XS400 Rebuild with Blue Smoke

[bswinn]

Greetings and salutations to everyone!!!

Alright, to the quick and dirty. Posted a couple questions a number of months ago when I started the rebuild of my '77 XS400D. Over the past year or so I tore the thing down to all it's bits and pieces. Cleaned it all up, repainted it...unfortunately a rattle can was all I could afford, and rebuilt it with mostly original parts. I FINALLY got the thing started this morning and as far as I can tell it's running top notch except for a high idle which I think I can fix with a carb adjustment.

Now to my problem. As soon as it started there appeared some blue smoke in the left side exhaust. I thought not to worry since there is oil in the cylinders from lubing them up to slide the pistons in. After a couple of 3-5 minute start up cycles the right hand exhaust shows the same amount of blue smoke. It doesn't appear to be going away. So my question is this...after tearing the engine down, cleaning it, reinstalling the original rings, pistons, etc. will there be a break in period where the rings have to seat themselves in the sleeves? Is this the reason for the blue smoke? If this is due to a break in period how long before I should see the smoke go away?

I know the worst case scenarios would be bad rings, worn out sleeves, bad or over worn valve stem guides, and/or a bad gasket somewhere. I'm crossing my fingers this isn't the cause because I DO NOT want to have to tear my baby apart again. Nor do I want to go through the process or re-boring, honing, finding new rings, or replacing a valve stem guide.

So please tell me it's a break in period....but please don't lie to me to make me feel better either I eagerly away anyones advice.

[drewpy]

did you mix up the rings and pistons to bores? if you used the same componets together, i would say the valve guide seals are not sealing!!

[bswinn]

I know I didn't mix up the pistons and rings. I only did one at a time. I can't say with 100% certainty I didn't mix up the pistons to bores. Would it make that BIG of a difference? I guess it could be the valve guide seals, but they were brand new.

[bswinn]

Oh...one more piece of info that might help. If the engine is cold and I start it up there is no smoke and it's running fine. Once the engine starts to warm up is when the smoke starts appearing. Once the engine is at running them the smoke is at it's worse. And in addition once it's hot the idle jumps form around 1000-1500 RPM all the way up to 4500 RPM.

[HoughMade]

What kind of oil are you using?

[bswinn]

I can't remember off the top of my head, not at home to look at the bottle, but it's whatever is recommended in the Haynes manual. I think it might be 10W40 or something. I bought it at the local auto parts store just based off the recommended weight. Is there something specific that I should be using?

[HoughMade]

I doubt this is the issue, but you should not use automotive oil and it should probably be a bit thicker. The Yamaha service manual recommends 20-40 in most situations (I use 15-40). Motorcycle oil or diesel oil is the stuff to use. Automotive oil will not play friendly with your wet clutch.

Like I said, I doubt this is the issue. I was thinking that if you used something real thin (10-30 in warm weather or thinner) it could be easier to get in the combustion chamber one way or the other. However, I'm thinking that with a recent assembly, it would not be too unusual to see blue smoke for quite some time- maybe the first 1/2 hour.

How did it run before you tore it down? Any hint of smoke then?

[bswinn]

I just got home and checked. It's in fact a 20W50 motor oil. So motor oil could foul up the clutch huh? What's so different about a motorcycle oil?

The engine never ran for the previous owner. He was a fellow college student who didn't have the time or patience to put into the motorcycle. So I have no way of knowing how the engine ran before it was broken down and reassembled.

I pulled the plugs and found wet standing dark oil on the right hand plug, and the left hand plug while dry looked like it had some pretty decent build up after only running for like 15 minutes and they are brand new plugs.

More and more it's looking like I'm going to have to pull the engine and rip apart the top end to find the source I guess.

[drewpy]

I just got home and checked. It's in fact a 20W50 motor oil. So motor oil could foul up the clutch huh? What's so different about a motorcycle oil?

The engine never ran for the previous owner. He was a fellow college student who didn't have the time or patience to put into the motorcycle. So I have no way of knowing how the engine ran before it was broken down and reassembled.

I pulled the plugs and found wet standing dark oil on the right hand plug, and the left hand plug while dry looked like it had some pretty decent build up after only running for like 15 minutes and they are brand new plugs.

More and more it's looking like I'm going to have to pull the engine and rip apart the top end to find the source I guess.

if the right hand side isn't firing, it will be wet and oily. can you confirm it is firing?

[bswinn]

Well the right hand side muffler gets AWFULLY hot for it NOT to be firing. Perhaps it's not firing ALL the time? I did notice that the right hand muffler is quite a bit quieter then the left hand muffler.

[bswinn]

Alright, took the engine out of the motorcycle and disassembled the top half. Took the valve cover off and it looked good. Took the cylinder head off and found what I considered substantial pooling of oil on the top of the pistons. The piston walls were also wet with oil. Wetter than I imagine they should be. The vertical distance between the piston rings was also substantially wet with oil.

In my last hopes how do I check to see if it's bad valve stem guide oil seals? Also, is there a good way of measuring the inner diameter of the piston sleeves? I personally don't have an internal micrometer. I could possibly find one at the machine shop I work above but it's no guarantee. Could this oil that appears to be leaking from between the piston and piston sleeve be due to the fact that I didn't hone the piston sleeve? Would a smooth internal surface really cause this much oil to leak?

[Airhead]

is there a good way of measuring the inner diameter of the piston sleeves? I personally don't have an internal micrometer. I could possibly find one at the machine shop I work above but it's no guarantee.

internal micrometers are hard come by whereas external ones are commonplace.

You could either use the piston plus feeler gauge to fill the bore then measure these to find the bore size...or use spring loaded and lockable bore gauges which again are checked using an external micrometer.

[HoughMade]

I'd take a close look at the rings before I'd worry too much about the liner.

[Speedshop]

Sounds like you put the rings back upside down or misassembled the oil scrapper ring. In which case you can probably bin them now if you run them like that.

Putting the old rings back - it sounds like there couldn't have been much wrong with it in the first place......isn't there a saying about things that ain't broken......?

[HoughMade]

You didn't cap off or otherwise block the crankcase breather, did you? This will cause a buildup of pressure in the crankcase and can force oil into the combustion chamber...and this is a personal thing, but if I had the piston out, I would put new rings on no matter how they lookes...unless i knew with certainty that they were perfect. Rings are not that expensive.

[bswinn]

Well since I had the Cylinder housing off the bike I had the guys at work check it for me and it's hardly worn at all. When I get home I'm checking the rings. Fairly certain they aren't upside down or in the wrong order but ya never know. Also gonna check the gaps and make sure those are right too.

I believe the breather is fine. I know it's not plugged in actual crank case. I'll check the breather tube that goes up to he carbs but I believe that to be clean. Maybe the hole in the breather gasket was installed poorly? It's a solid square of a gasket with a rectangle cut out near one edge. Should that be closest to the actual hole in the crank case, or further away in case of oil being flung up?

I would install new rings in a hearbeat, but I can't seem to find the stock size. All I appear to find are the oversize rings. And those go from the cheapest at $20 a set up to $50.

I'll be checking the valve stems, valve guides, and valve guide seals tonight along with the rings and let ya'll know what I find.

I really do appreciate all the replies to this thread. It's helped out a lot.

[bswinn]

Alright, been lagging behind on what I thought I'd get done.

Here are some images I've taken of something I've found.

Imageshack link to photos.

I hope that link works. If not just let me know. So one exhaust port is soaked with oil, while the other is dry but is quite charred. Now remember the bike has probably only run about 30 minutes and before that it was cleaned out thoroughly. There are little pools of oil around the valve guides but I can't be sure that's not just from having to move the head around to get the valves out. I haven't checked the seals or the guide tolerances yet.

What I found the most interesting was the amount of oil that made it's way between the cylinder head and the head gasket. So much so that it got up to the metal part of the gasket. Does this mean that the cylinders are sucking in oil through the gasket? That would be pretty shitty right? Warped head?

Any advice based on the images?

[Speedshop]

If its pulling in a large amount of oil and it wasn't before its something you've done. This it isn't going to be down to a slight clearance on the valve guides suddenly causing a massive problem. Unless it was like this before you took it apart.

This sounds like a ring fault or a gaket/seal failure. You haven't forgotton a dowl that goes on the studs?

[bswinn]

I don't know if it was sucking in oil before I dismantled the engine.

I checked the ring end gaps. They were slightly larger, about .005" larger, but that shouldn't lead to the amount of oil in the pistons. Cylinder bores are in spec, valve guide diameter are in spec, valve stem diameter is in spec, nothing is loose.

The only thing I've seen that could result in the amount of oil was the oil on the head gasket. But I checked the head and cylinder housing mating surface and they are at a maximum of .001" out of true flat. I torqued the cylinder bolts to spec so I have no idea how this is happening. Should I torque the nuts down slightly tighter?

I guess it could have been valve stem guide oil seals but they were super tight on the guides and on the valve stems. When I took them off I inspected them and they looked in good working order.

[Speedshop]

Well you need to have a good hard look at it.

In 23 years of working on motorcycle engines i've only ever seen cylinders fill with oil after rebuild only for the two reasons already given (knackered rings incorrectly fitted back in to glazed bores and damaged or missing seals).

There are other possibilities, I managed to kink the engine breather on my own XS650, which made the gaskets squeak a bit. But from what you describe a blocked breather doesn't sound like the cause. I've seen missing seals plenty of times, but I did have an XS650 in my workshop where the owner fitted the 2nd ring upside down and damaged the oil control ring on one pot, basically it was pumping oil into the cylinder instead of controlling it. also a SR125 where the owner had missed out the seperator between the oil rings and the oil ring had snagged up as a result - that was a rebored cylinder and we managed to save it with just a new set of rings and a touch up with the honing blocks.

Are you sure it wasn't like this before you stripped it?