Crazy valve clearances

Today I bought a beyond super rough running 1982 XJ750J[-corrected] maxim. When I started it up dead cold on a forty degree day it shot through the rpms, which screamed pilot jet or vacuum leak. A couple hours later after some investigating I cracked the timing case and have two major problems.

1) the cam chain tower is super loose, I can almost remove it out from under the cam chain without any effort(spring missing?)

2) I measured the first cylinder exhaust valve clearance, a whopping 2.083 mm clearance with a 275 shim

Now this obviously isn’t right, and I had to wrap up this project for the night so I only got to measure the one clearance, but I hope someone could provide some insight.

Could this super loose clearance be from bent valves causing the valves to sink at the valve seat?

Any insight is appreciated.

 

could be carbon on the seat and valve or a broken spring. grab a boroscope and peek in the plug hole. (that sounds dirty eh? lol)

 

82750maxim, welcome to the forum

+1 about the carbon and take a look through the spark plug holes. See how much carbon is on those valves. Your cam chain tensioner could just need to be adjusted.

How many miles do you have on your X? If it has never been serviced and has lots of miles, that could be a telling sign as well. Those shims are costly, there are some shim pools around for the air heads but not too many for the water cooled X. Just double check what shims you need before ordering.

 

How would the chain tensioner affect the bucket and lobe contact? I'm not familiar with the 750's chain setup. Is it like the 550?
-NVM- you were referring to the chain support being loose.

 

Ryengoth 650's and 750's are shaft driven. I believe the tower is missing a spring. When I pulled the current sparks the were super fouled. The ones I put in just last night are fouled after two attempts at starting it to try and diagnose the problem. Im sure the carbon build up is crazy, I will try to inspect the valves through the spark plug holes.

the bike has 26k. I have a sneaking suspicion that the PO tried to adjust the valves and did a terrible job.

With the valves so far out of adjustment, isnt it safe to assume the valves are destroyed?

 

Also, if valves are bent will that cause the clearances to loosen?

 

I was referring to the timing chain, not the drive. It's only relevant if the timing chain is allowing the cam lobes to shift during cycle and fall out of timing.

Carbon can cause the exhaust valves to seat too far down into the combustion chamber and not seal properly.

A bent valve will be obvious, inside with a boroscope, from an open exhaust valve during intake stroke. Stick a rubber-tip air gun in the spark plug hole and see if air comes when the intake valve is open at full lobe. You can also just screw a compression tester in the spark plug hole and see how much compression it will build up to get a real picture of what the valves and rings are doing.

 

BTW, CRC DI intake cleaner will eat that carbon for dinner when spray directly. Put the piston just under TDC, fill it up and let it soak for 15-20 minutes in the cylinder. Flush it with some brake cleaner. You may want to pull the headers back and carbs off before you do that when the valves are open, though. Otherwise, you'll just make a big mess.

 

I appreciate the input, I will do some tinkering tonight and give an update tomorrow.

 

airhead or watercooled I ask because to read the shim om the x you have to take the cams out

 

I sure hope we are talking about the "X" as that what was posted in the first post. Yes if this is a air head then most things change and IMHO is much better than the water cold bike.

 

not at all. you may need a new chain and sprockets, or a cam chain tensioner. chain guides

bent valve would make the valve stick
look at the bucket and compare its position to the others when you measure the valves bucket could be stuck too.

start with a compression test.

if the bike is running you can feed small amounts of seafoam into the vacuum port to remove carbon or use atf


Sticky Valve? Transmission Fluid Fix. Experiment. XJ650

 

240 is the thickest shim for an X and he would have to remove the cams to get at the shim

 

1. I would assume the same. 26K is the first valve clearance check on a Maxim-X, ant there is no chance that the valve seats have recessed that far in such a short time (even taking into account abuse).

2. No. Excessive clearance would not harm the valves in any way if it's just because of the clearances being set wrong. Performing a leakdown test is in order though. That will help you diagnose if there is excessive carbon buildup or bent valve stems.

IF no leaking is detected from the valves then they are seating fully and you can go ahead and set the clearances correctly. Carbon buildup could still be possible, but it's highly unlikely to have that much buildup, even if all of the oil control rings had collapsed.

 

The x was a typo. It’s an airhead

 

Intake clearances are worse than the exhaust, it looks like the tops of the pistons have what looks like rust deposits, could just be severe carbon build up but I feel like there is a red tint to it. There is very slight rust in the gas tank and it was filled with five year old gas, no stabilizer.(fair to assume PO was a jag off) surprisingly the valves looked clean.

I’m going to pull the head tomorrow, my service manual hasn’t arrived yet, are there any good forums or videos of someone pulling the head? Tried to find a guide on google, maybe I’m not being patient enough with my searches.

Any suggestions, or guesses at diagnosis are appreciated.

 

To reiterate once again, the x was a typo, we’re talking about an air-cooled maxim.

 

Springs weak or cam lobes are worn beyond spec would be my first guesses. The head may need some help to pop off. dont hit fins tho.

 

So many people are not reading your note so I currected the typo for you. The rest if the forum was left alone so someone might still get confused til they read this....its a 1982 XJ650J Maxim, NOT a 1982 Xj750X. The X was not produced until 1985.

 

You must wait til valves are overnight cold. Don't check on a recently run engine. even just starting then shut down and measure roll be inaccurate. Overnight cold is the way to go.

 

My advice still stands.

26,000 miles is only the fifth valve clearance check for an airhead, and it shouldn't be loose by 2mm at all...ever.
The valve clearances tighten up as the valves beat the seats into the head.

Also, the cams lobes can't wear anywhere near that fast. They are harder than the shims. They can get scratched up by turning the cams over with a shim out of the bucket, but that's becasue of the higher surface pressure from the smaller contact area, and the sharp edge of the bucket lip.

 

The lobes are slightly blued. I was wondering if a lifter spring could be rusted, or just super junked up not allowing a proper return.

I appreciate the fix.
I let the bike sit for more than 24 hours before performing this check. The clearances all are about the same. They have a .2 mm difference across the board, but the clearances are 2.083 for each exhaust, and the intakes varied, very slightly, but stuck around the 2.2 area. It was difficult to get an exact measurement.

The bike was fired up twice. Once when I met the PO, and once when I got it home. I honestly thought it was pilot jet related due to the way it revs when it starts dead cold. I thought I’d start off simple and check the clearances, that’s when the can of worms opened.

There is definitely a rust issue.

 

If the valves are severely bent or not seated properly, that would throw off the clearances correct?

 

Seems if its revving like that, there's not going to be a lack of compression......but a compression test is definitely in order, like K-Moe said.

Let us know what you find. First we need to find out if valves are sticking open or not. If any valve is sticking open and you don't know it, but setting the clearance correctly, you'll end up open the valve even farther, and THEN you could run into valve/piston contact issues. DONT ADJUST CLEARANCE TIL WE KNOW THAT ALL VALVES ARE CLOSING ALL THE WAY

 

I haven’t adjusted anything. All I have been doing so far is investigating. I know somethings screwed up here, so I want to diagnose the problem before doing anything. I will do a compression test, but I’m still certain I need to pull the head. Again, if anyone has seen/made a tutorial videos it would be a nice aid with the service manual. I’ll be starting that process probably Saturday since I have Sunday off work.

I will report back, thanks again.

 

.102

sorry but first I have to ask if you are reading your feelers correctly

how did you measure the 2 mm gap?


2.083 mm clearance with a 275 shim cannot be fixed with a shim.

2 mm across the board is not a natural thing to happen to all the valves

 

Xj550h yes. I am aware that this is not fixable with a shim, which is why I’m here. It’s definitely weird. I’m using my feelers correct. I measured the gap using multiple feelers and adding them up. The valves I believe aren’t seated properly amongst other things. Won’t know for sure until I pull the head this weekend.

 

You will know if you just do a compression test

 

Btw what is a good compression reading on the air blocks? On the 550 block I got around 180psi on each except 4 which was 175. The service manual does not state an acceptable psi range, unless I missed something.

 

One other thing, the cam chain tower is super loose, has play back and forth underneath the tight chain. I can almost push it out from under the tight chain, can I adjust this? Or is this possibly a broken spring of some sort

 

The compression specs are in the factory manual, and on this website.
The Information Overload Hour

 

What part are you calling the cam chain tower?
Are you referring to the top cam chain guide?
Pics would be of help.
Your machine has an automatic cam chain tensioner, but it is possible for them to get stuck (rarely, but possible).
When you spin the engine do you notice a link on the cam chain that looks different from the others? (there should not be, but that would indicate that the chain had been replaced at some point).


Pulling the head on the YICS engines is not something that should just be done without thoroughly diagnosing the problem. There is some additional cost involved due to the YICS port o-rings, and a bit more effort involved due to the additional clamping studs on the inderside of the head.

Save yourself several hours of work and do the compression and leakdown tests before pulling the head. You could be doing all that work for no reason. You might have to do it anyway, but diagnosis should lead the way.

 

Appreciate the feed back, my buddy has the same bike just an 83. I just helped him do his valves last night. Tower probably isn’t the right term, the chain isn’t super loose but the guide between the two visible sprockets has side to side play underneath the chain. His was solid, which is why I was worried, I’m at work and won’t be able to take pictures until tonight

 

My 82 550 support tower had side-to-side play but it contacted the chain and you could not move the chain downward between the timing sprockets.

 

The upper guide just sits loosley in place. The only thing holding it is chain tension, and the guide does need to move a bit to allow the chain to track the sprockets as the cams move.

 

yeh, my top chain guide also moves from side to side, tho mines a 600
stu

 

One less thing to worry about! thanks.

 

measure your cam lobes

 

edit

 

Well maybe I read it wrong. I will be testing again with the new head installed.

 

Let's be careful to not mix two bikes into this thread.

 

So just to get the clear, you are going to get a new head to fix the valve issues? The compression was way up and or out of spec along with the valves so new head? Just want to make sure I/we have that correct.

 

If the compression is waaay to high,
Either the tester is out of whack, or the valve train is not right.

BUT--- we STILL have two different bikes we're trying to discuss. As K-moe said...let's NOT MIX BIKES. Can we discuss just one

 

Yes, sorry you can delete my post.

 

you should be able to edit it your self as a premium member

 

I can edit, but not delete.

 

just change the post to a smiley face

 

Just leave them. There is info that the PO may need later.