Topic: Hot oil and WD40 for stuck rings

[Tim.]

My '76 CB550F is in the shop, and Cylinder #3 tested with very low compression (40% lower than the others which were all within 5 lbs of each other).  So, they filled the cylinder with hot oil and WD40 (don't ask the ratio - I don't know) and that apparantly got the rings loose.  They got the mix out (don't know how) and did another compression test and WHAM - #3 right up to the same level as the others.

I have to assume they accounted for the left over oil in the cylinder which for a time would have provided the additional compression.

Is this concoction a known remedy to stuck rings?

[Quail "Owner of the comfortable k8"]

1 of many.  GM makes an item called top engine cleaner, works like a charm.  It is made to decarbon engines.  The spray makes carb cleaner look like water.  I do not know if it is sold to the public now, for years it was not .

[kghost]

15 years as a Aircraft Mechanic and Authorized Inspector. Mainly with piston engines, everything from 65hp Continental to 2400hp Pratt and Whitney.

The best I have found to unstick rings is Marvel Mystery Oil. Squirt the cylinder full, Let it sit overnight. With the spark plug out, spin it through. The oil will come out the spark plug hole. Makes kind of a mess if your unprepared but it will loosen up stuck rings. DO NOT SPIN WITH SPARK PLUG IN.

The engine will smoke a little when you first start it up. Don't worry its just the oil burning off.

Works in the gas too. Supposed to lubricate the valves, guides and rings. Although I have no firsthand proof of that.

[Greg]

sorry for the stupid question, but what does it mean for rings to be stuck?  I thought low compression was a result of rings that no-longer sealed, letting some oil slip into the combustion chamber...

greg

[kghost]

Burnt oil and carbon can decrease the clearance in the piston ring groove to the point where the ring "sticks". Then the ring is no longer free to follow the contour of the cylinder wall and becomes "stuck" in the ring groove on the piston.

Remember combustion gases in the cylinder act on the rings to promote sealing. This is where the carbon/burnt oil comes into play. Remember the bevel on the rings? Its there for a reason.

Low Compression in a cylinder can be caused by a number of things:

Worn Cylinders.
Improper ring clearances
Stuck rings.
Burnt Rings (Hot combustion gases leaking by rings and piston)
Valves improperly adjusted (too tight)
Valves not seating (worn seats, Burnt valves, etc)

To Name a few.

On Aircraft engines we do a differencial compression check. This is different then a "Pump up check" in that it measures the pressure retained in the cylinder reference what is applied. For example: 80psi is applied to the cylinder and the cylinder holds 70psi. This gives an better indication as to the state of the cylinder. You can then listen at various points and tell where the problem is. Air escaping out the exhaust indicates an exhaust valve problem. Air escaping out the valve cover or engine crankcase breather indicates a piston or ring problem, Etc.

Oil slipping into the combustion chamber is just an indication that fuel/air is also getting out (thus lost horsepower). Unfortunately, Oil bypassing the rings contaminates the fuel/air mix and when in the extreme, fouls out the spark plug.

Keep in mind that oil burning is not always rings. Worn valves, valve guides and seals also have caused thier share of oil burning.

Hope this helps.

[Tim.]

If I'm not mistaken, the differential compression test you describe below is also known as a 'leak-down' test which is fairly common (at least for a decent mechanic  ).  A very very valuable test if you have poor compression and can't resolve it.  While I've never done it myself, I understand that some people even run the piston up and down the cylinder under pressure to see if there is a problem at a particular point in the cylinder?

Burnt oil and carbon can decrease the clearance in the piston ring groove to the point where the ring "sticks". Then the ring is no longer free to follow the contour of the cylinder wall and becomes "stuck" in the ring groove on the piston.

Remember combustion gases in the cylinder act on the rings to promote sealing. This is where the carbon/burnt oil comes into play. Remember the bevel on the rings? Its there for a reason.

Low Compression in a cylinder can be caused by a number of things:

Worn Cylinders.
Improper ring clearances
Stuck rings.
Burnt Rings (Hot combustion gases leaking by rings and piston)
Valves improperly adjusted (too tight)
Valves not seating (worn seats, Burnt valves, etc)

To Name a few.

On Aircraft engines we do a differencial compression check. This is different then a "Pump up check" in that it measures the pressure retained in the cylinder reference what is applied. For example: 80psi is applied to the cylinder and the cylinder holds 70psi. This gives an better indication as to the state of the cylinder. You can then listen at various points and tell where the problem is. Air escaping out the exhaust indicates an exhaust valve problem. Air escaping out the valve cover or engine crankcase breather indicates a piston or ring problem, Etc.

Oil slipping into the combustion chamber is just an indication that fuel/air is also getting out (thus lost horsepower). Unfortunately, Oil bypassing the rings contaminates the fuel/air mix and when in the extreme, fouls out the spark plug.

Keep in mind that oil burning is not always rings. Worn valves, valve guides and seals also have caused thier share of oil burning.

Hope this helps.

[kghost]

Correct. Its a little easier on an aircraft in that you can turn the prop to position the piston where you want it. Little harder on the 750 but you can use the "T" mark on the crank.

[bryanj]

Leak down is a really good test BUT do be sure you are exactly on TDC or that engine will turn over at a high speed when you put the air pressure on and the spanner you left on the crank will "fly" till it finds something to hit which by Sods 6th law will be either the most expensive item you possess OR the the most vunerable part of your body!!!

[MRieck]

Leak down is a really good test BUT do be sure you are exactly on TDC or that engine will turn over at a high speed when you put the air pressure on and the spanner you left on the crank will "fly" till it finds something to hit which by Sods 6th law will be either the most expensive item you possess OR the the most vunerable part of your body!!!

Well....I've never seen that happen!!

[Tim.]

Leak down is a really good test BUT do be sure you are exactly on TDC or that engine will turn over at a high speed when you put the air pressure on and the spanner you left on the crank will "fly" till it finds something to hit which by Sods 6th law will be either the most expensive item you possess OR the the most vunerable part of your body!!!

On a positive note, you'd be a shoe-in for the grand prize on America's Funniest Home Videos    Then you could go out and buy an artificial leg (or whatever other appendage was severed by your flying wrench  ) and a new bike.

[phylo101]

Best mix is....unmixed diesel/derv. A tablespoonful down each plug hole, tread on the kicker for five minutes....works wonders. AND itll burn away sharpish if smokyish lol

phylo

[74cb750]

hey phylo101, what is diesel/dri ? to clean out the carbon?

[Terry in Australia]

No-one has yet mentioned glazed bores causing low compression, which happens quite frequently with infernal combustion engines, I had this problem with one of my suzuki engines when I got a little over exuberant with the amount of engine oil I used to lubricate the cylinder walls after honing an engine for new rings, it smoked like a bastard!

Earthmoving equipments are commonly afflicted with cylinders glazing up, a friend of mine runs a Cat dozer that actually comes with a can of abrasive (they recommend Ajax if the Cat product isn't available) that you are required to sparingly tip into the air intake while the engine is running, which fixes the problem instantly.

Another friend had this problem on his CB750K2, it had been sitting for many years with oil in the cylinders to stop it from seizing, but was using oil at an alarming rate once put back into service, so having a tin of Ajax available, we warmed the engine up, took off the airbox and passed a teaspoon of the stuff past the rear of the carbs, allowing the suction to draw it into the engine.

The engine momentarily farted and burped, and coughed out a cloud of black smoke, then cleared itself. We took our bikes for a brisk 100 mile ride and so far the smoking and oil consumption have not re-appeared. I've also been told that spraying a mist of water with a little pump pack into the carbs while the engine is running will cause super heated steam inside the cylinder and combustion chamber which will have a similar effect. Certainly worth trying if you think your engine is on it's last legs and you've got little to lose! Cheers, Terry. 

[Kixx007]

1 of many.  GM makes an item called top engine cleaner, works like a charm.  It is made to decarbon engines.  The spray makes carb cleaner look like water.  I do not know if it is sold to the public now, for years it was not .

That stuff is hard to find, and $10 a can when you can find it.  OMC (Outboard Motor Company) makes it too, and most marina's carry it.  It works AWESOME as a carb cleaner. I've filled carbs on the bike with it, let it sit overnight, drain the bowl, and the bike will run when it wouldn't before.  We use it as carb cleaner in the shop, rather than regular carb cleaner.  "Carb Cleaner" eats rubber seals, its crap, we dont even have a can in the shop.

[galaxian]

Kixx what is the specific name and brand you are reffering to?

[Harry]

I've also been told that spraying a mist of water with a little pump pack into the carbs while the engine is running will cause super heated steam inside the cylinder and combustion chamber which will have a similar effect. Certainly worth trying if you think your engine is on it's last legs and you've got little to lose! Cheers, Terry. 

The old blokes always tell stories about how they, in the day, would pour soda water into their carbs to remove carbon buildup. Always thought it was BS but having been hearing more of the same recently. Yeah, if I was Bruce Springsteen damn! I would have lot of stuff to write songs about...