as per subject, this engine is causing me much grief and a large dent in the wallet. for the past year this engine has been eating glow plugs like a fat kid with chocolate. I recently replaced the head gasket as the old one had been corroded in the hope that this might have helped. but no, i got 2 runs lasting about 30 seconds each before the glow plug was fried. what could be wrong?

Constantly blowing glowplugs can be caused by a number of things:

1. too much nitro. If the nitro level is too high you'll get pre-ignition and that physically destroys the glowplug element in a *very* short space of time. The solution: reduce your nitro content and/or add some extra gaskets under the head. Believe it or not, some engines are designed to run on little or no nitro and perform very well despite this.

2. damaged bearings/liner. Any small bits of metal floating around inside your engine will take out the glowplug in a very short space of time. If you've got a bearing that's failing or a liner that's peeling, the tiny flecks of metal that are produced will knock out your plug very quickly. Solution: check for bearing wear, liner peeling or other foreign bodies. Pull the backplate and take a look. Note that this can also happen sometimes when using an electric starter if the pressure of the starter cone causes the crankpin to rub on the backplate.

3. wrong plug choice. If the plug is too long or too hot it can cause pre-ignition or (in a worst case) foul the piston. A good place to start with a 52-sized engine is with an OS#8 plug. These are "medium" length and have a modest heat rating.

4. wrong size prop. Too large a prop (especially if combined with excessive nitro) will also cause pre-ignition, thus killing your plugs. A 52-sized engine should have something like a 11x6 for a sport-type plane.

thanks for the reply XJet.
basically everything you said is what i am using with the engine and i recently dismantled/cleaned the engine there is no sigh of wear. the only thing that you suggest that could be the problem is the fuel which has 10% nitro. I used to use 5% nitro and i think i found it to be pretty useless thats why i changed to the 10% but that was about 2 years ago.

EDIT.

Just checked the specifiaction of the fuel im using. its 8% synthetic oil and 2% castor oil. Is this killing it?

sounds like its running weak to me on the bottom end, try winding out the mixture screw quarter of a turn, jon

Are you saying your fuel only has a total of 10% oil?

A .52-sized engine needs at least 17% oil, and preferably 20% with at least 1/4 of the oil content being castor.

10% oil will ruin your engine pretty quickly!

What engine is it ???

If you are blowing plugs like popcorn you need to lower the nitro content to 5%,
put a colder plug in it, and put a smaller prop on it.

Yes , you need to run proper fuel in it, and run the engine slightly rich.

FBD.

thanks for all the help im going to chang my fuel to one that has 5% nitro and 20% castor oil. Will let youknow how it goes. Now what to do with 1/2 gallon of the old fuel? hmm my brother has a pile of wood in his back garden that he needs rid of, i think the fuel will give it that extra kick

Fuel has been sorted andthe engine is running sweetly

I have used fuel containing 10% total oil and 10% nitro on my OS FS-52 without problems. The plug was OS F type.

Its the Modeltechnics Dynaglo fuel with 8% synth and 2% castor. Isn't it?

To be honest I have run this engine on this fuel with up to 25% nitro again without problems. Perfect idle at 1,800 rpm, transition and peak power.

Prop was MA 12x6.

For sure the difference is in the superior quality of OS engines compared to clones like SC.

Stelios

Four-strokes can (in theory) get away with less oil than 2-strokes -- mainly because the oil tends to pool in the crankcase so a lower oil content just means it takes longer for that pool to form and it will be smaller.

Two-strokes however, are a totally different kettle of fish.

The only lube available to the 2-stroke is the oil that's mixed with the methanol. There's no "raw oil" in the crankcase of a 2-stroke so it really needs a highler oil percentage (because it's so diluted by the methanol/nitro) if you're to avoid excessive and premature wear.

Despite this, I run my 4-strokes and 2-strokes with at least 20% oil (by volume). An extra few percent of oil is much cheaper than new bearings a new conrod and/or new piston ring/liner and it offers insurance against the engine going slightly lean due to atmospheric conditions, dirt in the line or whatever.

Normally I am flying my engines on 14% oil, at least until today without any problem. OS FS-52 was run most of the time on 10% oil without any problem. Of coarse longevity is an issue.

Anyhow I didn't mean to open an oil % fuel discussion because there is another thread for this.

All I wanted to underline is the superiority of OS compared to clones like Magnum, ASP and SC in terms of metalurgy and operation.

Keep in mind that apart from OS and Saito I do have a Magnum (4-stroke 120) but I do know that it is of inferior quality.

You always get what you pay in this world!

Stelios

hi are you related to costas or something? os sure have had their share of bad engines, let me mention the 46 fx, 91 fx, 70 fl, 70 ultimate and the pumped fourstrokes, 21 vzb-vspec(buggy engine) with bearing issues. So sometimes you don`t neccesarily get what you pay for, thats for sure.