Jerrod's 82 Yamaha XJ-750 Maxim

Popped* the valve cover off.

 

The riding season in Ohio isn't wrapped up for me. At least not if this winter is a repeat of the last. It hardly ever got cold last year. You're a bit further north though.

The collective will help you get your XJ running like a brand-new machine.

 

Im about a half hour north of Columbus, and I don't plan on winterizing either of my Bike's. I'm gonna take em out once a week probably until January. And once the snow comes, I'll just start them up. Not interested in hitting a patch of black ice on 2 wheels lol, no thanks.

 

The great thing about our bikes is that the more miles they do the fewer shim changes they need, they still need checking though. I had a CB 750 K2 and I didn't bother trying to get a feeler gauge into the gap. I used to just slacken them of and reset them.

 

Bingo. Honestly, with screw-type adjusters on rocker arms, that's the best way. But you are correct; once the valves are in spec, and the engine is broken in, the "pounding into the head" lessens and all that is often needed is a simple check.

The absolute most important valve clearance check and adjustment is the FIRST ONE, which was supposed to have been done at 600 miles, then again at 3000 miles (that is considered "initial break in".) Then it relaxes to every 5000 miles. This was COMPLETELY NEGLECTED on a lot of these bikes because of the expense involved in having a dealer do it. And it's why you find 7000-mile XJs with 7 out of 8 valves TOO TIGHT.

Valve adjustment is the single most critical factor in the early service life of these motors, and if it has never been done then any bike with over 3K on the clock is not only going to need it, but the more miles beyond that it will begin to lose performance gradually until you end up with a bike that seemingly resists all efforts to get it running properly. 'Tain't gonna run right if the valves open too early and stay open too long.

You cannot simply ignore it, things will just get worse.

 

Winterize them anyway. Startups during the winter wthout actually getting the engine to work leads to condensation in the exhaust and crankcase, and acidified oil.

 

So disaster has struck kind of. My 1 and a half year old decided he was gonna give the adjuster knob on the back of the Yamaha's carbs a few good twists. And it's running really bad now. I had to shut it down, becuse I started hearing valves tapping. An it was running hot as hell. Didn't seem to want to rev up either.

 

1. You're supposed to hear the valves tap.
2. Have you checked the valve clearances yet?
3. It's not a disaster.

 

I'm not like freaking out or somethin lol, but they haven't made a sound up till then, when I started it they were good, and after about 5 minutes of running they started tapping. And the motor is very unhappy. And no, not yet. I was waiting on my service manual to come in the mail before I did anything else to it. But the boy kinda changed that lol.

 

It's reving slow, almost like a cylinder isent fireing, But all 4 are. And seems to be running hot. It's not happy at all.

 

Ok just got home and started it for a second. And the valve tap has gone away. So I'm officially taking a step back. Need to learn about this screw he was turning, pretty sure it adjusts the air fuel mixture. But I need to do some studying up before I go turning any screws I'm not familiar with

 

yeah that. and quit trying to run the motor we already know needs its valve clearances checked. The big knob on the back of the rack is the main idle adjustment for the whole rack, essentially it operates all 4 carbs' idle setting. If the bike weren't out of tune, the results of turning it that far would be more conclusive. Idling too low means insufficient oil pressure so the motor will be unhappy. Let me say this again: QUIT RUNNING IT until you have a better handle on things.

 

If you have not checked the valve clearances how can you be certain the noise is coming from the valves?

 

Talked to previous owner last night, and he says they were adjusted when he got the carbs rebuilt 2 years ago. But I'm not so trusting in him, so I checked them today. Counting from left to right, Cylinder 1- Intake: .004. Exhaust: .004- Cylinder 2- Intake: Between .003 and .004 Exhaust:.006- Cylinder 3- Intake: Between .002 and.003 Exhaust: Between .004 and .005- Cylinder 4- Intake: Between .004 and .005 Exhaust: .004

 

Are those measurements in inches or millimeters? (I actually think that I know, but again never assume).
If you're using an inch set of feeler gauges invest $12 or so in a metric set (KD Tools has a good set, available online or at NAPA). The feeler gauges in a SAE (inch) set just aren't as easy to use, nor are they as useful when determining the go/ no-go state of a shim on the shim table.

 

That's Inch/Thou. I have 3 different sets, the one I used just says OEM TOOLS, it has both MM and Thou reading on them. They go from .0015 up to .024. And yeah they ran me about 12 bucks. I'm not sure what the factory tolerance's are supposed to be, but if I had to guess based on what they were, I'd say 4 thousandths Intake side, and 6 Thou exhaust, maybe 5. But the lash was all over the place no 2 intake valves were the same. And both the Intake and Exhaust were both 4 Thou on the number 1 cylinder, which can't be in spec.

 

My Grandpa was a Tool and Die maker, and he thought me in Thou. So that's where I feel comfortable. Never really used MM.

 

The math is easier. I understand though. Dad was a machinist, and my lathe is from the mid 50's.

 

Bigfitz's AIRHEAD VALVE ADJUSTMENT with Pics - parts I & II

You will need to pull the shims one at a time to find out what's installed. Then you can use the chart to find the new shim that's needed. Keep in mind that you will very likely be able to swap shims around so you will only need a few replacements. @hogfiddles runs the shim pool, so don't go out and buy shims before contacting him.