os fs40,v/ little compression

[Guest]

hello all

i have a pair of os f/s 40s

i used lay up oil and one has almost zero compression i checked valves etc , it trys to start but its so weak as it cant really spin the prop, went to model shop he felt just keep trying and it will un-gloop its self, i was going to fit a new ring /liner if totally required any thoughts.

thanks ian

[wonwinglo]

Sounds like the cam lobe,four strokes are prone to heavy cam wear and the power loss can be substantial,the only real solution is an overhaul with part replacement.

Also when you lay the engines up remove the plug and replace with a slave,the layup oil wrecks the plugs.

Wonwinglo.

[Guest]

just an update

i kept trying with this engine as most of these on ebay are not the surpass , just the fs variant any how using my cordless as a starter it got very hot around the barrel but still would almost backfire and run backwards almost, so i filled the motor with Wd 40 and spun it backwards for a minute reconnected clip dammed thing nearly chopped of my finger so it seems to run ok ticks over and revs.

i have bought another now from the states an surpass about £80 inc p&p thus this one will be a spare for the mossie when in france.

regards ian

[wonwinglo]

Some Four strokes will really throw props and need a locknut,usually the reason for the backfiring is that the engine is excessively rich,watch those fingers,use a chicken stick,you can make one from a oieces of broom handle with a rubber finger stall pushed onto the end.

[Guest]

hello

i tried the stick to be honest i had set the prop just so a flick of the finger would do the job , it seems to start very well now although as you mentioned it is running on the rich side as a side note its been 15 to 20years since i last flew the models so i checked all the motors they had all gone the same way , iwas really worried as i had bought a brand new os20 fs i only ran it for a few minutes when i got it and it felt almost seized after all these years ( for bb junior 60) its ok now but it seems lay up oil has a life as well.

regards ian