Symptoms of an air leak?

[KROGOTH]

What are the symptoms of an air leak exactly? If I'm thinking right, my TRX 3.3 may have one. Its hard to tune, runs real lean (overheating) no matter how rich I tune it (of course it eventually reaches a point where it wont run its so rich), bogs down on full throttle, sometimes as much as half throttle, and such. These symptoms came and went, together or individually throughout trying to tune my Slayer tonight.

I didnt have too many problems with it in the states when I bought it, but I suppose its easy to figure that the abuse it took during being shipped to Iraq could have easily loosened something or broke something loose to cause such a leak.

And to clarify, when it would bog down at high revs/full throttle, it sounded like someone took the engine sound and was running it through a turn table, if that makes sense. Thats what it sounded like to me. (And when its too lean, it just loses power/cuts out at high revs/full throttle, amirite?)

I'm not willing to give up on my TRX/nitro yet. I know it would be all too easy (and pricey) to convert to an E-Slayer and be done with it but I like nitro. That and I have like 2.5 quarts here and 2 more on the way so I have to at least use those before I convert lol.

 

[Monkey Wrench]

Sounds like one to me. I'd replace all the fuel lines to begin with. If it continues, get some RTV sealant and seal the carb throat and engine backplate.

Hopefully that helps!

 

[olds97_lss]

I'd also check your fuel tank seals and exhaust header seal. Once those start leaking, you get inconsistent pressure that mucks up the tune.

Definitely sounds like a leak though.

Personally, I'd pull the engine, seal the carb and backplate just to get it done. Then work from there.

How much fuel is through the engine? Could also be a leaky front bearing. Noticing any buildup of oil towards the front of the engine behind the flywheel?

 

[KROGOTH]

Monkey Wrench- I dont think its the fuel lines for reasons I will mention here shortly, but I will probably either put some on order or buy some from someone who runs nitro at my track out here. Once I find some RTV in my motorpool, I'm going to go ahead and seal the carb throat and backplate while I h ave the engine out. Its not leaking there yet, but better to do it now.

olds97_lss- The engine only has around a gallon and a half through it, tops. I took the engine out during my lunch break and sure enough, around the entire circumference of the crank casing behind the flywheel is an oil+dirt residue. Go figure that may be the problem.

By any chance would there be a quick way to fix the bearing for now? I'm going to go ahead and order the part of course but I'm SoL for the next week or two until the part arrives.

 

[Monkey Wrench]

I tell ya, I doubt it's a main bearing simply because you have such little fuel through it. My suggestion is to seal the backplate, carb throat and exhaust opening with the RTV and see what happens. The fuel residue you are seeing may be as a result of a leak where the pipe mounts to the engine. I've had it happen to be before as well.

Does the pipe mount to your engine with screws or springs?

 

[KROGOTH]

Currently its screw mounted. Once the parts get here, its going to be spring mounted. And there is no way that fuel residue is from a leaky manifold. I understand that it shouldnt be the bearing but I really think thats what it is. I'm going to seal everything up with RTV anyhow mind you though.

And well right now, I can't run my engine no ways. I was taking the clutch and flywheel off to take a looksie (didnt get far removing the flywheel, dont have a piston stopper yet) and turns out my stock clutch was crushed inside the clutch bell.

 

[olds97_lss]

If that's the case... could just be a fried clutch causing your heating issues. Too much slip causes it to rev too much and overheat too.

 

[KROGOTH]

It may be the cause but for now I can't test it. I have a piston stopper, new bearings and a 3shoe clutch+40mm flywheel from M2C.

When all that junk gets here, I will fit the new flywheel and clutch and try putting a tank through it to see how it runs. If it still overheats, then I will check for a leaky bearing again and such things. If it runs fine, then i will have the bearing on hand when it eventually does give out.

What I'm trying to figure out now is the best, easiest, least messy way of putting RTV on the carb throat and back plate is. The carb throat is going to be difficult because of the small area i have to work in. Anyone have any advice?

 

[olds97_lss]

I use a q-tip to apply it. I cut one end off the q-tip, then use the paper round part to dip in the RTV then smear on the parts I want it on. Make sure to clean all areas your RTV'ing with DA to get any oil residue and dirt off.

 

[KROGOTH]

DA?

And that seems like it would make alot of sense. Once I get ahold of something less than a giant tube of RTV from my motor pool I will have to get onto doing that.

 

[olds97_lss]

DA=Denatured Alcohol

 

[KROGOTH]

Does anyone happen to have any pictures of properly RTV sealed engines?

I figured that out earlier while i was walking to chow. lol. I have nitro cleaner spray. Cleaned the area around the backplate and carb just a lil while ago. Still need to find a tube of RTV thats not ginormous sized.

 

[olds97_lss]

Found a vid on utube:

Also, found a tutorial on an alternate forum. I quoted and put it in a post locally on this forum:
https://www.rcnitrotalk.com/forum/showthread.php?p=726280

 

[KROGOTH]

Alrighty. Got a new clutch from a Revo driver at the track today. Installed it and well, pretty safe to say its not the broken clutches fault. So this week I'm going to seal the carb and backplate with RTV like in that tutorial.

Though, should I wait for my green slime to get here so that I can do that part as well, or is it mostly un-necessary?

In the meantime, is there another carb that fits the TRX 3.3? One of the Revo drivers I talked with said that the carb is problematic and doesn't hold a tune well, and apparently alot of people who run the 3.3 replace the carb. I'm going to ask on the traxxas forums as well as here, but this is the place to start asking around for me.

Alrighty. Got a new clutch from a Revo driver at the track today. Installed it and well, pretty safe to say its not the broken clutches fault. So this week I'm going to seal the carb and backplate with RTV like in that tutorial.

Though, should I wait for my green slime to get here so that I can do that part as well, or is it mostly un-necessary?

In the meantime, is there another carb that fits the TRX 3.3? One of the Revo drivers I talked with said that the carb is problematic and doesn't hold a tune well, and apparently alot of people who run the 3.3 replace the carb. I'm going to ask on the traxxas forums as well as here, but this is the place to start asking around for me.

 

[Metalhead Matt]

Make sure your head bolts are tight while your at it.

 

[ThunderTiger]

he thought it was so nice, he posted it twice ! lol

Having read this, and since i'm going to a 3.3, i would be interested to learn of an alternate carb aswell.

Better get researching.

As to the overheat issue, you may aswell replace the exhaust seal, and make sure that the engine head itself is securely fastened. My 2.5 was scorching hot the first time i ran it (320 F) so i stopped it. I later found when the engine had cooled, that one of the head bolts was loose, not by much, but enough to cause a leak. I also found one of the backplate bolts loose.

 

[olds97_lss]

Doing the RTV is doable without the slime and without taking the engine off the truck, so yes, it can be done later.

I tried getting a 2.5 to run better by buying an OS carb for it. It ran better, but still ran hotter than it should have. Regardless what I did to it, it ran hot and was weak. The carb was a $60 carb... spent $40 on a new head. Looking back, it seems really stupid that I spent $100 to try and get a $120 engine to run better.

If sealing it up doesn't fix it, I'd suggest getting a new TRX carb off ebay. Maybe yours is flawed. The few TRX engines I've had, only that one 2.5 sucked at holding a tune or tuning properly. I've had 2 other 2.5's and 2.5R's. All held a tune just fine.

 

[ThunderTiger]

DAYAM MATT !! u beat me to it while i was typing !!!

LOL !! hehehehe

 

[KROGOTH]

Man I'm getting waaaay too good at pulling the engine on my slayer. Anyhow I got the RTV today so I'm sealing my engine tonight. I still consider the front bearing suspect. I cleaned the engine area and behind the flywheel when i pulled it last and I can see an oily mess thrown in the engine area by the flywheel and a small amount of dirt soaked oil behind the flywheel again.

I think I may be setting my LSN too lean but I didnt have the time to test that theory after work before it got dark. So I'm going to seal the carb throat and backplate tonight, and let it all set overnight.

And personally, if I can't get this engine to work without replacing major components Ill just buy a new engine worth a crap and give this one to someone to ERP it with. Then Ill buy an O.S. .21 for the Revo, seal it all up before I break it in, heat cycle it and be happy with a quality engine. I will know more about break-ins and tuning and that engine will do better than this one. Of course, nothing goes according to plan, lol.

Wish me luck. Ill keep ya posted I suppose.

 

[KROGOTH]

Alright, I totally just screwed up sealing my backplate.....I instead sealed the back of the backplate, where the E-Z start/pullstart/whatever seals to. I fail at life!

Its too late to take it apart and try again. Ill let it all set tonight and hope my back plate wasn't the problem. Gah!

Whats an easy way to remove RTV, I'm guessing just take the stuff apart and scrape/brush it off?