Idea for sealing valve guides

[johnny1320]

I have an idea to seal valve guides any input would be appreciated, you can use a viton "O" rings or a sheet of Teflon and punch a square "O" rings the spring keeps tension on the seal

View attachment Valve seal concept.pdf

 

[Cogsy]

Looks good, I've had a similar idea myself.

As I understand it though, full-size valve seals are really more like wipers than seals and just keep excessive oil from running down the valve stem into the guide, rather than actually sealing the guide itself. I'd be worried that to put enough pressure on the valve stem to fully seal the guide would introduce too much drag on the valve itself.

I am toying with the idea of fitting unrestrained o-rings on top of the guides to act as oil deflectors, if I ever build a positive oil pressure engine.

I could be wrong though - this may work perfectly, I'm certainly no expert!

 

[goldstar31]

If you look at full size practice on the old BMC A series engines , they had O Rings as mentioned.
We changed the guides from hard steel to bronze and streamlined them, re-worked the valves etc- but still put the o rings on the valve stems.

 

[Ripcrow]

I can't display the PDF but I am building an engine and my valves sealed by orings .my gasses flow in from the side at the bottom and the valve stem is above the seal and guided by a piece of machinable plastic.my valve spring sits on top of the plastic guide much the same way as a normal engine valve arrangement.i need a solid spring to get the valves working and will use leverage to overcome the additional forces required to operate them. My workshop is fairly bear and knowledge lacking but just thought I would add this

 

[johnny1320]

I can't display the PDF but I am building an engine and my valves sealed by orings .my gasses flow in from the side at the bottom and the valve stem is above the seal and guided by a piece of machinable plastic.my valve spring sits on top of the plastic guide much the same way as a normal engine valve arrangement.i need a solid spring to get the valves working and will use leverage to overcome the additional forces required to operate them. My workshop is fairly bear and knowledge lacking but just thought I would add this

you just gave me a great Idea to make my setup cleaner and get rid of an extra part. don't know why the pdf isn't working for you Ripcrow.
John

 

[mu38&Bg#]

you just gave me a great Idea to make my setup cleaner and get rid of an extra part. don't know why the pdf isn't working for you Ripcrow.
John

Many automotive applications use that concept.

http://www.skf.com/group/industry-s...pplications/engine/valve-actuation/index.html

 

[johnny1320]

The is a better design

View attachment Valve seal concept.pdf

 

[gbritnell]

The idea is good but the biggest problem as I see it is there is not a great range of sizes in the smaller sizes. Most small rings are .062 dia. cross section so even if you used a standard I.D. fitting the outer cap would make it large so that the valve spring would have to be large enough to accommodate it. That's one of the problems with miniature engine work, in most cases you have to adapt your design to off-the-shelf products. Here's the specs for a #004 O ring.
size I.D. O.D. Actual I.D. Actual O.D.
004 5/64" 13/64" 0.070" 0.210"

 

[johnny1320]

The idea is good but the biggest problem as I see it is there is not a great range of sizes in the smaller sizes. Most small rings are .062 dia. cross section so even if you used a standard I.D. fitting the outer cap would make it large so that the valve spring would have to be large enough to accommodate it. That's one of the problems with miniature engine work, in most cases you have to adapt your design to off-the-shelf products. Here's the specs for a #004 O ring.
size I.D. O.D. Actual I.D. Actual O.D.
004 5/64" 13/64" 0.070" 0.210"

I was also thinking that a Teflon seal could be made in place of the "O" ring, you could make a simple punch die. Thanks for the input George, I follow all your builds with amazement. After looking at your work I am now looking to buy a collection of files.



John

 

[mu38&Bg#]

Metric O-rings can easily be had down to 1.5 ID x 1 thick. McMaster has then in 0.5mm increments at 1mm thick starting at 1.5mm ID. Teflon would be good too. I recently milled some to make a needle seat for a fuel system and it seems to be working well.

Greg

 

[Herbiev]

For some reason I can't display the PDF either. Must be an iPhone thingy problem.

 

[johnny1320]

For some reason I can't display the PDF either. Must be an iPhone thingy problem.

It's a PDF generated by Alibre, there is imbeded software so you can see it in 3d and move it around and veiw it in all directions when you click on picture, I can open it on my Blackberry but no 3d so maybe the phone is the problem

John

 

[Ripcrow]

I am on an I pad so that's why I can't view it.best of luck my valves are rather large but my design calls for them so I can get away with powerful springs and orings

 

[Charles Lamont]

Is stem/guide leakage a problem in well-made model engines?

 

[johnny1320]

Is stem/guide leakage a problem in well-made model engines?

Gbritnel says that when he had a pressure fed rockers he had a problem with oil going past the guides and when he took the pressue system away it fixed the problem and now he just lubes the top end before running, I think George builds a great engine so I think seals will help

 

[Brian Rupnow]

Johnny1320---Its a great idea. My question is why? I have built 4 i.c. engines, and with a properly drilled and reamed valve guide and a correctly machined valve stem, I have never experienced enough leakage around the valve stem to have any perceivable effect on engine performance.---Brian

 

[johnny1320]

Johnny1320---Its a great idea. My question is why? I have built 4 i.c. engines, and with a properly drilled and reamed valve guide and a correctly machined valve stem, I have never experienced enough leakage around the valve stem to have any perceivable effect on engine performance.---Brian

I was reading Keith5700's build and he has a smoking issue, George had mentioned that pressure fed rockers can be a problem. I am thinking that if you have a closed in rocker assembly then oil drain back especially on a v8 can be a problem I just started thinking, how can I seal the valve stems? I am designing a parallel twin push rod engine with an enclosed valve train, so here I am.

 

[Jordan]

Interesting topic - I have a couple of observations, based on full sized engine experience, both air cooled motorcycles.
As an all-metal alternative to rubber seals, a guide made with a sharp bevel at the end may keep enough oil from getting sucked down. It's only the inlet that can make smoke - the exhaust is nett pressurised from the port end, so tends not to suck oil down.
I have a bike with O-rings fitted within the guide, to internal grooves. Not something that could easily done at model scale I think. Anyway, these never work for long. Later models used lipped seals successfully. I think a new O-ring could seal for a while, but as it wears the contact surface increases in area, creating more friction and heat - a vicious cycle that makes them ineffective pretty soon. I've noticed similar shortcomings when O-rings are fitted to rotating shafts, rather than lipped seals.
I think, if using rubber parts for sealing valve guides, the best result would be with lipped seals, if they can be found small enough.

Jordan

 

[johnny1320]

Interesting topic - I have a couple of observations, based on full sized engine experience, both air cooled motorcycles.
As an all-metal alternative to rubber seals, a guide made with a sharp bevel at the end may keep enough oil from getting sucked down. It's only the inlet that can make smoke - the exhaust is nett pressurised from the port end, so tends not to suck oil down.
I have a bike with O-rings fitted within the guide, to internal grooves. Not something that could easily done at model scale I think. Anyway, these never work for long. Later models used lipped seals successfully. I think a new O-ring could seal for a while, but as it wears the contact surface increases in area, creating more friction and heat - a vicious cycle that makes them ineffective pretty soon. I've noticed similar shortcomings when O-rings are fitted to rotating shafts, rather than lipped seals.
I think, if using rubber parts for sealing valve guides, the best result would be with lipped seals, if they can be found small enough.

Jordan

I think you my be right about the "o" rings not lasting, I was also thing that you can make a seal using Teflon sheet, just use a round die to cut the circle and a small fixture could be made to either dill to size or a sharp scribe pushed through the Teflon creating a simple lip seal.

 

[Hopper]

I too question why valve guide seals would be needed on a model engine. Although, my experience with IC is mostly with motorcycles. Motorcycle engines, with pressure fed rocker gear, have been running just fine without them for 100 years or so. I know some of the high-revving late model Japanese engines use those seals, but older bikes and even newer Harleys etc don't.

If pressure fed rockers are causing smoking, the problem perhaps lies in the oiling system itself.

A few things you might want to take into consideration, based on standard motorcycle engine design:
Volume and pressure of feed to the rockers. Motorcycle engines use only a few PSI to the rockers, not full bearing pressure. Many take the rocker feed from the oil return line to the oil tank, just a few PSI there as return is virtually unrestricted flow. Hondas, with a wet sump, use tiny jets, like carburettor jets, to limit oil flow to the rocker gear and OHC bearings.
It does not take much oil to lube valve guides and rocker spindles. Just a tad is enough. They are not like white-metal main bearings or roller bearings.

Drainage: Rocker box bottoms must be designed so accumulated oil drains away from the valve guides. Large enough drain holes must connect the rocker box bottoms to the crankcases to allow oil to drain quickly and freely. Some motorcycles use the pushrod tubes to drain the top-end oil, but the cam follower blocks must have drain holes drilled through them for free flow. Other engines (Harley) use holes drilled from the rocker box bases down throught the thick cylinder wall and exiting on the bore below the pistons.

Crankcase breathing: Consideration must be given to the compression and expansion of air in the crankcase BELOW the piston. If suitable ventilation is not provided, air can push oil back up the rocker drainage system into the rocker box, causing over oiling.
Suitable ventilation can be in the form of a timed breather valve that opens when the piston is on the downstroke to stop pressure building in the crankcase. Or it can be a simple reed valve or spring loaded disc valve that allows air to flow out of the crankcase but not back in. (eg, automotive PCV valve).

If all these are correctly designed, and the valve guides and stems are a good neat fit, there should be no need for valve guide seals for general use.

I am not sure what size engine you are building, but if you decide you must have seals, take a look at the valve guide seals on a 250cc Honda four-cylinder CBR250RR. They are four valves per cylinder so they are tiny. Might be small enough for what you need?