GP26R big end bearing wearing off crankshaft?
 

I am replacing the big end bearing in my GP26r after it failed after only 6 hrs running. After comparing the new bearing with the old one it looks like the old one wore out due to contact with the crankshaft. The edge of the cage of the old bearing seems to have been worn down to the point where the roller pins were released.I noticed when assembling the new bearing with the crankshaft and conrod that things were a fairly tight fit. Is this how it should be? The bearing is a loose fit on the crankshaft but then putting the con rod on over the bearing on the crankshaft results in a fairly tight fitting assembly. Is it supposed to be like this to prevent the bearing coming out from in between the crankshaft and conrod? I thought that if I just replace the bearing it will fail again like the first one so I decided to look for some advice on here first.


http://www.rcuniverse.com/forum/atta...mentid=2051873http://www.rcuniverse.com/forum/atta...mentid=2051874

What does the engine backplate look like? Has there been rubbing there?

This is a rather odd problem. Is the crankshaft fully seated all the way forward? Do you use an electric starter aggressively? That puts rearward force on the crank and can push it backwards. However, that usually causes wear against the back plate on a cantilever crankshaft engine. And since the back plates are usually aluminum, it doesn't wear the rod nor the rod bearing that are steel, but instead wears the backplate. Make really sure the crank is situated all the way forward and that the rear bearing of the crankshaft is fully seated forwards in the case.

Things should not be tight. The connecting rod should float freely, centered in the piston when all is assembled. I wouldn't run it until I figured out the problem.

AV8TOR

Maybe it is the pic, or my eyes but it does not look right to me. Do you have another pic with just the crank journal W/O the bearing on it?

There is some scratching on the backplate. I had to replace the crankcase after the bearing failure as the conrod cracked it. There is about 2mm clearance between the crankshaft and backplate.

http://www.rcuniverse.com/forum/atta...mentid=2052141http://www.rcuniverse.com/forum/atta...mentid=2052142

I just gave the inside of the big end a quick sand with a dremel and the crank, bearing and con rod assy is free now.

Are you saying you just ground away the surface hardening from the big end of the rod? The ID of the rod is the outer bearing race for the crank bearing.

Whoops! Did I? I removed very little, only polished it really

Only time will tell whether too much material was removed.

Yep...

Man, that back plate is a mess. There is something seriously not right here, like maybe the crankshaft sliding rearwards, or something.

AV8TOR

Looks and sounds like there are / were several things going on in that engine. I would be curious to know whether the cylinder is 90 degrees to the crank axis. Cylinder straight? Mating surfaces on case straight, etc. Is the rod straight?

Does the rod have an offset, and is it mounted backwards? Just a "WAG" (wild assed guess)

I took a harder look at the latest pic of the crank, and I would say it is ruined now, sorry to say.... A big end bearing won't last long.

Edit: Just did a Google search on this engine, and then clicked on "Images". There are numerous pics of the rod bearing, including trashed ones. Looks like this is a known problem area with this engine.

AV8TOR

A problem known to me also. It's just a bad design and poor quality. Mine ran very well with lots of power for a few months and then suffered the same: Aluminium from the backplate chewed up the big end and also the piston/bore on mine.

The side induction redhead had other issues (flaking bore). So no more CRRC 26 for me! B1N.


The CRRC 40cc kit seems to be a different animal and much harder wearing - a little low on power but a good-un.

So I rebuilt the engine and have flown it for about 10hrs until the big end bearing failed again last friday. Damage was not as bad as last time, just the piston and ring.The problem seems to be that there is nothing to stop the bearing making contact with the backplate which wears it away. Is there any mod or fix for this problem?

It's clear to me that the crank pin is shot , and possibly was never tempered correctly at the factory. You need a crank and rod with bearings at the very least . I would replace the entire engine.

Lets say the crankshaft, conrod and bearing are replaced whats to stop the bearing shifting back slightly and wearing off the backplate again? What I cant understand is why there is apparently nothing to prevent this happening?

Well that is just the way they designed that engine .... right or wrong. That way typical of some of the early Chinese engines to have glaring errors in their design.

Regarding retaining the rod / bearing on the crankpin, that can be a major problem. Engines like the OS line of larger gas engines have a successful system for doing that. They use drilled and internally tapped crankpin. Into this they use a special hardened and flanged screw that screws into the crankpin from the rear and retains the rod assembly. Other engines use a flanged and hardened crankpin that is pressed into a hole in the crankweb retaining the rod to the crank as a semi-permanent assembly. Most of the cantilever crank engines use this later system. The problem is that neither of these systems can be adapted very well to an existing engine. It would be difficult if not impossible to drill and thread the crankpin, etc.

There is one thing you might possibly try ..... you can install some small washers on the wristpin inside the piston between the rod and the rear piston pin boss. This would prevent the rod from moving rearward and sliding off the crankpin. Some Chinese engines used this system .... some with success and some were great failures. You need a material that won't wear away inside the piston and that can be difficult to achieve. The washers would be contacting the steel rod on one side and the aluminum piston on the other. Hardened steel would probably be the best material. Zenoah uses such washers on some of their engines to center the rod on the crankpin between the crankshaft's (2) counterweights. Not a cantilever arrangement but the washers are there and they don't wear away over time .... so the system can work.

Good luck ..... probably easier to just replace the engine!

Yes, time to abandon the gp26r I think, wont be buying anymore CRRC !

Hello,
after years of honorable service my GP26R suffered the very same failure. The big end bearing grinded up to the point of losing needles inside the engine. A decent repair woul require replacement of crankshaft, bearing, conrod, piston and ring, but I am rather going to buy a different engine
In the meantime I am trying to just replace the bearing with a bronze bushing and see what happens. I don't mean to fly this engine, just to run an experiment on a test stand. I found a rather inespensive source of bushings and bought ten pieces. I don't expect the bushing to last more than a few minutes, but at least they probably won't spread chunks of hard metal inside the case.

Had two CRRC 40's, both leaked air thru the cases-sent them away as at best they were underpowered dogs. One 26 R that was a pain and dumped it also. All were of poor quality in my view and I decided Cheap Engines
are no bargin.

Hi as far as useing a bronze bushing for a rod bearing, i would save the time and energy.
it will not get the lubrication thats required and promply burn up.
and even if it does oil ok it will not stand the beating, a min or two
of run time will have it egg shapped and useless.
your right not expecting it to last long theres a reason they dont use brass in our engines.
lets us know how it goes .

Hi I am trying this experiment because I noticed that some glow derived gas engine (like Saito) actually run on big end bronze bushing. No doubt they use good materials and superior engineering but you know.... let's see what happens.
I'll let you know

They've had rod seizure problems in the radials, but not much failure with the singles.

Glow plug engines have had had bushed and unbushed rods for decades. If you use enough oil and the bushing alloy is compatible with the crank, you should be okay. But be prepared to use a lot of oil I'm afraid.

Yes the glows do use bushings but like has already been said the oil content is 18-22%.
it may run with that much oil only time will tell.
good luck.
Now if i can figure out my sons DLE35 RA We would both be happy lol.

What problems are you having with the DLE 35?

Hi Truck Racer I have tried 2 times to send a post from my phone W/O any success. Id rather not talk about the 35 in here this isn't my thread and I don't want to steal it. So I will open up a new one where we can talk W/O issue.