I've recently purchased a 05 Yamaha Majesty 400. I have no history on the maintenance of this machine and she has 40k miles exactly on the clock! I stripped the bike of all it's plastic for a full inspection and maintenance. Well I have everything done except the oil change and valve lash adjustment, I obviously held off on the oil change since I was going to open the engine. I've been all over the web and on this forum and have not found one post, video or picture of anybody doing this. I did however find many people discussing taking them into the dealer, trading or selling them off and down-rite being scared of purchasing on of these machines used or advising people to stay away do to "it's due for a valve lash adjustment". Nobody has really mentioned exact cost at the dealer but has stated the dealer said "it's a big expensive job", and "the engine has to come out' etc, etc, etc.
Well I will tell you it's not very hard at all, in fact I had the lash measured in about 15 min and had the cams out only 20 min after that, a little math on what shims I need and all that under an hour.
I will state I'm not going to show you how to remove the plastic and I'm showing this step by step presuming you already have the plastic off. Valve lash can be checked through the access cover but adjustment will require removing the trunk (and what's necessary to remove that) and either way you need t have the belt cover off to access the nut on the crank.
This may take a few days to post, so bare with me
Let's get started.....
NOTE: if you just want to check lash it can be checked through the access door in the storage. For adjustment you WILL have to remove the rear body plastic.
The storage box needs to be removed as well as any parts to get said storage box out. The factory manual lists in order of removal and shows where the fasteners are located. Keep your hardware in order for each part, I find this is best done with paper cups. Remove a part and set the cup with the hardware together and so on.
Remove belt cover and filter etc. to access the front variator nut. This is needed so you can turn the engine over by hand.
Remove spark plug wire, spark plug and cylinder head cover. CAUTION: I'd advise washing cylinder head cover area and spark plug hole with brake cleaner and compressed etc. before removing the spark plug or any cover bolts. This will prevent debris from entering engine upon removal.
My engine was absolutely filthy under the plastic. I assume previous owner did a lot of rain riding so I opted to wash entire engine.
This is what you're going to see after the cover is off, not to scary huh? Be cautious of any RTV sealant that may have been used and remove it so it doesn't get into the engine. It's not factory practice to use sealant on this gasket and I don't recommend it.
Remove timing plug. Note: you will need to remove dipstick first.
Now you need to put the motor at TDC (top dead center) By rotating the engine counter-clockwise from the variator nut. This is not hard but since the timing window is on one side of the bike and the nuts on the other, use two people if needed.
This is what you're looking for and you need to verify that you're TDC on compression stroke and not exhaust. This is done by visually looking at the camshaft lobes, they should be facing AWAY from each other and NOT at each other. I neglected to take a photo detailing that and if you need help explaining this just ask.
Now we're going to check the lash.....
You're going to need a feeler gauge set and these come in many different ways and size range and can be purchased just about anywhere. I like the angled end ones and they are ideal for this job. I recommend using metric scale (easier to do math IMO) but that's up to you and almost all are marked both.
The need to be ABSOLUTELY clean! and you need to keep them clean the entire time! Use a lint free cloth to wipe the one you're using before you use it.
No RUSTY or DAMAGED in any way.
Now let's do some measuring!!!
Let's look at the book.....
Starting with the intake valve (top cam) the book says 0.15~0.20 mm cold (I forgot to mention the engine needs to be cold) so find the feeler gauge that says 0.15 mm
or the closest size to 0.15 mm. This is where things get weird. Since standard and metric don't exactly match up you will find that feeler gauge marked both will favor one over the other such as mine in the picture favoring standard so the closest I can get is 0.127 mm, we will round this to 0.13 and if you had a strictly metric set you would find 0.15 exactly.
NOTE: I'm showing the exhaust cam in the picture, procedure is the same for both cams.
Now insert the gauge between the cam and the lifter. It's hard to teach the "feel" but your looking to find the gauge that fits snug without having to force it between. Check several times and to both intake valves. If the first gauge is too thick (won't fit) go to the next size thinner and if the gauge is too thin (loose) go to the next thicker etc. until you find the gauge that fits perfectly. Record this number for each intake valve like shown in the next photo. This will be your valve lash.
Repeat the process to the exhaust valves. The book says 0.25~0.30 mm, record these numbers too.
Pay no attention to my numbers shown. I wrote the standard number here for whatever reason.
My measurements came out to:
Intake - 0.13
Exhaust - 0.23
So my intake valves are .02 too tight
and my exhaust is .03 too tight
So this means I need to ADJUST valve lash.
You may be asking yourself why are the valves too tight? shouldn't they get loose at the engine wears? Yes and no, lol the valve over time wear into their seat (valve seat) and this causes the stem (valve stem) to get closer to the cam (lifter and shim between the two) and making valve lash tighter. Does this matter? yep! sure does. As the engine heats up metal parts expand from heat (some more than others dependent on material etc.) and the valves get quite hot especially the exhaust valve. If your valve lash gets too tight the valve can actually stay open a bit and cause problems such as loss of running compression and burnt seats causing loss of compression valve float is increased and of course poor performance and likewise if if your valve lash is too loose, this increases wear to valve stem tip, shim, lifter and camshaft and of course valve "ticking" noise.
You really don't want to see your valve lash increase as that usually indicates lifter and/ or camshaft wear and you may have bigger problems.
In short terms, you want to be a touch too loose than a touch too tight.
Well if your valve lash is in range then you're good to go, reverse the disassembly and get riding. Replace cylinder head cover gasket as needed. Check the half moons too. If your head area was not all oily indicating gasket was leaking you can reuse it as long as the rubber is still soft. The gasket is about 13.00 online, no biggy.
If your valve lash is out of range, temporarily install the cylinder head cover, spark plug, timing plug and dipstick so when you're removing the plastic for adjustment, debris don't get into engine.
Next we need to take the cams shafts out and remove the lifter buckets to obtain current shim number so we can order some parts!
I'll give you sometime to get the plastic's off...............