I came across an issue today that I have never heard or seen before. I recently bought a barely used tower .46 engine from the internet and have it mounted on the tower trainer .40. Took it out today for it's first flight and the engine gave a bad noise. When either hand flipping the prop or using a starter, at the top of the stroke, the engine will "lock" basically and make a knocking sound when you finish turning the prop over. I know that a compression tightness occurs at the top of the stroke in an ABC engine but this is not smooth and makes a loud racket. The engine starts ok, but the knocking sound is so annoying it sounds bad and so I didn't even want to continue to run the engine. Anyone have some tips or ideas? When you hand flip the prop, you can feel the "locking" at the top of the stroke and so makes me think it is a seating issue. But, I took the head off the engine and the piston seats fine without issues so makes me think it is the bearings??? Like I said before, the engine is barely used at all so I can't believe the bearings might be bad? Hope there is an easy fix like lubing the bearings?? [&:]

I see the problem as it was in the mid 30's F there today.

Bring thhe engine in the house and warm the engine head up with your Monokote gun and see how it feels

No, this issue was happening the other day too when I had the engine inside. I just didn't pay much attention to it as I thought it would work it's self out when I ran the engine. The temps here don't really cause much issue for the flyers here. They actually perform best in the winter!

Pull the head and back cover and see if it still makes the knock

I'm thinking it's just real tight, Ive heard new Evolutions make a racket at first till they get warm. You want to get this engine up to speed and load quickly, prolonged low speed could hurt it's potential. Even better if you can bring the piston to bottom stroke than heat the head with a heat gun or intelligent use of a propane torch just before start. It could make that sound the next 6 starts or so. Make sure the fuel has some castor as part of it's oil package.

I've heard of some guys in cold parts of the country put a 3/8" wide band of aluminum duct tape around the head till the weather gets warmer.

Ok, got the engine off the plane and worked on it a little. Took the head, carb, and backplate off. The backplate was pretty tough but finally came off. Inside the back of the engine there is some rust [:'(] But this is just on the back of the shaft thing. Seems the last person to run the engine left fuel in it too long. I got my afterrun oil and oiled up all I could, the piston, shaft, and back side. It seems to be better now but still has a spot that sticks. If I start to spin it around and around it seems to do fine but will get stuck every 15 revolutions or so. I don't think it is the head because when it is at the top of the stroke, I can very slightly twist the shaft to where it is changing position from pushing to pulling the piston and it feels like it is getting stuck. I am letting the after run oil sit tonight and will hopefully make everything a little happier. I don't want to have to take the shaft out and check the bearings if I can help it. Thanks for your guys help. I will try heating the head tomorrow. Maybe that is a little tight? I can certainly tell the engine has not had any run since the top of the piston is clean and shiny

You just have a tight engine. If the rust came off with just some afterrun oil, it wasn't rust, but oil stains. Some engines in the past, especially racing engines, were so tight initially that they would bend a rod if you did not heat the cylinder. Your engine simply caught the tight end of the parts tolerance range.

Sounds like a new engine. Break in with liberal amounts of Castor oil in the fuel. Use the heat gun to warm it up, then fire it up. After the first run it will be looser.

Old heads say use fuel with 20% Lube in it. If you have the "Standard" blend with 17-18% lube, add a couple of ounces of Castor oil to it. After the first gallon is through it, use what you want, all synthetic or a blend of standard mixed fuel. I would always have some Castor in the blend, but that's me.

Cheers,

Chip

Hi!
Sounds as bent piston rod or a bent con rod!
It could also be too much nitro. Use 5%!!!

Ok, will get the engine back together and get it broken in. Currently running 10% nitro on 18% oil so may put more pil in the mix. The rust did not come off with the after run oil, it's just there. Thanks again for your help and I will just have to get it broken in! Sure is an annoying racket! lol

if it is rust, and it's in the bearings, too, you may want to put new ones in it before you run it.

Don't replace bearings just because you see some stains which may or may not be rust. If the bearing are bad they will have too much radial play. The cage can rust without affecting the bearings themselves.

i had a ttpro 40 that someone gave me and it always knocked loudly when running regardless of temperature. I ran that engine for 3 seasons with no problems and then gave it to a newbie and he is still running it.

Hi!
An engine should not "knock"! If it does something is wrong!
As I said earlier ...it's not a running in problem ! If it "knocks" at all needle settings it is most likely a bent con rod or a bent piston rod...or too much nitro.

Ok here is an update after putting the engine back together and re-mounting. I now have the engine not "knocking" for the most part. Overall I think the engine just needed some care and oil for lube. Putting the engine back together I have come across the fact that your right, the engine is very tight and close to being too tight. I put the backplate on and secured it then noticed the shaft wouldn't move at all! Took some strength to move it a little. Took the back plate off, and turns out the piston wasn't seated properly in the shaft ring so was grinding against the backplate and leaving some metal shavings inside. So, cleaned out the shavings and re-lubed a little. This time the backplate seated fine and no problems. However though, putting the head back on the engine created the issue all over again. Once I had the head seated back on, the compression was really great and my "knocking" started again This made me suspicious that the compression ratio was too high with the bolts on the head really tight. After about 10 minutes of playing with the bolt tightness I was able to make the head be snug and the knocking go away! Got the glow plug on and check for any air leaks and found none and the knocks are gone and the engine feels normal now when turning over. SO, very interesting finds today. Seems this engine is needing a breaking in and was manufactured a little tight. Good news and glad I figured out a way to make the knocking go away because it was sure an annoyance! Thanks again for all your help and tips Will keep them in mind again if I encounter a similar situation.

Hi!
What do you mean by " the piston wasn't seated properly in the shaft ring"????

Do you mean the crank pin on the crankshaft? The connecting rod goes on the crank pin.

What glow plug are you using??????

Yes, the piston wasn't seated in the crank pin properly. Sorry, didn't know the proper terms. Glow plug is what came with the engine, don't know what type but it does have an idle bar. In my backup stash though, I just bought some OS A8 plugs. Would these be good for the Tower 46 and my GMS 47 do you think?

Stamey,


By all likelihood, there is ABSOLUTELY NOTHING wrong with your engine.

Tower engines are particularly tight at TDC and this may make normal clearances; between the piston and the wrist-pin, between the wrist-pin and the con-rod and between the con-rod and the crank-pin; more audible; especially when there is a relative lack of fresh oil.


You are just giving us a scare...

Using fuel with a lot of castor oil, do the break-in as described [link=http://www.rcuniverse.com/forum/m_1850473/tm.htm]in this elaborate thread[/link].

When a two-stroke engine is running normally (i.e. two-cycling, firing on every revolution), the con-rod is ALWAYS under compression and the relative movement between those parts is minimal and inaudible.

All engines have these same clearances and particular high-performance engine have even larger clearances. Yet this bothers absolutely no-one.


None of them make any unusual mechanical noise while running.


Just run your engine, lean it to a rich two-cycle setting and see.

Hi!
What do you mean??
"the piston wasn't seated in the crank pin properly"

The piston is running in the cylinder liner...and the piston has in it's center a piston rod...that is connected to the connecting rod which in turn is connected to the crank pin and crank shaft...that spins the propeller around.
All these parts are mounted correctly if the engine can be run. So the crank pin cannot be loose...or mounted incorrectly if you have been able to run the engine!

So what was wrong?? Just curious!

Quote:

ORIGINAL: Stamey

...I just bought some OS A8 plugs. Would these be good for the Tower .46 and my GMS .47, do you think?

While OS #8 plugs are medium-heat, which makes them good for many engines; they are also medium length, which makes them imperfect for all engines...

...That includes OS engines, by the way...

Larger OS engines need a LONG glow-plug and small OS engines need a SHORT plug; so it is a perfect fit to none of them.


Tower .46 and the GMS .47, both need long plugs, like the Rossi R4, the K&B 1-L, the Novarossi C-6S, the Fox long and many, many others.

Darzeelon;
Great info Thanks for the conlcusion. I have just run OS and GMS and never encountered this before so was a bit scary mainly with the loud noise! Like I said above I think I have got it fixed and will just need to let it get run in now. Sure is a fidgety thing, lol. For the glow plug, the one in it right now is long, with an idle bar. What does that idle bar do exactly? Most plugs do not have them so it's curious to find one that does. I bought the os 8 plugs for a backup but did find they are slightly low when screwed into the head. I found if I put them on without a gasket, they seem to be darn close and should be ok . Will get some long ones when I can though. Tower website should take the word "long" out of their posting for the #8 [:@]

Jaka;
LOL. I am sorrry, I should have never mentioned this tiny thing as I can not describe it! Trying to use your terms.... I had been fidgeting a little with the piston rod and so had not seated it all the way back on the connecting rod. So, when turning over the engine they were not going through a fluid motion. Just opened up the back plate and seated it all the way on the connecting rods nipple. Sorry for the confusion. I am good with lamens terms but with an engine and so many parts I rarely get the perfect name for things.

Use the OS 8 plug and throw the idle bar plug away

Hi!
Yeah! Get rid of the old time idle bar plug and use an OS 8 or Enya 3 plug!

Jim and Jan,


I don't agree!

The idle-bar is intended for older engines.
These had a baffle-piston and/or a 'less than satisfactory' carburettor; both of which can lead to rather large fuel droplets being thrown directly at and possibly dousing the glow-element...

This in turn could lead to the engine conking-out, especially during idle...


But; many engines that have a very good carburettor that finely atomizes the fuel and modern Schnürle porting that does not 'throw' fuel directly at the glow-plug, run just as well with an idle-bar plug of the correct heat-range, as they do with a normal glow-plug.

One such engine is the MVVS .49 GFS/R, which I am sure you, Jan, are well acquainted with; and which has one of the best carburettors around.
When an idle-bar plug is installed, it loses none of its reliability and there is no RPM loss either; I have been reported.

The plug was a Fox R/C Long and the comparison was both to an OS #8 and to its original Novarossi C-6S, although it was the OS got a slightly lower top-end (50-80 RPM less).


The idle-bar does not 'keep the fuel away from the fire', as some people fear it could.


If either of you can show that in a certain engine, the idle-bar will actually cause running to become substandard, compared to a normal plug of the same heat-range; go right ahead and post these results!