Blown Bearing ?????

[militarymaxx]

K, this is what's happening. The buggy starts up fine and runs great for a few laps then starts to die at high speeds. Low speed seems fine but when I open the throttle it dies. When I can coax it into running at speed, the temp goes through the roof and re-starting shows almost no flow of fuel through the lines. And here's what I think is the tell-tale sign. I have quite a bit of fuel/dirt liquid mess around the flywheel, mainly between the flywheel and the block. So, do I have a bad bearing that's allowing air to enter the engine, maybe causing the high temps (too lean), lack of compression, etc. ?

 

[Candyman]

I'm inclined to think that you're just running generally lean. It seems that your engine runs fine until it gets up to temp. Then it starts dying. As the temp increases, the engine will lean itself a little. As as it dies at that point, I'd say richen it a bit and see if that helps. Usually engines will throw a bit of fuel through the front bearing. That's how they keep the bearing lubed. I wouldn't be too concerned.

It is also possible that there is an air leak somewhere which might be contributing to your lack of fuel flow. You may want to check areas like the carb seat, back plate, exhaust header, cooling head, fuel and pressure lines, gas tank and filler cap. These can all be sources of air leaks.

 

[militarymaxx]

Juat dis-assembled the engine. I have these very tiny little pits on top of the piston and the head, they're very small. And I have three marks along side of the piston, like it was scored or scrathed that go from the top all the way down to the skirt. They're not deep at all. The bearing closest to the flywheel just fell right out. I thought these things needed alot of heat to remove. I broke it in per the instructions and always cleaned it up proper. Not sure how all this happened or is this just part of normal wear ? So, do I rebuild or replace. A friend recommended the OS RG. Tomorrow is payday. It's either order parts or buy an engine (maybe both if you think I can save this one). Thanks.

I get great flow when I first start it up. But when it's warmed up, acting up, there is none. That would have to be a fairly good air leak. I have replaced all the lines and secured them accordingly. Now that I have the engine apart, I will look into the carb. But like my last post says, maybe it's to far gone and it's time for a new plant.

Oh, and the bearing inside the clutchbell is shot also. Should have gone with the kit and got the better stuff.

 

[LarryA]

The scoring on the piston and cylinder wall indicate that some form of contamination entered the cylinder. Either through the fuel line or the carb. Even the slightest scoring (scratches) will destroy compresion. I'd also think that if the case's crank bearing just fell out that the engine got extremely hot, possibly from the crankcase sucking air at the loose bearing fit and causing a very lean condition.

 

[DarthRacer]

The piston pitting could have been caused by a hot plug running high nitro fuel. This will cause the fuel to detonate before the piston gets to TDC causing the damage. It will be even worse if you have a .21 or larger. You may need to use a medium or cold plug.

 

[militarymaxx]

As I look at my completely dis-assembled engine, I wonder where I could have gotten an air leak from. Maybe from around the carb but the buggy is new and I have never touched it. But I did remove the pull start shortly after I purchased it as I was going to use a starter box. Maybe I didn't get a good seal around the backplate/pull start housing (it's plastic). As careful as I am with afer run maintenance, I can't understand how something got into the engine. I'm thinking that engine contamination is more common than once thought. Anyways, Thanks for the feedback. I'm getting an OS and will probably rebuild this one.