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Discussion Starter #1
Looking for some thoughts. Recently got a 20hp vanguard that had a broken rod. It looked very clean as though it had very low hours. Found out the cam broke as well, and likely went first, taking out the rod. Cylinders were clean as was pretty much everything else. Got replacement parts and buttoned everything up and it fired right up. After about a minute of running, it starts to smoke. Most rebuilds smoke a little, but this seemed more than what I usually encounter. Full disclosure, I didn't measure end gaps on rings, but I've also never had to adjust any either so it seemed low risk.

I put some oil on the Pistons and rings, and i put some assembly lube on the cylinder walls, valves, etc. Could the smoke be from burning off the assembly lube or is it more likely that the oil rings got goofed up in the assembly?

The engine seems to run good, but I live in the city and my neighbor is a real pita, so I didn't run it for more than a couple min. Let it cool and tried it again with the same result. After a minute, it slowly starts smoking heavier.

I plan to take it to our farm in a few weeks to just let it run for a while and see if it clears up, but thought I'd quiz you guys first.

Thanks
 

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Sounds like you got it without ever seeing it run...sounds like it was possibly run low on oil which caused the cam and rod failures...could the rings have needed replacement also?
 

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Discussion Starter #3
Yes, I got it without hearing run.

Rings could have been bad I guess, but they looked ok and it looked like the engine had such few hours. There were no marks on the crank or Pistons like they overheated, but there was a large buildup of scaley carbon on the piston tops which seemed like more than normal.

The valves and guides all looked good and seemed tight. I'm now paranoid that the rings were somehow very worn and I now have a massive end gap - but the delayed smoke still doesn't work add up. Was thinking maybe the lube on the exhaust valve stem is burning off once it gets hot?
 

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How long has it run in total since the rebuild? It does usually take a while to burn everything clean, especially if some oil and stuff got into the muffler.

How do the plugs look?
 

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Discussion Starter #5
It's only got about 3-4 minutes on it. Like I said, didn't want to smoke out my neighbors. It wasn't smoking so bad you couldn't see through it, but enough to fill the garage up.

How much air should be going in and out of the crankcase breather? Seems like there is a big hiss each time I turn it over by hand, and the previous owner had the tube disconnected and plugged. Thought it was odd
 

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I'd mic the cylinder with a bore gauge if you have one; failing that, a set of telescoping gauges and a micrometer or good caliper, failing that I'd take it to a shop that has a bore gauge. If you just want to get a fair estimate, check the ring end gap. If the bore is worn out of spec, the gap will be beyond spec and will leak in much the manner you are describing. The amount of slop required to cause problems can be quite small and not really noticeable with the naked eye. It sounds to me that at this point you're throwing parts at an engine without knowing what condition it's really in, at that point it's upto chance.
 

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It can take awhile for oil to burn off completely..some engines I have gotten that sat a long time took an hour to finally stop smoking,the rings were probably stuck in the grooves..


A car a friend had that we replaced the blown engine in smoked for 2 days after we got the supposedly good used salvage yard engine in it and running..

He was about to drive it to the place he bought the engine from and demand a replacement or refund,but it finally stopped smoking after the second day,when he drove it about 20 miles on the highway...evidently the muffler and whole exhaust system had been "oiled" by the dying first engine--must have been a quart or two in the muffler..
Weird thing was it didn't start smoking till it had been run a good 10-15 minutes,I guess it took that long for the muffler to get hot enough ?..
 

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It's going to need to run at least 30-45 minutes before you make any decisions.
If the breather was plugged up I bet it was sucking oil out and into carb. I had a vanguard do that. They are more picky than other engines but great!
The dipstick tube on mine was the culprit. Put a new one that sealed 100% and no more oil coating inside of air filter housing in middle of filter.
Head gaskets will cause a lot of smoking too. The vanguards have old style with is thin metal and new style with is graphoil.
They usually have an intake valve stem seals too.
 

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It's only got about 3-4 minutes on it. Like I said, didn't want to smoke out my neighbors. It wasn't smoking so bad you couldn't see through it, but enough to fill the garage up.
I'd say drive it for an hour like you stole it and see what happens. Probably the worst that will happen is you kill a bunch of mosquitoes.

If it hasn't cleared up by then it'd be time to maybe dig deeper.
 

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Looking for some thoughts. Recently got a 20hp vanguard that had a broken rod. It looked very clean as though it had very low hours. Found out the cam broke as well, and likely went first, taking out the rod. Cylinders were clean as was pretty much everything else. Got replacement parts and buttoned everything up and it fired right up. After about a minute of running, it starts to smoke. Most rebuilds smoke a little, but this seemed more than what I usually encounter. Full disclosure, I didn't measure end gaps on rings, but I've also never had to adjust any either so it seemed low risk.

I put some oil on the Pistons and rings, and i put some assembly lube on the cylinder walls, valves, etc. Could the smoke be from burning off the assembly lube or is it more likely that the oil rings got goofed up in the assembly?

The engine seems to run good, but I live in the city and my neighbor is a real pita, so I didn't run it for more than a couple min. Let it cool and tried it again with the same result. After a minute, it slowly starts smoking heavier.

I plan to take it to our farm in a few weeks to just let it run for a while and see if it clears up, but thought I'd quiz you guys first.

Thanks
I've not much smoke on a rebuild. Maybe I have been lucky. Any chance you put a ring or two in upside down? The plugs should tell you after some run time if the breather checks out.

BTW - I would think the failure was most likely the other way around, rod failed and took out the camshaft. As someone else pointed out, perhaps it was low on oil albeit I would expect the crankshaft journals to answer that question.
 

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Discussion Starter #11
Did a little inspection last night...I know compression values aren't particularly meaningful with compression release, but I did have about 23% difference between cylinders 1 and 2 which is high (but still in spec). I don't have a real leak down gauge, but with the homemade job I've got, I can clearly tell that cylinder 2 has got a significant leak to the crank case. Valves seem to be sealing as do the head gaskets, so I guess I get to tear it down again. At least everything is already cleaned....

I leave for a work trip tomorrow so I won't be able to get to it for a couple weeks, but I'll post back what I find.

Thanks for the responses. Fun and helpful to read
 

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I'm guessing that since it was apart and disturbed maybe the rings just haven't seated properly yet... but that's just guessing.

Let us know how it goes, and have a safe trip.
 

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Discussion Starter #13
Well, I'm back in town and I got some work done on this engine. Before I left, I had 40psi compression in one cylinder and 52psi in the other. Tore it all down and found ring gaps ranging from .100" to .200". Couldn't believe it - I've never seen anything that large before.

I honed the cylinders, put in two new sets of rings, and lapped the valves. Checked the new ring gaps and they are .020". Started it up, and within a minute it started smoking again. I rechecked the compression and now both of them are at 135psi.

At this point I guess I'm going to have to just run it for a while and see what burns off. Perhaps my muffler has some oil in it as well - that's used too
 

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If it doesn't stop smoking, run 20-50 SYNTHETIC oil and a half can STP in the engine....It won't stop it from using oil....but it won't smoke....just check the oil frequently
 

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I'll bet you nailed it with the new rings, those were some awful big end gaps. Agree run, keep an eye on the oil level for a while.
 

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But how much did you run it before you took it apart and change the rings? Will you ever know if it would have cleared up on its own? Ring end gaps just don't get bigger by themselves so that's quite a mystery.
Someone would have to put the wrong rings in a machine or overbore one upon assembly and that should smoke its entire life. Do you know if this thing ever ran without smoking?
I would have changed the oil and put some restore engine treatment in it and ran it for 3 or 4 hours to see if the smoking improved. Also, the old bon ami trick people used to use. You put about a teaspoon or two of bon ami into each cylinder and turn it over by hand a little bit to disperse it and then run it. It's supposed to help scuff up and see if the Rings. But I can't say I've ever seen it in person work.
I have seen lots of small engines that smoke like a freight train until you ran them for at least 45 minutes plus to burn all the oil out of the muffler. Then they were as good as new. Having that low compression to start with it's quite odd but I don't ever bother with a compression tester as these engines have compression releases and stuff like that. If you put your finger in the hole and it blows it out forcefully it has enough to run.
 

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Discussion Starter #17
Been a while since I posted but I finally got back around to this project. I started it and let it run for a while and about 5min in it stopped smoking. Not sure if it was the rings seating, oil in the muffler or assembly lube burning off, but it stopped and I'm happy. The carb seems to be a little plugged because it wants to run on about 3/4 choke, but that's an easy fix.
 
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