Cylinder head removal questions

Hello all,
Haven't been on the site for quite a while. I hope everyone's doing well and a merry xmas and happy new year to all.
Okay, the bike is a 1981 XJ650H Maxim with just over 100,000 kms (60,000 miles).
Compression is very good, between 145 and 148 across the four cylinders.
But an oil leak has developed in the head gasket at the front of cylinders 1 and 2. The exhaust header mounting holes are also pretty chewed up.
I want to remove the cylinder head this winter a do a couple of things.

1- Tap out and re-thread the exhaust header mounting holes. They are currently 6mm but I think there is room to make them 8mm

2- I'm thinking of replacing the cam chain and guide while I've got the head off.

Questions:
Is it possible to replace the rubber cam chain tensioners while I've got the head off?

Any advice for removing the head?

Can I use a thick piece of glass to measure the flatness of the cyl. head or do I need a steel plate made specifically for that purpose?

Thanks in advance for any advice, info, answers.
baz

 

Long time no hear Baz, good to see you are still kicking.
Q#1- Yes, but they are expensive, about $70 a piece last time I checked (and that was close to 20 years ago).
Q#2- Glass is fluid (it does flow, slowly but it does flow) so I would avoid using it. A steel rule is best.
Merry Christmas to you Baz, keep in touch.

 

At 60,000 Miles you:

Yank the Head.
Decarbon
Replace Cam Chain
Lap or Resurface Valves
Knurl Guides
Replace the Valve Seals.

Since you are going to replace the Cam Chain; youi can't "Save" the Timing by not separating the Cam Drive Sprockets from the Chain.

Drain the Oil
Mark the Starting Point of the New Chain with some Bright Color Nail Polish after attaching it to the Old Chain after the Old Chain is split.
Secure the Joining Spot of the New Chain to the Old Chain with a Very-well fastened linkage.
Use the heaviest gauge wire you can fit to join the two Chains and have complete confidence the joint will NOT separate as the Crank is turned to thread-on the New Chain.

 

Great info. Thanks for the prompt replies.
About the timing. If I replace the timing chain, I guess the timing has to be re-set. So this is done with a strobe gun, I'm guessing.
I did it with my old carburated Celica.
Are are there any other specific tools I'll need for re-setting the timing?
thanks again,
baz

 

Unless I'm mistaken the timing on these bikes is run off the pickup at the crank under the left side cover. Your cams need to line up to get the valves in time with the crank. should be marks on the gears for that.

Timing strobes are used with a distributor because it can be rotated in relation to it's drive gear. You'd also need a wheel of somekind out side the motor with degree marks to use the light on.

 

It only requires lining up alignment markings; cams to the head and pickup rotor to base plate (under left side crankshaft cover)

 

After a Chain Replacement ... you go to the Default on TIMING the Engine.
Bring the #-1 Piston up to Top Dead Center.
Look at the MARK on the Timing Rotor

Each Cam has a Timing MARK to Align with a Timing Mark on the Engine.
Without refering to the Text ... I think the 650 Bikes have POINTERS which align to Marks on the Thrust Bearing Bridge close to the Cam Chain Opening on the Head.

There are Hex Flats on the Cams to help you Position each one correctly before re-installing the Cam Sprockets.

(Before you Un-Bolt the two Cam Drive Sprockets ... Spray them with Carb Cleaner and let them dry.
As a VISUAL REFERENCE to help you during reassembly ... MARK BOTH Sprockets at "12 O'Clock. Use a small straight edge.
COUNT the Chain Links >> Between 12 O'Clock on the Intake Cam ... and, ... 12 O'Clock on the Exhaust Cam.)

When you reassemble the Sprockets to the Cams:
Pull-up the Slack from the Crank to the Exhaust Cam.
Position the Cam PRECISELY on its Mark with the Crank on 1's TDC.
Lay the Chain over the Sprocket and using your VISUAL CUE ...
Move the Chain a Sprocket or two either way to Line-up the Sprocket's Bolt Holes to the Cam's.
Bolt the Front Sprocket finger tight.

Zero the Intake Cam to its Timing Mark
COUNT the Links from the front Cam back to the rear cam.
Place your VISUAL CUE in the appropriate LINK.
Bolt the Intake Cam Finger tight.

Before Torquing the Cam Bolts down ...
GINGERLY << !!!
Turn the Engine over by Hand using the Flats on the Crankshaft Rotor 2 (two) FULL revolutions ... VERY Slowly to insure that the Timing is CORRECT and there is NO BINDING or Piston Crow to Open Valve Collision.

Stop the Hand Cranking with the Crankshaft Rotor on the TDC Mark (Or Dial Gauge Measurement of the #1 Piston at TDC.

Check all the MARKS for Precision Timing. The marks must ALL be precise.
There is NO "Pretty close"
There is ONLY Perfect.
If the Marks are ALL on the Indicators ... You're TIMED.
If NOT ...
Start ALL over from Square One.

 

Rick-o-matic comes through again. Man, that is one very detailed and very useful set of instructions. I'll be it all them out and taping it to the bike when I do the job.
Thanks for all the help, everyone.
Once the holidays are out of the way, I'll be getting down to work on the Maxim.

One other question. Can I replaced the rubber cam chain guides while the cylinder head is off the bike? Or do they require further engine disassembly?

thanks,
baz

 

That was off the top of my head.
The step - by - step outlined in the Manual needs to be followed.

But.
There's NO Timing Light.
There's Procedure.
Somebody with the Book can chip in.
Mine are out in the Garage and the Driveway's under 3 feet of snow!

 

Yeah, I've seen on tv that you guys got walloped! We were lucky. That same system just missed us, going south of Lake Ontario instead of north of it. But I'm sure we'll get our own avalanche of white stuff sometime soon... Ah well, gives you time to work on the bikes, I guess. But isn't that why you're supposed to have 2 bikes? To work on one while you're riding the other? That theory goes out the window when you live in a place that turns into a winter wonderland several months per year!

 

Yeah but you still gotta have more than one bike. Just ain't natural.

 

Truer words have never been spoken...

By the way, BigFitz, I like that 'toxic asset' reference.
Funny, when I worked as an emergency ward orderly about 3 lifetimes ago, 'toxic assets' was a polite way of saying sh*t.
So I guess these really smart bankers and traders turned our money to sh*t? Wow, real magicians, ain't they?