Found Collection

A friend of mine replaced the front bearing on his Supertigre S61
by force(used a bearing puller), I subsequently discovered
that the proper way was to heat the case in an oven and it would easily drop out.

What are the implications now ? The engine has not been started and appears
to turn ar normal.

Thanks,

J

The 'homebrew' way is to put it in the oven.

You think the factory puts bearings in the oven?

Ken

SOME use heat when heat is called for and some do not.

Take a look at what Clarence Lee has to say on this very subject.

He states that heat should be used when needed if the bearing will not come
out easily when using just a puller alone. UNLESS the factory instructions
specifically indicate that you should apply heat.

The bearing is held in place on the crankshaft by an interference fit. It is
also held in the actual engine case by this very same interference fit.

My only concern would be just how "secure" the bearing is on both the crank
and in the case. In most circumstances even a slight interference fit will
suffice.

What CAN happen when these interference fits become too loose is either the
bearing outer race will spin in the case or the inner race will become loose
enough for the crankshaft to begin spinning inside the inner race.

These are a couple of fairly easy and usually successful "fix's" to remedy
either problem.

BTW: Some years back we would modify cheap (at the time) engines for high
RPM use. Some were used in model boats, some in model cars and some for
pylon racing. The crank spinning inside the inner race used to be one of the
first failure points on these highly stressed engines. Application of the
above mentioned "fixes" would allow us to use the engine for a "few" more
runs before they would self destruct!!

CK

There is some really bum gouge in this thread....

Bill Vail

Could you be a little more vague?

--
Paul McIntosh
Desert Sky Model Aviation
Engines, planes, bearings and boats
http://fly.mcintoshcentral.com
.

Success is much more likely if the case is heated just enough to allow both
bearings to be slipped in at the same time, with the crankshaft serving as the
alignment jig and holding the bearing alignment while the case cools.

Your mileage (and opinion) may vary.

John P.

I was feeling cranky:-)  Here is a little more....

Clarence was a great engine man and still very knowledgeable if not somewhat
dated. He is now (and has been for years) a very respected engine collector.

He was also very involved in the development of the K&B/Veco line of engines
30+years ago and to my knowledge K&B's were the only engine that the bearing
was not a slip fit on the crank. They were press fit.

Bearings should NOT be held in place on the crankshaft by an interference
fit!  They were in some K&B's and  it was a nightmare. On K&B's where the
main bearing was press fit on the crank I would remove the crank and stuck
bearing from the engine, chuck the bearing in a vise and hammer the end of
the crank until the bearing slipped off.  That of course destroyed the
bearing.  I would then polish the crank until the bearing was a tight slip
fit and put in a new bearing.  I own 300+ engines from Nelsons to Nova
Rossi's, 40+ K&B's to OS and Fitzpatricks and with the exception of some
older K&B's, the bearings are NOT and should NOT be a press fit on the
crank.

Now to answer the original question. "What are the implications now (of cold
pressing the bearings in place)?"  In all likelihood nothing.  Just run the
thing.  I've seen folks run engines orange with rust and while I don't
recommend it and performance and life may suffer, it will be fine.  If you
are running your engine in the 30,000 rpm range it would matter but for the
average OS, TT, GMS, ASP... turning 12,000 rpm and making 1.2ish horsepower
it just doesn't matter. Any possible damage to the balls or races (if the
cage is damage, that matter!), or any misalignment will not be a factor in
sport flying.  VERY few model engines are flown enough to find the service
life of the bearings even if poorly installed and misaligned.  Look back at
the years of SPORT flying at your club...when was the last time you saw a
bearing failure?

My guess is that we will disagree but that is OK...

Bill Vail

Brian Hampton
Adelaide, South Oz

One of the statements made puzzles me.  They state that heating the bearings
to 100-150C would damage them.  I can't see this happening to properly heat
treated materials and modern lubricants.  Most all bearings are supplied
with light greases that can easily withstand those temperatures.

--
Paul McIntosh
Desert Sky Model Aviation
Engines, planes, bearings and boats
http://fly.mcintoshcentral.com
.

Brian Hampton
Adelaide, South Oz

I didn't read the entire article but I would guess they are worried about
the bearing retainer.  Just the other day I was removing a set of ceramic
bearings and without thinking, damaged the nylon bearing retainer with too
much heat.  Doh!  Most if not all bearings fail because the retainer fails.
Low cost low speed bearings usually have a retainer that is riveted or has
bent tabs which work loose.

Just a guess

Bill Vail

--
Paul McIntosh
Desert Sky Model Aviation
Engines, planes, bearings and boats
http://fly.mcintoshcentral.com
.

  Don't worry about it.

  CR