K5.9 Mysterious Air Leak

[rjvader]

Hey guys, I'm having a rough time with my 5.9 and was hoping I could ask for some help here. I apologize in advance for the lengthy post!

My original k5.9 engine destroyed its piston, so I bought a new case, crankshaft, and piston/sleeve combo and went for the rebuild. All was good through the break-in process, and the truck ran great for about 1.25 gallons of fuel, but during one afternoon of running, the truck rapidly developed signs of an air leak.

I'm talking out-of-control hanging revs, the dreaded "Chewbacca" gargle, and temps over 240 degrees (previously was running good at 200 degrees and below). At that point I resealed the backplate and carb neck using RTV, but it didn't help one bit. Since then I've been going through a trial and error process trying to find the leak. So far this is what I've done:

• Submersed the fuel tank in water, and blew through the fuel lines. No bubbles, so all good here.
• Bought a new carb body, as well as new o-rings for the carb needles. Still running bad.
• Changed the exhaust gasket, and checked the silicone exhaust coupler for rips. Also checked the exhaust and header for any holes. All good here.
  
• Bought a new backplate, one way bearing, and starter shaft, as well as replaced the motor bearings with steel Avid bearings.

After the change of backplate, bearings, etc, the truck actually ran a little better. The idle was more steady, but was still higher than normal. However, even with the LSN set at the stock position, the truck was still taking off as if I had leaned it way out, and it was still giving me the Chewbacca gargle.

At this point I'm at a loss, I've changed just about everything on this engine and it still isn't running right. One last bit of info: I'm running O'Donnell 20% racing fuel, and a MC59 hot glow plug.

Thanks for taking the time to read all this, any help will be greatly appreciated!

 

[Bauerdog]

Did you seal up the pinch or clinch bolt?

 

[Jam Racing 1]

Change that hot plug for a medium plug, I am betting thats half your trouble

 

[rjvader]

Did you seal up the pinch or clinch bolt?
View attachment 2135

Yep, I covered up the pinch bolt with RTV as well. Forgot to mention that in my post. I also sealed up the fuel inlet fitting on the carb

 

[rjvader]

Change that hot plug for a medium plug, I am betting thats half your trouble

I might have one of those lying around in my parts bag, I'll see about giving that a shot. I've been running the hot plugs for 1.25 gallons of fuel, and it was running great up until recently, do you think I just got a bad plug?

Thanks for the responses guys, I appreciate it!

 

[rjvader]

I finally had a chance to mess around with my Savage today, I took Jam Racing's advice and threw in an OS8 medium glow plug. I also took my carb apart and cleaned out the needles and the needle housings just to be sure that nothing was clogged up.

Unfortunately the truck is still having issues. I knew right away that there was a problem because I was able to easily start the truck with the HSN and LSN at factory settings, with a medium glow plug (it's usually a bear to get started at stock settings). The truck was very responsive at factory settings, as if I had leaned it way out.

I leaned out the HSN about 1 turn and cruised around like that for a while, temps were mostly in the 200-220 range, but when I had about a quarter tank of fuel left, the throttle started hanging really bad and the temps hit about 255, so I called it quits.

At this point, I'm almost convinced there's some invisible hairline crack in the case, even though I inspected it real good when I was changing the motor bearings.

 

[Jam Racing 1]

Sounds more like the dreaded HTL issue is causing it, try to keep the fuel level above the 1/2 mark and see if that helps at all.....

 

[rjvader]

I was keeping a good eye on the temps throughout the run, when the tank was over halfway full, the highest I saw was a little over 220, would it be safe to run at that temp? Previously it was never running higher than 200-205, even with the needles leaned way out.

I'm not able to lean out the LSN more than a quarter turn now, otherwise it starts gargling like crazy. I remember after breaking in the engine, I had to lean out at least one full turn, otherwise it would bog down on takeoff. Now it shoots off like a rocket at nearly factory settings haha.

Thanks for the continued responses, it's keeping me from turning this 5.9 into an expensive paperweight.

 

[Jam Racing 1]

220 is a good temp to run at, even 250 is ok on under hard throttle operation on a warm day, sounds like your tune is pretty close and all so now it is time to run it and enjoy the fun.......

Remember to always have some smoke under throttle and not worry too awful much about temps, they are a baseline and every engine is going to have its own settings it likes to run at....

 

[rjvader]

Many thanks for the advice! That makes me feel a lot better knowing that I can run it in that temp range. Next time I run the truck I'll be sure to keep the fuel level above half a tank. The exhaust was shooting out a good plume of smoke today so it looks like I'm good to go for some bashing!

 

[Mike Anson]

The same thing happened for me with the HPI 5.9. I did everything I could think of but nothing worked. I put my 'new' truck on the shelf for awhile, then bought the OS.30VG. I'm not sure what the issue was with the original 5.9. When I was breaking in my new engine, the RPM's were really high, then I had the overly lean gurgling you were referring to when accelerating. I was a nitro guy, but could not figure it out.

 

[Jneusavyxl]

I had tons if issues with my 5.9 as well. Recently purchased an lrp .30 and awaiting its arrival now. Its lightly used so its been broken in ran about a gallon and half. If anyone has any advice out there that has knowledge on the lrp .30 please let me know feel free to any advice you can offer. I'm planning on running byron gen2 20%. Thanks