Case Study - Compression and Leak-down Test Results

Patient Description:
1982 XJ650
17,860 miles
Stored in father-in-laws attached garage for 19 years.

Symptoms:
Compression test results - Dry:
1 = 0 (zero) psi
2 = 0 (zero) psi
3 = 50 psi
4 = 50 psi

Compression test results - Wet:
1 = 180 psi
2 = 180 psi
3 = 180 psi
4 = 180 psi

Leak down test (all blow by coming through crankcase, not intake (filter) or exhaust valves (exhaust)):
1 = 30% loss
2 = 35% loss
3 = 35% loss
4 = 30% loss

Initial diagnosis tells me patient has piston ring-a-titus.

Procedures performed since cylinder testing (not all were directly performed to address ring-a-titus) :
- Rebuilt carburetors completely (19 years of hard varnish and green slime)
- Bench synchronized carburetors
- Checked valve clearances and replaced shims to put back in spec
- petcock rebuild (not due to symptoms, just due to open opportunity
- New plugs
- New battery
- Was able to get engine started relatively easy after performing the above.
- Carbs vacuum synchronized (using two bottle method, plus oil soaked t-shirt strips in YICS chamber).
- Engine runs relatively smooth (did I mention it's been 19 years since its last gasp of air)

- Ran another compression test after having warmed up the engine with the following results:
1 = 80 psi
2 = 80 psi
3 = 80 psi
4 = 80 psi

I see improvement!!!!

Seeking second, third, fourth, opinions from the community regarding rehabilitation plan for ring-a-titus.

- considering running engine through several heat cycles after having added 8 oz of Marvel mystery oil into engine oil. And continuing a series of compression and leakdown testing to track results. Doing this in hope of dislodging carbon or oil crud or whatever may be causing ring-a-titus.

If the rings have 19 years of crud around them and they have stuck to the piston, perhaps the rings will work themselves free after several engine running cycles?

Other thoughts out there? Is there an additive I can squirt into the piston chamber to help dissolve or free up stuck rings?

Thoughts?

 

I'm more inclined to think the rings have "harvested" a nice load of rust dust off the inside of the cylinder walls that will just get packed behind them eventually. Or they are indeed just gummed stuck.

With that few miles, and the "evenness" of the numbers you're getting I would STOP RIGHT NOW and pull the cylinders off and clean everything up real good.

Dumping stuff in the cylinders and running the engine might help eventually, but you stand to damage an engine that currently is probably in pretty decent shape.

 

Thanks for the reply Fitz.

Ok, so talk to me about engine gaskets. How many times can I re-use a new cylinder head gasket or do I need to reach for a new one each time the cylinders get pulled? Would imagine I don't need to heat up the engine to get compression results and therefore wouldn't bake the cylinder head gasket? thinking if the cleaning does not do the trick, new rings and re-honing are needed. Just want to avoid any unneccesary additional new gasket purchases because I didn't approach it correctly.

 

after 19 years of sitting those gaskets are gonna be brittle ans probably original.
I agree with fitz here bro dont run it with all that crap in the cylinders.
Also it wouldnt run if it was only really producing only 80 psi for real I 'd think. you probably have a pretty good plant. get some gaskets.
you seem to have a really good hande on things though. +1
Chacal has what you need

 

did i miss something ? did you say NEW HEAD GASKET ALREADY?

 

No gaskets have been replaced, appear to be all original. Didn't want to start breaking her down before I picked up some additional knowledge and confirmation. Sounds like she needs to be opened up and cleaned. In that case, I am planning to buy the complete engine rebuild gasket kit (chacal)and refresh everything.

Would you recommend lapping the valves since I would have access to do so?

 

If it was mine and I had it down already I would. kind of a case of "why not"
that's just me though, you dont have alot of miles on that engine but it cant hurt anything, can only do it good but I dont think it would be critical.

 

Are you talking cylinder head gasket or are you talking about the valve cover gasket?

The cork head gasket, if new, is a $90 gasket. And, yes, if you didn't goop it up with RTV you could re-use it if you were careful pulling the head again, since you haven't put any miles on it. Put 100 miles on it and pull the head again, I'd buy another gasket.

But I don't think that's the gasket you are referring to.

I think you mean valve cover gasket. Otherwise you would have looked at, and hopefully attended to, the ring problem.

The valve cover gasket for your bike is rubber, and yes, a new one can be re-used quite a few times. As well as the rubber donuts that actually hold the cover on. I hope you replaced those as well.

They're right, you probably have an excellent motor, but you need to pull the head and get the rings/cylinders fixed before running it again.

 

tskaz - I am referring to the Cylinder head gasket. I have not purchased any new gaskets yet and haven't opended her up yet past the valve cover to swap out shims.

The valve cover gasket is also needing replacement too, along with all the other 30 year old gaskets/rubbers. Sounds like there is a limit to how much heat you might put on a new cylinder head gasket before it becomes unusable? The bike is not in riding condition, so the engine would only be running while parked to get tests completed.

Once I get the rings cleaned, all new gaskets will go in. Just won't know until she is buttoned up if the cleaning boosted the compression numbers to an acceptable range. If not to an acceptable range and the head gasket received one cycle of no load normal operating temperature, would the head gasket become unusable?

 

while you have it open....
measure/check the cylinder... out of round, etc...
measure ring end gap
check the rings
check the cylinder walls
if you lap the valves, consider the seals
check the valves.. roll them on glass
all this checks out and you get the head on good with a new gasket your numbers should be great
lastly..MANUAL MANUAL MANUAL refer to to manual several times as you work
I figure you got a good handle on this and probably already know all this just throwing it out there.
THEN once done.. coupe oil changes often for the first thousand miles and dont dog it, its almost a new engine now and lots of those miles are erased, not all but lots

 

One short heat cycle won't compress the gasket to the point of not being able to re-use it, but if you do everything we are suggesting I really don't think you would have to worry about pulling it again.

 

Intend keeping the bike?

Personally, if you are going to disturb the rings, I would replace them and give the bores a light hone.
Your results show the valves are fine, but you may regret not replacing 30 year old stem seals while its apart.

A quick top end freshen up done properly would not require it to be looked at again for a long time.

Open it up and then work out what you really need before acting.

 

tskaz & darkfibre are right-once you're in there and put it right, you won't need to go back in anytime soon. By your first test I would have said you have major problems, but looking at your wet test and your even numbers after it ran (and that it ran at all)-it sure looks like it's in better shape than you would initially think.

New rings are likely needed or at least a good idea since they aren't expensive, and a honing. Because it sat so long I would replace what you can while you can and go over everything carefully. Might as well do it right rather than do it again. Mileage is not bad though and once you're there it should have much life left.

+1 to not running it more until you get in there. 80psi is barely enough for it to burn. If it was a lawn mower I would say put in the heaviest oil you can find and run it, but it's a much finer engine than that.

Nice work on your diagnosis! Looks like you have it well in hand.

 

Given the information supplied for the Patient.

If the Head is coming off, ... Don't stop there!
Like the Old Saying goes:
If you're going to New York; see the Empire State Building!

The prudent thing to do is Hone and Cross-Hatch the Holes.
Clean the Pistons.
Gap-check to see if you need Std or Over-std Rings.

Service the Head.
Clean all the Valves.
Clean-out the Ports.
Lap the Valves and use New Valve Seals.

 

Bingo.

Clean, diagnose, MEASURE. Measure cylinder bores, piston diameters, ring land clearances, ring gaps, etc. As pointed out above, all of that is in the manual. Don't buy rings until you know what's going on.

And just because of the PIA factor with the DOHC, I would certainly lap the valves and replace the valve stem seals while it was apart.

Do it right the first time and there'll be no need to take it back apart. Proper and careful diagnosis will eliminate any guesswork.

GET A FACTORY MANUAL if you don't have one.

 

+1.
Even though 17k is just a good really long brake in period,
sitting for so long has it's own negative affect.

One could hardly imagine any power plant needing honing,lapping, seals
etc. at those miles if new. But the other guy's are right on the mark.

As long as you'er there-do it right and never look back.

 

+1 to ring-pack clean-out and all the other preventative maintenance.

Trying to "Marvel" an engine back to life should be kept to lawnmowers.
You could hopelessly score the bores and mar the pistons.