AC Mr43T

[Dyn0d]

This is the third spark plug that blew the porcelin out of it. Was not overheated as otherr people said in a previous thread. Looks hot due to it blowing exhaust gases by it for a period of time before it blew the end out. Plug was still in head and came right out. Only had about 50 hours on it. Last picture shows how i found it laying in the bilge. Have to remove alternator to get to it.
I am installing NGK BR6FS will se if it continues.

 

[Bondo]

Ayuh,..... Welcome Aboard,..... My 1st guess is,... You've got some detonation goin' on,.....

Tell us more about yer motor,.....
What do the rest of the spark plugs look like,..??

 

[dubs283]

Did the three plugs exit the same cylinder?

 

[Scott Danforth]

If plugs were not tightened correctly, they will overheat and blow out

 

[Dyn0d]

Ayuh,..... Welcome Aboard,..... My 1st guess is,... You've got some detonation goin' on,.....

Tell us more about yer motor,.....
What do the rest of the spark plugs look like,..??

All of the other plugs looked great. It has been a different cylinder each time it happened. I have 2 crate 350 mercruisers inboard. Temps run 180 do not hear any pinging. Looks like they start leaking around the crimp and then blow the ceramic part out. That is why they look burnt. Escaping gasses melt the plug wire. Scares the heck out of me when they blow. Also was very careful not to crack the insulator when installing. I think the pluds are crap.

 

[Scott06]

All of the other plugs looked great. It has been a different cylinder each time it happened. I have 2 crate 350 mercruisers inboard. Temps run 180 do not hear any pinging. Looks like they start leaking around the crimp and then blow the ceramic part out. That is why they look burnt. Escaping gasses melt the plug wire. Scares the heck out of me when they blow. Also was very careful not to crack the insulator when installing. I think the pluds are crap.

Do your crate motors have vortec heads on them and corresponding 8 bolt intakes

 

[nola mike]

Do your crate motors have vortec heads on them and corresponding 8 bolt intakes

Good point, wrong plugs if so. Ya think that would cause them to blow out like that?

 

[Scott06]

Good point, wrong plugs if so. Ya think that would cause them to blow out like that?

Wouldnt think so but who knows. Either he got a bad lot of plugs or he is detonating and doesnt know it

 

[Dyn0d]

Do your crate motors have vortec heads on them and corresponding 8 bolt intakes

Yes the motors are Vortec with 8 bolts holding the intale on. The ACMR43T were in it when purchased. Wrong plugs??? Head is a taper fit not washer.

 

[dubs283]

Yes the motors are Vortec with 8 bolts holding the intale on. The ACMR43T were in it when purchased. Wrong plugs??? Head is a taper fit not washer.

Yes wrong plugs for voretc heads.

You need AC MR43LTS

Guessing the MR43T plugs were getting blown out due to the electrode not being fully placed within the combustion chamber. The threaded portion of the plug is too short to reach properly. Ignition was occurring within the plug hole rather than within the chamber

 

[stresspoint]

Ayuh,..... Welcome Aboard,..... My 1st guess is,... You've got some detonation goin' on,.....

Tell us more about yer motor,.....
What do the rest of the spark plugs look like,..

that's pretty bad detonation to cause a plug to blow apart like that , i too would be interested to see the rest of the plugs.

I'm thinking OP should check the cam for a worn out lobe on the exhaust .

 

[todhunter]

Mine did this on lean detonation. Looked exactly the same. I tuliped the valves on the cylinders that blew the plugs out, though.

 

[tpenfield]

I ran Mr. 43T plugs in my 454's . . . never a problem. I would rule out other possibilities vs. bad plugs.

 

[dubs283]

I ran Mr. 43T plugs in my 454's . . . never a problem. I would rule out other possibilities vs. bad plugs.

Which generation of 454?

454 is a complete different engine from an sbc btw. A 7.4 is light years ahead of forgiveness towards an operator/owner as an sbc

 

[stresspoint]

i would be interested in knowing the outcome of this thread .