Valve Clearance Adjustment Question

Hi guys,

My bike is an 83 Midnight Maxim xj750mk.

The valve clearances are as follows:

Intake #1 .203mm, #2 .203mm, #3 .203mm, #4 .076mm
Exhaust #1 .127mm, #2 .279mm, #3 .152mm, #4 .152mm

As you can see some of the valves are under spec and some are over. Using the chart in the service manual seems to be only adding thickness to the shim. Logic tells me that I should be changing out to thinner shims in some cases but I wanted to bounce it off someone with more knowledge.

I got the bike from the original owner and it has 3500 miles on it. I asked him if he took the bike for the initial valve clearance check after the break in period and he did not. Could this be the reason that the valves are out in both directions? Is this something that is more common than I think?

 

For starters, you're using "American" feeler gauges with metric equivalents on them; you'll have an easier time of it if you use actual metric gauges, like K-D Tools' 2274, widely available.

Next, are you sure you have those oriented right? Exhaust is at the front of the motor (pipes,) intake toward the carbs, or toward the rear. Your intake numbers look like exhaust numbers, and vice-versa. If YOU have them right, I'd suspect somebody who got in there ahead of you had them backward.

You use a thinner shim to increase clearance; and a thicker one for the rare instances where you want to decrease it.

It's not common at all for valve clearances to increase; it usually indicates a problem of some sort. They usually get tighter; although on really high-mileage motors they can and do occasionally loosen up.

 

Thanks for the response.

I am sure that I measured them correctly(triple checked). I am sure the cam lobes were in the proper position. I am sure of the exhaust vs. intake.

It seemed strange to me as well. When you say a problem of some sort can you elaborate? I should have mentioned that this bike hasn't run in 10+ years. I got it from the original owner who claims that he only brought it to Yamaha for oil changes, no other maintenance. The bike has 3500 miles.

I'm glad I read the thread(s) on checking the clearances.



Rob

 

Something's sure not right.

The valve clearances tighten as the valves pound themselves into the head. This happens most drastically in the first 3000 miles, which is why Yamaha spec'd the first check at 3K miles.

The only way the clearances can be too great is if the valves aren't closing fully; or if the guy lied (always possible) and had them adjusted by someone who got the intake and exhaust orientation mixed up. I find it really hard to believe that 3 of the 4 intake valves are "stuck" open exactly the same incorrect amount.

Suggestion: Unplug the TCI unit and spin the motor a bit via the starter, then re-check. If those clearances are indeed for real, then put 'em in spec and do a compression test.

 

Good point about 3 of them incorrect but exactly the same. The gentleman is a customer of mine and gave me the bike so I don't think the motivation to lie is present. I guess it doesn't really matter at this point how they got that way...

I will turn the motor via the starter and recheck, then I'll order the pads and proceed.

Thanks for the help.

 

I'm wondering if there could be something keeping the valves from seating properly since it sat for so long. The motor oil is clean and visually moisture free. The top of the motor looks clean and well lubed for having sat so long.

Would there be any benefit to running the motor and getting up to temperature for while, then let it cool and check the clearances again?

 

Does it run? I had assumed not. If it runs, it shouldn't hurt anything but don't rev the heck out of it or expect it to run well. And be sure it's stone cold again before checking the clearances; as in, overnight cold.

I'm still thinking the most logical explanation is that the valves got adjusted along the way by somebody who was a bit mixed up. Maybe PO simply forgot he'd had it done.

 

It hasn't run for 10+ years, and will not until I am finished rebuilding the carburetors.

I am working at the previous owners home and I talked with him again today. He is sure that they were never adjusted as he bought it with zero miles. Let me ask you this, is it possible that it was an error at the factory during original build? Would it run well enough that he thought it was fine for 3500 miles?

I think I want to try and fire her up before I change any pads just to be sure.

 

Something is definitely weird.

Do a compression test. That won't hurt anything, and will involve spinning the motor with the starter a few times. Let's see what you get.

It wouldn't have been a FACTORY error. However, it very well could have been a dealership error; perhaps they were chasing an issue pre-delivery and some pimply-faced seventeen year old junior snoid didn't know intake from exhaust.

That or they're all sticking open the same small amount which would be bloody weird.

 

Compression test:

#1 90
#2 60
#3 130
#4 90

Finding it hard to believe that the piston rings could be gone, unless they could deteriorate from sitting. Starting to think there may be crap not letting the valves properly seat. I'm wondering if I could get it to start after I'm finished with the carbs, let it run then recheck everything.

 

First thing to do: another test with a different gauge.

Next thing to do: drop the exhaust system and have a look at the actual valve stems.

Something isn't right; and yes the valves could just be stuck open because of displaced carbon, corrosion or rust.

But here's the hard, honest truth: If those are accurate numbers, the motor will probably not run; or if it does it will only run on 3 cylinders. #2 is essentially "dead" at 60psi; and 90psi is just barely enough for the motor to run.

It's possible that some judicious use of Kroil might free things up; or you might be looking at pulling the head and "doing" the valves.

You are correct in that the mileage is so low that the rings are probably OK; unless choked with rust. But based on your valve clearance check, I'm more inclinded to think the issues are up top.

 

When I first started taking things apart the motor was "stuck". I pulled out the plugs and saturated the cylinders with lubricant. Over the course of the next few days I was able to move the motor back and forth by hand little by little while lubricating.

The motor came free and now turns easily with no weird noises. I guess its not out of the realm of possibility that it was the rings that were rusted to the walls and I further damaged one or all...

I'll check the compression again with a borrowed gauge and I'll take a peak at the stems. I'll lube the hell out of it and let it sit while I rebuild the carbs. Thanks again for the suggestions.

 

The problem is, the rings are now probably packed full of powdered rust/lubricant mix and aren't free to seal; and the cylinder walls may or may not be rusted enough to have had their surfaces seriously compromised.

You didn't tell us about the fact that it was seized up to begin with; that would have shed a different light on things from the beginning.

The probability of being able to resurrect this motor without pulling the head and probably the cylinders too is very slim. You're wasting your time on the carbs until you have a viable mill. Soaking it in penetrating oil won't fix it.

And seriously, get thee some Kroil. http://www.kanolabs.com/google/ Works when all others fail.

 

Yeah sorry should have mentioned that. Didn't seem to be that stuck, I just didn't force it. I will get some Kroil and further investigate the motor.

 

I feel like there might be hope.

After soaking about 24 hours with Seafoam(its all I had), and turning the motor via the starter with exhaust REMOVED:

...again with my standard feelers:
Intake .152, .152, .127, .076
Exhaust .127, .152, .127, .127

Compression: 130, 130, 125, 90

I've ordered the Kroil and

 

Now that's more like it. Those clearances at least make sense; plus they're either in spec or too tight as expected.

I would say now you can proceed with the clearance adjustments on intake #4 plus all of the exhaust valves.