Puzzling Laser 150

[Jon H]

2 hours ago, Martin Harris - Moderator said:

That is truly interesting information - was this in the original design or one of your developments?

 

been that way since 1984 🙂 

[Anthony Scott 2]

My thanks to everyone who responded to my cry for help.  All sorted by a new OSF plug-red face!!

[Frank Skilbeck]

Glad you've got it sorted. Having problems with a friends Saito 150, which keeps spitting props, new plug is the next stop.

[Martin Harris - Moderator]

Good to know that it's sorted. I thought you'd tried changing the plug (in your second post).  Was it an old one or was that a faulty new one?

[Paul De Tourtoulon]

4 hours ago, Martin Harris - Moderator said:

Good to know that it's sorted. I thought you'd tried changing the plug (in your second post).  Was it an old one or was that a faulty new one?

It sounded like one of our club members, a box full of useless old plugs.

 

8 hours ago, Frank Skilbeck said:

Glad you've got it sorted. Having problems with a friends Saito 150, which keeps spitting props, new plug is the next stop.

I have 2 Saito 100's a  litho gasket under the cylinder did the job on both.

[Engine Doctor]

3 hours ago, Paul De Tourtoulon said:

It sounded like one of our club members, a box full of useless old plugs.

 

I have 2 Saito 100's a  litho gasket under the cylinder did the job on both.

When a FS continually throws props/pre-ignites a shim ysually sorts it. My first experience of this was a Enya 60 4c . It would idle all day open throttle and just as the revs approached max .... bang. Alter mix while opening throyle and would rev all day no issues . Close the throtle and bang .... prop would throw. A shim cut from some anealed litho sorted that engine and its now in my 2 x Ladybird .

Apart from thtowing props pre-ignition caused a bent gudgeonpin, damged piston and con rod. 

Changing plugs , fuels etc made no difference to the issue but shim fixed it. 

I currentky have a Enya 120 4c with same issue waiting for the treatment.

[Chris Walby]

"Changing plugs , fuels etc made no difference to the issue but shim fixed it."

 

Be interested to know if its just compression that causes prop chucking? I am not familiar with 4 stroke glow, but the only time we experience kick back was on 4 stroke methanol racing engines (single cylinder) when we moved ignition to 42 degrees BTDC. Once running there may have been some improvement at the top end, but was outweighed by the difficulty of starting an engine with very aggressive valve timing.  

We did run a 2 stroke with very high compression with no ill effects on petrol, but that was with the last ingredient on the oil container "octane booster" and that was nearly as fast as the same methanol fuelled engine.

So does % of nitro factor into prop throwing?

[Martin Harris - Moderator]

I believe it does, Chris. 
 

Reducing nitro content may help but I added a second shim/gasket to an ASP 180 which was rough and finicky to tune on our “standard” 10% club fuel although I don’t remember it throwing props - but I do tighten my nuts properly with suitable spanners. It transformed it. 
 

Glow ignition timing is purely heat/chemical reaction related. There’s an element of automatic advance built in as revs/load are increased. Changing the plug specification will influence it. 

[Nigel Dell]

Blimey that’s above a beyond Martin! 🤔🤭😂