Leaking fuel from front of engine

Hello all, I hope everyones 4th was a good one. I have a problem with a few engines I have. They are bushing engines and are leaking fuel from the front. One is a stallion 35, an OS 20, a fox 35 and a OS 40FP. Before they started leaking they all ran well. Then I started notising eratic runs. Is there any hope for them.
Thanks in advance.
Dennis Parsley

Nope 2 stroke engines have to have crankcase pressure to run. Any loss of pressure causes the erratic engine runs. So the only thing to do is seal up the leaks by re bushing them. Probably not worth the time or money. Just buy New. Sorry for the bad news.

We have a member in our c/l group that has a temporary fix for the Fox engine and I don't see why it wouldn't work on other engines as well. He use a fine thread tap to build new inside dimensions to the bushing. I am not sure what size, but he can be reached at the following email address. [email protected]

Hope this helps. Lee

Like they said, new bushings or new engines. I am curious as to how they all started leaking at the front bushing. Did this happen to all of them at about the same time period? If so, I think you may be using a fuel too low in lubricants, namely castor oil, and/or running them too lean. Just a thought.

I do warn on the plain bushing engines that you still need good oil just for the bushing. If they have been run on low oil content fuel, I can see this happening. We ran our first FP for 7 years, and ran it hard before there was any leaking out the bushing. By then the engine engine was worn out. If it is just the leaking out the front that is the problem, purchasing a new case may be cheaper than rebushing the existing one.

A read of Randy Smith's article on plugs, fuels, etc. in May/Jun SN could be useful. I get the impression this will become one of the definitive articles on stunt motors.

Of course a little leakage is normal for bushed engines, since after all, this is the only way the bushings get lubricated. Some manufacturer's do a better job than others in minimizing the leakage, usually by devising a means (spiral cut, groove,..) to pull the fuel back to the carb inlet. I have had some pretty big leakers (Fox, OS35S) which still ran fine, although they certainly make a mess to the front of your plane.

However you say that the engines are running erratically, and as someone posted, it is essential that the crankcase can support some pressure, otherwise no fuel will be pumped into the cylinder. Also as someone else noted, that you say this has happened to a bunch of your engines, and that does sound like you ran some low lubricant fuel (or a lot of dust was sucked into the venturi). I think bushed engines should be run with at least 20% oil, and half of that being castor (Canonical Fuel).

Thanks for the replies, I have to explain that they didn't all start leaking at the same time. They all have seen a lot of, I might say , hard use in the past. The 40 FP started out as a RC engine back in '87 and has been in a few,(many) planes. I converted it to a cl engine last year. The fox was run in it's early days on superfuel, lately I have been using Byrons 5% nitro with 16% oil with extra castor to bring the oil content to 29%. Thanks for all the help, I was just trying to get out of having to buy new engines. I allready have little stands made for them all so as to put them on a shelf for keeps sake.
Again thanks,
Dennis Parsley

Dennis,
Oh yes. The hated "wet-nosed" engine syndrome. Most of my CL retread engine purchases over the past couple years have been used OS .35/.40FP and FOX .35 engines. They were bought off Eb_y or at swap meets. Some ran great but I got stuck with several that ran OK but leaked raw fuel out the front between the crank and case. I inquired on this forum about possible solutions but most suggested either installing a new crank/case (costly) or just scrapping the engine. With a limited modeling budget I looked for another solution.

PAMPA's STUNT NEWS magazine (May/June 1998 issue) had an article titled "The Two Cycle Stunt Engine" by Scott Bair. One of the topics he wrote about was named "Curing Front End Fuel Leak". He wrote "If a groove is made in the bottom of the case in front of the path of the crankshaft port as shown then the fuel that would have leaked out the front will pass back into the intake port". He included a drawing that detailed the modification that could be made with a Dremel tool.

Desperate for a solution, I tried his fix and cut a groove in the case of my leaking OS .35FP. Eureka!!! No more front end fuel leakage and the front end was now "dry". This first sample is still flying on a Twister and after over 150 flights it still doesn't leak out the front. After this sucess, over the next 2 years I sucessfully applied the same fix to another OS .35FP, two OS .40FPs, a FOX Stunt .35, and a TOWER .40.

I thought that I now knew how to fix any front end fuel leak on plain bushing engines. WRONG! I had bought another OS .40FP off Eb_y. During the first test run it leaked fuel like crazy out the front end. I cut the usual groove in the case same as I had done with the other engines. Unfortunately, this only reduced the amount of leakage but didn't stop the leak. So I tried another suggestion mentioned on this forum. Using a cut-off disc in my Dremel tool, I cut a shallow spiral groove in the crankshaft surface (between the port opening and the end of the crank). A test run showed that this eliminated the front end fuel leakage. Based on my limited experience, it appears that the case groove can solve mild to moderate leaks but that the crank spiral groove is also necessary for a really bad leaker.

The Eb_y and swap meet engines previous owner's use of low oil content (i.e. 16%) RC fuel and lean runs probably contributed to the excessive bushing/crankshaft wear that caused the front end leakage. I'd like to add that all my ABN/ABC engines are run with a minimum of 22% oil and the iron/steel engines are run with 25-29% oil (mainly castor). I have an OS .40FP that I bought new 3 years ago. It has over 35 hours running time in my Banshee and there is still no indication of leakage out the front.

I know that some modelers wouldn't think of grinding on an engine and would either prefer to install new parts or just scrap the engine. I can see their point and have no problem with that. For myself, however, I get a feeling of satisfaction if I can rescue an engine and give it another shot at flying again.
DennisV

>Dennis,
>Oh yes. The hated "wet-nosed" engine syndrome. Most of my CL
>retread engine purchases over the past couple years have
>been used OS .35/.40FP and FOX .35 engines. They were bought
>off Eb_y or at swap meets. Some ran great but I got stuck
>with several that ran OK but leaked raw fuel out the front
>between the crank and case. I inquired on this forum about
>possible solutions but most suggested either installing a
>new crank/case (costly) or just scrapping the engine. With a
>limited modeling budget I looked for another solution.
>
>PAMPA's STUNT NEWS magazine (May/June 1998 issue) had an
>article titled "The Two Cycle Stunt Engine" by Scott Bair.
>One of the topics he wrote about was named "Curing Front End
>Fuel Leak". He wrote "If a groove is made in the bottom of
>the case in front of the path of the crankshaft port as
>shown then the fuel that would have leaked out the front
>will pass back into the intake port". He included a drawing
>that detailed the modification that could be made with a
>Dremel tool.
>
>Desperate for a solution, I tried his fix and cut a groove
>in the case of my leaking OS .35FP. Eureka!!! No more front
>end fuel leakage and the front end was now "dry". This first
>sample is still flying on a Twister and after over 150
>flights it still doesn't leak out the front. After this
>sucess, over the next 2 years I sucessfully applied the same
>fix to another OS .35FP, two OS .40FPs, a FOX Stunt .35, and
>a TOWER .40.
>
>I thought that I now knew how to fix any front end fuel leak
>on plain bushing engines. WRONG! I had bought another OS
>.40FP off Eb_y. During the first test run it leaked fuel
>like crazy out the front end. I cut the usual groove in the
>case same as I had done with the other engines.
>Unfortunately, this only reduced the amount of leakage but
>didn't stop the leak. So I tried another suggestion
>mentioned on this forum. Using a cut-off disc in my Dremel
>tool, I cut a shallow spiral groove in the crankshaft
>surface (between the port opening and the end of the crank).
>A test run showed that this eliminated the front end fuel
>leakage. Based on my limited experience, it appears that the
>case groove can solve mild to moderate leaks but that the
>crank spiral groove is also necessary for a really bad
>leaker.
>
>The Eb_y and swap meet engines previous owner's use of low
>oil content (i.e. 16%) RC fuel and lean runs probably
>contributed to the excessive bushing/crankshaft wear that
>caused the front end leakage. I'd like to add that all my
>ABN/ABC engines are run with a minimum of 22% oil and the
>iron/steel engines are run with 25-29% oil (mainly castor).
>I have an OS .40FP that I bought new 3 years ago. It has
>over 35 hours running time in my Banshee and there is still
>no indication of leakage out the front.
>
>I know that some modelers wouldn't think of grinding on an
>engine and would either prefer to install new parts or just
>scrap the engine. I can see their point and have no problem
>with that. For myself, however, I get a feeling of
>satisfaction if I can rescue an engine and give it another
>shot at flying again.
>DennisV

Ron B.
F4Fguy

Scott Bair was writing about well fitted engines with normal clearances.Going at a worn out engine with a Dremel is not only poor practice,it's simply curing the symtom(a worn main bearing),not the cause.If the bearing is worn the only cure is to resize the bearing to a proper fit.It's true ,rebushing is expensive,but ,if you have an auto engine machine shop in your area they can "knurl"(it's not really that,but that's what it's called)the bearing with a valve guide tool and ream it back to size.This has the added benifit of work hardening the surface and leaving enough of the knurling to act as a spiral groove.