centaur gas engine

[brickyParticipant @bricky]

I have been having problems getting my engine to run.I am running it on petrol.I have made and renewed the piston rings and have got a bounce back on compression.I have the hall sensor set at 4 degrees before TDC and the inlet just starting to open at 15 degrees before TDC.It has fired on several occasions and has run for about 2 seconds, but after nothing.,the throttle is half open and the fuel is a quarter turn of the valve .I am doing something wrong but I don't know what.I have had a lot of help from forums in building this engine and I hope someone has the answer.

Frank

[brickyParticipant @bricky]

[JasonBModerator @jasonb]

What ignition systemn are you using? Some have auto advance which can get mucked up on these slower reving engines.

Are you using the standard carb or something else?

[brickyParticipant @bricky]

Good morning Jason.

I am using the standard carb that comes with the kit,and am using a hall sensor with the magnet set in a plastic disc on the crankshaft.

Frank

[JasonBModerator @jasonb]

But what ignition do you have the hall sensor plugged into?

[Andy HoldawayParticipant @andyholdaway]

Is the plug wet after it has failed to run? I have found Colman fuel far more forgiving than petrol on small engines (apart from being less smelly!). You can get it from camping shops.

I also set my engines at TDC, and as Jason says, be aware that some of the RC ignition kits have an auto advance feature.

Andy

[brickyParticipant @bricky]

The ignition system is the Minimag low powerr capacitor ignition 3volts MCL-1 1006

Andrew ,do you mean you set the sensor to fire at TDC or the inlet to open at TDC.

Frank

[brickyParticipant @bricky]

The ignition system is the Minimag low powerr capacitor ignition 3volts MCL-1 1006

Andrew ,do you mean you set the sensor to fire at TDC or the inlet to open at TDC.

Frank

[Andy HoldawayParticipant @andyholdaway]

Frank, I set the sensor to fire at TDC. My inlet valve is atmospheric (not cam operated) so it opens at some point on the downstroke.

Andy

[John RuddParticipant @johnrudd16576]

It could be that the spring on the inlet valve is too strong, holding the valve shut?

Does the valve appear to open with relative ease?

Does the piston/rings give a good seal? Poor vacuum will prevent the valve opening too…

[JasonBModerator @jasonb]

The Minimag should be fine.

I generally set my engines to spark a few degrees before TDC on both pushrod operated valves as well as the atmospheric ones on the hit and miss engines.

What level is your fuel tank? For initial testing I tend to use a plastic tank and flexible hose so I can play about with the best position, should not be such an issue on your throttle governed engine but on the hit & miss engines there is a risk of fuel draining back between hits.

Have you tried choking the carb, a finger part covering it or even a bit of tape will do.

[Nick_GParticipant @nick_g]

Posted by John Rudd on 12/04/2017 16:33:14:

It could be that the spring on the inlet valve is too strong, holding the valve shut?

Does the valve appear to open with relative ease?

Does the piston/rings give a good seal? Poor vacuum will prevent the valve opening too…

.

John,

Are you thinking that Centaur is a hit and miss engine.?

If you are it's not, it's a 'normal' 4 stroke.

Nick

[John RuddParticipant @johnrudd16576]

Nick,

My comments were based on what Andrew said about his inlet valve being an atmospheric type, not cam operated…

Maybe I'm not understanding the differences between different types of engine?

I'm ready to be enlightened…

[JasonBModerator @jasonb]

The Centaur along with Westbury's similar Wyvern engines have both the inlet and exhaust operated by pushrods from a rotating side shaft and the speed is controlled by the governor operating on the throttle. This is what Nick would call a normal 4-stroke.

The major of hit and miss engines have the exhaust valve operated by a push rod and the inlet has a weak spring that allows the valve to open as the piston is on the down stroke due to teh vacuum formed. Their speed is governed by the governor holding the exhaust valve open causing the engine to miss a beat until the speed drops enough for the exhaust pushrod to allow the vale to close which then allows the engine to hit (fire) in most cases, there are exceptions such as the Callahan Cam stopper.

[brickyParticipant @bricky]

The engine is mounted on the fuel tank.Am I right in setting the inlet to start opening at 15 degrees before TDC or should it be fully open at this setting and is 4 degrees the setting for the sensor.I didn't get a good seal on the rings that I bought with the kit.I had a leak at the base of the valve cage.I made new rings which give me a good seal and I have sealed the valve cage base.The engine has fired emmiting smoke from the exhaust and it did run for 2 seconds therefore I think the valve is opening.I do appreciate all the advice and will try any ideas that will help.

Frank

[John RuddParticipant @johnrudd16576]

Aahhhh….

A faux pas as the french would say….I got confused not reading the posts properly…..

[martin perman 1Participant @martinperman1]

Frank,

What stops the fuel running back to tank, does the tank have a breather hole!

Martin P

[brickyParticipant @bricky]

Martin ,the tank dose have a breather hole in the filler cap.

Frank

[MichaelRParticipant @michaelr]

I run my Centaur with a Minimag Mic 1A ignition controller with the magnet on the camshaft, and set to fire at TDC, the inlet valve opens at TDC and closes just before BDC.

The exhaust valve starts to open just before BDC, and closes at TDC with these settings the engine starts and runs OK.

Mike.

[brickyParticipant @bricky]

Michael,thanks for that I am going to try at these settings.

Frank

[Ian S CParticipant @iansc]

With an atmospheric inlet valve the spring needs to be very light. I read on another forum, "The only reason for a spring is to shut the valve when the engine is stopped, to stop the bugs crawling inside the motor". The pressure, and suction in the motor is enough to move the valve, but it needs to start closed. Snip 1/4 of a turn off and try, keep doing that until the valve visibly moves a fraction.

Ian S C

[Nick_GParticipant @nick_g]

Posted by Ian S C on 13/04/2017 12:51:40:

With an atmospheric inlet valve the spring needs to be very light. I read on another forum,

Ian S C

.

The Centaur does not have and atmospheric inlet valve. It's a pushrod valve engine on both the inlet and exhaust.

Nick

[Ian S CParticipant @iansc]

Nick, sorry I miss read things, I read Andrew Holdaway's post on 12/4/17.

With a push rod valve the only problem with too strong spring is a high rate of friction. The motor in question sits on it's fuel tank, does it need a foot valve on the fuel pipe?

Ian S C

[brickyParticipant @bricky]

Ian is the foot valve a non return valve.

Frank

[JasonBModerator @jasonb]

Yes its a NR valve, can either be done with a stainless ball or a flap. That I why I suggested earlier using a platic tank for testing as you can play with the height and then if it does not run so well with a tank below the carb you know the problem is fuel starvation. Some engine carbs have a NR valve built in such as the Lunkenheimer you see on a lot of the American engines.

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