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AQ170 smoke from breather

C

cj270

Member
"Hi,
I bought an AQ170 engine

"Hi,
I bought an AQ170 engine from a vendor in the USA (I live in Sri Lanka)
I was told by this guy that the engine had only run 250 hours from new.
I started the engine for the first time today.
It starts immediately and runs very smoothly with no mechanical noise at all.
I ran it with the air silencer off and I noticed a slight mist or smoke from the rocker cover breather. This engine has sat around not being used for a long time.
Is it normal for this model of engine to emmit a slight mist from the breather ?
Could it be because the engine has sat doing nothing for a long time ?
Will it go away with use (after the rings bed in again)"
 
"Chanaka, I too have an old A

"Chanaka, I too have an old AQ 170. It is new to me and has many hours. It puts out so much smoke from the breather tube that the previous owner was changing spark plugs quite often due to the oily breather gasses going into the intake system fouling the plugs. Folks on this site tell me it is probably a bad rings problem creating so much blow by gas. I have re-routed the breather tube away from the air intake box through a thru-hull fitting out the transom (WELL ABOVE WATERLINE!). Now I can see how much blowby gas is being produced, and my plugs won't foul. Eventually I will have to pull the motor and do the rings. However, as I run the motor more I notice less blowby gas behind the boat on each trip. I have also noticed that once the motor warms up it produces less blow by gas also. The boat is currently out of the water waiting for me to put a fresh rebuilt head on it. Not sure I helped you much but based on what I have seen with my tired motor I think you might see a reduction in the blowby gas production in your motor as you put more hours on it. I am sure others on the site will weigh in soon too.

Good Luck!

Matt"
 
"What weight oil are you using

"What weight oil are you using? It has been suggested that less oil will blow-by the rings etc if a heavier weight oil is used.

fwiw, Tom"
 
"Thanks Matt and Tom... my mot

"Thanks Matt and Tom... my motor is producing very little smoke from the breather. It is supposed to have run only 250 hours from new. This is why I am wondering if it is smoking due to lack of use rather than too much use.
When I turned the crank with a spanner for the first time, it turned very tight after about half a turn, it turned like normal. May be the rings or bores had a light coating of surface rust. I hope the smoke will clear with use. I have still not run the boat. I am just starting it out of the water. At the moment I am using 40 weight oil but will change to 50."
 
"I am not sure that I would us

"I am not sure that I would use a 50 wt oil, seems too thick to me. Maybe a 20W50. Pumping straight 50 weight may not be good for cold starting. My engine also sat for a long time when I bought the boat. I did a compression test and found two cylinders low, one at 90 and the other at 120 psi. Sounds like it needs a rebuild, right? Wronmg, after running it a few times I redid the compression test, this time all 4 cylinders were at 150 to 155 psi. Just needed to be run in a little ro reseat the rings. If you are worried about the engine, run it a bit and then do a compression test. It will tell you whether or not you have excessive blowby and the condition of the engine.

Have a great day,

Rob."
 
"Thanks for that Rob. I too ho

"Thanks for that Rob. I too hope that my slightly smoky breather is due to un seated rings.
Here in Sri Lanka, the temparature is 86 farenheit or warmer all year round so we use 50 weight oil in a lot of our older vehicles. We don't use multigrade oils here because we do not have a Winter."
 
"Chanaka,
I have an AQ 1

"Chanaka,
I have an AQ 130 an even when new there was always a little vapor from the breather tube and it never really burned any oil. If in fact you are burning excessive oil then you do have a problem. I would do a compression test to see if you have a problem cylinder."
 
"Just beware that the reason f

"Just beware that the reason for crankcase ventilation is because when you disable it, the crankcase fills with coke! You are doing your self a disservice if you disable this flow from being routed back into the cylinders and allowing it to be re-burned. If there are carbon deposits on your plugs you need to determine the source and if your cost verses benefit agrees, then correct it. Sometimes fowled plugs come from bad valve stem seals, sometimes it is the rings, and sometimes it is from burning a rich mixture. Seeing some smoke coming from the breather tube is absolutely normal. It is from 2 sources: blow-by from the piston rings and from the oil itself smoking when it gets hot. This smoke needs to be removed from the engine block because it is bad stuff that clogs up everything when it condenses back into a solid we call sludge or coke. Finally, I would never use an oil viscosity that the manufacturer did not recommend. You may fix one problem and introduce several other new problems that are worse. Remember Plugs are cheep and can be cleaned. If your compression is good and you have plenty of power and are not polluting the lake, then don’t worry – be happy!"
 
"Handy Man, are you saying tha

"Handy Man, are you saying that to properly vent the blow-by gasses the crank case vent MUST be attached to the intake manifold? Just letting it dump out to the open air via a tube out the back of the transom is not good enough (enough flow/draft)? I know that on commercial diesel engines like semi trucks at least some of them use a RDT or Road Draft Tube that carries the crank case gasses out to open air, typically dumping it out under the engine next to the oil pan I was assuming that this principle/method would work on a boat motor as well. Maybe I am wrong. If so, hopefully my rings will seat more positively with use and I will continue to see less vapor out my "marine RDT" and then I can re-connect the tube to the intake manifold.

Thanks for the warning!

Matt"
 
"Matt you need to keep the eng

"Matt you need to keep the engine clean because internal sludge lowers the life of an engine. Venting your crank case into the atmosphere is a time honored option, but not very efficient. I remember seeing that commonly done in the 50 and 60's. And also remember seeing a lot of sludge in the valve covers when the valves needed to be set. Granted, they now have detergent and synthetic oil which cuts down on sludge. In the 70's they invented positive crankcase ventilation (PCV). The idea was to pull the smoke out of the block by routing a vent line to the low pressure intake manifold. I modified my engine years ago by installing a PCV valve that connected directly to my intake manifold (not my air cleaner like Volvo Penta did). This vented in through a modified oil filler cap. It actually helped my engine to run better and cleaner by making my mixture slightly leaner."
 
"Handy-man, Thanks fo the inf

"Handy-man, Thanks fo the info. BTW, how did you get the gasses into the intake manifold through an oil filler cap?... wouldn't that dump it into the valve cover right back into where you want to take it out of? I don't see how that set up would work....seems that set up would put the gasses on the wrong side of the valves, up by the stems.

Matt"
 
"Glad you ask… I disassembled

"Glad you ask… I disassembled the cap and drilled three ¼ inch holes through the lower section. The gap between the upper and lower sections appeared to have plenty of breather space due to the hand grips so I left the upper section alone. Then I purchased a small crankcase breather element and removed the filter part of it that looks a lot like the green scott bright only it is white in color and I stuffed it into the space between the upper and lower sections of the cap. Now I have a vented filter/filler cap...

To me, the intake manifold was the larger effort. Here, I had to find a good welder that could weld aluminum and have him weld 2 solid round stock pieces on to the thin tubes that cross connect the three larger manifold sections in their centers. This balanced the flow between all three carburetors and the thick stock pieces welded on to my manifold gave me something to screw a pipe threaded fitting into. From these 2 fittings, I cross linked the vacuum hoses to a T fitting that connected through a third vacuum hose to the PCV valve.

If this site allows, and I can think about it, I will go home and take a picture to upload for review. It will be a picture of the manifold with the modification and no engine. After 32 years, I am finally getting around to overhauling the engine. It was running fine, but that is too much time and the parts are getting more expensive and rare the longer I wait."
 
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