What is the cause of this?

Looking at picture #6, those two plugs look like they may be at two different heat ranges.

 

How much plug gap are you running? Have fixed a lot of rod kicking Nitro Coupes by lowering gap to .011-.012. Wide gap under compression makes it easier to fire another cylinder before its time. It will spit a rod out every time, usually on burnout or hit of the throttle.

 

you said the fuel system calls for a 180 jet and you put in a 125 jet. The question i have is what was the corrected alt. ..... and what jet did the fuel system call for? i have never seen a fuel system call for a 180 jet.

 

They are indeed old plugs. They are all one run TF plugs that we used for warmup, setting idle etc in the pits.

About the main, yes i thought it odd too, that it called for a 180 main, When we know that this setup usualy uses around a 130 main. This is also the reason that we didn't use the 180. Yes it was at corrected alt. But i again I am in serious doubt about this. it just seemed way off to me. I will run the numbers again and see what i get. could be something stupid as a typo or something.

We ran the plugs at .016

 

@ Mike if it went lean as you suggest wouldn't i be able to see brunt pistons, valves etc?
The other pistons crowns look like new

Regard timing what is a sensible starting point on an engine like mine?

It has been suggested to me that we might have hydraulic'ed the engine, we have talked about this, but i am no expert so i don't know, i thought running a 44 pretty much guarantied that the mix would fire.

 

no expert here (just dumb electrician)

if your plugs were closed up there would be no gap for the 44 to jump so it could hydrolic.
But looking at pics the plug that is closed up i would suggest might have been caused when the piston hit it after it went booom.

 

What RPM have you been running? Looks to me like too much RPM with what looks like a heavy rod, piston and probably wrist pin. What happens is the heavy components at high RPM will tug on the bolts on the down stroke and fatigue the aluminum threads in the rod and they will pull out like a Helicoil. Look for the threads pulled out of the rod and for movement and embeding of the bolt, washer and cap interface. Fuel cars need these heavy components but don't see the RPM that most alcohol cars see. If you want to send me the parts I would be glad to give you my opinion. Or call me at 303-935-7565.

Thanks
Brian Scollon
GRP Connecting Rods

 

Just a thought , if there wasnt enough grounding to the motor / chassis , the plugs would crack and drop the cylinders.
Could this affect things ?

 

After going back and looking at the extra pictures it sure looks like it spun a bearing. Specifically looking at the crank journal and a couple of the bearing pictures. What is the thickness of the bearing out of the broken rod? Might have to straighten it out to measure but it looks like the soft bearing material is gone.

Brian
GRP Connecting Rods

 

The Heads are each grounded to the same point as the mag. with propper sized wire

Regarding rpm. I am fairly sure it didn't go crazy, as i have 2 warning light and neither went off. But unfortunately i don't have a datalogger. Planning to get one tho.

@ Brian

You may be on to something. After reading you post last night i went and looked at the bearing pieces again.
The 2 pieces that are really mangled may have spun, I am not certain as it is hard to tell because they are so busted up and folded over onto themselves.
One thing i did see after looking at them closer was that they seem to be wider than the normal bearings, if there is bearing material left on one side is hard to tell. wether they spun or not. That is also hard to tell.

Yes I would very much like you opinion on them. If you would be so kind. I will need a shipping address. Feel free to pm me, email me or post it here whichever you feel like. Here is my email: grauen@gmail.com

Thank you all for taking time to comment here.

PS The Short block is almost sorted, I ended up putting in new rods, 3 new pistons, new crank, new cam, and one new sleeve. Next up is the heads need to check all the valves etc etc.

 

Not being smart or anything and I know all about enough money to race, been there and done that with three blown motors in one short season, but...if you just had a whole motor destroyed, why would you not put all new pistons in with the rods and crank instead of only three new ones? I don't think I would trust anything out of the blown up one. JW

 

Parts- New vs Used

One point that sort of came up was that this was a motor put together out of used fuel parts? Just because parts are new to 'you' that doesn't make them "new'. I have friends who buy used parts and put motors together and then are amazed that it breaks. Rods, cranks, pistons, blocks and even heads have a life expectancy. There is a time when the stuff is just used up and fuel stuff reachs that point even sooner than alcohol parts. Another issue is rods from a fuel motor are different than rods for a alcohol motor. Nitro motors see more compression forces pushing down on the rod so they are heavier than alcohol rods. But alcohol motors seen much higher RPM so the stretch factors on the rod is much higher. If your rod is heavy then you increase the stretch factors greatly. The guys at GRP could probably explain this better than I could. I really hate to say this but used fuel parts aren't any kind of a bargain no matter how cheap they are. And unfortunately some used parts aren't ever worth trying to use- rods especially and most anything that has been through an explosion already. That motor went from a lot of RPM to none in a very violent manner, don't trust anything in the rotating assembly again. Dave Germain