Head Gasket Replacement

I'm looking to replace the cylinder head gasket and head cover gasket on my '81 XJ650 Midnight Maxim. Aside from the two gaskets themselves are there any other gaskets or parts that I would additionally need to replace?

Also, if there is a link to a video or anything like that with instructions that would be awesome. I have an understanding on how to do it, but some detail would be much appreciated.

Thanks!

 

There are two oil seals on the right hand side of the cylinder head which seal the oil feed to the camshafts. You should replace those and if it is a YICS motor the four O Rings between the head and cylinder block.



20.28 minutes into Mezzmo's assembly video the two large oil seals for the oil feed to the camshafts and one of the four O rings for the YICS are visible. The two copper crush washers below the right hand cylinder head nuts need replaced too to seal the oil feed.

 

Cylinder base gasket is almost guaranteed to be disturbed and leak later, along with o-rings at the bottom of the studs and cylinders.
Don't trust 40 year old soft bits that have become baked and hard to remain leak-free when worked on anywhere nearby.

 

Bingo. Valve cover gasket=no biggie, normal maintenance item. Head gasket=more of a project and as above could have knock-on consequences creating a potential need for an even bigger project.

So, my question would be: why do you want to replace the head gasket?

 

Exactly I should have told him to do a compression test first good point.

 

I haven't done a compression test just yet, but the head gasket does have a leak on the left hand side of the bike. The valve cover gasket on the other hand, has a more noticeable leak. I figured if I was going to take it apart to do the valve cover gasket, I might as well do the head too. Is it more common for a valve cover gasket to fail before a head gasket?

I read somewhere that you can always try to re-torque the cylinder head bolts before tearing it apart to see if that fixes the leak. Is there some truth to that?

 

This is one of the more detailed videos I've ever seen for these bikes. Thanks for sharing! If I end up going that route, it'll definitely come in handy.

 

Makes sense, thanks. I was actually wondering about the cylinder base gasket too.

 

Do a compression test first to make sure your head gasket has failed. Check the easy things first the 8 cam cover bolt seals and the cam cover to head gasket.

 

Valve cover leaks very often (as in almost always) make it look like the head gasket is leaking oil too. Change the valve cover gasket and doughnuts, clean the engine thoroughly, and see if both leaks aren't gone. Be sure to use a thin film of RTV on the half-moon portions of the valve cover gasket so that they seal well against the head.

 

Awesome, thanks. I'll do a test this weekend and see what it reads.

 

Makes sense, thanks for the advice. It sounds like the valve cover gasket will have to definitely be changed. Hopefully there aren't more issues, but I'll see what the test reads.

 

As I said, valve cover gasket is a common maintenance item, whereas head and base gaskets involve a lot more than just the gaskets.

Another thing to keep in mind: oil seepage, especially on a motorcycle, can be very "sneaky" in that things will appear to be leaking that are not, the leak is elsewhere and "migrating." Valve cover gaskets often leak into the inner spark plug galleries (#2 and #3) and then the oil runs down between the fins onto the front of the motor and makes you think you have a head gasket leak. I was just sure my '81 had a base gasket leak when in fact the cam chain tensioner gasket was the culprit, with the oil migrating all around the base of the cylinder block. Another potential source of sneaky leakage is the tach drive housing; because of its location, when the bike is in motion the oil can and will end up about anywhere.

 

I don't think the head gaskets fail very often on the XJ's. I had to change one on my 1974 Honda CB 750 years ago.

 

They don't. But they sure do have a propensity for "sneaky" leaks, oil migrating quite a ways from the source. Fooled me more than once. Not like my Norton, when it drips oil at least you know where it's coming from.

 

Off subject but it is just like flat roofs they are the same.

 

750 years ago?????

 

he also installed a flux capacitor

 

My CB 750 did more than 88mph.

 

Well, I did a compression test this morning and am not having great results... I had a reading of only 65-70 on each cylinder. I read that if you drop a teaspoon of oil in where the spark plug goes that that will give you an indication of whether it's the valves or the piston rings that could be causing the issue. I did it, and it bumped the compression up to about 90. Any ideas or recommendations on what a good next step would be? I'm wondering now if I'll have to tear the entire engine apart to replace the rings.

The bike ran great all summer, but just started giving me issues these past couple of weeks. I brought it home after putting a few hundred miles on it and it's been riding terribly ever since. The only thing that changed was that I had the headlight off at one point and didn't know if I had messed up any of the electronics that go through the headlight housing, but now it's looking like it's something unrelated.

 

Valve clearances first.
The low compression on the ring end of things may be from stuck rings from siting over the winter.
They can be freed up with a soak of Seafoam. The can has directions.
You can also use a 50/50 mix of ATF and acetone, Diesel, or Kerosine. A tablespoon down each plug hole and let it sit for a few days.
Whatever you use be sure to start the bike up outside, and let the fire department know what you're doing so they don't roll out when the neighbors call.

Also make sure that your compression gauge is reading accurately. Test the compression on your daily-driver before messing with soaking the rings.

 

Did you do your compression test with the throttle fully open?

 

I just tested it on my car and it looks like it's reading just fine. Do I just try to run it normally with the tablespoon in each hole? How long would you run it like this before doing another compression test?

 

I did a test with it closed, waited a bit then did a test with it wide open.

 

I let the mixture soak for a few days (at least overnight), then let it idle until the smoke cloud clears. After that go for a short ride and retest compression the next day.

 

How about we start here before we go dumping Sea Foam or whatever down the cylinders? Get the valves in spec first. Then, I'd use a good healthy shot of engine fogging spray, or maybe Kroil if stuck rings are suspected.

Was the motor slightly warmed up prior to the compression test? All plugs out (TCI disconnected) and throttles wide open? Did all four cylinders give you the same reading within a couple pounds of each other?

A couple things to think about (don't start pulling things apart just yet) the reason for the compression test is a suspected head gasket leak which could be the issue but we should see uneven compression test results.

"Replacing the rings" involves a lot more than you might think, and if all the cylinders are equally soggy it is probably not the solution here;

and a bunch of tight valves will give you low compression test results.

 

Agreed. The only reason for mentioning rings was the increase in compression with oil in the cylinders.

On thing at a time though, otherwise we'll never know exactly what the culprit is.

 

Nice, might have to consider trying this next.

 

I tried a cold test and a warm test and got almost the exact same reading for each cylinder. Each between 60-65. Are there any other things that I could be missing in doing the compression test? I'm curious if I'm doing something wrong that could be giving me an inaccurate reading. I'm also starting to see why it would be odd that each of the four cylinders have a low reading.

 

I just love how the most important thing here keeps getting glossed over or flat ignored, or did I miss something? GET THE VALVE CLEARANCES IN SPEC or you are simply wasting effort. You may not have an actual problem other than some long-neglected critical maintenance. You're talking about replacing rings, which is one heck of a lot more wrench work and expen$e and you still haven't done the basics.

 

My engine valves were tight reshimmed it and motor ran great.

 

That's why valve adjustment is the very first item in the "maintenance" section of the manual. It is critically important, and a lot of other things depend on it.

 

Exactly my clearances were tight opening the valves too early.

 

I have just noticed that 750 years ago in my post lol. No wonder you had the ??????.

 

Two interpretations.

 

I understand. I was just thinking of taking a step further back to determine whether or not I did the compression test incorrectly. Someone mentioned that it was odd that each reading for every cylinder was around 60-65, so I'm wondering if there was something else that could have caused an incorrect reading. My manual wasn't super descriptive in the testing procedure. I'm not planning on tearing into the pistons right away, just a theory if that what was going on. Getting the valve clearances in check is going to be my first remedy.

 

Good plan. There are many things that can cause odd compression test results, especially if the motor has not been regularly run. Valve clearances are the most obvious. The fact that all of the cylinders are testing within 10% of each other is a good sign, and the fact that the motor runs or was running tends to lend credence to faulty testing; at 60psi it likely wouldn't have run at all. If you were getting say, 100, 100, 60, 100 then yeah, big problem. The fact that they closely match is a good sign.

My suggested course of action would be to get the valves in spec, then re-test compression and see what you get. Get ahold of a second gauge and do another test, regardless of results. Replace the valve cover gasket and the donuts on the bolts; and clean off the outside of the motor thoroughly (use mineral spirits) so you can ascertain the source of your seepage. And go from there. Get a factory service manual if you don't already have one, and leave it in the bathroom. STUDY it every day, read up on what's involved with removing/replacing the head; the intricacies of fitting new rings; etc. Learn what makes your bike tick.

If you plan to keep and actually ride this motorcycle, go through the "maintenance" section, IN ORDER, STEP BY STEP, and don't leave anything out. Don't skip a procedure because it seems daunting. If it's in the "maintenance" section, DO IT. Clean, inspect, refurbish, repair or replace anything you come across that isn't 100% serviceable. (Plan to spend some money in the process.) Once you've done that, you will have a reasonably reliable 35 year old bike. I say reasonably because, due to the age, it's gonna send you a surprise every so often to keep you on your toes no matter how thorough the recommissioning. The secret is to "pre-eliminate" as many of those surprises as possible. Here's the real key: anything you skipped over or weren't thorough enough with IS going to come back and bite you; so those shouldn't be considered surprises.

 

Makes a lot of sense, thanks for the insight. I wondered that too, it sounds like if compression is that low across the board, it should hardly run at all like you mentioned. It still definitely runs, it just doesn't run well. It bogs and has been having issues with acceleration. At first I thought it was a carb-related problem, but I've been noticing the somewhat leaky gaskets on the engine, which is where this all started.

I 100% see where you're coming from with up-keeping maintenance. I've owned it for about 4ish years now and it has about 35,000 miles. I've had to do a decent amount of repairs here and there so far. It definitely gives me it's fair share of surprises, this obviously being one of them. I actually enjoy doing maintenance and working on it, it's the troubleshooting that I struggle with sometimes.

The manual also states to have a fully charged battery and to have the headlight unplugged for the test. I guess a weak battery on an electric start can cause it to crank slower giving an inaccurate reading? Either way I'm going to read through the manual about getting the valves in check too.

 

Bogging and lack of performance are likely not directly related to gasket weepage. TIGHT VALVES ARE. Start there. There's a reason valve clearances are the very first item in the maintenance section.

 

The more maintenance you do the better you become at troubleshooting, well that's my experience anyway. Yes do the valve clearances first.

 

So I ended up checking the valve clearances this last weekend after ordering all of the tools I needed. They actually are all within range. There was one intake valve that might have been questionable, but not by much or enough to warrant a replacement. The timing chain felt pretty decent too.

I tried my compression tester on my friend's 800cc v-twin and his engine was reading correctly, it did, however use a different size adapter on the tester for his spark plugs. I'm thinking of renting a compression tester from somewhere to see if mine is still causing issues for some reason and to compare readings. I'm just not sure why all cylinders would be reading as low as they are especially since the last time I road it, it ran perfectly fine. It flipped like a switch the next day when it started not running well. Any thoughts on what a good next step might be?

 

Do you have access to a leak down tester? If valve clearances are with in spec, doing a cylinder leak down can identify why your cranking compression is low, be it rings or valve seats. Air escaping past rings will blow out thru the crank case, air blowing into the air box says bad intake seats/valves, air out the exhaust pipe says bad exhaust seats/valves.

 

I just looked over this thread and as your valves are now checked and in spec and assuming there is a problem with the adapter for your engine perhaps this problem is to do with ignition? I cannot be sure of course but if the bike was running great all summer and you had the problem after the headlight was off you should check what voltages you have at your coils etc. The fact that the compression readings don't have a big variance over the four cylinders suggests the head gasket is unlikley to be the culprit I think. Compression cannot drop suddenly unless the head gasket fails and it surely would not drop equally accross the four cylinders.

 

That's kind of my hypothesis too, I was wondering if it is electrical-related since it happened so sudden, but an inaccurate compression reading is throwing it off. I'll try to check the voltages. Would it also be worth it to try and turn the engine over with the air filter removed to see if that changes the reading?

 

I don't own one, but I can get one. The local auto parts store rents them out. I can try this too.

 

Well you could as the air filter will reduce the airflow a bit.

If your piston rings were not sealing right l don't know if there would be a way of checking the crankcase breather because there should be increased pressure in the crankcase. It is because the change in your machine running well to the present situation l would check the ignition system. Carburettors are the same as before, you valve clearances are fine. It is because piston rings, valve clearances and valve seats and carburettors don't change quickly l think the problem is elsewhere.

 

Go back to the headlight retracing your steps and look to see if there are any broken wires or harness plugs not connected properly. What is your battery voltage when cranking the engine? I think it needs to be a minimum of 10 volts to make the transistors work in the TCI. Is the bike on the centre stand with the sidestand up? Have you checked the ignition fuse? What about your sidestand switch? Is it working properly?

 

Makes total sense. I'll check the connections. I didn't check the battery voltage, but did try hooking it up to a booster the second time I took the test, unfortunately, it gave me the same results. I can definitely check the voltage though to see where that's at.

The bike has been on the center stand every time I did the test and the kickstand should have been up every time. I'll check the fuses!

 

Yes if the kickstand should be up as the engine wouldn't start with it down.