need valve work: total re-build?

my xj has started to give me a little bit of very slightly blue smoke from either #3 or #4. after talking to a few people it seems that valve seals may be the problem. Len suggests about $250 in parts be replaced. another suggests I have the valve holes kneralled. I doublt that is the correct spelling. to do that I have to remove the head and take it to a parts store. he also suggested I have it put in a vat of hot acid to clean it. if I really need to take the head off, and have it dunked in some stuff that will make it nice and shiny, home much more work am I looking at to send the part under head sent in also? I have been planning on polishing my valve covers, but didn5 know what to do about the coolong fins. the po rebuilt much of the lower end, as well as new valve shims, about 10k miles ago.

the other hickup is that I have been offered an 81 maxim that has been garage kept, but parked for about 7 years. he wants $300 for it. I'm leaning toward not worring about the 82 for a bit. getting the 81 and seeing what it would take to get her on the road. if not much then I can ride her while I do a total teardown of the 82.

I have already spent my fun money for awhile. the wife isn't going to be too happy if I try to get the 81 and buy the valve parts at the same time.

 

Maybe you should do a leak down test on your motor to see where the problem lies. Or just do a dry compression test and then do a wet compression test. If the compression comes up alot when wet you may be looking at rings and pistons vs valve job.

 

Leak down test? Can you elaborate?

 

You would have to get a leak down tester. This tool enables you to pressureize your cylinders and locate the leakage and give you a percentage of leaking, You may find your rings might be leaking nore than your valves are. If for example you have been running lean for along time you might have worn rings and burn't pistons. You could do a compression test and narrow it down or you could leak test and find out how bad it might be.

 

Scoop the 81 and ride while you save up to fix the head right (new valve guides and such, like Len suggested). You need to do a leak-down test to determine if it is valves or rings. Big difference between the two.
You can change out the guides yourself and save a few bucks on machining. Knurling isn't a bad way to go but for the cost and time invested, you may as well have the guides replaced.

 

How do you know you need valve guides? The seals are 26 years old, and can leak without having bad guides. How many miles on it?

In either case, I wouldn't do the rings unless I knew they were a problem. I believe you can get the head off with engine in frame, but will have to remove engine to get the jugs off.

 

The guys at the engine shop would know not to do it, but just in case, do not hot tank anything made out of aluminum. It will disappear.

 

Jugs? I'm a little slow on engine terms.
Top to bottom:
Valve cover
Head
"jugs"?
The rest of it..

MacMcMacmac (what a SN..) disappear huh? Not quite the way I wanted to eliminate my problems...

As for miles...unknown. Somewhere between 60k and twice that. PO had it for about 20k.

 

You think this bike has 60,000 miles to 120,000 miles. That would be concidered to be on the high end of the scale for these bikes. Most don't make it that far due to lack of maintenance. I think you should do the tests we have told you about and see where your at. If it were me I would look for another engine before I would spend any hard earned cash on that one, just for the fact it has so many miles. I'm sure some of the guys here have a line on a lower mile motor for what you would have to spend on rebuilding that one. Keep it for parts for sure.
I happen to have a spare 81 650 engine with less than 10K on it. Tryed to sell it but no one was interested at the time. So it just sits under my work bench all oiled up for a rainy day. Its not a YICS engine so I guess its not very desireable.
Good Luck and hope all works out for you.

 

How do you know you need valve guides?
You need to break down the head and gently rock the valve (freed of it's collets and springs) in it's bore. More play than a few thousandths (don't have the book handy for specs on this one) and you should consider new guides. If your guides seem ok, just replace the seals. You can go the easy route and just replace seals to begin with and see if that clears up your problem. If it doesn't, you might need new seals again when you rebuild.
You would have to pull the engine to get the "jugs" (cylinder block in our case) off.
Aluminum in a hot bath tends to erode away because the bath is caustic (acidic). Not a good idea on aluminum heads with tight tolerances. If left in the bath too long any aluminum part will dissolve.

 

First off; yes, from top to bottom: Valve cover; cylinder head; "jugs"=cylinders (with pistons inside crankcases (everything else.) If this motor really has between 60K and 120K more than just the valve stem seals are going to be worn out. While an XJ motor with that many miles on it can be rebuilt, at what exhorbitant cost, in both time and parts? These things get parted out all the time, I would go for the newer bike and then look for a MUCH LOWER mileage mill. Lots of XJs get torn down and sold as parts with less than 20K on the clock. I just bought some stuff from a 550 that went for parts with 9985 miles on the odo.

 

You Could just replace the Guide Seals ? In place on the bike with the head where it is now. No big deal it's done all the time.
Two methods available:
One: is an Airline into the spark plug hole Fill the cyl with PSI then remove the valve springs and replace the seals.
Two: stuff the combustion chamber wirh a soft flexy sailing type rope again filling the chamber to keep the valves firmly against their valve seats. Then remove the valve springs and replace the seals.
Seals are like $2 each or less.

 

After talking to the PO at great length I can give a better explination of the work that has been done to my engine.
It has about 80k on it. About 30k ago he did the following:

Head gasket (I have since redone this, as the gasket was contaminated).
He pulled the engine and:
resurfaced the head, replaced all bearings in the tranny and about 1/2 the seals.
He changed the starter seal, carb seals (?).
He did nothing to the valves except check/change the shims. He did a 95% rebuild of the carbs. I don't remember their name, the things that have the rubber cone that raises or lowers the pin? Kinda like a speaker... you see them when you first open the top of the carb? He didn't change those, but they are in decent shape from what I remember when last I opened them.

Did NOT change the exhaust deals, rear main seal (now leaking), shifter seal (now leaking). Did not remove the crank or the pistons.

MN-Maxims: Whats the going rate for that mill? It may be worth it depending on the shape of this 81. I haven't seen it yet, but from what I understand it is in good cosmetic shape. I can't help but wonder what parts I can use on the 82. Of interest would be side covers, seat, shocks, forks, bars and exhaust.

I think I'm going to ride the 82 for just a bit longer and see what happens. About when the snow starts I'll take it back up to the inlaws shop and see what kind of damage I can do then.

Does anyone know of any books that would give details on some of the tests that were mentioned? I just don't understand the mechanics of a leak down test.

Thanks for the input everyone!

 

How much does it cost to have 4 cycinders honed and then valves lapped and then for a set of rings?

 

Here is a pretty good description of a leakdown

http://www.carcraft.com/techarticles/11 ... index.html

 

bill: Thanks for the link. It explains a lot!

 

Lapping valve and replacing seals is probably easier than changing your oil.