What wears out?

Like Jason says, these little engines will run fairly well on pretty low compression, but you could mix and match cylinders/pistons to maybe get a combination with a bit more.

Also, don't forget the gaskets and reeds.  The poor reeds can take a beating, especially from guys that don't realize their delicate nature.  New pick-up tubes, along with tank and intake tube gaskets can give a big jump in dependability, and a fresh glowhead gasket can restore some compression.

All of these are available in quantity from Matt or Bernie, and I'm careful to keep a good supply in my fieldbox.

Agree with all that has been said.

jarboy wrote:So, if I buy a big pile of used engines, a mix of all sorts, what is most likely to be wore out.

Can't say, it is on an "as case" basis.

I assume glow heads are number one, followed by pistons/cylinders. After that, what is wore out, and can it be fixed, or must it be replaced?

You don't know until you examine what you got. Some I got toast, others had a good head.

Is it different if poor fuel is used, etc?

Most engines being sold are over 20 years old. Back then, most if not all fuel was 100% Castor oil. Fuel was off-the-shelf at hobby and department stores. As stated, many engines being offered were donor engines from crashed ready-to-flies. They had less than a dozen runs, some were only one flight. I'd say more than likely you'll not encounter that problem.

Do the bearings last?

I have a very well used late 1970's .049 R/C Bee engine with cast crankcase. It is on its second set of piston and cylinder. It is said this crankcase is of softer aluminium than the machine extruded ones. It still has very good fit without any slop in the crankshaft bearing area. It is possible that you may come across one that has many hours on it, but this I believe will be rare. If it was involved in a hard crash may distort the crankcase bearing area and cause slop. For .049's, crankcase parts and cranks are still available.

Can anything be refurbished? Can cylinders be pinched, or pistons expanded and relapped?

Parts are still available through Cox International and Ex Model Engines, and other sources. They aren't that expensive and for me, it is easier just to replace (if you plan to run and not collect them for their historic value). Also, if you get a batch of used engines, you can swap parts to make the others run.

Regarding expanding pistons, sometimes one whacks the domed piston on a Testor McCoy .35 Red Head with a hammer to expand it and restore compression. Never tried messing with Cox pistons. We have a few here that are competitive and have done all sorts of tricks to fix things. They'd know.

It is a hobby, so time versus money isn't everything. Thanks.

True. It's your prerogative on how you solve problems and issues. I'd say more likely than not, a simple cleaning does wonders, most look worse than they really are. Reeds, springs, heads, needle valves, fuel lines, screws, etc. are still available.

Welcome to the forum!

I usually pull the crankshaft forward and try to rock the piston up and down with a propeller on to check for the case being worn out. If worn out, it will not hold a setting. Very common source of leaks. Fox and Cox are bad for this. If the piston holds a seal for even two seconds it is ok. Maybe a bit hard to start after a while, but will run faster until completely gone. Gaskets and overhaul kits are fairly reasonable. Even crankcases aren't too bad.

While I still have a dozen or so Cox Reed engines...I focused on Medallions and TeeDees .049/.051

Sold or gave away all .09 and .15 versions

Learned way back when to "Buy it Now", or low bid on LOTs....I mean the E-Bay ad with 13 engines and separate parts for $58 or Best Offer kind of offerings

My collection, right now, of HARD back plates ---was worth the bidding ( I really do NOT like the plastic back plates)

Said above but worth repeating.... COX sold MILLIONS of their engines

Every Xmas from 1955 to 1985 hundreds of thousands of kids got a Cox airplane or Car under the tree
Hell the Sears and Roebuck Catalog had five (5) pages of Cox (and other MFG) toy cars, boats, and airplanes

The next day, 26 December---50%~75% of them were dead, broke, and put in the back of the closet for that "some day" fix

NOW, 50+ years later ----every day is a new bucket of busted engines for sale....real good bang for the buck ...mostly because the only thing wrong ....is improper storage.... very few ever got used enough to be near worn out

fredvon4 wrote:While I still have a dozen or so Cox Reed engines...I focused on Medallions and TeeDees   .049/.051

Sold or gave away all .09 and .15 versions

Learned way back when to "Buy it Now", or low bid on LOTs....I mean the E-Bay ad with 13 engines and separate parts for $58 or Best Offer kind of offerings

My collection, right now, of HARD back plates ---was worth the bidding    ( I really do NOT like the plastic back plates)

Said above but worth repeating.... COX sold MILLIONS of their engines

Every Xmas from 1955 to 1985 hundreds of thousands of kids got a Cox  airplane or Car under the tree
Hell the Sears and Roebuck Catalog had five (5) pages of Cox  (and other MFG) toy cars, boats, and airplanes

The next day, 26 December---50%~75%  of them were dead, broke, and put in the back of the closet for that "some day" fix

NOW, 50+ years later ----every day is a new bucket of busted engines for sale....real good bang for the buck ...mostly because the only thing wrong ....is improper storage.... very few ever got used enough to be near worn out

This Makes Me Want to go buy More Engines < Your a good Salesman Fred

Fred is right in assuming there are tons of hardly used COX production engines on ebay that have only less than an hour runtime on them, having ended up in storage after the failed 1st or 2nd flight..I bought a few such early abandoned orphans on Ebay in very good condition. If the exhaust port  is seen undamaged by wrench marks and the engine relatively clean chances are you are looking at an almost new production engine from COX heydays earmarked by thin walled or stepped wall (sometimes thick wall) cylinders and excellent compression. That lil thing - unless you abuse it - will not wear out before you get bored with it, you bet..

aspeed wrote:I usually pull the crankshaft forward and try to rock the piston up and down with a propeller on to check for the case being worn out. If worn out, it will not hold a setting.  Very common source of leaks.  Fox and Cox are bad for this. If the piston holds a seal for even two seconds it is ok.  Maybe a bit hard to start after a while, but will run faster until completely gone.  Gaskets and overhaul kits are fairly reasonable. Even crankcases aren't too bad.  

I guess it boils down to prop balancing. I hate to refer again to my TD051 with around 300 hrs runtime on it that has as-new crank and shaft fit and still good compression even if the tapered fit is gone. The only sign of wear is a detached bottom fin on the cylinder abrased off by the exhaust throttle drum that had some axial play enough to remove that fin in contact with it.

COX ran experimental stock engines for 400 hours that still ran well but needed electric starter though..

I used to run the Babe Bees in mouse race, and the bottom rear of the case bore was egg shaped when the crank is at the bottom of the stroke. I made up bushings on a couple but have not run them since. I don't really like the reedies. I only used them because I had to. A new case assembly would normally solve the erratic runs. TDs don't seem to have that problem. One of mine has very little compression left but the case does not leak. I use a starter on it and it ran great last few times. I hardly use them now because our local field has a muffler rule, and I just stuck a Norvel on. Ya I know it is the Cox forum. I might try some of the non tank version reedies some time. I have heard they are more steady runners than the tanked ones because of the other possible leaks.

Never had a problem with tanked Bees, but then these were the ones with the metal back, not the plastic. Regarding leaks, they were more or less bulletproof. Never had a problem with my R/C Bee, but then I think the plastic tank was Delrin nylon.

There are some engines that started out really rough and were restored to running glory again. Bob has done such and others here. Here is a 1960's Babe Bee that was a field find by my son, before and after.







Here with a late model K&B .35 Stallion CL engine, I turned soured apple cider into pure ale:

CEF: K&B .35 Stallion Acquisition

Even if the engine seems rough, may turn out satisfactorily, also with a little elbow grease. You'll never know until you give it a shot. Sometimes it works out well. A few times I've had an unsalvageable situation.

GallopingGhostler wrote:Never had a problem with tanked Bees, but then these were the ones with the metal back, not the plastic. Regarding leaks, they were more or less bulletproof. Never had a problem with my R/C Bee, but then I think the plastic tank was Delrin nylon.

There are some engines that started out really rough and were restored to running glory again. Bob has done such and others here. Here is a 1960's Babe Bee that was a field find by my son, before and after.







Here with a late model K&B .35 Stallion CL engine, I turned soured apple cider into pure ale:

CEF: K&B .35 Stallion Acquisition

Even if the engine seems rough, may turn out satisfactorily, also with a little elbow grease. You'll never know until you give it a shot. Sometimes it works out well. A few times I've had an unsalvageable situation.

Pretty nice resto! As an aside, though, that patina looked amazing. Almost wish you coulda got 'er pristine on the inside but left 'er lookni' old and neglected on the outside. Woulda looked boss on a post-apoclapytic themed bird that way.

Also a lovely read on that K&B 35. Makes me wanna grab a random reedie off eBay and restomod it into a throttled SureStart like the ones I've been buying brand new from Bernie.

I seem to find reedies thrown in with packages when I buy other motors.  Got an .010 and PAW .06 once with a few reedies, and another G Mark package had a couple Bees in.  I counted around a dozen downstairs. Not as many TDs unfortunately. Here is a parts one.  A bit low on compression, and I had to make a drive washer.  The case repair was done well by an old flying buddy a long time ago after the rod broke.
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