Barry W Posted October 17, 2012 Share Posted October 17, 2012 I have a problem with my OSMax 15LA engine. When running the engine at full throtle there is a fuel leak between the black fiber back plate and the crank case. I have replace the back plate and tightned the four fixing screws but there is still the fuel leak at high power. Has anyone had this problem and if so were they able to fix if? Barry Quote Link to comment Share on other sites More sharing options...
Major Posted October 17, 2012 Share Posted October 17, 2012 Did You try new gasket? Quote Link to comment Share on other sites More sharing options...
will -0 Posted October 17, 2012 Share Posted October 17, 2012 Major - I don't think there is a gasket on an LA, look here. The seal relies on a good surface one the crankcase and backplate. I had this problem with a 25 LA, but tightening the screws solved it. The screws are JIS Cross point which doesn't help. Check that there is no debris or scratches on the rear face of the crank case and the mating face of the backplate. Quote Link to comment Share on other sites More sharing options...
will -0 Posted October 17, 2012 Share Posted October 17, 2012 PS it's worth fixing as you'll probably be down on power with added deadsticks otherwise. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted October 17, 2012 Share Posted October 17, 2012 For sure a leak from the crankcase is bad news & will certainly affect the running of the engine.... Is it new? I wonder if a warranty claim might be indicated here.....its possible the plastic backplate isn't moulded quite right & is causing the leak. OS are great motors but you pay top dollar for them so you should get top drawer quality too..... If its not new then maybe you could add a gasket yourself...just because there isn't a gasket as standard doesn't mean you couldn't make one out of thin paper......or a smear of silicone RTV might be easier.....replacing the backplate screws with capheads might allow you to tighten the backplate up a bit more....try tightening in the screws when the motor is hot.....assuming you can get in there.... Just another thought...is it actually coming from the crankcase.....? Might it be from the needle valve assembly via a leaking 'O' ring or such like? Final thought......someone hasn't applied threadlock to the backplate/crankcase joint have they? I came accross this in a 46LA a while ago......definitely NOT a good idea!!! Quote Link to comment Share on other sites More sharing options...
will -0 Posted October 17, 2012 Share Posted October 17, 2012 Steve- actually I'd suggest you'll have more luck tightening when cold as the plastic will expand with heat much more than the metal screws will, so it should be tighter when hot. If it helps, the screws are M2.5 x 7, I think. A neat trick to make a paper gasket is to use the oily back surface of the crank case (minus backplate) to print an outline on the paper. Cut this out with a very sharp scalpel. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted October 17, 2012 Share Posted October 17, 2012 I'm thinking the plastic will be "softer" when hot & allow the crankcase to "embed" slightly...... Quote Link to comment Share on other sites More sharing options...
will -0 Posted October 17, 2012 Share Posted October 17, 2012 FWIW, I would follow steve's suggestion and replace the screws with cap heads. The cross point screws are JIS standard not Phillips and you probably won't have a driver for them. They are truly the work of beelzebub and are IMHO the worst feature of the LA range. (Try removing the head from one that's been on for a while) Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted October 17, 2012 Share Posted October 17, 2012 Try sealing the backplate with silicone gasket in a tube. You get it from car places like Halfords Quote Link to comment Share on other sites More sharing options...
Major Posted October 17, 2012 Share Posted October 17, 2012 Will - I suggested gasket because I have seen one in my .40LA while stripping it down a few days back... If there isn't any - of course didn't want to mislead anybody! Quote Link to comment Share on other sites More sharing options...
Barry W Posted October 18, 2012 Author Share Posted October 18, 2012 Thanks for all your suggestions. The problem started after several hours running the engine so I am not sure what has changed. I had bought a new back plate and the leak persisted. There is no gasket between the back plate and the crank case. In fact the wall of the crankcase is so thin it would be difficlt to make a gasket that thin considering the vibration and fuel that woulddamage the gasket. I will try some silicon gasket paste and see if that fixes the problem. Again many thanks to all who replied to my post. Barry Quote Link to comment Share on other sites More sharing options...
Ben B Posted October 18, 2012 Share Posted October 18, 2012 I would also suggest a smear of hylomar blue universal. Just don't be too generous, the aim is to create a seal not leave clumps of it inside the crankcase which might come off and do all kinds of bad stuff Quote Link to comment Share on other sites More sharing options...
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