Question about Blow-by

[listerboy]

How much blow-by is acceptable and what are the contributing factors to excessive blow-by?
The engine in question is a 2cyl liquid cooled 15hp @ 1800 rpm. It has about 90 hours on it and the blow-by has improved somewhat from what it was when new. Under full load the amount of blow-by would fill the 10x12 shed in 10 minutes. It came out of the breather cap which is actually the oil filler cap and breather cap combined. The top of the cap is drilled through horizontally to form four holes that allow the engine the breath. Theres just a piece of course steel wool packed into the cap as a crude filter.
Problem is, the cap is in the top of the valve cover and the combination of blow-by from the crankcase and oil splash from the rockers lets out not only fumes but drops of oil as well, creating quite a mess. I ended up running a 5/16" hose from the valve cover to a tap on the air filter which created enough of a vacuum in the engine to solve the problem. When I crimp off this vacuum line to check the blow-by it seems to have improved but I'm just wondering if there is something else I can do or check. Or do you think it will continue to improve with more hours on the engine?
 

[compig]

well by any standards that sounds excessive !!  Blowby is a result of substandard ring to bore seal , either through wear of bore or rings or both. Do a compression test to determine the extent of the problem.

[listerboy]

If I remember correctly, the compression test I did at about 40 hours was around 435psi on one cyl and 450 on the other. The blow-by is a little more than half of what it used to be. If I can find the time I'll do another compression check just to see if anything has improved. While doing the check I remember hearing air escaping from somewhere but didn't pull the intake and exhaust manifolds or valve cover to see if I could find out where. The engine seems to run OK and the temperature spread between the cylinders is less than 10 degrees if that means anything.
Thanks for the reply.

[1958steveflying]

Hi. what oil are you running on. sounds like the bores may be glazing.

  Steve

[listerboy]

Sorry, should have stated that in the first post. It's Rotella T 15/40. The engine has a block and oil pan heater. Think a straight 30 or 40w would be better?

[1958steveflying]

This is just my opinion, modern oil reduced wear technology doesn't help engines break in/run in.  A basic straight sae30 or 40 diesel grade oil and only running the engine under a reasonable load is the best to avoid glazed bores and rings. i would change your oil for one of these types and see how it goes, maybe if it is glazing its not too late.
http://www.morrislubricantsonline.co.uk/scripts/prodView.asp?idproduct=165&product=Golden+Film+SAE+30+Classic+Oil

  Steve

[oliver90owner]

Under full load the amount of blow-by would fill the 10x12 shed

Does this mean that you are not generally running at full load?

If you are running it on light loads the engine may never get run in satisfactorily.

Comments on oil are probably correct also.

Regards, RAB

[listerboy]

Thanks for the link Steve.

For RAB: the engine is connected to an 8kw gen head and has never been loaded less than 6kw except for the few seconds it takes to for the oil pressure to rise, and the two or three minutes it takes for water temp to get to around 160f as the load is gradually raised to full. I run it at around 185-190f, thermostaticaly controled by a 12v automotive fan monted on the radiator. It had .2 (2/10ths) hours on it when I got it. Most running has been just below the level at where the 60A main breaker trips. Got tired of resetting it so I dropped the load down to an estimated 6850-7250 watts. That estimate is from the data plates on the heaters and hair dryers I've been using for testing and break-in. But, if what Steve says about modern oils is true, there still could be some glazing on the walls anyway.
The engine manual and the data plate on the engine say it is rated for 18hp @ 2200rpm. Would that make a difference as to how much load should be put on it at 1800rpm? Do you think that a 6-8kw load would be sufficient to prevent glazing and provide and adequate load for break-in?

[diesel guy]

I would run 4 - 1,500 watt heaters on high output, left outside to stay engaged, for an extended time. 48 hours run time should solve the problem. If not you might have to tear into the engine to deglaze it.

Diesel Guy

[SteveU.]

Hello Listerboy,
The oil/load/glazing problem is probably the correct one.

However are you sure your running crank case oil level isn't too high and the crank/counter wieghts are not whipping oil. It's called windage (loss). Some of the engines I've had, my listeriod for one, have to ran below stick marking to keep this from happening. 2.0 SOHC and DOHC Chryslers were another. Just a thought.

Good to hear from you
SteveU.

[listerboy]

That sounds like a good plan Diesel Guy, I might give that a try. The longest run time has been about 2.5 hours, shortest runs have been around 45 minutes. I always bring it up to full temp for at least 40 minutes at 3/4-full load before shutdown. 48 hours should give me an idea of the fuel consumption too!

Hey SteveU, nice to hear from you again. I think I'll look into your suggestion about the oil level. The dipstick is a home-made looking thing, just a 3/16 rod with a loop in the end for a handle and level marks filed into it in two places, so it could be off by quite a bit. It's must be factory because it has a nice moulded-in rubber stopper at the top but there again, it's Chinese-engineering-cost/time-saving-crude with the hand filed markings. Now to figure out the counter weight level without dropping the pan. That should prove to be interesting. Any suggestions?

Dave

[Tom]

I concur on the glazing. Since it is improving you might just want to switch to a straight 30 wt and do the loaded run as suggested. Sometimes rings can be seated by dumping a bit of Bon-Ami down the intake. I know it sounds crude, but do a search on it we've had a long discussion about using it to seat rings a while back.

Also please be careful that your new breather tube does not feed crankcase oil into the intake. Dealing with a runaway engine is not fun.

Just curious what kind of engine is this?

[listerboy]

I've debated several times about the Bon-Ami trick Tom, but was worried about the potential of over-polishing the intake valve stems and guides. Someone mentioned that in an earlier post. What do you think?

About the breather hose, I don't think I'll get too much oil through it. That seems to have calmed down too. It's connected to the top of the valve cover through an adjustment plate for the decompression lever. Before I put the aftermarket 2 stage air cleaner on it I had the same configuration on the original single stage air cleaner. I would check the element occasionally and didn't see enough oil contamination to contribute to a run-away. But, you never know....... I'm thinking the 2 stage might help prevent that from happening.

Here's a link to the website where I got the unit. It's the Power King 8 model;  http://www.imperialdiesel.com/generators.html#eight

The website says "assembled in America" but doesn't clearly tell you the engine is from China. Rather crude looking thing but never fails to start. At least not since I overhauled the starter. It was pretty gunked-up and wouldn't spin the engine fast enough for an easy start. Although it was a new unit when I bought it, it was one of those un-sold units that apparently sat in the warehouse for some time so it needed a little TLC. I got a pretty good deal on it so I guess I can't complain too much.

[mobile_bob]

bon ami is not a fix, it is a cob/bodge that might work at the expense of wearing out other stuff.

i cannot tell you how many times i have heard of this over the last 35 odd years, and have never seen a single
shop do use it.

however i have seen what very fine dust will do to an engine is short order.

if you care about your engine, do it right
if you can't get it to settle down, tear it down
deglaze the liner and replace the rings

then when you put it back in service, put a 1/4 load on it till she warms up
and steadily increase the loading over a couple hours, carefully watching the crankcase pressure
if you see the pressure rise, lower the load a for a while, then increase the load incrementally

done in this manner an engine can be fully broken in properly in an hour or two

also after you take it down for inspection, you may find that the ring gaps are all in a line, causing the problem
bon ami wont fix that!

bob g

[Tom]

I've never needed to use the Bon-Ami treatment so I can't say how well it works. On a IHC board I frequent, some of the old timers said the factory would do this to help the chrome rings seat. Since he is seeing improvement, if it were my engine I would go with the 30 wt oil and run it hard.

On the crankcase vent hose. I may be being a bit anal  about this, but if the fuel pump could possibly fail in a way that diesel went into the crankcase it could pump oil/fuel into the intake. A remote possibility true, but Murphy law always applies. This is one of the things I like about the Listeroid design.