Air leak during break-in??

[Cjsur57]

Hey guys after being out of the game for a while a buddy of mine got me back in to the world of nitro. Got my rtr HoBao SS nitro truggy in the mail and a few minutes into the break-in it started to idle up and down and then eventually revved about mid range. Plugged the pipe, killed it, started it again, same thing. I noticed a significant amount of oil that had flung out from behind the flywheel.
So now I’m thinking front bearing? Is it common for hard parts like this to be duds? Upon breakdown I did not notice any play in the bearing or crank.
Pretty disappointed, waiting for the new bearing to come in the mail so I can piece the motor back together and give it another shot.
I double checked, all of the carb settings were set for break-in as they should. So my other questions would be have any of you guys experienced something similar? And what about the oil that flung from the bearing? This can’t be normal.

 

[olds97_lss]

Well, break-in settings are usually pretty rich, so you can see excess seepage like that. Plugging the pipe to kill it will severely flood the engine with fuel which makes this even worse.

After breaking in many many engines, I've found that it's best to do a tear down of the engine, clean it out, lube it well with some ARO internally, then seal the carb/backplate before even firing it up the first time just to ferret out those issues. Break-in can be enough of a battle in itself, so sealing before starting removes one headache.

Many engines don't run right for the first few tanks anyway until the piston/sleeve wear into each other properly.

 

[Cjsur57]

Thank you for the reply!! I think lubing and sealing the engine is something I will start doing. So this seepage can be normal under super fat conditions.. I really wish I didn’t loose the bearing when I popped it out so I can lean things outa tad! ( I swear the little bugger grew legs).
Oh well, I’ll be patient, wait for my new bearing, lube and seal, and I’ll get back to you. Thanks again.

 

[Rolex]

Oh well, I’ll be patient, wait for my new bearing

Since you ordered a new one, you'll soon find the original. Trust me.

 

[olds97_lss]

Since you ordered a new one, you'll soon find the original. Trust me.

Or if your like me, it will show up, then you will find the 3 spare ones you ordered 2 years ago and forgot about. lol

 

[Cjsur57]

Since you ordered a new one, you'll soon find the original. Trust me.

Well I got the new bearing, sealed it up, no more spuratic idle! (And I did end up finding the other bearing Rolex ) I ran 2 tanks thru it, all broke in. Now just waiting for the snow to melt and some warmer weather so I can bash!

 

[Cjsur57]

Also looking into a bump box, started a thread in the tools category.
Thanks again guys!

 

[olds97_lss]

2 tanks and broken in? Pretty short break in.

 

[Cjsur57]

I should have said putt it around for a few tanks instead of “bash” it. But from what I understand after a couple of tanks idling you can progress to more rpms. Maybe a few more tanks at idling is needed?
I still have a month or so of tinkering around and trimming servos I can do before the snow melts and I can take it off the bench.
Glad to at least hear it idle normally! I’m pretty sure it was an o-ring on the boss that holds the carb on, there was a small thread of rubber on it.
I used red high temp rtv to seal the motor, seems to hold up fine.

 

[olds97_lss]

I do a type of heat cycle method. I don't let it sit and idle much at all. I drive it at low rpm's for the first tank with it pretty rich. Drive on pavement to reduce strain. I lean it a bit on each tank, but keep RPM's low for the first 3-4 tanks and for tanks 1-3, I let it cool down between tanks with the piston at BDC. On average, by tanks 8-10, it should be responding well to tune and settling in. From tanks to 4 through 7-8+, I just keep it running and ease the throttle up in a 1-2-3 count to WOT, let off. By the time you get 3/4 gallon through it, they are running pretty well and should be relatively broken in. I still take it easy on it for the first full gallon. Not a lot of flat out WOT running. Usually, once I get 1-1.5 gallons, they are running stable, tuning well and I drive them normal.

I never tried this guys method, but his theory sounds good and it seems to work well for him:

Pre-heat the engine to 200+F, start the engine and let it idle for 4-5 minutes. Then put it on the ground and drive it around keeping the rpm low for the first half gallon. Drive it as much as you can without shutting it off and letting it cool down, you can re-fuel while it is running and keep it going until the receiver pack dies, then put in a new one and repeat. The heat cycle method does nothing more then wear the starting components while everything is still very tight causing a lot of stress.

Once the "mechanical" pinch has loosened up so when you turn the engine over with no glow plug, and there is only a little bit of resistance at TDC, then you can start tuning for performance and there is a guide in the link below.

I recommend 30% nitro with 8-10% oil content. I also recommend using an MC #59 (hot) glow plug for break-in. Don't be afraid to twist the needles and lean the engine slightly so it will stay above 200F and if needs be then cover the cooling head with a sock or whatever to help contain the heat. Once break-in is done then I suggest going to a MC #8 (medium) plug for the performance tuning.

https://www.rcnitrotalk.com/forum/showthread.php?t=76808

 

[Cjsur57]

Some really good feedback. One thing I have been doing is heating up my block with a heat gun before I turn it over. Not too concerned about your heat cycle method wearing on starting components since I will be getting my bump box this week You seem to know what you’re doing olds97, I think I will give your method a try.

 

[olds97_lss]

Some really good feedback. One thing I have been doing is heating up my block with a heat gun before I turn it over. Not too concerned about your heat cycle method wearing on starting components since I will be getting my bump box this week You seem to know what you’re doing olds97, I think I will give your method a try.

Yeah, that was a truncated version of what I do. I typically start leaning things out a bit as I get through the tanks, but keep it on the richer side for the entire first 1/2 gallon. Not blubbery rich, but richer than I run after a gallon just to keep a bit of extra lube in the engine.