Should a novice attempt head gasket change XJ550?

First time poster here, but I've found this forum incredibly helpful!

Found out not too long ago that my 1982 XJ550 Maxim has a compromised head gasket. It idles in very high RPMs once the engine gets hot, which I imagine has something to do with this, and also something to do with an exhaust leak (I'll be replacing header-to-exhaust pipe gaskets, nuts, and bolts soon). I've heard it's not that simple to replace, requires messing with the cam chain, as well as readjusting of headspace (above pistons?). Local shop isn't interested in doing it until the fall/winter, and it's going to cost me a pretty penny. Is this something I should attempt, and any recommendations on a good how-to guide if so? I want to learn the ins and outs of this bike, learn how to work on it, but I'm not a mechanic by trade, so I feel like a project like this might be too big for now and end up leaving me frustrated.

If this isn't something I should attempt and can't get fixed until the fall, should I be continuing to ride on this bike?

 

There are folks here that can walk you through it. You don’t have to be a mechanic by trade but you should have some mechanical ability. If so, you can do it. Listen carefully to the advice you will soon be receiving, follow it, don’t be in a hurry (biggest problem for me), and you can do it and know it has been done right. My experience with shops when I first got my bike was not good and I had to redo everything I paid them to do. Most of us will agree that if you can’t work on your bike then you should get a newer bike. But, if you can work on it you will learn a lot, have a good bike and have a lot of fun. I would suggest that you get a goo set of JIS screwdrivers.

 

Please tell us how you know that the head gasket has failed. That is a very unusual problem, and there are more common issues which can lead one to beleive the head gasket has failed when it has not.
The high idle when hot is going to be carb related, not head gasket related.
And who told you that BS about adjusting the headspace ? (that's gunsmithing talk, not engine talk).

How long have you had the bike, and what work have you (not someone else) done to it?

 

Thanks Tabaka, JIS screwdrivers are on the way...you don't have to tell to buy a new tool twice.

Head gasket leak is (apparently) evident because spraying carb cleaner along the gasket in certain places will cause the engine to rev, or at least I was told by the shop I took it to. This is not something I've tested myself, but I suppose I should soon. Same shop mentioned cam chain, and head space (?) adjustment, though I may be misremembering what they were referring to. Let's just say they've told me multiple things that I've now realized we're incorrect (for example, told me the bike wouldn't start due to a bad neutral safety switch...turns out I just didn't have a side stand switch on the bike).

My experience is pretty limited, I've spent a good chunk of time working on the wiring harness (switching to LED lights), recently replaced the intake manifold boots. Is carb cleaning/jetting/calibrating the first logical step for me then? Working with pod filters currently.

 

Don't take their word for anything except for the bill total. Test it yourself and verify it is actually a problem. Check the head studs first and see if any are loose.

 

You can do it, just takes patience, attention to detail, and a desire to do things right. Cleanliness and proper tool are a must. I would be darn sure it's the head gasket before you tear into it. The gaskets and other items needed to replace the head are pricey, even if you determine the gasket is leaking i'd try a re-torque of the head bolts first.

 

Never heard of headspace and I have used guns in the past. The guys on this forum know their engines Chivin, I am learning from them and I can assure you you are better to check the simple things first, that way you will get your bike sorted at minimum cost and make it reliable.

 

first get the valves in spec then borrow a compression tester from a local auto parts store then loose the pods and get a air box.

headspace is the distance from the bolt face to the back of the cartridge

 

Or the rim, or the shoulder, the case belt, or the mouth, depending on what the cartridge is.

 

I have heard of squish clearance which I think is about the periphery of the top of the piston and the cylinder head. Don't know if it is creates swirl to mix fuel and air? Anyway thanks guys I learned another thing about firearms here.

 

The head and deck are machined to fit a specific type and thickness head gasket. Some squish, some don't. It depends on the type of engine and cylinder liner setup.

 

Squish has nothing to do with how the head gasket behaves. It refers to the part of the combustion chamber where the piston "squishes" the gasses suddenly because of the tight clearance. Not all combustion chambers do that, and it's mainly prevalent in 2-strokes.

 

I hope you don't mind me asking guys but are any of you mechanics or engineers? I assume the squish increases the efficiency of the engine with more power output? The speeds some engines work at it is amazing they stay together.

 

Squish (as I understand it. I'm just an advanced-shadetree mechanic when it comes to combustion chambers) accelerates the mixture towards the center of the combustion chamber (adding turbulance along the way), therby aiding in completeness of the burn. It also helps with thermal transfer to the cylinder wall.

 

The squish band starts at the outer edge of the piston where it meets the wall and the head. As k-moe stated, it helps create swirl and provides a design mechanism for shaping the flame front when it's ignited as well as a cooling point for the super-heated air charge while avoiding combustion. You want as much fuel and air in in that gap as you can get without it causing detonation before the compression is complete. Take a look at GDi piston shapes versus MPI and you'll see a difference in how the squish bands and bowls are set up to control the flame front. The fuel is only a factor at the point of peak compression in GDi so the squish band acts differently for combustion behavior.

 

Just what I thought the squish helps the burn k-moe. Shadetree mechanic never heard of that one before, too rainy in Scotland to need for sun protection from trees. Language and phrases are interesting.

Or another definition a hobbyist mechanic who works on their own vehicles, often in their driveway, and often causing more harm than they repair lol.

 

Interesting clever how they design these combustion chanbers.

 

I have seen dished pistons for example on some of the cars I have worked on, presumably to force the mixture towards the centre of the piston? The best burn happens so I have read when the ignition is advanced to the maximum ie the point just before detonation would occur. If there is a maximum of fuel and air in the squish area of the combustion chamber I assume the ignitor advances the ignition before the compression is complete to avoid detonation? Do the XJ motors use the YICS system to create the same effect as squish or do they use both? I know Suzuki had the TSCC was that a form of squish to mix the fuel and air?

 

The piston face controls the swirl of the mixture during intake and compression strokes. It also has a direct effect on how the flame front is contained during combustion. Bowl faces encourage full port mixing until ignition. Then the shape of the head and position of the spark plug determines how the flame front forms. GDi faces have a fuel swirl divot in the middle of the piston to catch the injector mist right before ignition and hold it in the center of the combustion space.

 

Chivin, I would guess you are getting way more info on the head gasket, but knowledge is a good thing. Let us know what course you are going to go with? I would start out with the head bolts and go from there. If you were spraying the back of the heads by the carb intake boots and the engine was reving, I would make sure that the boots are isolated from the spray. The boots on these bikes get cracked much more common than the head gasket. What location are you spraying when the engine starts to rev?

 

Yeah if it's the head gasket it would be dumping exhaust too so I'm still not buying the carb spray deal. Re-torque head studs and check compression.

 

Engine revving with carb cleaner or some type of flammable liquid or gas sprayed around the outside of the carbs, boots, connection at the head, etc indicates a vacuum leak, not a head gasket.

What I believe you guys are referring to as squish area in a piston/combustion chamber is primarily to increase octane tolerance. It's a tradeoff though because it increases the surface area to volume ratio, dropping efficiency for the same compression ratio. The theory is that an increase in compression ratio allowed by the squish, quench pads, whatever they're called more than offsets the increase in surface area to volume ratio, resulting in a net increase in power/efficiency. I believe the perfect chamber shape would be a sphere, at around 20 degrees past tdc, or whenever peak cylinder pressure occurs.

It's pretty sweet how the years we've spent learning about all this stuff will be rendered obsolete quite soon. Then we're all going to be learning about frequency drives, induction motors, the newest battery and capacitor tech, etc. Yay...

 

Define "obsolete quite soon" in a timeline Just saying I am all for self driving cars as people here in the USA can't seem to drive safe if they own a cell phone and a car. But to get rid of all gas engines and the vintages bike...hmmm Not in my lifetime.

 

Hey all! I'm going to re-torque the head studs first (assuming I can find the correct torque specs somewhere on here, which I'm sure I can). I sprayed carb cleaner along the gasket on both sides but didn't notice any change (like the shop had said). Being that I don't know if I actually have a head gasket leak or not at this point, are there any sure fire ways to know that I could test out myself?

Timbox, I actually replaced the carb intake manifold boots and gaskets recently, had some cracks, so I would I assume that if I have a vacuum leak it's not there.

Thinking I should move forward with a carb clean, tune, and rejetting first and see how it's running after? Main issue is that it's still just running very high rpms while idling once the engine gets hot.

p.s. never thought I'd learn so much about gun mechanics here...

 

Exhaust leaks would be a tale-tale sign more than anything else since there is no cooling jacket on these air heads. Compression is about the only other clue.

Heh, sounds like there's a bunch of reloaders on here. \o/ I miss 3-gun competition and building AR-15s.