chall

I've been fussing with a couple of old .40 glow engines without much luck. The closest I can come to success is that they'll run for about 4 minutes then die, leaving me to make a dead stick landing.

I've done everything I can think of: new fuel system, hoses, checked for air leaks, etc. They'll start fine, and sometimes idle indefinitely on the test stand or at the field.

So when a glow engine gets old, can the piston/cylinder clearance just get too big? And maybe as it heats up things just get too sloppy? Are there things I can measure with my micrometer that will be revealing? Compression? (I have a tester but don't quite know what the readings mean.)

These things are pretty old, one's an OS FP-Max about 10 years old, the other is an older K&B 40.

Thanks for any and all suggestions!

CRFlyer

You could try cleaning the engines using the crock-pot method. Sometimes they get gummed up and then when they are hot get sticky and this can cause the engine to stop.

Jim Thomerson

Your K&B 40 is a Dykes ring engine. If the gap in the ring is more than a few thou. you probably need a new ring. If it is one of the earlier models without bronze bushings in the piston for the piston pin, you may need a new piston as well.

Jim

Bax

My Feedback: (11)

Old engines have problems running only if they've had a lot of use or abuse. If the engine's just worn out, the idle will be the first to go, being unreliable. The engine may run perfectly-well on the top-end, but may also quit after a few minutes because the compression's loosened-up enough that you've inadvertently set it a bit lean. The engine will gradually overheat and die because of being slightly lean, or because it warms up enough that the clearances separate too much to sustain good compression.

If the engine's just had a lot of varnish buildup over a lot of use then the overheating's caused by friction. The fact that the engine's running a bit and then dying means the clearances are still loose enough for some running, but tight enough to cause a gradual overheat. Cleaning the engine of any old fuel residue and running it will then tell you if it's worn out or was just had too much fuel residue buildup.

Abuse, of course, is self-evident. You'd see signs of internal damage...scoring, scuff marks, a lot of dents and dings on the piston crown and bottom of cylinder head, and so on. Maybe even a slightly-bent crank or rod. They'd not fit right, and would build up heat due to mis-fitting as the engine ran.

A careful check would help you determine the actual difficulty.

judoguy

I have an old gummed up engine - what's the crock pot method? Probably similar to cleaning a old carborator on car, right?

w8ye

My Feedback: (16)

Yes.


Regular antifreeze and awater mixture.

Use a crock pot that will never be used for food again.

Don't boil, just get hot.

Enjoy,

Jim

chall

By the way, thanks for all the tips. These ideas all sounds promising. The OS engine has never been cleaned (by me) and sat up for a while, so the crock pot idea seems promising.

The K&B was cleaned by me, but I did not replace the piston ring. The good folks at mecoa.com have put the old owner's manual on-line and it explicitly says not to put an old piston ring back on if you've taken it off. So worn out or not I probably need to replace it.

donkey doctor

Hello; I would say that an engine is worn out when you can no loonger get the parts to repair it. I have tried to wear engines out, but can't find any way to do it, unless you start with an obsolete engine. On my oldest, and most used engine, a Saito 45 that I bought in 91, I have replaced;p the crankcase, the head/barrel, the piston, the camshaft, the rod thre times, the back cover three times, the push rods and pushrod covers, the rocker covers, the carb and intake pipe, the bearings three times, and the ring three times. I might have put two gasket sets in too. About the only time anything broke or wore out was when a piston developed a porousity. I didn't really have to replace the rings, I just did it in an attempt to get more power otu of it. All the other repairs were due to crashes, or unimformed re-assembly. This engien was in our club trainer for more then ten years.

chall

This is long after the original posting, but I finally got around to tackling one of my two pesky engines. I de-varnished the OS FM Max 40 and tried it out. No luck, but I noticed two clues: it would run forever at low speed, and it would run forever if I left the glow plug igniter attached.

Those clues seemed to point to the glow plug, so I replaced it and IT WORKS! The de-varnishing probably helped too, but I suspect this was the culprit. I guess I've never had a glow plug last long enough to get fouled (or whatever killed it), mine usually burn out like a light bulb.

Charles.

britbrat

Don't add water. Use the anti-freeze straight from the jug. If there is too much water, not only is the mixture much less effective, you can get corrosion of the aluminum parts.