Where is this smoke coming from?

[ironchop]

So a few years ago I built three first gen 200X's and one of them got a Megacycles cam, some porting and polishing, and all new goodies in the head including valve guides, seals, seats recut, valves hand-lapped, new springs, keepers, and retainers rocker shafts and arms were replaced with NOS parts.

In the process of removing/installing the guides, I cracked the shoulder on one from tapping it too hard because the head cooled too much before I could get the second guide in. I reheated the head and tapped it out and got another ordered (OEM Honda iron guides). In the mean time, I had lost the o-ring that goes under the guide flange to seal it but luckily, my Vesrah complete gasket kit came with two green orings for the guides according to Vesrah package. So I popped on the green one and heated head better that time and tapped the chilled guide easily into the head. The OEM Honda oring was a dark blue color and of a slightly thicker and harder compound of Viton(?) than the green one in the Vesrah kit. I thought nothing of it at the time.

Fast forward to lately and after a stator explosion, it sat in a shed for a year and when I couldn't get to looking at it for the kid who bought it from me a couple years ago, I had him send it to yaegerB for a looksee which is how the stator issue was discovered. We thought it needed a rebuild because the kid told me it ran out of oil. Turns out it didn't and everything else was good so he gets motor back and installs it and it smokes for the first time. I told him the valve seals were aftermarket so maybe they got hard and I'd replace them for him using OEM stuff instead. He pulls the head off and brings it to me where I find the exhaust valve absolutely caked with oily deposits on the back of the valve which is a sure indication that your drawing alot of oil down thru the guides. I assumed the guides to not be worn as they were installed, checked, reamed all by me using pin guages for accuracy.

So I noticed under magnification that the exhaust valve stem had some slight galling and scratches and one guide had a bit of a "sticking spot" about halfway down the inside. Lubed, the valve slipped ok, but dry you could feel the bad spot easier. Valves were Shindy and I wasn't impressed with the surface finish on the stem. Seemed a tad rough to me. Both valve stem seals were in great shape, very pliable, and wiped oil from the stem correctly when I tried them out manually with some old dark oil for visibility sake. I was a bit confused as to how good seals were still letting oil get sucked in so it occurred to me that maybe the guide was cracked since I put refrigerated cast iron guides in a heated head. I'm not sure if thats possible but something didn't seem right and the guide had a funky spot inside it that I wasn't comfortable trying to re-ream it because you run the chance of oversizing the hole if you aren't very careful. I also noticed looking into the chamber side of the exhaust ports, I could see where the guide tapers coming out of the head there is a bit of a crack between the head and guide for a short depth and it was filled with fresh oil. Another clue.

When I originally installed the new guides, I wondered why Honda felt the need to add o-rings under the flange that set in a counter bored pocket in the head. I would think that the press fit would insure the seal but they must have known something because they were obviously engineered into the design. The only reasons I could think a guide need a backup seal was because maybe the guide holes were out of round but that made no sense unless you think about the odd shaped head and the thermal dynamics of cast aluminum, perhaps the different rates of expansion causes the holes to yawn a little too much? Anyone know? The inside of the holes in the head for the guides were not galled or scratched in any way and appeared shiny then as now so that eliminates deep scratches as the culprit for oil consumption.

So I get the guides out easily after a good bake in the oven and one guide is all shiny under the flange and all over the part that presses inside the head. This one had the OEM o-ring. The other guide on the exhaust side had burnt oil stains all under the flange. The green Vesrah o-ring was dark brown stained on one side. The part that presses into the head had more burnt oil staining under where the o-ring goes and there are tiny dark burnt oil lines running from the flange area all the way down to the tip that's exposed in the exhaust ports runner. This oring was also pretty mushy compared to the other like it was breaking down. I tried to take pics with my phone but I can't get the lighting right to show the oil staining in the pic. It was definitely drawing oil in thru here which blows my mind. I'm going to take the head to work and swing an indicator in the guide bores to make sure they are round. One thing is for certain, if they put o-rings under there, they were needed. They must have known those bores yawn open sometimes and they use these orings on valve guides in all kinds of Honda four strokes. I also googled and found issues on XR's sucking oil thru the outside of the guides when those o-rings get old and brittle.

I've got Kibblewhite bronze guides for a 200X somewhere in my stash but I might buy new iron Honda guides. I'm definitely using OEM valve stem seals and guide orings this time.

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[barnett468]

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The guide would have to be passing a massive amount of oil to cause it to smoke significantly . Many engines that don't have positive type valve seals don't smoke at all even though there is clearance between the valve and guide of up to .002".

Also, crusty oil build up on an exhaust valve is not a definitive indicator of oil coming thru the exhaust guide because the exhaust valve will always get more build up than the intake even if the exhaust is not leaking at all . This is because the intake valve runs much cooler than the exhaust because it is cooled by the incoming fuel and air charge, therefore it doesn't cook the oil nearly as much, plus the detergents in the fuel itself are designed to minimize deposit build up and can even remove some deposits in some cases, however, this works primarily on the intake valve as the fuel charge enters the engine because there are no detergents in the fuel after it is burned.

I would also measure the bore and piston properly and look closely at the piston rings, however, it is difficult to determine if the oil rings are passing oil.



PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR

[El Camexican]

I'd make 100% sure the head isn't cracked and that the oil rings didn't get messed up during assembly. Like Barns said, it would take a fair bit of oil to smoke. We didn't run valve seals when I was drag racing and all it ever amounted to was the occasional small puff on start up.

Is there any sort of crankcase ventilation system on that engine that directs crankcase fumes back into the intake tract?