Hello,

I have a new engine and after a few tanks through it i noticed that where the con rod connects to the crank shaft it was rubbing the rear removable part of the motor case.

Thought it was an easy fix, put some really thin washers on there in order to move it back just a little bit, I thought problem was solved.

But now it seems it has moved even more towards the rear and is rubbing the rear of the case even worse. so bad I can't run the motor.


What could cause this?

Net

Which model engine do you have?

Enjoy,

Jim

And where did you put the washers?? if you put them between the crank pin and the rod you moved it back more///// Remove the washers make sure the prop drive washer is firmly seated on the shaft this will pull the shaft foward and the rod with It is normal
in some engines to have a very slight rub mark on the back plate. If the main bearing is not firmly seated in the case this will allow\the shaft to be displaced rearward on re reading your post I assume now you put the washer between the rear cover and the engine case
hence you did not move the crankpin/rod back

I have a Picco P7-R

And the washers were to make the rear case set back just a little bit, I didn't move the con rod or add washers to it.

not much you can do....the rod is either going to rub up against the crank or back against the backplate depending on the engine and it's tolerances.

only real fix is to anodize or nickel plate the backplate to cancel out the wear you get when aluminium rubs against aluminium. the particles from this wear have been a long time suspect in premature plug death


dave

By putting washers between the rear cover and the case you introduce play into the system... your conrod can now move backwards on the crankpin, and that means it will also move backwards on the piston pin... this causes a considerable side-load on the piston when the engine is running: THIS IS BAD!

If you haven't run the engine yet like this, then just remove the washers, and pray nothing was hurt.
If you have run the engine, then also pray and remove the washers... and then run the engine to see if anything was hurt. If it doesn't work anymore you probably need a new conrod, piston, sleeve and piston pin.

The one thing keeping the conrod in the right position is the rear cover... it is entirely normal they make contact.

Castor oil in the fuel blend will minimize the metal to metal contact.

That engine backplate is designed to rub against the rod.

Dave.

I knew it was normal to rub up against the back plate, but not so much where it made the engine basically seize.

I don’t have the washers in there any more, as soon as I saw it made no difference I took them out, maybe went 1/4 of a tank with the washers in.

But this is much more then normal back plate rubbing.

My guess is the crankshaft shifted to the rear somehow.

That's what it sounds like to me...

Can you put a dowel or brass drift, etc. in the induction passage and try to tap it w/ a small hammer to possably push the crank back into it's proper position?

Only other thing I can think of is it got shifted back during a clutch/flywheel change, or it was made with a crankpin that's a little bit too long???

Hello; Could it be that the rear bearing hasn't been pressed fully into it's recess? I have seen this in Saitos. They would rub the back case cover then they would brea the connecting rod, usually at the bottom of eh eye. Don't ask how I found that one out.

I rebuilt several Enya's in the 60 size and noticed all rubbed real hard. One day I traded for another Enya and the front housing had a spacer on it. The spacer was metal and factory made and guess what yep very little rub, so some engines which include Japan made models are simply designed wrong and they do fix them.
I suspect a crank that is pushed back in the case slightly. Take the carb off and muffler and put it in the oven at 250 for 1/2 hour. Use a towel of glove, put a prop on it and snug it up tight. That will shift all into correct alignment. Turn it over by hand a few times and when cool oil it. I think your problem will be over

If that doesn't fix it , you may have to look at getting another backplate( thinner) or removing some of the metal off your old one with some wet and dry. It obviously ran a little like that so it cant take much to get it freed up properly.
I definitely make sure that the crank IS all the way forward first though.

Since it is a new engine, why not send it back and let them fix it? You might have a bent conrod.

George

Thanks for all the quick responses, I really appreciate it.

I did take the flywheel off, pushed the crankshaft as far out as possible, but it’s still rubbing very hard.

I’m thinking if it were just the crankshaft that needed to go forward a little bit, with nothing on the crankshaft it should spin relatively freely when I put the back plate back on because nothing is pushing it back, instead it pushes so hard on the plate that it seizes the engine right up.

Also, I checked the bearings and they seem to be ok.

The only part that baffles me is it ran fine for a few tanks, ever since then it has been locked up against the back plate.

Do like Proptop says and hit it with a drift and a hammer through the back, right in the middle of the crank. It will move forward to where it should be.

I did hit it with a hammer to get it to go forward a little more, but it didn't work.

Hi!
It doesn't work!!!!
The way all ball bearinged glow engines are made is by having the crankshaft secured to the front ballbering by a ridge on the crank on one side and by the drive washer cone on the other side of the ballbearing...this front ball bearing is the only part that holds the crankshaft in position when the engine turns.
When you try to start the engine by using an electric starter then you push the crankshaft back a little...the front ball bearing take up this pushing action but if the bearing is a little worn ...the crankshaft pushes against the back plate.
But this is not that critical, small scuff marks on the inner surface of the backplate is just normal.
But if the whole backplate surface is scuffed you better replace that front ball bearing.

Regards!
Jan K
Sweden

gcb had a good thought about a bent rod. Is it still tight to turn when you remove the backplate? With the bearings you need to make sure that you press against the outer race to seat them fully in the crankcase. Hitting the crankshaft against the bearing inner race won't take up the clearances in the bearing so the rear one won't fully seat.

Did you ever flood it? Sometimes it doesn't take much to hydraulic (or Hydro-lock, or liquid lock ) an engine enough to put a little bit (or a lot ) of bend in the rod. I didn't think of that...Maybe those guys are right, and all it takes is a few thousanths to induce a bind...Hmmm

Are you using a starter box? That would make it real easy to put possably too much stress on the rod...
The engine doesn't nessessarily have to be locked up either, to do damage.

NetMaster....

....just as a reference, this is a good running used K&B .61 engine. See how the rod
is barely touching the backplate. The machining marks aren't even worn off the
rod. I would make 100% sure the bearings are seated, then if the rod was rubbing
too hard on the backplate....I'd take a few thousandths off the backplate on the
flat plate....with some emery paper, or make a thicker gasket.

When the engine is running, the thrust from the propeller pulls the crank forward.
It shouldn't be rubbing very hard against the back plate. When you shove the crank
rearwards with the electric starter, it may well rub, but it shouldn't be rubbing all
the time.

FBD.

I just wanna make sure we're all talking about the same thing...We ARE talking about a buggy/truck /car engine, right?

Hi!
All glow engines are the same! Nothing special with a car or boat engine....
JK

Jan, I was just replying to Dave's statement about the elec. starter shoving the crank back...
When you use a starter box to start a buggy, etc. the thrust loads are vertical not horizontal...so it won't push the crank back.

Netmaster.
I have had the same thing happen to my Old 120. I hit a tree head on with a 14 lb plane. It had a hard drag when I would turn it by hand. I thought the crank was bent but after I took the back off the motor it turned free. It was hitting the back. I put the motor in a hand press and pressed the crank back in to the right spot. It turns free now. I haven't run it yet. Have to buy other parts. Racker covers ect. If you use a hammer support the motor on side mounts. It shouldn't take much to move it. I have heard that buy using a elect. starter it will push the crank back.
If it is a New MOTOR you should send it back.

Dave

I did send it back.

And it was not the con rod that rubbed; it was the crankshaft pin that holds the con rod that was actually doing the rubbing.

I did everything I could think without damaging the engine to try to get the crankshaft to sit slightly more forward.

Thanks all for your responses, they were very helpful.