Sidevalve single

[mu38&Bg#]

The timing figures for the Vega 30 are much wilder than your engine, ownthesky2010. http://modelenginenews.org/cardfile/vega30.html I think plug location would be the first thing to investigate. Being side valve it simply won't make a ton of power. Anything you can do to make it run better than it is, should make a little more power. In the video it seems pretty rich, but that could be poor combustion due to plug location. You want to try to get the plug centered to the chamber. Later Ricardo chambers put the plug over the exhaust valve to reduce knock, but I don't think knock will be much of an issue here. Opening the passage to the cylinder would be worth trying. I would think compression ratio shouldn't have much effect, unless it's knocking.

How much oil is there in the fuel you're using?

Greg

 

[ownthesky2010]

Thanks for the advice Greg. I have read that side valve engines can be choked by too much compression and that's why I'm considering lowering it but I will move the plug first. It would be great if I had some idea what to aim at as far as rpm is concerned. I know the vega series were considered under powered but can't find specific prop and rpm info.
in the video it is running rich at lower rpm but the carb only had a high speed needle. I will revert back to the original carb I used with twin needles and a larger bore as the first run was definitely better.

 

[ownthesky2010]

also I have found no difference between 25% and 18% fuels.

 

[canadianhorsepower]

please have a look at the complete engine configuration
before making any statement .

 

[mu38&Bg#]

Sidevalves require a lot of compromise in combustion chamber design. That's why they were abandoned so long ago. Ricardo did a lot of work with this head design. His work would be well work the read if you intend to optimize it.

Here's another sidevalve, the Puck by Little Locos. http://modelenginenews.org/ed.2008.03.html 9.5:1 compression ratio.

https://www.facebook.com/media/set/?set=a.10151419042489804.542453.173276619803&type=3

Greg

 

[canadianhorsepower]

did I mention this before......

please have a look at the complete engine configuration
before making any statement .

anybody can copy and paste article. understanding them is another matter

 

[ownthesky2010]

Thanks for all the advice. Dieselpilot I will do a bit more research into head design.
I have done another video with the first carb I tried. I get 7380 rpm do there is some progress.
I have cleaned and smoothed out the combustion chamber since then but is too late to get rpm measurement so I will try it tomorrow.

 

[ownthesky2010]

[ame]https://www.youtube.com/watch?v=NDNAYWDaQfw[/ame]

 

[mu38&Bg#]

That sounds much better. It seems to sag as it warms up at full power? Are you familiar with the carb you're using? Some have a lot of interaction between the two needles, I'm not sure about the one you have. ASP?

 

[mu38&Bg#]

.. some valve lift information from the deep bowels of my hard drive Take this FWIW, probably did it when I should have been sleeping. Note the comparative metric to valve diameter, found that rather interesting.

Peter, does valve lift include rocker ratio?

 

[canadianhorsepower]

it does sound better but before trying any major change
block that plug hole and relocate your plug.
that massive extra fuel sptiing out must be fixe first

good luck

 

[petertha]

Peter, does valve lift include rocker ratio?

No sorry, I'm glad you brought this up. Its inconsistent to the point of being borderline useless. I should probably remove the chart altogether to avoid any confusion.

I remember starting a spreadsheet that took rocker arm geometry into consideration. For example the Edwards has short length of 0.500" & long length of 0.625" (short is to pushrod side, long is to valve side). But around this point I also recognized its still not a simple 1.25 ratio either because of geometry. The pushrods move the rockers in varying 3D space because they are driven by the cam followers moving radially outwards against the cam ring, but in offset plane. Actually this engine gets more interesting. The intake & exhaust cam followers are positioned fore & aft but on the same clock position. From what I can see, the max lift on both Intake & Exhaust cam lobes is 0.075", so that infers a (slightly) different resultant lift between I/E valves on that basis.

Because I was then specifically comparing valve lift of radials, I spot checked a few engines (Edwards, Ohrdorf & Jung) with Solidworks assembly motion, determined they were somewhat similar on resulting valve lift & called it good.

Good catch, please disregard my table. One day maybe I will backtrack & fix, but right now I'm working towards making swarf!

 

[petertha]

Thanks for the advice Greg. I have read that side valve engines can be choked by too much compression and that's why I'm considering lowering it but I will move the plug first.

I don't know anything about side valve engines, my table was meant to be helpful about methanol glows in general FWIW. But the other thing I wanted to point out is, how sure are you of the CR? Did you do the syringe & liquid trick to validate head & displacement volumes?

Reason I mention is, when I was messed around with this aspect, I was quite surprised at how 'little changes' can have a large affect on the CR number. I pylon race 2-S methanol engines & its a daily ritual to play with shims, plugs, even plug washers depending on the conditions. The rpm effect can be quite dramatic. Here is the post, but the part I wanted to illustrate was the 'effect' table.

http://www.homemodelenginemachinist.com/showthread.php?t=23705&highlight=compression+ratio

 

[mu38&Bg#]

Peter, I have not checked lift/diameter ratios in model engines at all. Books say .25 valve lift/diameter is common. More lift than this requires careful port design to take full advantage of.

Greg

 

[Niels Abildgaard]

Found this:

http://www.google.dk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCEQFjAA&url=http%3A%2F%2Fwww.ukintpress-conferences.com%2Fconf%2Fpmw07%2Fpdfs%2Fperformance%2Fpendlebury.pdf&ei=N6SjVIiYJ6GeywPvuoGQCw&usg=AFQjCNHbh2XqMDfY2FHKsAFZv6fkJ3b4Pg&bvm=bv.82001339,d.bGQ

where a fourstroke bike engine with 35 mm valves was made to go 16000 rpm.
There is not much more mass and flexibility in a sidevalve train than in a DOCH valve.Speed is not going to be the limit.

 

[ownthesky2010]

Dieselpilot there is definitely an issue with the carb. If I lean out the low speed needle it covers too much of the metering slot and affects the high speed mixture. I am focussing on the high speed for now. My plan is to make an air bleed carb at some point.
Peter I have knocked up a quick and dirty multiplug head to test various plug positions. I am also considering ultimately using a twin plug head so it will be interesting to see what affect it has.

 

[canadianhorsepower]

[quoteDieselpilot there is definitely an issue with the carb. If I lean out the low speed needle it covers too much of the metering slot and affects the high speed mixture. I am focussing on the high speed for now. ][/quote]
this is how these carbs work. you set up the secondary way ritch.
then you set your Idle 1 and 2 to youre needed then at full RPM you set the second one
the total of the first and second needle is what you need for the complete fuel range
the change in comp ratio I sugjested was only to have a faster acceleration

 

[mu38&Bg#]

That's definitely a way to get through some plug position testing quickly. The carb issue is a little surprising. I don't think I've run into a carb that simply wouldn't tune. It would be worth finding the initial settings for the engine that carb is supplied with and starting from there. Usually just starting rich on both needles and adjusting the main needle at wide open throttle, then the low speed needle for a good transition, will work just fine.

Greg

 

[Hopper]

Wow. Looks to me like you need to get rid of the restrictions between the valve area and the bore area. I would get rid of those two pointy bits that stick out into the gas flow area and neck it down to one small channel. There needs to be a direct channel the width of the valve straight from the valve to the bore, in line with the centre of the bore. This gives maximum flow.

I don't know much (anyting) about model size side valves but I have been working on and hotting up side valve Harleys for 40 years or so. Below is some pics of the cylinder head and cylinder from a Harley KR side valve racer that lapped Daytona at 149.8mph in 1968. Note how the head cavity offers no restriction to gas flow and is open all the way from valves to bore. Also, if you want max flow without too much compression loss, you can do like the picture of the cylinder and carefully grind "trenches" from the exact top edge of the valve seat contact area across to the bore. Just don't let the trenches get down too close to the top ring. Even so, the racing Harleys found that more than about 6:1 compression restricted gas flow too much.

If you want more info on tuning side valve (flathead) Harleys, google Harley KR, or Victory Library or Beautyofspeed.com.
It may not be directly relevant to model engines, or it may be. I don't know. But Harley developed those sidevalve racers for 40 years and they are the yardstick by which all others are judged. And fascinating reading if you are a side valve fan.
\

 

[Hopper]

PS, forgot to add that the Harley design in the pics allows full exhaust gas flow at the same time as full intake gas flow during the period of valve overlap. It looks to me, and I may be wrong, that in your model head, the incoming and outgoing gasses are all fighting to get through that one narrow notch at the same time.