'81 650H with leaky head gasket

Greetings! Been a LONG winter and spring up here. So glad to finally be back in the shop working on some bikes.

This is a first for me, though. The '81 650 Maxim I'm working on (and thought I had ready to sell) appears to be leaking oil at the head gasket on the left side. I have not yet pulled a head on one of these and haven't observed this on the other XJs I've worked on.

I tried torquing the two outside head bolts to which I had easy access, but they both appeared to be tight. I suppose that a cracked head is also a possibility but I guess I won't know that until I have it pulled.

QUESTIONS:

1) How much time should I allow for this?

2) Planning to order upper and lower exhaust gaskets for the headers. In addition to the head gasket, are there other parts I'll need that may not seem obvious? (The valve cover gaskets were just replaced last fall and should come off easily with the covers.)

3) Is there are other work I should do or parts I should inspect once I'm in there?

Thanks!

 

Cylinder Head Removal can be a challenge.

I recommend you get a Genuine Yamaha Factory Workshop Manual.
Highly recommend it!

To get the Head off, ... you must remove the Timing Chain Sprockets from the Cams followed by removing both Camshafts from under the Timing Chain.

Then you attach a strong String or Nylon Cord to the Timing Chain to suspend it and lower it down into the cavity in the center of the Plant.
The Cord needs to be long enough to let the Chain down to be pulled-up after the Head is reinstalled.

Following the reinstallation of the Head, ... the Chain is pulled-up from within the cavity and reattached to the Sprockets.

Getting the Chain, Sprockets and Camshafts all repositioned PRECISELY for the correct TIMING requires some finesse.

The Factory Workshop Manual will guide you through each step with illustrations and precautions to make sure you get it right.

 

OK, thanks, Rick. I do have the factory manual, but I thought I'd check to see if there were any special details not mentioned that I should be aware of.

 

One little detail that often complicates getting the Head off are the two Hex-nutted studs on the front of the bottom of the Head.

Under the Head, ... between the Middle Pipes.

 

Meaning that they are hard to remove or break off?

 

More that the book does a really poor job of illustrating them so they're easy to simply overlook.

REPLACE the o-rings on the oil galleries around the bolts on the RH side and be sure to use NEW copper washers under those two head nuts. Be sure to oil the threads when reassembling and torque in stages as specified in the manual.

You may also discover that you need a new cam chain gallery seal ("cam tunnel gasket") they tend to get baked.

Are you 100% sure it's the head gasket and not -- still the valve cover (did you replace the donuts not just the gasket?) or -- the cam chain tensioner body gasket leaking and the oil "migrating" around?

 

i just recently pulled the cylinder head off my 550, due to a broken head, and then ended up lapping the valves and replaceing valve seals. its not super complicated to pull it off, but reassembly is tedious to get everything back inline and in spec. its good to have a second person, even a somewhat unwilling wife if she does nothing else than read the manual to you while you get your hands dirty. you will for sure want to change out the orings and head gasket (duh), wouldnt hurt to do exhaust crush gaskets and intake gaskets as well. all of these could come in a nice gasket kit; which can be cheaper than buying the head gaket alone. check out my broken engine thread for some more details

 

Thanks for the replies. Fitz, I did replace the doughnut washers when I did the valve cover gasket. A close inspection makes me confident that it's not leaking up there. Everything is dry above the head gasket and there is really only oil present on the left side. The cam chain tensioner gasket may also be leaking...

There is a little bit of oil present near the front acorn nut down next to spark plug #2. I took that nut off and there was oil under the washer, so it seems like it must have been coming up from below.

Is the cam chain gallery seal to which you are referring part #16 in this diagram?

Also, I adjusted valves last fall and this thing has great power. It actually is the best-performing XJ I've worked on so far. Will I be able to slap the head back on as-is with shims in place when I reassemble, or will I need to adjust them again?

 

"Remove the four cam chain sprocket bolts."

Uh...so what's the trick to get at the two lower bolts AND keep them from falling into the motor once they're free?

 

Stuffing every space and orifice where something you might drop would be unretrievable with a Safety Net of enough Linen Sheet from a Thrift Shop to make the unthinkable, ... impossible.

One whole piece.
The whole thing.
So that nothing you drop gets away.
And, ... when you pull-out the Linen ... it all comes-out in one piece.

 

RE: #16-- Yep, that's the part alrighty but man do they want way too much for it. Even MamaYama gets less than that; but check with Len.

If you're not going to seize the opportunity and take the time to do a valve job and replace the valve stem seals while the head is off, then there would be no need to re-shim.

 

The two cam chain sprocket bolts in the upper position came out easily. I can't get the two lower ones to budge. I've used six different 10mm wrenches and none of the open ends will turn them. The box ends are too thick to fit in the space between the bolt head and the wall of the head itself. I actually took one wrench and ground the box end so I could just barely slide it onto the bolt head but it actually rounded off the head a little. It was a 12-sided box end and I don't have a 6-sided. That might help. They're not always easy to find in that small a size, though.

I'm at risk of not being able to get this thing off if I damage the bolt any further. The book says that you can break the chain, although it shouldn't be necessary. Would I be crazy to do that?

 

Two thoughts on this matter:

1) The bike will be sold soon.

2) It runs so great that it really doesn't seem like it needs a valve job.

 

The Camshaft has Hex Flats to help rotate the Cam.
Rotate the Cam so you can get a 6-Point Socket on the Bolt.

I have a SEARS Craftsman Ratchet Handle.
It can take some abuse.

Place a moderate amount of Undo-torque on the fastener.
STRIKE the Ratchet a good lick with a Hammer Handle.

Don't use the Open end of a Combination Wrench on those Bolts.
Buggering them will just make matters worse.

 

I thought I wasn't supposed to rotate the cam shafts or motor once I got it to TDC.

 

TDC?

You're taking the Head ... OFF!

When you put it ON, ... and set-out to TIME it ... it starts at TDC.

 

Hey, Rick. First time pulling a head as previously stated, so maybe I'm not understanding what you're saying. I'm following the factory manual which says to position the motor at TDC before you start the procedure. After the cam sprockets are off it says, "From this point on, do not rotate the camshaft or valve damage will occur."

Without having ever done this before, I'm unclear about what can be done once the chain is hanging loose. Can the motor be repositioned at that point?

I suppose I could put the other two bolts back in, turn the motor to access those bolts and just loosen them, then rotate back to TDC for removal.

Thanks.

 

I went ahead and rotated the motor to gain access to those bolts, then made sure it was repositioned back at TDC before I took the last two bolts out. Seemed to work fine. Cam shafts are now off and I'm ready to pull the head.

Thanks.

 

I'm headed to the machine shop to get an opinion about the head and valves. Here's what I'm looking at...

Cylinders 1&2







Cylinders 3&4







Cam Chain Gallery Seal




Head Bolt/Stud Sleeves(?) Are these replaceable?

 

Good news from the machine shop: head and valves look fine! Got a couple of final questions before I order parts...

1) Clean top of pistons? Is there any advantage to doing this while the head is off? Are there risks to doing it? Can I turn the motor to access the two pistons that are currently down inside the cylinders if I make sure the cam chain isn't getting wanked?

2) Should the head gasket go on dry or with adhesive/sealant? I've Yamabond on hand.

3) The protective sheathing/shrink tubing around the front head bolts on the exhaust side is all cracked and broken. I understand that the function of these is to protect the cylinders during installation. Since the cylinders aren't coming off, it doesn't seem like it would serve any purpose to replace the sheathing, right?

Thanks!