Somebody somewhere said "if it smokes at start up, it's the valve seals and if smokes while riding it's rings". Well, I'm going to show you how to fix both.
You will need to buy
Valve seals (2)
Rings (optionally piston)
"lock washer" (banana shaped metal piece behind the cam sprocket)
Optional valve guides
Beg borrow or steal:
Basic metric hand tools
Valve spring compressor
long 10X1.5 mm bolt
First of all, the pictorial is on a TT-R225, this same basic motor is in the TT series, the TT-R series, XT series and TW below 250 cc.
It was also used on the YFM known as the Moto-4 and YTM code name shopping cart missing a wheel filled with bowling balls. There's probably others that I don't know about.
Your experience may be slightly different. Also, check your manual or ask someone for torque specs on your specific application.
First, remove the body panels, everything but the fenders, you'll find that the side panels don't need to come off, but just get in the way. Aside from the strange gas tank supports, this is pretty straight forward. I mention the lower tank brace because you may not know to look for it.
Second, wash the bike. I realize in my haste, I did not which when time came to reassemble meant I had to be extra careful. It won't hurt to give the motor a good hosing off after you've removed the body.
Your bike should look like this
Remove the exhaust header (muffler can stay on), carb and spark plug.
Remove the cam chain cover, both valve adjustment covers on the head and on bottom end, the flywheel nut cover, the timing mark cover.
Line the motor up at TDC on the compression stroke. There is a big line or arrow that will point to a mark on the head. It's very hard to see in this photo, so I've enhanced it. If you should happen to move the motor during the next few steps, you'll want to recheck the cam position.
Using a 17 mm socket, remove the cam nut. It takes a lot of force to get it off. You'll need to lock the motor in place by using another 17 mm socket on the flywheel nut.
Then, you can remove the cam sprocket.
I highly suggest putting a zip-tie through the chain this will make it much easier to fish out when you drop it through the cam chain slot.
Next, you'll need to remove the cam keeper parts. These are the black pieces held on by two bolts, only one is visible in the photo. You'll need to flatten the one piece Yamaha calls a "lock washer" using a hammer and flat head screw driver so you can undo the bolts.
Do not drop anything! This is a tight spot, it may not be a bad idea to stuff a rag in the cam chain slot to prevent dropping something.
Finally, the cam needs to come out. If your bike is like my bike, it won't just pull out and you'll wonder why on earth Yamaha uses the cam keeper deal in the first place. I made a slide-hammer out of a 10 mm engine mount bolt a few washers and a large socket.
But before you do, check again that the cam is at it's proper position. Both intake and exhaust valves should show a little bit of clearance, if either is tight, something is wrong. If something is wrong, do not remove the cam, you will damage something.
If you're following along using the service manual, I ask myself, why on earth are you reading this? But thanks for read. Yamaha wants you to remove the rocker arms. I mention this because if you can't get the cam to TDC for what ever reason (perhaps a stuck/bent valve?) remove the rocker arms instead of slide-hammering the cam out.
Once this is out, remove all the bolts connecting the head to the cylinder or frame and then remove the head. Two of the frame bolts are held in with lock-tight although I don't know why.
Remove the cam chain tensioner.
Now return the piston to BDC, inspect the cylinder and measure it. Mine had shiny parts and parts that still had hone marks. Upon removing the cylinder there was lots of evidence of blow-by on the piston. I decided to replace the piston. No one offers a high-compression piston so I found my own.
I'm using a Wiseco 4312M07050 0.50 mm over YFM 225 piston 10.25:1 compression ratio an improvement over the stock 9.5:1.
Regardless of which piston you use, if you need to bore the cylinder, I recommend discussing a tighter than spec piston to cylinder clearance than recommended by Wiseco. Wiseco spec says 0.002" (two thousandths or twenty ten-thousandths). However, Yamaha spec is between 0.0014" and 0.0022" (fourteen to twenty-two ten-thousandths). I found this out too late and will be stuck with the twenty ten-thousandths unless I move to a larger bore.
I encourage you to ask a machinist before you give him a 0.0014" spec. He should know a lot more about metallurgy than I do.
While the machine shop is boring/honing your cylinder to the piston, you can start on the valve seals.
Using a valve spring compressor I borrowed from Advance Auto Parts I had to add a 1/4" or so thick washer over the valve retainer. Once compressed, remove the valve keepers using a magnetic screw driver. Be very careful not to lose these or you'll spend 10 minutes crawling on the shop floor looking for it like I did.
Release the valve compressor.
Remove the spring which exposes the oil seal. The outer part is brass or silver colored. This comes off easily with needle nose pliers. The valve will fall out so hold on to it from the underside.
As you can see, there's a stark difference between my old one and the new one.
It got worse once you took it out of it's retainer, fell apart in three pieces.
Add some molybdenum grease and push it over the valve stem till it locks in place.
Put the springs back on with the retainer, then using the compressor and washer compress the spring and put the keepers back in place. It may take a few attempts to get it right. It should look exactly like the other side.
Release the compressor, set the head on the work bench and tap lightly on the valve stem with a drift and hammer to ensure it's seated.
Then repeat the process on the other side.
Re-install the cam lobe side down, you'll need to hold the valve rockers down against the valve stems while aligning it. Turn the guide so the detent is roughly between two and three O-clock. Then you'll need to tap it back in place using a hammer and drift.
Then reinstall the cam keeper and what Yamaha calls a lock-washer, the banana shaped dealie under the bolts. Don't be surprised if you need to use the drift to re-align the cam guide.
Drink a beer, you've earned it, and you're not going anywhere for a while unless you paid your machinist a lot of dough to get your cylinder done in an hour.
Once you've received your cylinder from the machine shop, scrape the old base gasket off the bottom. I had to soak mine in parts cleaner, scrape what I could get off and then soak it again. If you soak it, you must remove any rubber or non-metal components as parts cleaner will damage them. It took many soak-scrape cycles to get it clean.
If you're replacing the piston, remove one of the circlips on the piston using needle nose pliers. Then push the piston pin out the side you removed the circlip. The piston is now free. Install one circlip on the new piston. Install rings and then install the piston, piston pin and circlip.
If you're reusing the piston, install new rings after cleaning the old piston's ring grooves.
Scrape any remaining carbon off the head and/or piston.
Add a few drops of oil to the rings.
Install the new base gasket.
Slide the cylinder over the piston.
Screw the two allen head bolts with anti-sieze into the motor but don't tighten them yet.
Fish the cam chain out of the cam chain slot.
Install the new head gasket.
Then feed the cam chain through the head and align the head on the dowels.
Install the four head bolts and the two allen head bolts with anti-sieze. The head bolts should be torqued to 16 ft-lbs in a diagonal manner and the allen heads to 7 ft-lbs. Don't forget the two on the base.
Now we can install the cam chain.
Bring the piston to TDC again using the flywheel marks through the timing hole.
Cut off the zip-tie.
Check again that the cam is still in TDC position, the guide pin will be around 5 O'clock, you can put the sprocket on to check 100%.
Once aligned, install the cam sprocket on the chain and then on the cam.
Install the cam chain tensioner. You'll need to return the plunger all the way back by turning the screw (under a 10 mm bolt) all the way clock-wise. Then hold it until you've screwed it down. The long allen head bolts hold this in. The short ones are for the valve covers.
Torque the bolt to 43 ft-lbs.
This is the detailed instructions for the "hard part", it's all down hill from here.
Edited by Smacaroni, 12 November 2010 - 04:41 AM.