips

Maybe a good time to replace the timing chain while I am in there...

YESSSSS I don't want you to replace ALL parts, but the wearing parts ! It's to bad when you're forced to re open an engine 2 weeks later, getting a new problem you could avoid ! then you'll have regrets

All those infos thanks to XS 250/400 Yamaha service manual

Have a good WE

Patrick