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Author Topic: Excessive Blow By  (Read 1443 times)

High On Octane

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Excessive Blow By
« on: April 09, 2013, 04:34:07 PM »
I fired up the Trailblazer over the weekend so I could test the electrical system to make sure everything was working in that department, and everything was.  But as the bike was idling, I noticed that I was spewing oil out of the breather tube/vent set up.  I finished my electrical tests and shut it down.  I checked the oil level and it was a little over full, like maybe a 1/4-1/2 qt, not a lot.  However, I did notice when I got the bike that it had a blow by problem because there was oil all over the chain, chain guard and swing arm, as the breather tube just lead to nothing but exiting next to the front sprocket.

So my questions are;  Is there supposed to be a valve, that may have failed, behind the actual breather tube outlet, AND/OR is there supposed to be an oil tank on my bike and that is why it's spewing oil all over the back end of my bike.  Thanks.

Scottie
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barenekd

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Re: Excessive Blow By
« Reply #1 on: April 09, 2013, 06:17:29 PM »
My first guess is that the engine has wet sumped. How long has it been sitting without running? drain the crankcase and put the oil back in the tank if you can. It could have leaked by a leaking seal in the tank, or by the oil pump.
Bare
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High On Octane

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Re: Excessive Blow By
« Reply #2 on: April 09, 2013, 06:37:14 PM »
I actually just filled the oil a few minutes before I started it.  Before that it was sitting for maybe 2 months with no fluids at all.  Am I supposed to have an oil tank?  My bike didn't have one when I got it.

Scottie
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barenekd

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Re: Excessive Blow By
« Reply #3 on: April 09, 2013, 06:40:32 PM »
It has an oil tank built inside the engine. it is not a wet sump engine.
Bare
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High On Octane

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Re: Excessive Blow By
« Reply #4 on: April 09, 2013, 06:49:10 PM »
Hmmmmmm.  Maybe just overfull then?  Is there multiple drain plugs on the 700cc twin like on the newer engines?  Maybe I didn't get all the old oil out?  Just kind of weird that every time I've ever started it I've had oil coming out of the blow by tube.

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barenekd

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Re: Excessive Blow By
« Reply #5 on: April 09, 2013, 07:10:40 PM »
The wet sumping is just the first place I'd check, After that, the big culprit would be rings and/or valve guides. Have you done a compression check?
Bare
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High On Octane

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Re: Excessive Blow By
« Reply #6 on: April 09, 2013, 07:15:15 PM »
The wet sumping is just the first place I'd check, After that, the big culprit would be rings and/or valve guides. Have you done a compression check?
Bare

I haven't.    Mostly because I can feel plenty of compression through the kick starter.  Could still be leaking down I suppose.  And I thought these heads didn't have valve seats, do you mean I might need to grind them and reseat them?

Scottie
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barenekd

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Re: Excessive Blow By
« Reply #7 on: April 09, 2013, 08:16:32 PM »
Unless it's an iron head, it does have seats. But the seats aren't the problem, they can show bad compression, but they won't blow oil. The valve guides are where the excess crankcase pressure will come from, or the rings.
Not having read all the history on the engine. How much time has it been since it as overhauled? How many miles after overhaul?
Blow by is actually the gases blowing out of the combustion chamber into the crankcase causing high pressure in the crankcase. It can blow any oil in there out the breather. The only places it can blow by is bad or broken rings, worn valve guides, or maybe a crack or hole in a piston.
If the crankcase is flooded with oil (wet sumping) because of oil leaking into the crankcase from the oil tank or or seeping through the oil pump, then normal crankcase pressure will blow that oil out the breather. that's why you check the crankcase for excess oil before you worry about the top end of the engine. You should be able to drain the excess out of the crankcase. There should be a drain plug under the crankshaft of the engine, usually where the sump pump (the return oil pump, it may have a screen there) is. Take that one out. There should be a little oil in there, but not much. Maybe a t-spoon or so. If you get several ounces out it's probably wet sumped. Dump that oil back in the oil tank and try starting it again. The blowing oil should clear up within a minute or so after starting. If it doesn't, check the level of oil in the crankcase and see if it's filled again. The return oil pump may be the culprit.
Bare
« Last Edit: April 09, 2013, 08:36:38 PM by barenekd »
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High On Octane

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Re: Excessive Blow By
« Reply #8 on: April 09, 2013, 08:25:44 PM »
I forgot to mention before that I'm not getting any smoke out of my exhaust what so ever, if it was wet sumping wouldn't it be smoking?  Also, I just now checked my oil level and it was 3/8" below the full mark, so maybe it wasn't overfull after all.  I went ahead and took a pic of my breather set up so you could see a little better what was going on.  Basically I have my blow by hose going into Lucas Fuel Treatment bottle with a threaded fitting in the opening and 3    1/8" holes drilled in the bottom (now top) to breath.  It's a primitive hillbilly catch can, but it's functional.  Problem is that I had oil all the up to the red line and it was gurgling away, spewing oil all over out of the 3 tiny 1/8" holes.

The bike sat for almost 20 years before I picked it up, and I'm pretty sure it's been sitting because the magneto went bad.  And it's a '58 700cc Twin Iron Head.  I only pulled covers and did visual inspections through the exhaust port and spark plug hole, but everything looked in tip top shape.  The only thing that really needed to be adjusted was the valve lash and points.  Primary chain was a little loose, but not much, carb was basically shot.  And like I said, I didn't test it but it has plenty of compression when kicking it over.

Scottie

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barenekd

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Re: Excessive Blow By
« Reply #9 on: April 09, 2013, 08:49:51 PM »
Check the post before your last one again. I added some stuff to it. If it's not blowing exhaust, the rings, etc. are probably OK.But there are some one way valves in the oil pump that are probably leaking and letting the oil down into the crankcase.
Bare
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ace.cafe

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Re: Excessive Blow By
« Reply #10 on: April 09, 2013, 09:45:32 PM »
IF it's a fresh set of rings on a fresh hone, it will take some mileage to get them bedded in. During that time, it will have some blow-by, and cause some crankcase pressure that will blow some oil out the breather. It might help to have a catch can on the end of the breather hose during this time, and empty it periodically. Less messy  that way.
If you put a catch can on, it will obviously need a vent hole at the top, to the atmosphere.

Other causes could be wet-sumping as mentioned, but that should clear up within a couple minutes after starting.
Over-filled oil tank might also cause it.
Broken ring can cause it.
Believe it or not, a blown head gasket can cause it, if the cylinder pressure leaks across the head gasket to the push-rod tunnels, and that will cause high crankcase pressure.
Try the easy stuff first.
« Last Edit: April 09, 2013, 09:49:05 PM by ace.cafe »
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rotorwrench

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Re: Excessive Blow By
« Reply #11 on: April 10, 2013, 07:13:54 PM »
There have been several breather set ups over the RE & Indian years for the 692 cc twins. They started with a duck bill breather tube. They then changed over to a dual breather set up with a breather disc in the crankshaft drive end retention bolt that holds the alternator rotor (vents to inner primary) and a dual pin steel disc set up in the side case breather where the duck bill tube had previously been attached. They then went to an interconnect set up that connected the side case breather and the top of the primary cover to the engine oil reservoir through two tubes & a banjo fitting. It still used the disk valves but would put the blow by back into the oil reservoir.

You can have a situation where the cam tunnels flood and oil might come out the breather but there would have to be a problem with drain back for the return pump piston/rocker in the oil pump assembly. You can check for return by looking into the reservoir while the engine is running and see the flow from the return tube. They always used a smaller piston/rocker assembly for the pressure pump side than they did the return pump to prevent build up of oil in the crankcase. The cam tunnels usually have no problem draining out. I've seen engines modified to change the drain in there to a higher point to add better oiling for the cams. I'd have to find the old issue of the REOC/NA news letter to find the diagram of that mod.
« Last Edit: April 10, 2013, 07:16:15 PM by rotorwrench »

ERC

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Re: Excessive Blow By
« Reply #12 on: April 10, 2013, 11:24:19 PM »
I'd check to see what breather set up you have like Rotor says. The only way these motors can wet sump is if it leaks from the oil tank into the crankshaft area or if it's way over filled in the oil tank. There's only one drain for the oil tank to answer your question. It's the big plug on the right side at the bottom. When it's removed it should have a screen on it. Another way they can wet sump is if the cam tunnel drains weren't drilled from the factory. I have a factory bulletin that shows how to repair this. So I guess that happened more than once.  ERC
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High On Octane

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Re: Excessive Blow By
« Reply #13 on: April 10, 2013, 11:27:47 PM »
I was just thinking...  Would the fact that the right cylinder isn't firing have anything to do with this problem?

Scottie
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ieatalot

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Re: Excessive Blow By
« Reply #14 on: April 11, 2013, 09:17:39 PM »
Mine blows if the oil level is anywhere near the upper line. On another subject, The problem I am having is when I go to tighten the rear wheel nut after replacing the rear wheel, the right side backs away from the pin that marks the snail adjuster when I tighten. Any ideas?. In other words it pulls the front of the wheel to the right.