Jerrod's 82 Yamaha XJ-750 Maxim

Ive had it out probably a dozen times, one day for the better part of 3 hours.. And I have to disagree, Valve seal's do more then keep oil out, they keep exhaust gas's in as well. Valves seal's can become worn over time, not allowing the valve's to seat properly. And then not only will oil start coming into the combustion chamber, but the exhaust gas's that create the compression will escape right past the unsealed valves resulting in low cylinder compression..

 

But I've had the Head off for 2 days now, as soon as parts arrive it's going to my buddy's shop.

 

You do what you need to do Jerrod, but get your terminology right and it saves confusion. The things that seal the valves to engine gases are valve seats, not seals. Valve seals are on the stems - sometimes called stem seals. I believe that's the same both sides of the pond.

 

The valve stem seal never sees any exhaust gasses. The valve guides don't have enough gap to them for that to happen, but do have enough gap that oil can leak past. Your #2 plug shows no signs of any oil getting into the combustion chamber.

 

Number 2 plug is on the left, the inside of the number 2 cylinder is very moist also. It's down right wet compared to the others. And my piston rings are good. And how can the valve seals not be exposed to exhaust gas's, when the valve seats in them? Everything the valve is exposed to, the seal would have to make contact with as well..

 

Oh and I poured a ounce of fluid into each intake tube, and the only valve that leaked was number 2. It came dribbling right out. The valves in 2 are functioning properly, but they are not making a good seal when closed.

 

Hmm, I've always been told Valve seals. And both terms bring up the exact same part when entered. May be a matter of preference, idk. Either way eBay knew what I was talking about, and the new parts will be here Saturday, so that's all that matters i suppose..

 

Valve stem oil seals are to stop oil getting into the combustion chamber.

 

Yeah, I've heard of valve stem seals. I was saying valve seals, which some people are saying are valve seats. But I've never heard them called that. I've always heard Valve seals, and Valve Stem seals. Never heard them called valve seats.

 

I've never read a manual for any engine that calls them anything other than valve seats. I've done all my own wrenching for 40 years, and have worked on engines twice as old as I.

 

@k-moe and me both, maybe slightly more than 40 years for me. Valves are sealed by the valve seating ring (on the valve), and valve seats (in the head). Valve stems run in valve guides, which have valvebseals, or stem seals (same thing), to stop lubricant dribbling onto the back face of the valve and getting burnt off. Now, if your valves aren't sealing, and the thing hasn't been run with closed valve gaps/lash/clearances, the chances are that both the valve and valve seats may be fine, but have some carbon fouling. Running the engine would either improve this or not. If not, you remove the valves, regrind or recut the seat (in the head) and the seating on the valve (or replace the valve), then redo the clearances.
You do not fit new seats. Oh, but you would change the stem seals since they are pennies (cents?) and need no machining...
Good luck.

 

It's amazing really the times valves open and close over an engines lifetime that they don't fail. Very rarely do engines drop valves.

 

I had a Mazda car drop one back in the early 80's. The piston didn't like that.

 

The only time I have heard of that happening was at Santa Pod in England on a GPZ 900, the owner wouldn't have liked it.

 

I'm not trying to say your wrong, I'm just saying I know quite a few people that say valve stem seals, and valve seals. And I suspect that everyone knew the exact part I was talking about, when I said I have low compression becuse my valves aren't sealing off. It's not a big deal, different people use different terms, i certainly have no interest in going back and forth about it..

 

Proper terms matter. Not everyone here understood what you meant. And that does matter when we try to give you good advice.

 

Personally, I couldn't care less, if you're daft enough to have new valve seats pressed in, then recut, reground, lapped, also replace the valve, lap it in, set clearances - good luck to you - you'll never be short of something to do.

 

Been reading up on everything I'm doing right now. And there was miscommunication between me and my buddy looking at my head. He never did a compression test. But if he were to, it would likely indicate High Compression level's according to what I've been reading. I assumed becuse seals were bad that it was low compression. But I now know my assumption was wrong after studying up. So that's where I'm at. Yes the technical name of the parts I ordered is Valve Stem seals. But I did think they were just called valve seals. Never heard the stem part till this conversation.

 

I have the stem seals, and my current pain in the a*# is tracking down a valve spring compressor that will work on an unexposed valve spring. Bought the wrong tool. But I'll get it figured out.

 

Oh, and I cleaned my head up and made a discovery. It seems that at some point in the past 40 years, Someone has had some work done to this head. There has been a significant amount of material removed from each intake and exhaust port, and it definitely doesn't look to be factory work.. this is just 1 exhaust port, the intake work is much more conservative then the exhaust side. But is definitely there.. what do you guys think?

 

Here's an example of the Intake side, I suppose this could have been done at the factory, but I'm guessing these bikes were mass produced, and I just don't think Yamaha would be taking a die grinder to every head they made. But I could be wrong..

 

Intake side looks exactly like mine also '82 750 Maxim. I just did some port matching on both intake and exhaust sides. Not much but just cleanup and match the headers and carb boots.
Cheers, 50gary

 

Alright guys, for anyone that still may be paying attention to this thread. Valvestem seals are replaced, the engine is back on the Bike, the Head Gasket has been replaced, and the Head nuts have been Tourqed down in the correct sequence. Packing it in for tonight, and I'm setting the Valve timing in the A.M., so hopefully I'll be Pissing off the neighbor's by noon. I've doing SOHC Cam, and from what I've seen it's very similar just 1 more Camshaft, its rarely that simple but we'll see how it goes.

 

Did you replace the oil-feed o-rings and crush washers as well?

 

Yeah, all new everything. It sealed up just fine, But there was no change. Runs exactly the same. The stem seals were shot, but apparently that's not the reason it's down on power.

 

I talked to the P.O's brother a few days ago, and it appears I bought this thing from a complete moron. When he got new tires for it, he decided to burn the tire he was replacing off until it exploded. He said he's the guy that go's around pinging his Engine off the rev limiter, cause he thinks it sounds cool. Has me thinking I should just start looking for a new motor.

 

It takes a lot to destroy one of these motors. Never head of an XJ engine being wrecked so far.

 

I don't know why you would, Yamahas are obviously idiot proof....
Did you have your valve seats lapped and checked and clearances set?

 

There is no rev limiter on an XJ.

 

Just explaining the kinda dude he is, his older brother said they would throw party's, and would go out all drunk, and power break it until the exhaust started to glow. Apparently he thought that was just the coolest thing..

 

And my buddy did all the valve work at his shop, not positive on everything he did. But I know he set the lash to what it's supposed to be, I just didn't have the money to pay him to change the stem seals, so I did that myself.

 

It's just not right guys, it's rideable it will do 65 all day. It just has no pick up at all. My Honda is strong for a CB-750, it's up over 70hp, but this XJ should be eating it's lunch, not the other way around. But the XJ has really grown in me, its a really good feeling bike, very well balanced. But I think the dumb hillbilly I bought it from wore the motor in it out.

 

You are as illogical as he was dumb...
You should know, since you know everything else, that power is made above the piston. You've had the engine to bits, so you should also know (in fact you've told us) that the rings are good, you've had the valves done, set the cam timing, etc.
So the power producing bits are good?
Your loss of power is elsewhere - carbs or ignition timing. Try another tci - it's easy. Then maybe need to look at the carbs, it's been known to get jets fitted in the wrong place...

 

Carbs.

 

I'm inexperienced really, this is honestly a learning curve for me. I've done fuel pumps and BS like that on cars, but replacing the Camshaft and Rocker Tower's in my CB was my first time inside an Engine. And all I really learned was how to set valve timing. Now I've learned how to remove and install Valve's, but I'm far from a Mechanic. I'm learning, but there's alot more to these things then the average guy riding them around will ever realize...

 

And I will start looking into the ignition, and Carbs, what would be the result of one or multiple of the Carb Diaframs being no good?

 

Slow down.
Read.
Learn.
The Information Overload Hour
And most of all...stop jumping ahead of yourself.