| Author | Message | ||
     Arbalest |
Please note, this is not NECESSARILY Buell related (in my case at least), but may have some general interest, and this board is just CRAWLING with folks who probably know this stuff cold. This is for all you engineering types. How does the valve stem get lubricated? Some engines have valve seals to keep oil OUT of the valve guide. So what provides the lubrication? In the case of iron head Sportsters, even the valve guide is steel. I thought that lack of lubrication caused valves to stick in the guides, but how does ANY lubrication get to the valve stem/guide interface? In my case, the valve guides were brass. I stuck valves at least three times that I am aware of. I am now going to steel Sportster valve guides, since no oversize guides are available for the Dnepr. How can I keep the valves from seizing in the guides? | ||
| 99x1 |
" How does the valve stem get lubricated? " Oil mist - AFAIK, valve stem seals don't actually seal, they maintain the correct clearance as the guide wears. Other types of seals (ie umbrella seals over the spring) shield the stem from the oil mist to reduce the amount of oil on the stem. I once stuck a vacuum gauge on the oil dipstick hole of my BMW, oil mist would work it's way up the clear tube to the gauge on the tank bag fairly quickly. | ||
| Blake |
Arb, If working as intended, the valve guides don't see much load, very little load as a matter of fact. The valve stem is basically just sliding up and down with just the slightest lateral loading imparted by the arcing path action of the rocker arms. Oil drips/splashes from rocker arm and surroundings onto the valve stem, down and down to the seal where it is mostly wiped away, but a thin film does continue to coat the valve stem and guide surfaces. With little load, a little oil is all that is required. First thing would be to check the oil passage feeding the valve stem, this is probably a tiny passage in the lifter finger's contact surface. Or I may be totally imagining things.  If a spring exert uneven pressure on the retainer and in turn the valve... or if the rocker arm to valve contact point is not aligned optimally, the valve stem will be loaded laterally. The guide must then resist the lateral load. If the situation is bad enough the heat from friction due to the lateral loading can cause galling and a stuck valve. That's my take on it. Others may have more to add. I don't have a lot of hands on experience with failed valve guides, so I could be missing some important stuff. | ||
| Aaron |
Guide seals allow some oil to go by. Some seal up tighter than others. Teflon seals are notorious for sealing tightly ... common practice in stock car racing is to slice'em with an Xacto knife just to get some oil down them. Sometimes people have trouble with gapless rings causing smoking because they want to pull oil down the guides. When you use a gapless ring, you often need a tighter seal. | ||
| Arbalest |
Thanks for the input guys. In my case, the only top end oiling is what mist or liquid drips or fumes come out of the pushrod tubes. Previously, I had considerable side loading on the valves, due to whacky rocker arm geometry. The old valves were about .125" longer(including the lash caps) than the current valves. When the valve was closed, the heel of the rocker arm was at the very edge of the lash cap - not even over the valve stem. I put in shorter valves with hardened tips, no lash caps. The geometry is much better now. The rocker arm works directly on top of the valve stem. The problem is, I just stuck another valve and sucked the valve guide right out of the head. The previous valve guide was brass, not bronze. I am putting in steel ironhead Sportster intake guides. I hope this works. | ||
| Bomber |
Ara . . . . brass guides pretty much don't do the job (wear too easliy and like that) . . . .bronze works MUCH better, which is why it replaced brass pretty quickly back in the day . . . I have no experience with stell, but I would imagine that you might run into difficulties with a great deal of heat built up due to the steel-on-steel contact . . . also, it sounds like you've got a problem with the oil system, sir . . . I know of several of these scoots in my area, and, although they DO have more than their share of problems (way more, in fact, mostly electrical), none of the folks I know have had trouble with stuck valves . . you sure everythings OK with the oil getting to where it's supposed to go? | ||
| Arbalest |
Bomber, I have to assume that it is. I had the standpipe modification installed for awhile, and it certainly accumulated oil in the valve covers, about 300cc's worth, so I know oil is getting out there. ALL of the problems I have experienced with this bike have been valve train related. | ||
| Johnc |
Arbalest, in cases where the valve guide is horizontal like on your Dnepr, I have had good success using pourous metal guides such as cast iron or bronze. Since gravity can't push oil down the guide, the more pourous metal guide tend to absorb oil and prevent seizing. Try soaking the guides in oil for 24 hours before insatlling them and run .0015" clearance. This works in VW horizontal 4 cylinder air cooled engines. Cast iron and bronze guide are available in many sizes from K-Line. Any engine parts supplier should be able to get a size that will work for you or if you give me the dimensions I can look up the correct part # for you. |
