That engine sounds a bit sick! ...

... said Dave Bright as I started up for a flight on Sunday. It did sound a bit funny I thought but carried on anyway and had a good flight with the engine performing unusually well. On landing I noticed the exhaust goo on the plane was a bit darker than usual, a sort of black colour!

Back at the workshop, removal of the exhaust revealed this:



Not good. Further disassembly brought more bad news:



and



I guess this is the cause:



Has it really fired the missing bearings through the engine or were they never there in the first place?

Perhaps they were caged and it's that thats gone missing I don't know. It astounds me that the engine didn't grenade itself although it did blow two glow plugs in quick succession the previous week.

I'm not sure whether to get a new piston and liner and replace the bearings or just sling it.

What would you guys do?

Hi Alan

I would say that your engine has definately 'passed' the cage and bearings It is amazing that it didn't self destruct as you say, but you got away with it.

It is hard to tell from the photos just how much damage has been done, but as you have said that it was running very well other than the noise, you may well get away with just replacing the bearing initially. Whether you replace the piston and liner really depends on the value of the engine vs the cost of replacement parts. You should be able to get a bearing for a few quid from any bearing supplier, I would try that first and see how she runs.

Almost certainly the blowing of 2 plugs was as a result of the bits of bearing rattling around in the head before they got expelled. Just make sure all the bits are cleaned out before you run it again.

Jon

its amazing that the engine can grind up cage and bearings and still run !!!

Many thanks for the reply Jon.

JonTappin wrote: It is hard to tell from the photos just how much damage has been done, but as you have said that it was running very well other than the noise, you may well get away with just replacing the bearing initially. Whether you replace the piston and liner really depends on the value of the engine vs the cost of replacement parts. You should be able to get a bearing for a few quid from any bearing supplier, I would try that first and see how she runs.

Piston and liner are badly scored, running a finger nail around the liner and piston reveals deep gouges. I think they are both toast. I was also concerned about the pitting on the cylinder head, but as the engine was running ok maybe that's not an issue. A replacement piston and liner is 33 quid from Just Engines so whether it's worth doing or not I'm not sure. I've just ordered a replacement SC46 from Kings Lynne models for 50 quid to keep me going while I mull it over. I'd quite like to do the repair just for the experience.

Can anyone recommend a bearing supplier? Just Engines bearings seem very expensive.

Almost certainly the blowing of 2 plugs was as a result of the bits of bearing rattling around in the head before they got expelled. Just make sure all the bits are cleaned out before you run it again.

I hear you, I dug out a piece of glow plug element that was stuck to the conrod and there are bits of bearing or bearing cage stuck to the inlet slot at the front of the crankshaft; how did they get there?. I must remember to clean the silencer, pipework and fuel tank as well.

Happy Days!

simondean wrote: its amazing that the engine can grind up cage and bearings and still run !!!

Thats the bizarre thing, it was producing lots of power and throttling reliably whilst it was chewing it's internals. If it hadn't been for the strange noises and black exhaust I'd have kept running it.

Alan

There is Ashley Power in Parkstone and Henderson's in Ringwood you could try, if you get whats left of the bearing out and take it to the supplier, they should be able to match it.

To get the bearing out, strip everything off the crank case, clean it and put it in the oven at around 150 deg. When hot take it out and tap the back on a piece of wood and the bearing should just fall out. Good luck!

Alan
i have stacks of bearings, so you can have one for free if they fit, so far most bearings are the same in most engines that size in my experience to date. trouble is not sure when im going to be around as going back out to saudi on friday, i could perhaps pass them to dave bright as he lives near me.

At one point on Sunday I swear I heard it temporarily stop like it mis fired. Made me question if it was electric or not as it sound like it grinded to a stop for a split second as if throttled back.. and then started up again, so obviously cleared and carried on..... Lucky! Could have blown up on in the pits!

Thanks for the comments.

Jon

Thanks for the tip, 15 minutes at 160 did the trick for the front bearing. The inner race of the rear bearing fell out as I was cleaning the crankcase and it was more difficult to remove. I finally acheived success by wedging a nail across the race, re-heating the crankcase and whacking the nail with a piece of dowel and a mallet. The front bearing looks ok visually - no corrosion - but when you rotate it in your fingers you can feel it's not entirely smooth.

Incidentally, I found a piece of the bearing cage in the fuel tank!

Dave R

Thanks very much for the kind offer but I'm not sure whether to go ahead with the rebuild. It really needs a new liner and piston which costs not far short of a new engine. Although it would be kind of interesting to slap it back together as it is and run it to destruction :evil:

You're right about the bearings, it seems there is a lot of commonality between OS, Magnum, ASP, and SC in the 40/46 size motors. It's odd that the front bearing is imperial and the rear metric. I wonder why the mix.


Front Bearing :

Type R6 2RS - (RS = Rubber Seal)
Inside Diameter ... 3/8 Inch
Outside Diameter .. 7/8 Inch
Width ............. 9/32 Inch

Rear Bearing

Type 6902
Inside Diameter ....15 mm
Outside Diameter ...28 mm
Width ...............7 mm

Dave B

That's the thing though, it started first flick and apart from the noise ran fine. How it did that in the condition it was in staggers me. The rear ball bearings were held in only by the viscosity of the oil in crankcase, it seems that it was only the cage that went through the engine, the ball bearings remained in situ - Lucky indeed!

I am surprised the engine didn't self destruct with that damage. One of my JEN 90 two strokes had a bearing failure and I only found out when testing it in a model at home, the vibration was more like a four stroke and squeal noise when throttling up!

A lot of work and running about for what is a write-off for your 46, Alan.

I suggest you purchase "as new" OS 46 from me and get into the air asap..

I have two OS 46's available. PM me if interested.