# Idea for sealing valve guides



## johnny1320 (Jun 11, 2013)

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


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## Cogsy (Jun 12, 2013)

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!


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## goldstar31 (Jun 12, 2013)

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.


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## Ripcrow (Jun 12, 2013)

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


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## johnny1320 (Jun 12, 2013)

Ripcrow said:


> 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


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## mu38&Bg# (Jun 12, 2013)

johnny1320 said:


> 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


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## johnny1320 (Jun 12, 2013)

The is a better design 

View attachment Valve seal concept.pdf


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## gbritnell (Jun 12, 2013)

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"


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## johnny1320 (Jun 12, 2013)

gbritnell said:


> 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


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## mu38&Bg# (Jun 12, 2013)

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


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## Herbiev (Jun 12, 2013)

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


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## johnny1320 (Jun 12, 2013)

Herbiev said:


> 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


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## Ripcrow (Jun 13, 2013)

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


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## Charles Lamont (Jun 13, 2013)

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


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## johnny1320 (Jun 13, 2013)

Charles Lamont said:


> 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


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## Brian Rupnow (Jun 13, 2013)

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


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## johnny1320 (Jun 13, 2013)

Brian Rupnow said:


> 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.


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## Jordan (Jun 14, 2013)

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


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## johnny1320 (Jun 14, 2013)

Jordan said:


> 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.
> ...


 
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.


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## Hopper (Jun 14, 2013)

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?


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## gbritnell (Jun 14, 2013)

In this hobby the biggest use for O rings I suspect is for piston rings. While one can argue the success of this type of usage the design intent of O rings isn't made for this type of application. To generally be affective O rings need some type of compression to create the seal between the shaft or surface they are being used for. For reciprocating or rotating shafts the surface finish must be smooth enough to not abrade the O ring yet not so slick as to cause the oil to wick past the interface. In the case of using O rings for valve seals I'm sure it would work but with ever so slight variables in O ring sizing (past discussions on using O rings for piston rings) trying to get just the right fit in such a small diameter would be painstaking. 
As far as my engine smoking from top end leakage it has to be realized that the area under the rocker cover is bathed in oil as is it's full sized counterpart and even with tight tolerances between the valve and guide there is still that small clearance for the oil to be drawn past, especially when there is a vacuum applied. 
It's nice to have conversations like this because with enough responses you get to find out what successes, or failures, others have had with certain components. 
gbritnell


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## mu38&Bg# (Jun 14, 2013)

The MC14E engine is interesting. I don't ride, but my buddy does and has never brought this engine to my attention.

That reminded me of the little Honda GX25,31,35,50 utility four stroke engines. The GX-25 parts list shows a stem seal on the intake valve only. The stems in the GX-25 are 3.5mm nominal. What is the scale of your parts?

3D pdf files are large and the viewer is slow. I have it in SW, but  never use it. SW eDrawings is much better, and has more  functionality for the viewer.

Greg


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## Jordan (Jun 14, 2013)

There are many examples of oil control for inlet guides only. My AJS has an adjustable needle valve - just for the inlet. Even with a flooded rocker box, I'm thinking exhaust gas pressure should be greater than gravity?
For long term use an O-ring might not be best for dynamic applications. But it does work, until it wears out. Smooth surfaces definitely a help to reduce abrasion.


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## johnny1320 (Jun 16, 2013)

One problem I can see is then you have over head cams and you are running bucket followers the pumping action under the bucket could force oil into the exhaust and intake past the guides, even the hot exhaust will make it smoke and I am wondering if this is part of Keith5700's problem.


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## Jordan (Jun 17, 2013)

I'm not clear how a pumping action would happen in that scenario. I guess it could pulsate, but nett effect would be neutral.
Provide a passage between spaces above and below the bucket?


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## johnny1320 (Jun 17, 2013)

Jordan said:


> I'm not clear how a pumping action would happen in that scenario. I guess it could pulsate, but nett effect would be neutral.
> Provide a passage between spaces above and below the bucket?


 
Would not be neutral, if oil gets under bucket it will try to compress and will pressurize the under side of the bucket, on a large engine where there are large areas for the oil to go but on a small engine not so much. I build 600hp dragbikes all bucket tapets.


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## Jordan (Jun 19, 2013)

OK, I just remembered I've never had bucket tappet experience.


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