Ejected spark plug

[RJR49 129]

I was mowing, my C-160 was running normally. Then it stated knocking. Just a little under load at at first. Then steadily at idle. Then, as I was inspecting the motor, the plug blew right out of the head! I have No clue what would cause something like that. I won't have a problem installing a Helicoil to fix it but I sure would like to know what might be the cause

[Snoopy11 5,714]

I had this happen on a 2.3 Lima racing engine. It turned out to be a bad exhaust valve.

 

Sometimes, if you have a burnt exhaust valve, and are running the engine at speed... the pressure and compression goes too high and only has 1 place to go...

 

Don

[Snoopy11 5,714]

@RJR49 ...is all of the spark plug still attached to itself? Sometimes the bottom end of the plug blows apart and stays in the cylinder...

 

I'll post my other thought here... so @stevasaurus doesn't... eh... ... me...

 

Also, talk to me about the threads on the cylinder head... how do they look, stripped, probably? What about the threads on the spark plug... are they stripped?

 

The knocking sound that you heard makes me lean towards burnt exhaust valve... especially if it just started knocking out of the blue... but I also wonder if perhaps the spark plug was loose... maybe it was cross-threaded... things like that.

 

 

Don

Edited April 14, 2022 by Snoopy11

[RJR49 129]

  I guess it could have been caused by a loose plug but there is aluminum all the way to the last two threads. The plug itself looks pretty. Good. I've been neglecting the valve adjustment so a burned valve is a distint possibility. I guess that I'll find out when I pull the head

[Snoopy11 5,714]

Just now, RJR49 said:

there is aluminum all the way to the last two threads

How long was that spark plug in the engine? It doesn't sound like a loose plug to me... and it having aluminum all the way to the last threads solidifies my analysis of that. I don't think that is the cause of your issue.

 

BUT... what I do think could be and issue is found in what you revealed.

 

Let me change one word for you:

 

1 minute ago, RJR49 said:

I've been neglecting the valve adjustment so a burned valve is a DEFINITE possibility

 

If the threads on the head are stripped... you might be able to chase them... or redrill and tap with a kit... or buy a new head...

 

Don

[Handy Don 12,240]

I'd say that If you still have good thread, the plug was loose.

[stevasaurus 22,765]

If the threads are bad in the head, another option is a Helo-Coil.  probably not spelled right.  

[squonk 41,163]

I remember in Junior High shop, one of the guys tuned up his father's push mower. He went out side and mowed some grass wearing shorts. The plug blew blew out and went right between his legs. 

[Pullstart 62,921]

@squonk note to self: when I’ve got my shorts and Jesus cruisers on, don’t sit near the spark plug.  

[RJR49 129]

I was glad I didn't have my head over the plug when it fired. Not sure how high it went but real happy I wasn't there to slow it down

Puzzeled over the burnt valve explanation. If the valve was burned it seems that compression would be low not high. I'm thinking that it is out of adjustment rather than burned

[Snoopy11 5,714]

1 hour ago, RJR49 said:

out of adjustment

Could be... but worthy to disassemble the head just to find out...

 

Don

[Snoopy11 5,714]

1 hour ago, squonk said:

tuned up

We know what that means...

 

Don

[Bill D 1,926]

Any pictures or updates?

[RJR49 129]

Took the head off. Everything looked great! A guru that I rely on for all things automotive said "fix the blown thread, put it back together, and let's listen to it." Thought overheating timing, or just old age were probably the issue. Anyone have any thoughts on the best thread repair kits? He likes inserts over Helicoil type coils.

[squonk 41,163]

This a good kit. The insert has serrated threads that lock them to the hole

 

Heli coil 5334-14

Edited April 16, 2022 by squonk

[johnnymag3 2,520]

That engine is done....I will get it out of the way for you....no problem....  

 

Fix the head...its all fine

[RJR49 129]

25 minutes ago, squonk said:

This a good kit. The insert has serrated threads that lock them to the hole

 

Heli coil 5334-14

That one isn't the wire coil?

Edited April 16, 2022 by RJR49
Mispelling

[squonk 41,163]

24 minutes ago, RJR49 said:

That one isn't the wire coil?

No.It's a steel insert 

 

[RJR49 129]

Thanks!

[Snoopy11 5,714]

1 hour ago, RJR49 said:

overheating timing,

or just old age

Those 2 things mean nothing to me. This isn't a "common" occurrence. Overheating, in my experience... does not cause spark plugs to eject and you would have been seeing other signs of potential issues. Off timing... would make it run like hell...  and old age alone is NOT the cause. I would be wary of whoever you are listening to that told you that.

 

Routine maintenance should help avoid some of the obvious reasons this might happen... i.e. tightening the spark plug every once in a while... adjusting the valves... checking over the machine. Proactive, not reactive.

 

You still haven't shown pictures of the spark plug hole itself for our analysis. This is important for us to see.

 

Be sure to check valve springs to ensure that they aren't broken or weak.

 

Don

[RJR49 129]

Don

I appreciate your input. Weak springs and the other suggestions didnt occur to me. RS wouldn't let me post another picture. I thought you could subscribe to have additional features but can't find it. I'll keep looking

[RJR49 129]

Have to admit that I haven't checked how tight the plug was but given that only 2 threads didn't have aluminum stuck to them I'm confident a loose plug isn't the problem. I'm  seriousely bad about the valve adjustment. I've been running Kohlers for over 50 years and never had a problem. Negligence for sure. However, the valves look to be in great shape. I have a picture of the Exhaust  valve up and there isn't any evidence of burning. In fact, no discoloration anywhere. Weak springs may be the answer. But, that's just a guess too.

[Bill D 1,926]

Any chance it was running lean?  That would cause overheating.  Also wondering about the knocking you heard before the plug let go.   Could be simple metal fatigue that caused the threads to fail.

[WHX?? 48,833]

4 hours ago, RJR49 said:

RS wouldn't let me post another picture. I thought you could subscribe to have additional features but can't find it. I'll keep looking

https://www.wheelhorseforum.com/store/

Helps keep the lights on and you can post endless 

[Tractorhead 9,064]

Helicoil is IMHO the best way to fix an destroyed Sparkplug thread.

 

One of the benefits as a side note is, it improves the stability in the head because the coil changes the fixation diameter a little more up, 

so it give you also a more safety especially in weaker Alu cylindreheads