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258 puff of smoke

3K views 72 replies 11 participants last post by  Matt1981CJ7 
#1 ·
258 Engine has about 50 miles on it from a complete rebuild and rebuilt head, runs great only problem I get this puff of smoke just when I first start it up. can be a good size cloud of smoke happens even worse when engine is hot, any idea what this may be. is it common on a rebuilt engine does it just need to break in more. It's only when I first start it no smoke when moving along down the road
 

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#4 ·
I'd give it a few more miles to see if the rings need more seating.

Is is light or dark smoke? It's difficult to tell from the pic. If dark, is it blue or black?

Matt
its more blue defiantly not black, i pulled the plugs and they look like there firing OK.
this has me a little worried i drove it to the store yesterday jeep sat for 3 minutes started it and there was a large cloud of smoke and then it goes away
 

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#7 ·
Polaris,

Bluish/grey smoke is usually oil in the combustion chamber. Black is usually too much fuel.

Did you check ALL the plugs? A leaking valve seal may only show up on one plug.

Matt
it is a blue/grey smoke and it does do it at idle as well i was just out there running it and it smokes at idle. also second plug from the back had oil on the treads and didn't look the same as the other 5
 
#9 ·
thanks for the help, i think i will take the cover off and have a look. hoping its just a seal do you think its possible it could be a valve guide they should be all new it was just rebuilt. also if its the seal i was hoping to replace it with the head on. reading in here some people use the compressed air to keep the valve up but if i just put the piston at TDC I would not need the air correct.
also i dont have the tool to measure the guide so i hope its just a seal
 
#10 ·
thanks for the help, i think i will take the cover off and have a look. hoping its just a seal do you think its possible it could be a valve guide they should be all new it was just rebuilt. also if its the seal i was hoping to replace it with the head on. reading in here some people use the compressed air to keep the valve up but if i just put the piston at TDC I would not need the air correct
No problem.

Be aware, your engine doesn't have replaceable valve guides. The guides are just holes bored into the head. When they get worn and leak too much oil, the holes can to be bored larger and you can to use valves with larger diameter stems. They may also be sleeved, I believe, but that's a more involved repair.

Yes, if the cylinder you are working on is at TDC, the valves will not fall into the cylinder when you remove the valve springs.

Matt
 
#12 ·
Shortly after my rebuild I had a floating valve stem seal. It was the 6th cylinder, so on inclines it would puff, also upon start up, and it would puff when you ride the gear.

I took nylon rope and jammed a bunch in the cylinder 6 and then turned the engine over by hand until it compressed it, this forces the valve to stay put.

Replaced the seal on just that stem and all was good.

kov
 
#13 ·
Hi, Puff of smoke at start up is valve guide seals. What you are seeing is when the motor is shut off and the seals are shot oil runs down the valve steam and into the cylinder. and is burned off when it is started. You most likely can NOT see the seals by just taking off the valve cover the springs hide them well... If the head was not rebuilt then I would say seals..
good luck
tim
 
#30 ·
You most likely can NOT see the seals by just taking off the valve cover the springs hide them well..
tim
Huh, when i did mine I could easily see thru the springs, it was clear that the #6 on mine was floating. Maybe shine a light behind the spring and then maybe you can see if its floating.

I agree, the Nylon rope method is probably the best insurance way to go, the valve will be in there like a rock and will make it easier when putting back together, I wouldn't trust the compressed air method.

kov
 
#14 ·
the head was rebuilt and your right i took the cover off and could not see a thing. i had to order the spring compressor should be in Wednesday. i am hoping its just a seal the head was just rebuilt so i would think its not a valve guide. what i did notice before taking the cover off yesterday that at idle it was also smoking not as bad as the first start up but it was smoking. i probably should have done a compression check on that cylinder that i found oil around the plug. because i am seeing smoke at idle i am now wondering about that pistons rings.
 
#17 ·
Un-seated rings would cause excessive blowby, which is a symptom the OP hasn't mentioned.

Personally, I don't think you should see much smoke at all after a proper rebuild and break-in. Below is a video showing off my new exhaust system. At the time, my engine had less than 50 miles on it after its rebuild. I've never noticed a single puff of blue smoke from this engine since the rebuild.

Polaris, I think you are doing the right thing by investigating, now. There's no sense in letting one cylinder get carbon-fouled, while you hope that it self-corrects.

Matt

 
#18 ·
yes it doesn't look like that video at all. i will pull the springs off tomorrow when the tool comes in. at this point i am only hoping its a seal the only thing that has me worried is the blue grey smoke at idle if it was just at start up i would say seal. hope for the best we will see tomorrow
 
#21 ·
My 2 cents:
Sounds like a classic valve stem seal. Piston rings would burn oil while running, but when you shut it off, the oil drops, so if you’re getting a big puff at startup, gravity is pulling oil down from above and building up in the cylinder. The stem will leak the whole time the engine is running, just at a low rate so you don’t always see it.

I don’t think waiting is going to solve the problem (it sounds like you aren’t going to wait anyway).
Buy OEM replacement seals. You have a leak because something isn’t quite perfect and the factory seals are likely the best money can buy (and the most forgiving).

I wouldn’t try the TDC method for holding the valve up there. I’m not saying it won’t work, but I wouldn’t trust it and I don’t want the valve moving at all. Obviously your piston does not hit the valve every time it comes up, so there must be a gap and that’s how much it can move. too much? I don’t know. How much do you want it to move around while you monkey with those little parts? I’m looking for zero. Besides, if you're wrong about TDC, you're going to crap your pants when the valve drops onto your piston, then you're going to pull the head.

I would use the rope method, manually putting the piston all the way down, feed in some nice clean rope (just buy a soft nylon rope, say 6 feet of 3/8” or so). Then MANUALLY turn the engine with a socket until you feel it bind near TDC with both valves closed. If you don’t get it the first time, try again with more or less rope.
 
#24 ·
My 2 cents:
Sounds like a classic valve stem seal. Piston rings would burn oil while running, but when you shut it off, the oil drops, so if you're getting a big puff at startup, gravity is pulling oil down from above and building up in the cylinder. The stem will leak the whole time the engine is running, just at a low rate so you don't always see it.

I don't think waiting is going to solve the problem (it sounds like you aren't going to wait anyway).
Buy OEM replacement seals. You have a leak because something isn't quite perfect and the factory seals are likely the best money can buy (and the most forgiving).

I wouldn't try the TDC method for holding the valve up there. I'm not saying it won't work, but I wouldn't trust it and I don't want the valve moving at all. Obviously your piston does not hit the valve every time it comes up, so there must be a gap and that's how much it can move. too much? I don't know. How much do you want it to move around while you monkey with those little parts? I'm looking for zero. Besides, if you're wrong about TDC, you're going to crap your pants when the valve drops onto your piston, then you're going to pull the head.

I would use the rope method, manually putting the piston all the way down, feed in some nice clean rope (just buy a soft nylon rope, say 6 feet of 3/8" or so). Then MANUALLY turn the engine with a socket until you feel it bind near TDC with both valves closed. If you don't get it the first time, try again with more or less rope.
thank you, all the info i can get helps
 
#26 ·
With only 50 miles on it, there may be some ring seating issues. Even if a valve seal is leaking, it's doubtful that would really be a reason not to run it, at least a bit.

BTW, there is a lot of shade tree advice about tradtional break-in, I found this guidance from Lycoming informative (especially the push it hard at times advice)

https://www.lycoming.com/content/hard-facts-about-engine-break
 
#28 ·
Polaris,

I had a similar issue to yours on my engine at around 5K miles. My #3 plug showed fouling, while the others looked fine. Other symptoms were a slight vibration at idle that didn't exist before, and a 1-2" tick/shudder in my manifold vacuum readings, the needle was usually rock solid.

I started a thread, here, about the problem. As you will see, I got multiple guesses ranging from carb to ignition to plugs/wires to carbon buildup. I even won a few bets (that haven't been honored, yet) along the way. It wasn't until I lifted the valve cover that I discovered the real problem, which nobody had previously guessed, btw.

I'm not saying your problem is the same as mine. I'm just suggesting you may save a bunch of needless goose-chases by removing the valve cover for a closer look.

Matt
 
#31 ·
Hi here's a couple of possibilities if the overhaul was not done properly
1) might not have spaced the rings apart properly
2) might not have broke the motor in properly 2,000 rpm's for 20 minutes varing to 3,000 rpm's
I've rebuilt several and never had one smoke at all...
good luck
tim
 
#32 ·
the one thing i could not do was.
1) might not have broke the motor in properly 2,000 rpm's for 20 minutes varing to 3,000 rpm's
reason why was the auto parts store gave me the wrong water pump. i told them i had the v belt and they gave me one for serpentine. serpentine spins if i remember correctly counter clock wise so i was not getting the engine cooled. took me a week to figure out that problem, i never let the engine get over 200 degrees i always kept a very close eye on the temp and would shut it right down. but i could never let it run for the 20 minutes
 
#34 ·
Well now i am really confused, i got the spring compressor in the mail this morning took both springs off looks like one was up about 1/4 of an inch and the other an 1/8
now that i have the spring off and see how the boots look and sit i can use a flashlight and see all the others, the one in the back cylinder intake looks like its all the way up to the top of the spring. and there are more that look like they are up as well, the boots dont feel like they clip onto or press onto anything to hold them down. i have attaches a photo of the two with no springs and i took a photo of the one right next to it with the spring i think u can see from the photo its all the way up. is this common? R they suppose to stay all the way down or do they go up and down with the valve.
dont think i like the design of these at all
 

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#36 ·
Polaris,

The umbrella type valve seals are designed to travel up and down with the valve. They are actually called oil deflectors, because they don't really seal anything. They will always work their way to the top of the valve stem, as you are seeing. That's normal.

Well darn. I was hoping you were going to find a deflector that was broken or cracked, but that doesn't appear to be the case. It's never as easy as you hope.

I'd check the valve guide-to-stem clearance next. Perhaps you can rent a dial-indicator, if you don't want to buy one. The lateral tolerances are .001"-.003", which is barely perceptible to the eye. Try just wiggling one of the valve stems. If you can feel any side-to-side movement at all, it's likely the guides are too worn.

Matt
 

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#37 ·
i grabbed the top of the valve stem, tried the side to side and there is absolutely no movement at all they feel nice and tight in there. i will call a couple auto parts stores today see if i can rent the tool. the boots fit tight around the valve stems as well they look good. with the head being rebuilt wouldn't u think valve guides would be considered part of the rebuild on the head
 
#38 ·
I wouldn't assume anything about the rebuild. We've seen some shoddy machinist work lately, especially on heads. That said, if the valve stems feel nice and tight, the guides are probably OK. I'm starting to run out of ideas, here.

One thought, did you ever check the #5 plug for good spark? Perhaps swap the plug and wire to another cylinder just to rule them out.

Matt
 
#39 ·
when i tried moving the valve it was tight in its seat when i pushed the valve down a little i did have some play in one and not the other. it wasn't much but there was movement. i have a friend that has been a tool maker for over 30 years i am trying to get in touch with him see if he will come over and take a measurement for me before putting it back together.
 
#40 ·
I had a similar problem with a little different symptoms on my fresh rebuild. On mine it never did it at start up but after you drove it a while I would get a puff of blue smoke when accelerating from a stop. There is a long thread on here regarding it. My plugs looked just like yours, a little rich. After doing what you have done I decided to turn my attention to the rich condition. My engine builder told me to avoid a rich condition, especially on a new build because #5 and #6 cylinders were subject to "washing out" when you run rich causing the rings to not seat correctly. So I got a AFR and vacuum gauge and got the carb dialed in to a nice tan color and continued to put miles on it. I have 1500 miles on the rebuild now and my symptoms have gone away. As long as you used a reputable engine builder the odds that you have a problem with the build is very small. As long as you keep an eye on the plugs to make sure nothing more serious is happening, dial in the carb and put some miles on it. I was told to keep it under 3000 rpm for the first 1000 miles but other than that don't baby it. I don't know about ya'lls but mine is all done at just over 3000 rpm. I bought a Honda S2000 to compensate, does not even know it is alive until 3500 redlining at 8900.
 
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