Is the fact that oil's octane rating is below what the octane rating of the gas used in the motor not point enough? Ever tried running 87 on a 93 tune? Imagine it being twice that bad.

 

I'm not taking for granted someone says the octane of motor oil as gospel.

I'm not sure it has anything to do with this FRIENDLY debate anyway. There may be some issue that even if it did have a low octane rating, it would have to perfectly mixed with the fuel to cause some problem. But leave that part out of the debate for the moment.

Let me clarify what I said about oil doesn't burn. I was a little liberal in that statement. What I should have said was it doesn't burn easily and in particular in the combustion chamber. I think we can all agree oil resists being ignited otherwise why would it foul plugs so easily. Oil of all types is low in volatility that is why you use kerosene to start burning the leaf pile not gasoline.

The other point I was trying to make(but didn't do very well) was. Why if you mix something that is highly volatile (in this case gas) with something that is low in volatility (in this case oil) would you end up with something that is higher in volatility then either of the 2 original components??????????? That is ludicrous.

Now stop and think about that last statement for a moment before you jump on the "beat speedy" band wagon. High plus low = even higher ?

Next point is, detonation is the collision of opposing flame fronts. Some other point ignited in the chamber in addition to the sparked flame front. This second ignition comes from a hot spot in the combustion chamber. Why would oil increase the tendency for fuel to react with these hot spots? Forget the octane argument for the moment and think of oil as a fuel. Won't the oil tend to coat things and form either an insulating barrier or simply cool the surface it comes in contact with? So why would it cause an increase tendency to ignite or preignite.

Next point is, I looked up several documents regarding both detonation and preignition. They came from Hastings Mfg. located here: http://www.hastingsmfg.com/Service%2...reignition.htm
Here from Dyno Power http://www.dynopower.freeserve.co.uk...reignition.htm
and another here http://www.lycoming.textron.com/main...ineDamage.html

And they do mention octane as a factor in det/preignition. But they, NONE of them mentions oil specifically. Nor have I found any thing with regard to oil and octane of oil/fuel mixture.

Last point is, with regard to the person that started this thread. His was a 2 pronged point but a one part question. Does preignition cause a bent crank? I think that long before a bent crank might occur, it would have damaged, pistons, rings, valves before it would have an effect on the crank. If you look at documents regarding det/preignition, you see a list of effects it has on engine parts. I have yet to see a list that has cranks or even bearings in it.
I think (notice I don't say ***-U-ME) that he incorrectly assumed oil causes detonation and incorrectly assumed detonation caused the crank to bend. I think more likely the shop just said it was bent so they could charge to fix it. BUT that gets off point.

Let's remember that this is just a discussion not finger pointing and I personally love indepth discussions of why or how. I'm open to influence, dispute, anything to see anothers point.

Let's hear it folks.

 

Very well said speedy and will totaly agree with you. Yes if he was seeing detonation at a level that bends cranks it would have shown much more problems on the pistions and valves. As for hotspots that could have been one of the valves edge if it was hanging down and not seating.

 

"Can detonation bend a crank na?"

yes

SStrokerAce, where did you get the information of oil having a rating of 81 octane? I have searched and can’t find it, but that doesn’t mean its not there.

higher octane fuel burns slower like speedy said, so put that into perspective. if you add oil to gas, it’s only going to burn slower but I'm sure it will make things very dirty which is not good. I don’t know if you can get enough contaminates (from the oil burning or lack of burning) in the cylinder to cause the pressure to rise enough to get detonation but I think if you add the fact that the fuel is not completely burning (due to contaminants burning very slowly) and the fact that you are only adding more fuel and more contaminants with each cycle, I’m sure that you can get enough pressure to cause detonation. before things get that bad, I’m sure you will have fouled out a plug or two and the engine will be running very poorly. this is just my thinking so someone please inform me if it is not correct.

people should realize that higher octane ratings on fuel mean they burn slower, not faster, and that is what allows you to run more compression, advance timing, and such. higher octane is not what makes the power.

As far as the original post, I don’t think that the detonation caused your problem, but I think it would be a possibility.

 

Oil in the combustion chamber increases the engine's octane requirement in that cylinder. So yes, oil will contribute to knock.

 

Rich,
It takes 6 drops from my burett to equal 1 CC. If the DCR is/was on the ragged edge and the timing was set to "just under" rattle,taking 1CC away from the chamber = what?
If all the oil don't burn on "every" power stroke ya have a build up in the cyl. How much,don't know. Any amount would increase the compression and if the dilution of the fuel= lower octane then it will rattle.
http://www.avweb.com/news/columns/182132-1.html
http://www.avweb.com/news/columns/182084-1.html

 

LR: makes sense. I wasn't thinking about possible accumulation of oil. And as you say, if it's already on the ragged edge....

Rich

 

Noob here, but I agree with 1racerdude because oil buildup in the combustion chamber will cause a raise in compression and and the contaminants in the oil could cause detonation as stated earlier due to an incomplete atomization of the air/fuel.

 

Well we have a very interesting conversation here. Maybe the raise in compression is not that unfeasible. But I disagree with the thought that oil could cause detonation due to incomplete atomization. If fuel is not atomized properly, it is harder to ignite NOT EASIER.

That is why carbed engines are harder to start when cold. The fuel is not atomizing when it goes into the cylinder because the walls are cold. Yeah I know the intake runners are cold etc..... But for example when you start up a string trimmer. It takes a few moments to reach it's full speed. That is because the cylinder walls are cold. The fuel goes in and instead of atomizing when it hits the cold cylinder walls, it forms droplets. Now as the engine heats up, the fuel when it goes in the cylinder, hits the walls and now instantly atomizes to burn much more efficiently. Anything that causes the fuel to not atomize properly, would thus cause it to not burn properly and would IMHO not cause it to det/preignite but rather the opposite.

I would also like to thank racerdude for holding my opinion up regarding the possible increase in CR. I know we don't always agree on things and I have a new, entirely legitimate respect for you. Not because you agree with me. Because of the scientific way you have to look at this and some other things as well. I still like people to disagree but if you do, explain why.

And I thank firetird (that's funny right there) and imnotfast. For a while there, I thought I was going to get lynched.

 

Speedy,

Do me a favor and build a motor without a oil ring, 12:1 and run it on pump gas.

Oil does not have to be mixed with the fuel to cause preignition.... in fact having it not mixed will cause the situation to be worse.

Good luck with your findings.

Bret

 

Thanks Speedy,

 

Are you confusing misfiring with detonation/preignition? Read on.

Well I have torn apart hundreds of engines that have had a bad oil leak. NOT one of them has shown the typical signs of detonation. You can view that evidence here. http://www.hastingsmfg.com/Service%2...reignition.htm





I think what many refer to as detonation while oil is getting into the cylinder is in fact misfiring caused by a fouled spark plug.

Remember, the debate is over detonation/preignition. Not whether the cylinder is going to misfire. WE ALL KNOW THE CYLINDER WILL EVENTUALLY MISFIRE.

So the spark plug will misfire but I'm saying oil will not increase the likely hood of the cylinder to detonate or preignite.

One last thing everyone seems to be forgetting. On our engines, the KS is going to pull timing so the likely hood of detonation is even further reduced.

IF you still feel that oil is likely to cause detonation, why don't you suggest the method by which it will occur rather than saying to build something wrong and see if it fails? So far I haven't seen anyone offer up evidence of oil causing an increase in detonation.

 

We already have numerous times but apparently you don't like to listen.

 

the the contaminants from the oil not burning completely could cause the probability of detonation to increase. i *think (ouch it hurts when i do that) that the contaminants could increase the compression in the cylinders, which could lead to detonation, or they could be hot enough or leave hot spots which could cause the gas to ignite prematurely resulting in detonation. just my thoughts, but i could always be wrong.

 

I read through this thread quickly and may have missed it but this is the closest I've seen to the actual cause of pre-ignition combustion chamber detonation due to motor oil being introduced into the combustion chamber at an excessive rate. why? Hot spots is a term I will agree with.
Just my opinion:
The motor oil, 5w-30 or whatever, is designed to lubricate more-so than being of a formulation that will burn somewhat efficiently {such as 2 stroke chainsaw, ect. mixable lubricate} without producing a un-uniform carbon by-product that becomes a burnable, but not volitle or combustible, solid coating that covers the top surface of the piston and the chamber area of the head. After several occurances {RPM x XXX} of the repeated ignition of the A/F charge in the combustion chamber heating these carbon deposits, they become heated to the point of being able to ignite a compressed A/F mixture similar to how glow plugs are used to start a deisel engine during cold cranking situations. Therefore they could certainly cause the more volitle gasoline A/F charge being compressed to detonate prematurely, more-so when the A/F charge ratio is leaner, which promotes a more opertune enviroment for volitility to occur due to the oxygen providing enhanced volitle characteristics {to an extent} of the A/F charge being compressed in the chamber in relation to a poor {but adequate under the right circumstance}ignition source provided by the heated carbon deposits.
I agree with whoever said the pistons and rings will fail before detremental crankshaft damage will occur, at least with stock pistons and rods. I have trashed a very good quality set of forged pistons and rods due to a fuel supply failure in a blown SBC with no damage to the crankshaft as far as twisting. But that crank was not re-used for other obvious reasons.
As I said, IMO

I didn't know they had an octane rating for oil. I learn something new every day.