ameyam

This is a repeat post from the engine forum section because I want user opinions as well

This post will have a large number of pics and a lot of description on my previous problems with the engine for obvious reasons.

The engine in question is a OS 75AX which I bought three years back. I was in my second year of aeromodelling then and not much adept with tuning glow engines. I used to run plain castor, no nitro then. This was my second engine and 2 1/2 airplane. It was UCD60 clone on which we installed the 75ax inverted vertical. We didnt actually run-in this engine in properly, the club trainer ran the engine rich on the ground for a few minutes and then took off with its still very rich. The engine flew ok for a couple of months and then began deadsticking. It was a frustrating period- no matter who tuned it, what we did, how much we cleaned the carb, kept or removed the baffle, how rich it was tuned, it would run for a few minutes, then deadstick. I never figured out whether it was a tank height (that model did have a tank height issue, it got sorted out later when I put a FS91 on it and lowered the tank) or an engine problem or some other problem for that matter. At the end I was starting to lose it and we decided to move on to other engines and models.

Then last year, after I lost confidence with a 55ax in similar fashion, I ported the unused well-oiled 75ax to the Reactor 46. It continued to deadstick. Now I was running Klotz with 5-10% nitro in the peak on the Indian summer (40Deg C outside) and the engine would overheat- you could feel the engine radiate heat when you sat in front of it. As it got hot it lost compression. It would also lose power and deadstick in a hover. Subsequently, I put the FS91 on that airplane and it resolved most of my issues with almost the same setup.

So this year I was considering replacing the piston-liner on the 75ax now so that I could get it running again at low cost for some of my 'cheaper' models. Someone suggested to clean the engine and then run once to check before I changed. Having got the screws heads spoilt by over tightening during the deadstick times, I had them opened some months ago and washed the engine with alcohol then, so its a lot cleaner in the pics. I just took apart the engine to check today. I have never completely taken apart an engine before, the parts came apart...well... 'by themselves'. I have also cleaned the engine with a rag, so take that into consideration. These images were taken on my phone, so will look much darker than is actually. There is one image that is much brighter than the others, thats what it actually looks like

Its really surprising- I expected the piston and liner to be really cuffed but as you can see, they quite clean (the 55ax I had similar problems with is much worse). If you look very closely, you can see minor lines on the piston side but those are so small, they look like machining marks, I dont think you can see them in the pics

The inside of the crank case is also very clean

The crank has some wear marks but I havent rubbed it with a soft cloth as well as the piston and liner. I didnt expect to be able to remove the piston and liner assembly, they came apart purely by chance, so then I gently tapped out the crank. I ran the rag over it and then took the pic

The bearings are definately rusted but they do turn over without any problems or roughness. The rag did dark reddish brown though when I tried to clean them. If someone can tell me how to get them out of the crankcase, I will try to get them out as well. Light coaxing with a mallot didnt help.

The carb has one of the retaining screws on the sides stripped. I found metal shavings from that screw in the carb body but not in the engine. Will clean out or replace before I restart the engine. Its happened recently, not earlier when I had engine problems and I havent run the engine since

So my question is, based on these pics, do you guys think I need to replace the piston-liner? Where else could be the problem?

Ameyam

ameyam

more pics

opjose

Bearing glop and all your engine is practically pristine!

Why try to repair something that isn't broken.

A bit Dawn Power Dissolver squirted onto the insides, followed 8 minutes later with hot water and a toothbrush, and the engine will look brand new.

Your liner and piston look unscored.

Heck I would not have even taken it apart... I would have just pulled off the back plate, added the cleaner, rinsed the engine a few times, oiled and re-assembled it...

I've repaired engines this way that were utterly BLACK and the bearings looked far worst, but they had no play after cleaning. These engines were retrieved from a junk box and have since been working for 2-3 years without fail.

opjose

BTW: your "overheating" is more of an issue with improper tuning.

I have a few engines that seem to develope far less compression when warm or hot, but they are stump pullers never-the-less.

Don't over think this stuff....

jetmech05

Sounds like a tuning issue... the engine looks good

ameyam

Its not a tuning issue- what do I run the engine needle at? 3turns- 4turns out? It used to be so rich, oil would fly out the carb. And when hot you could turn the prop over with a finger as if no plug was installed. Dont know whether it was fuel or tank setup related though. I had discussed these things with you then Opjose, remember? It was so bad, I actually decided to drop glow all together and go gas. However, problems with the DLE20's throttle setup (too sensitive below 50%), weight issues and the pure simplicity of the glow setup along with the reliability I got from my 91FS brought me back to reconsider this engine

Moving on... if the engine is Ok, I will reassemble. I would like to get the bearings out and clean them one last time before I put this together. Would heating the crankcase with a heat gun and then tapping them bring them out of the case? How hot would it need to be. If I can get them out, I will put in some (make that a lot of) WD40 to try and remove as much grime as possible. There is no roughness in the bearings at all (the 55ax's bearings were worse and it still runs so-so), so I doubt I need to replace them

Ameyam

jester_s1

If it was impossible to get it rich enough to not overheat I would suspect an air leak, either through the carb o ring or through a defective front bearing. You can get the bearings out by putting the engine in the oven at 300 degrees for a few minutes. Try it at 5 minutes, then go longer if you need to. When it's warm enough, a firm tap on a block of wood will unseat the rear bearing, and then the front can be pushed out easily with a dowel. Assembly is done the same way; put the new rear bearing on the crank then press it into a hot engine, then press the front bearing on before it cools.

ameyam

I suspected the air leak too. Thats why I opened the carb and ended up stripping the screw. I dont want the problem, I am going to get a replacement carb atleast.

Tried to get the bearings out (I dont have an oven), used a heat gun for 5 minutes, they wouldnt budge. So forget it, I am cycling WD40 through them (they are starting to look cleaner and brighter already). After a cuple of times, I am simply going to apply 3-in-1 light machine oil on all parts and put then together

Then will bench test next week with a MAS 14X6 and see how it feels.

Ameyam

Bax

My Feedback: (11)

First off, any glow engine will get hot enough to cause a burn. That's normal. If you expect it to be so cool that it will not burn you when you touch the cylinder head, then you should not be running an engine.

Glow engines do not leak air through the front bearing. The seal is provided by the crankcase/crankshaft fit (which is a very close fit) and the oil film between them. If the fit is too loose, then the engine will spray raw fuel through the front bearing. The pumping action of the engine will cause fuel to be pushed OUT, not air in!

If you press the carb down so that it's against the rubber o-ring and then tighten it, you've created a good-enough seal. The engine's suction is not so much that it will suck air through the carb/case o-ring when the engine's running. More likely, you're getting air in through the fuel system: cracked fuel lines, pinholes in the fuel lines, bad needle seal, air agitated into the fuel that's in the tank (also known as "fuel foaming"), and so on.

The most common reason an engine overheats is a too-lean needle setting or a fuel with a too-low oil content. Bad airflow in cowled engines is also a prime cause. Even though you have a good air intake and a good air outlet in the cowl, that doesn't mean that the airflow is actually going THROUGH the cooling fins of the engine. Air follows the path of least resistance, and if it isn't forced through the fins, it won't cool the engine. You may need to make baffling to get the air flowing through the fins..

jester_s1

Bax, I've heard it before the the front bearing doesn't seal air out, but my experience seems to indicate the opposite. I have a .46 FX that went lean on top and wouldn't idle reliably, and the needles were inconsistent in the changes they made- a classic air leak situation. I changed all the o rings and checked bolts, and there was no change. I then replaced the bearings and the engine started running perfectly. I don't doubt your knowledge, but if the front bearing doesn't help keep air from leaking in I'd love to know how replacing the bearings in this engine fixed an air leak problem.

opjose

I've talked with you on many occasions/threads... one thing that has always been consistent is drawing conclusions when you tie two things together that are really unrelated.

Oil "flying out of the carb" is not related to this.

If the engine is overheating, and you are using the recommended prop, you have no cowling issues ( which I know you do not ), and do not have it set up in a pusher configuration... and it still overheats you have a tuning issue no matter what you may think.

( BTW: an air leak IS a tuning issue as it upsets the engine tuning... )

A glow engine's head temp should not exceed 300 or so degrees at the hottest point.

Technically that IS enough to burn you quite well, but the engine will not be smoking hot and cool off quickly once off.

If it gets hotter than this it will die in the air or sieze up. If it is indeed getting too hot then you do indeed have a "tuning issue".

A temperature probe will reveal the problem.

( Thanks to Downunder for setting me straight on this with my pusher engine! By using a temp probe and adjusting the tuning I was able to bring the engine temp to around 280, which resulted in a reliable engine... to me that seemed REDICULOUSLY rich, but it was exactly what was needed on my Pusher configuration.)

You're incorrectly assuming that the seeming lack of compression is caused by overheating.

Your engine is likely running at a temperature that expands the liner AS IT SHOULD.
From the looks of it though, you've been running synthetic fuels.

Synthetic fuels leave NO residue behind so compression seems to decrease once the engine warms up.

The fuel itself acts like a seal and lubricant when the engine is running, which is why the engine will still run at decent RPM's in spite of the appearance of no compression.

Castor based fuels leave a residue behind that looks like a burned or black deposit. This helps increase apparent compression from your perspective.

Once the engine gets hot the castor deposits re-liquify giving the engine additional high temp protection.

Switch to a castor based fuel and you'll notice that the so called compression "problem" seems to go away or deminish.



Oh, I remember all right... the discussions have been quite consistent....

The DLE20's are NOT "too sensitive below 50%", you're just not used to work with gassers and probably do not have things set up properly.

Someone needs to walk you through getting that engine going and tuned.

The 75AX is a very reliable engine ( as is the DLE 20 ), but it needs to be properly broken in, tuned and set up to get that reliability.

It is more powerful than your 91 four stroke and sucks in more air and fuel. The two engines are different in the way they operate so don't equate the setup for the FS to the AX. Treat each separately.

Forget about these perceived "problems" for the moment, and concentrate on tuning the engine.

While the "air leak" suggestion is good one, I suspect you don't even have that.

Your engine is practically brand new.

Many mistake the rusty look of the inter bearing clips as having the bearings rusted out.

The ball bearings themselves are clean and unpitted on your engine, as are the races.

The clips tend to get rusty looking as they sit in liquid all the time ( think brakes on a car in humid weather ).

I use "Dawn's power dissolver" to get rid of this "gunk" that forms on the bearings.

Dawn's power dissolver, is made to clean GREASE off of pots and pans. It is slightly caustic ( like oven cleaner, but oven cleaner is HIGHLY caustic ). If you let it sit for a few minutes it breaks down the rusty looking gunk. A flush with water often reveals no rust where people often think there is.

I've done this to 10+ year old engines where the owner insisted the bearings were rusted out... your engine is not even broken in yet!!!!

richardgerardi

i have been flyin a stick with a ax 46 for 5 years, a kaos for 4 years almost every weekend and still running strong.

ameyam

Ok, Opjose, Bax I got it.

This specific engine started running plain castor (no nitro) and in the second stint, Klotz 100 (the 80-20 synthetic castor mix).

When I say radiant heat, I mean radiant heat- from one foot away as you would position yourself to flick it over. No one would dare to touch the engine at that time

It may be a tuning or tank setup problem. I now pressure test my assembled tanks under water before I put them in the airplane. Like I said, bubble-less clunks are now standard issue, even for gas.

The reason I am considering retrying the engine is because I have picked up a bit since I last used these.

I know both the 75 and the 20 are reliable and that someone needs to take me through the gas throttle setup. I tried first based on the advice I got on RCU and when I couldnt resolve it, I had the couple of experienced members try their hands at it. With the Dle 20, I had the airplane either flyoff when I added a click of throttle in the approach or it would react too late and bounce. Ultimately we added in 100% expo to the throttle (9c doesnt have a 5 point throttle curve). I would have managed it with the 12FG but had to give up my heavier airplanes due to a slip disc problem right now. In any case, the airplane was meant for glow and I was using a gas engine, so there were compromises and I was (and still am) learning the gas setup

I had done instrumentation on the over heating engine- it would go upto 125Deg C or so around the time it lost compression.

The 91fs is less power than the 75 at the top end (midrange is debatable) but its on a 46 size Reactor right now and till I get the 75's problems resolved I have no other glow engine

Opjose, you are right regarding the bearing cage and Bax you are right about no front bearing air leakage.

The replacement carb is $75 and even after spending that, there is no way to be sure that the engine will run right. One screw on the carb is OK, the other will stay in place and I should get good seal with silicon sealant. I will bench run the engine this way and then see what it feels like. The bigger problem is I have no airplane to test the 75 on, I will need to borrow an airframe from someone (!!!)

I am awaiting replacement head and backplate screws (old screws have slipped heads). Once they are here, I will final assemble and go for a test with 5% nitro 80-20 castor-synthetic blend fuel

The Dle20 can only be setup and tested in October now

Ameyam

opjose

That's not an "overly sensitive throttle", rather that is an improper setup or landing.

One click of throttle is not enough to change the thrust so much that you cannot land.

Either you are coming in too hot, you have the wrong prop on the engine/plane, or you have it terribly mistuned.

The LS and HS needle on Gassers do NOT work the way they do on glow engines.

For instance the LS needle is NOT a "low speed" needle at all on a gasser!

It controls fuel mixture throught the range, but particularly as you back off from full throttle.

It has almost NO effect on idle speed!

If you set the LS and HS needle incorrectly, you'll get a very limited throttle range, and the plane will seem to want to rev quite high at idle.

Other than this idle speed is really controlled by the float valve which you do not have access to.


That's normal operating temp.

Now FORGET about what you think is "lost compression" and work on tuning the engine right.


Don't fix what is not broken.

So far nothing points to the carb, and glow carbs are EASY to check out.

Use the clean tubing technique... I talked about in previous posts to you.

jaka

Hello!
I get a little worried when I see the pictures of both the rear ball bearing and the piston.

A worn ball bearing can do things to an engine so change it! It's soo easy to do when you allready have the engine apart.
I don't say your rear ball bearing is totally worn out, but from the pictures I can see oxidizing marks (rust) on the ball retainers. That doesn't mean the balls or bearing surface is pitted but indicate that you better ivestigate how the bearing feels when the crankshaft is spunn. If it fells gritty and is hard to turn or rust is flowing out from the front bearing when you run the engine ...you better replace it! -If not every is just fine!

Second ! The piston.
As your engine is a ABN engine the piston should have such a fit in the cylinder that it grabbs the cylinder wall approxcimately 3-4mm under the cylinder liner upper surface. If the piston can be pushed right trough without getting stuck ...the piston is worn and you would not get as much power or throttle reliability from the engine as you got from when it was new. It doesn't say the engine cannot be run...it only says: "less power and less throttle performance).

This is how a piston should look like when the engine set right (treated right). Notice the grayish band around the side of the pison, just under the brown upper band .
That is the area where the piston expands and meet the cylinder liner when the engine turns.
A entirely gray piston indicate a worn engine!!!

opjose

Eh, no.

He's dealing with a NEW engine.

Sometimes newbies apply conventional wisdom seen in the forums thinking that this must be the cause of their own problems.

He has neither worn ball bearings nor problems with the piston.

The engine has not been broken in yet.

He's already stated that there is no "gritty" feeling.
The rust color he is seeing is the glop that forms when the engine sit idle for a few months.

It can easily be removed and does not affect the engine nor bearings.

ameyam

You are looking at a ABN unpinched piston. On the 75AX, there is a pinch line 3-4mm below the crown. Thats the one that gives the compression. Thats also the one I am concerned about

In the cold heavy lubricated condition, the piston locks before TDC. Then, because its cold, you get the pichk-pichk sound as the oil leaks past the piston. I have heard this on my brand new ringed engines as well. I will stop leaking oil past once the thing heats up. There is compression there, atleast when cold

Ameyam

opjose

Stop worrying about this and go back to properly tuning the engine.

jaka

Hi!
Agree!

Gray Beard

My Feedback: (-1)

electric motors have come a long way with all the new battery packs on the market. I'm building a couple of new planes and looking into electric power for them both. Instead of using a .91 glow I am checking out several electric motors. Just something you may want to start looking into also. Wet motors aren't for everyone and you may find electric a bit easier to operate and understand. Just something to give some thought to in the future. Hobby King may also be a better choice to order things from?? Shipping costs?

Kaos Rulz

I've been following this thread and just have to ask, how much fuel was run through this engine before uyou decided to tear it down, and how did it run? (except for the dead-sticks). DS's are usually caused by either running out of fuel or going too lean (kinda the same thing as running out of fuel). I'm willing to bet you had a tunig, or plumbing problem and you are now looking for an issue that is not there. Recommend you put the engine back together and run it on a bench stand with a good tank, properly placed, and fresh plumbing and fuel.

Many engines will dead-stick when being broken in. This is usually due to the low end not correctly adjusted.

jaka

Hi!
Agree!

Gray Beard

My Feedback: (-1)

To what??

opjose

... that he needs to stop "over thinking" this and get down to basic tuning and plumbing checkout.

The OP's engine is brand new. I've been responding to him since he first started posting about the problems he has had getting it running a few months ago.

Unfortunately he's new to getting engines set up and tuned ( e.g. the problems with the relatively reliable DLE 20 ).

An ( overly ? ) analytic mind sometimes looks for causes that are not necessarily there due to inexperience.... so he ends up tearing it down...

I wish he had just left it in once piece, but the same questions were posed elsewhere, so he received different answers ( not bad answers, just ones not applicable in this situation ).... and acted upon them.

IMHO this underscores why an instructor/club/training program is so important... an experienced hand would have sorted out his problems and taught him how tune the engines.

jester_s1

Agreed 100%! Folks on the internet tend to jump to the big stuff because we don't ever get all the information. I can sit down with an engine and tweak the needles for 30 seconds or so, and I'll either have it reliable (maybe not perfect, but definitely running) or I'll have figured out there's another problem.