I'll ask this question here both because I know you folks and because many scale fans prefer four strokes over those whiny two strokes.

A couple of months ago I bought a used Magnum .52 FS. I tried to get it running once with no luck. The compression however seems very weak compared to my other Magnum .52 FS. Now I know absolutely nothing about engines (model or otherwise) so I'm wondering what might be the cause for the lack of compression and what might be done about it?

Thanks.

The boys over on the Glow Engine forum suggested that this is common with Magnum .52 FS's and that "lapping the valves" might solve the compression problem -- now if I could just figure out what THAT means!

Lapping the valves is an automotive term. You remove the keepers and springs from the valves, then use a VERY FINE compound, and by hand, with LIGHT pressure, twist the valve into the seat.
(For automotive use there is a tool that is a stick with a suction cup on the end for twisting the valve back and forth. It should not be hard to fabricate something similar for your valves).

What lapping does is to remove any minor irregularities and allows the valve and seat to have a more perfect/positive seal. Once the springs and keepers are off, it only takes a couple of minutes per valve.

use a polishing toothpaste, and use the eraser end of pencil to spin the valve. spin the pencil in your hands like you do with one of the propellor-on-a-stick helicopter toys.

The intake valve is the culprit. Carbon build up in the seat or bent valve. If you lap the valve make sure you clean real well with soap and water. Comet cleaner or Borax can be used as a lapping compound.

I've never opened up an engine before (and only rarely the hood of my car) but I can swap out the HDD on my computer and convert an aluminum camping pot into a cowl. How hard is opening up and working on a glow engine.

I have this mental image of unscrewing a couple bolts and watching the guts of the thing tumble out all over the floor never to find they way back together again -- as always seemed to be the case with all those old watches I disassembled as a kid!

In short, is working on a glow engine something you can do, even if for those of us who don't know the difference between a distributor and a starter?

It might be best to find some one with experience, or send it to Global Hobby Dist for repair. They do a great job and some time all you pay is S&H. Most clubs have people that can check it for you, or your LHS. FS engines can be screwed up real easy.

Higley has a book called "All About Engines". I would highly recommend getting one before I tore into an engine. Definetly use nothing more coarse than toothpaste for lapping compound, or you will end up with no valve.

Les

http://www.rcuniverse.com/forum/m_23...tm.htm#2313166

The same question is asked in the Glow Engines forum. Follow the link to the open thread. I'm closing this one.

Eric