LS1 Silverado SS

7.7 was brought in for problems.
Wouldn't run for more than 5 minutes, figured the motor was bad.

When I went to run it, it'll start and run for about 10 seconds, and when it goes to an idle it jumps up and down.
Like bahh bahh bahh bahh bahh
Running temps were 160.

It started about 5 times, now I can't even get the thing to start.
The glow plug is good, it's getting fuel, and it seems to have some strong compression.
Glow ingnitor is good, tried a different fuel, tried a different glow plug.

The threads for the glow plug seem to be cross threaded, and when I removed the head you can see blowback around the block. I'm guessing it was an air leak, but am uncertain as to why it wouldn't start.

And as I look, the sleeve inside the block has play.
My question is: Is this normal?
I've been working for the hobby shop for 3 years and have never seen this, nor have I dealt with CEN.

And if this is normal, then what could the problem be?

chrobar

Did the owner properly break in the engine yet? If so, return it to stock settings if you have not done so already. If the glow plug screws into the block without problems, it's probably OK. Also check the idle gap in the carb. It should be about 1-2 mm out.

LS1 Silverado SS

The owner had so many problems with the truck at initial purchase and at the store we couldn't help with most of the problems due to factory defects. We sent the truck into CEN ourselves and they broke in the engine for the customer, then ran one more tank through it and sent it back to us. I then tuned the truck for the customer for our climate, and the truck ran great for me.

the truck is caked in mud now, and this is the problem that's occured. I've spent hours on forums trying to figure this out before I broke down and am asking here.

I've tried starting with the high speed needle at 3.5 turns out, 4 turns out, and the carb gap is about 1.5mm
low speed needle I've had a flush, gone as far in as 1 turn, back to flush and out as far as 1 turn.

I can get it to barley stutter like it wants to start, but not quite there.

derrick05

A running temp of 160 is too low for the sleeve to properly seat[X(]If the glowplug is crossthreaded,then theres a 90%chance that the headbutton is stripped/crossthreaded.It is quite easy to overtighten the glowplug on those.Sounds like the engine wasnt properly broken in[8D]

LS1 Silverado SS

we can't get the motor to run long enough to get it to proper running temps.
The button for the head does seem to be crossthreaded, but the glow plug screws in and out fine and tightens enough that I can't seem to see it as a problem.

however, when compared to a WASP .28 from Orion, with no glow plug the WASP has a pinch to it, while the 7.7 seems to have more of a drag compression wise.

I'm thinking the customer just got it too hot, but it's hard to say it was his fault either as he claims to have only had 2 tanks through it. Which I could see easily being truthful, as he's a regular here and although he is hard on his things, he's loyal and has been bringing this thing into me for many previous problems and hasn't gotten a tank through it since it's last cleaning 3 months ago.

derrick05

If he has run it hot,the color of the top of the piston should tell the story on thatIf the top of the piston is very dark and burned looking,then he has burned it upMost likely from running the wrong fuel.The top of the piston should be very clean and shinny,almost like new.[8D]Although CEN recommends 30%nitro,I have found that these engines run too hot on 30.If he must run 30%,I wouldnt do it until the motor has run for at least 2 gallons on 20%to make sure its broke in good,but a NX-76 new or broken in by the book will run hot on 30% every time.Most people make the mistake of breaking in one of these engines by the book and figure thats enough,but it actually takes around two gallons to break in one of those[8D]Let me know what you find.

derrick05

If the 7.7 is dragging like that,it either hasnt been broken in very good yet or the engine has dirt in it[]

yakfish

My Feedback: (27)

I 'm not a CEN owner but I'll through in my 2 cents. I didn't see anyone mention the exhaust. If the exhaust is leaking it will do all the things that was described. it won't stay running or won't evenstart even though it sounds like it is trying to start. if the exhaust has a leak it won't be able to push enough fuel to the motor to keep it running. I would say check the manifold at the engine and any couplers that there may be. make sure the exhaust is airtight. maybe this will help. Good luck.