View Full Version : Spark Plug Question

06-02-2008, 10:42 AM
Replaced the plugs yesterday on our 1997 ProStar 205with the 310 HP engine. Replaced with the plugs recomended in the manual AC MR43 LTS. Confirmed by Chicago MasterCraft - thanks guys!

I removed AC 24 Platinums. (installed by the previous owner). The only reason I am having second thoughts is the plugs removed had a short threaded area. The plugs I installed have a threaded area almost twice as long. It would just wreck my day to try starting and hear all 8 pistons hit my nice new plugs!

I know I have the correct # plugs. But would appreciate a confirmation that the MR43 LTS have a long threaded area and the previous owner installed the wrong plugs.

Thanks in advance for the help.

06-02-2008, 10:49 AM
You want the longer plugs.
There is a thread here that talks all about it and how to know for sure by looking at the bolts etc.


06-02-2008, 11:53 AM
Thank-you NU -Skier.... I am thinking that AC made the model # very simple:

AC -- AC Delco

MR -- Marine

43 -- Plug #

LTS -- Long thread sparkplug

The correct plug sure cannot hurt the performance. :o

06-02-2008, 11:56 AM
M is Marine, R is resistor, 43 is the heat range.

Since this boat has Vortec heads, it does use the LTS plug but this plug should never be used on a non-vortec engine.

06-02-2008, 12:43 PM
MYMC (my local dealer) suggested I run NGK plugs vs AC. Since I run NGKs in my MG, sounded like a good upgrade. Working great so far.