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how to rebuild your topend
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Posted by: Kickstarts_Suck

Once you've got all your new parts in hand and have taken a deep breath, it's time to roll up your sleeves and get started. The very first thing to do is spend about 5 bucks at the local quarter-car-wash and clean the entire machine as thoroughly as possible with emphasis on the motor area.

Get up underneath the tank, air box, and carburetor. The last thing you want is dirt falling into your motor as you painstakingly attempt to reassemble it with surgical cleanliness. Pull your machine in the middle of garage and clear a space on your workbench for all your take-off parts.

Either borrow a cup-cake pan from the kitchen (you might want to wipe it out and sneak it back in when you're done) or buy a couple at the supermarket. As you pull all those screws, nuts, etc off the motor it's a great help to keep them organized, collected, and in order of disassembly. You can even take a black magic marker and label each cup as you go.

As you reassemble the engine it's easy to see what's left so as not to forget any critical parts. Then start pulling pieces off in an effort to expose the entire cylinder head and jug area. If possible, reinstall the screws temporarily back into where they came from- it makes finding the right fasteners that much easier (and you won't need as many cup cake pans).

Before the engine is actually opened up you can even hit it with a garden hose and compressed air to get as much grime off the upper frame and cylinder head. Then you can proceed to pull the exhaust and carburetor (if you're putting a piston in).

Posted by: Kickstarts_Suck

After you've got the tank off and everything cleaned up, the next step will be to pull the top half of the cylinder head off. Some engines like the 'X will have an oil supply line that first needs to be removed. Don't lose the copper washers that go on the banjo bolt. Once the exhaust and carb are removed, disconnect any other ancillary connections to the engine. Remove the cylinder head cover exposing the valvetrain. Remove the cap that covers the flywheel bolt and the cap in the crankcase cover that hides the flywheel timing marks. Turn the engine to top dead center (TDC, or when the piston is at the very top of its travel) on its compression stroke. If the spark plug is out, you can feel this by holding a finger over the plug hole and feeling the pressure build and slowly drop. You'll also notice from the cam that both intake and exhaust valves are completely closed. More precisely, there should be a mark on the flywheel such as 'TDC' or 'T' that lines up with a mark in the inspection hole of the case (not 'F', which indicates full ignition advance). Make note of the position of the cam sprocket and verify its position with respect to the shop manual- likely there'll be alignment marks that'll line up with some feature on the head. This is exactly the orientation the motor needs to be in during reassembly. Remove the cam chain tensioner. It'll make reinstallation of the chain a whole lot easier since it will offer maximum slack and workability. Now the cam and cam-chain can be removed. Use an impact wrench or hold the flywheel bolt with a breaker bar or socket wrench to remove the cam sprocket bolts. Then grab a piece of string or wire and attach it the cam chain. This will help to keep the chain from dropping down into the crankcase. Sounds like a cheesy idea until the damn chain falls into that dark crankcase abyss. If all you're doing is a cam install, jump on to ...

Crack each head bolt loose one-by-one, then proceed to remove each bolt. It's even good practice to reverse the order of the installation torque sequence. Make sure every bolt has been removed, then using a soft blow hammer give the head a nice pop on any solid surface but a cooling fin to break the seal. Pull the cylinder head and cylinder off. Avoid using a screwdriver to pry the head off- it may leave marks on the sealing surfaces that might no seal properly with a new gasket. If you plan on reusing the piston (just re-ringing the piston) be careful to not let the piston swing against the case and get damaged as the cylinder is pulled up and removed. You should now be staring at your piston in all its naked glory. The next trick is to remove the wrist pin clips, wrist pin, and piston. Before you start, it's a good idea to seal the crankcase with a rag to avoid letting the clips accidentally fall into the case during removal and installation. Use a miniature size screwdriver to pry the clip out of either side, slide the pin out, and remove the piston.

Posted by: Kickstarts_Suck

Your next step is to send your cylinder and new piston to an engine shop to have it bored to the correct size. The X's cylinder went to Wiseco in Mentor, Ohio to be fitted with an .080" oversize piston. Wiseco's pistons differ from stockers in that they are not only Bigger, but they're made from forged aluminum rather than cast aluminum which makes the pistons stronger and more durable than stock.

Posted by: Kickstarts_Suck

The kit comes with rings, pin, and clips. When you get all your parts back you'll no doubt be chomping at the bit to get it all together. The cylinder may even look all clean and ready to go. Don't be fooled by the apparent cleanliness- the cylinder is generally only lightly rinsed with solvent and needs to be thoroughly washed with soap and hot water.

Use an old T-shirt (preferably a friend's Yamaha T-shirt) to verify its cleanliness by taking a swipe down the bore- if there's any sign of gray your job's not done yet. Once it's clean, dry it quickly and apply a coat of oil with your clean T-shirt to keep it from rusting.

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Don't waste time admiring your work, you'll be horrified to see it rust before your very eyes in a matter of seconds. Next, get your piston rings out, starting with the two thin oil control rings.

Although generally not an issue, it's absolutely necessary to check the ring end gap as installed in the new bore. Install the ring into the bore about an 1/8 inch down. A handy method is to use your old piston with only the oil rings installed to squarely push the ring down the bore.

Remove the piston and then check the ring gap against the specifications provided by the documentation with a feeler gauge, which should amount to about .004" per inch of bore. P7250001.JPG (458969 bytes) In the event it's too tight you'll need to file them down to the correct clearance using either a commercially available ring grinder, or a fine hand file and vise.

It's not rocket science, but you'll need to make sure that the gap is square and burr free. Hold the file in your vise horizontally with about 1/2" sticking up and slide the ring back and forth along the vise top surface while lightly squeezing the ring against the file.

Sneak up on your desired clearance slowly so as not to over-widen the gap. Too much gap will lead to excess combustion gas blowby and is not the sort of thing you want in a performance oriented motor rebuild. Too little gap and the rings will expand as they heat up, butt ends, and when they have no place left to go, they'll score your pretty new bore.

Take the extra time to check ring end gap (the X's end gap was about .005" too tight before re-gapping). Once that's under your belt, it's time to install the rings on the piston. Be careful to follow the instructions with respect to not only which ring goes where, but which side goes up. Rather than getting all messy, it's convenient to install the rings dry and then once all the rings are in place oil all the rings at once.

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Avoid lining up all the end gaps- stagger the gaps by 120 degrees. Next, install a single wrist pin clip into the piston opposite the side you'll be installing the pin from. Make sure the opening on the clip is either at the top or bottom (6 or 12 o'clock). This will minimize the risk of the clip compressing and dislodging during the rapid accelerations of the piston.

With the T-shirt still stuffed in the crankcase, lower the piston over the rod. Push the pin through the piston and rod and install the other clip. It can be real pain in the butt to get that clip in- keep a close eye on it in case it decides to go ballistic across the garage.

Lower the cylinder onto the head bolt studs and onto the piston. Don't forget the base gasket. It'll get tricky as the rings need to be compressed in order to fit into the bore. Again, there's no magic here, just gently wiggle the cylinder while applying light pressure until the rings compress and drop into the cylinder. Sometimes a little guidance with a small screwdriver is necessary to show the ring the way.

Once you've got the cylinder reinstalled the head needs to go on next. Before you do so clean all the gasket surfaces and remove the cam chain tensioner asssembly (to allow slack in the chain). Lightly oil the head bolts and snug them up. Follow the manufacturer's torque sequence and specification and finish torquing the bolts.

Posted by: Kickstarts_Suck

For the 'X, WebCam adamantly suggests replacing the rockers with a welded and reground piece they can supply. Apparently, these rockers have a tendency of wearing out- and this situation is certainly aggravated with an aggressive cam profile. It'd be an easy enough job if the dowel pins holding the rockers shafts in would come out easily, and if you're lucky they'll slip right out with light use of pliers.

But plan on ordering a pair of them before you start the job. The Honda service manual directs you to grind a notch into the pin and drive it out from the opposite side using a chisel and hammer (yikes). A more benign method is to grip it with a pair of vise-grips and twist it out. Judicious use of heat may help (but be careful not to soften the aluminum!). With these pins removed, pull the rocker shafts out and remove the rockers.
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Before installing the new rockers, lube the shaft and rockers generously with oil, and make absolutely SURE that you've reinstalled them in the correct configuration BEFORE you drive the new pins in. We you've verified it all, push the pins home. Apply camshaft break-in lubricant to the rocker pads. Drop the cam in place and apply cam lube to the lobes as well. Reinstalling the cam sprocket and chain with the correct timing can take a bit of trial and error.

Start out with the crank at TDC and position the cam with the lobes down. Pull the chain up (with your string) and pull it over the sprocket, remove the string, then position the sprocket onto the cam. If everything is right, your alignment marks will line up when the slack is taken off the forward (drive) section of chain.

If not, drop the sprocket off the cam and jump the chain over enough teeth to correct the alignment. Once the alignment is correct, reinstall the cam chain tensioner. On the 'X this can easily be done by first retracting the tension pin with a small flat-head screwdriver.

Then, while holding the pin from re-extending, run a screw down the tapped hole and bottom it against the flat-head screw such that it holds it from unscrewing while you reinstall the tensioner. Once reinstalled, take the screw out. As a final check, give the crank two full rotations and verify that the marks line up as expected.
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Posted by: Kickstarts_Suck

Startup & Break-in- Before you let it rip, it's a good idea to give it a couple kicks with the plug wire disconnected to pump some oil back up the head and to get some gas through the carb. At least that's what I tell the guys huddled around when it doesn't "start on this first kick". Assuming everything was machined within tolerance and the assembly was done correctly, you need not worry.

As far as start-up and break-in techniques go, there's only a few tips: keep the engine speed up if installing a new cam, vary the engine speed and load as much as possible, and avoid too much heat (heavy, sustained load). Some engine builders even recommend letting it run for a short time, then letting it cool down, and then repeat - just like shampooing.

But I don't do that- I mean the running and cooling... Ride it for a while like a normal person even though the urge to crack it wide open will almost certainly be too hard to resist. But take this time to look for oil leaks and listen for odd sounds. If everything is OK after, say, 30 minutes of operation... it's time to move on to dialing it in.

Dialing it in- Carburetor jetting is absolutely critical to any major engine modification, especially ones that involve the gas exchange process of the engine such as exhaust, carburetion, and for sure- camshaft. It's conceivable, and even likely, that after installing a cam your machine may not run as well as you thought it would.

That's where jetting comes in. In a nut shell (a more detailed article is in the works), you'll need to adjust the size of the main jet of the carburetor such that at Wide Open Throttle (WOT) the engine produces the most amount of hp. This is done by starting too big (too rich) and slowly backing down a size at a time until the motor feels right and the spark plug has the proper color indicating the correct air-fuel ratio.

Posted by: fastleo

holly crap....

its not that hard!!!

Posted by: tim colston

Nice write up. Very clear and to the point.

Posted by: 250X_project

Yes, nice job. Yet the heating and cooling (expanding and contracting of metal) is very important to breaking in an engine. Also there is no point in kicking it w/o spark, it has the same effect. All the parts that move while running are then moving. Over-all it was well done.

Also I really like the cupcake pan idea. That is ideal for holding nuts and bolt etc..

You went .080? Now you have a 260X!

What cam specs did you get?

Posted by: Anpo

nice

regards, Anpo