I bought my 1988 FZR400U as a former race bike with 17000km on it (~11k miles) and I wasn’t sure about the history of it or the condition of the engine so I decided to do a valve clearance adjustment and to replace the head gasket.
I decided that while I was doing the job I would try to document it as well as I could or at least take some pictures so that others doing this for the first time like myself could reference it and have something of an idea of what to expect. That being said, you should not attempt this job without a manual for your bike, they are very helpful and only really lack in the quality of the pictures. Once again, don’t do this without a manual.
In this guide I will try to steer you around the mistakes that I made and show the easiest way to do it. Sorry if I missed pictures of anything it’s really hard taking pictures while working on the bike and my helper was only there some of the time.
Step 1: Tools
Some specialty tools you might not have but will definitely need:
• Torque Wrench (essential part of any job)
• Thickness Gauge (should be able to measure 0.001 or at least 0.002 inches)
• Micrometer (somewhat optional to measure shims)
*Note: The convention for numbering pistons and in turn valves is 1 to 4 from left to right when sitting on the bike.
*Note: This job is being performed on a 1988 Yamaha FZR400. Any references to markings or parts are referring to this motorcycle in specific and may not be the same on other models.
Step 2: Step 1: Preliminary Work
1. Upper, mid and tank fairings
4. Possibly the gas tank
5. Radiator filler with hoses and thermostat
7. Anything else obstructing access to the head
If you’re going to be pulling the head (add on a few hours) you’re going to have to remove a few additional things such as:
2. Drain Oil and Coolant
3. Oil Delivery Line
4. Right Down tube
It helps to take some pictures along the way to help you remember some things you can easily forget such as cable routing and some item’s locations.
Once you have these things removed you should have a nice clean working area with enough room to move and work around the head, and you can move on to removing the valve cover.
Step 3: Step 2: Valve Cover Removal
Once that’s done, loosen the bolts on the valve cover in a criss-crossing fashion and remove the head by working it off slowly and evenly from all sides. Then move on to measuring the clearances
Step 4: Step 3: Measurements
Next you’ll need to remove the alternator cover and turn the alternator counter-clockwise via the big nut on it until you see the “T” on it line up with the line on the crankcase. Now you’ll need to check if the cam lobes on piston 1 are facing out (away from each other) if so good. If not rotate the alternator 360 degrees.
Now with the lobes for piston 1 at TDC (Top Dead Centre) you want to measure the 4 clearances for this piston’s valves (2 intake – top ones, and 2 exhaust – lower ones). Do this by trying the minimum clearance sized feeler gauge and working from there until you find the one that just barely won’t go in, you’re clearance is one less than that. (You may need to combine two blades of the feeler gauge to get the denomination you want if it doesn’t have it)
At this point you’ll want to make a neat and organized table for all your measurements. Here is an example:
Once you have your clearances for the first piston rotate the alternator counter clockwise 180 degrees to measure #2, 360 for #4, and 540 for #3.
Acceptable Clearances (Cold engine)
Intake – (0.004~0.008 in)
Exhaust - (0.008~0.012 in)
Once you have all your numbers you’ll know how many valves are out of spec and thus need to be replaced. If they are all in spec you’re bolt her back up and you’re done, if not move on to replacing the shims.
Step 5: Step 4: Making Adjustments
You should now see the valve lifters or buckets (16 quarter sized circles). Under each of these is a shim. Using a magnet pull the lifters off. ***Make sure you don’t drop anything in the crankcase
Once the lifters are removed you will either see the shim sitting in the middle or there will be hole where this shim should be. If the shim is not there it is most likely stuck to the inside of the lifter.
Go ahead and pull all the lifters off that need to be replaced and place them on a sheet of paper along with their shims and mark them so you know where they were. Now inventory your old shims and refer to the chart to see which size shim they need to be replaced with. (If you don’t trust the writing on the shim or can’t read it, use the micrometer to measure its thickness).
Now that you know what you have and what you need, check if you can switch any of them around and then go pick some up for the rest. They are 7.48mm diameter shims so if you want to get generic ones, that’s the size you need.
Once you have them apply some moly grease or assembly oil, put them back, and cover them up with the lifters.
Step 6: Step 5: Head Gasket
The most involved part of this procedure is the cleaning. Just remove the cylinder head nuts in the order the book tells you to (they use a 6mm hex socket). You may want to remove the oil from the nut cavities so it doesn’t pour into the coolant tracts.
Now slowly work the head off (be careful as there will be up to half a cup of coolant just waiting to spew out when you do this). Make sure you remove the head evenly and have someone feed the camchain through it. Discard the old head gasket and clean off the pistons and valves (make sure you don’t lose and lifters/shims while you clean the valves- it may be best to just take them off and just reinstalling them after). You should also try to get as much of the old coolant and the oil that probably leaked into it out of the cylinder (I used a little syringe with a small piece of fuel line for this). As you can see my pistons and valves were just disgusting.
Install the new head gasket after everything is clean enough and put the head back on, once again feeding the camchain through the head. Finish by torque-ing the head the same way you removed it.
Step 7: Step 6: Putting It Back Together
Check to see that the alternator shows TDC, you can also confirm that the crank is not off by 360 degrees by making sure the wire that’s holding the camchain is in the same location as before. If it is not, rotate the crank 360 so it is.
When putting the camshafts back in make sure you put the exhaust shaft on the exhaust side and vice-versa with the intake one.
Install the camshafts and put the chain back on them (you can remove the safety wire at this point). Line up the two markers (black dots) with the camshaft caps and tighten the caps down according to the manual.
Now if everything seems okay, push down on the camchain between the two sprockets just enough to make it taught (so it doesn’t skip on the gear), and rotate the alternator slowly to make sure that after 720 degrees everything is still lined up. Now install the camchain tensioner and rotate a few more time to make sure everything is perfect and you’re done!
Step 8: Conclusion
Reinstall the alternator cover and the valve cover, and put everything you took off back on. *Note: I broke a few of the bolts holding the valve cover in place. It might be worth investing in new rubber bushing and bolts if you're working on an old bike. If you drained oil and coolant make sure you refill those (a coolant flush would probably be a good idea too). You can now start the bike and enjoy the benefits of having your valves adjusted properly... probably starting with a carb sync/ tune :P
Well that’s it for my guide, I hope it was helpful for at least a few of you. If anyone has any suggestions or corrections feel free to drop a line. Good luck guys, rubber side down :D