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Need help determining the correct spark plugs for my 4.3L engine

B

boat:) owner:(

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I recently bought a boat with a MCM 4.3L LX engine S/N 0F595397 which has a Thunderbolt IV ignition and 4bbl carb. This information is listed on the spark arrestor cover along with spark plug info AC Delco MR43T. There is no other data plate or identification anywhere on the engine that I have found, and I have had the engine removed from the boat. Please continue to read or you will miss why I'm needing help. I also have valve covers that say VORTEC on them. I read somewhere in an earlier post that vortec heads require a longer reach plug like a MR43TS or MR43LTS. So here are my questions. 1. Can anyone tell me how to determine if these are truly vortec heads, I realize it may be possible someone in the past just put vortec valve covers on this engine.
2. If in fact this engine does have vortec heads does this change the engine identification.
3. If it does have vortec heads what is the correct spark plug to be using.

The current plugs installed are AC Delco CR43TS.

This engine is installed in a 1995 Regal Valanti 202SE

Thank you in advance for any knowledgeable help.
 
Hi, using your serial number indicates that Mercruiser had two designed heads and used plastic valve covers which I can recall them saying Vortec on them in that era of around 1995 but when it came to spark plugs, there weren't any changes made between the two heads offered on the GEN "2" engine models and Mercruiser didn't officially start using the newly (even better flowing) redesigned GM Vortec until 1996.5 as it became known as Mercruiser Gen"+".... The Gen 2 did have a low key vortec name because GM started calling it Vortec back in 1986.... https://www.reference.com/vehicles/years-were-chevrolet-vortec-engines-made-f7c86a1cdd3563da ....http://www.mercruisermotor.com/V6Motors.html

For Mercruiser, Gen+ went to the longer reach plugs AC Delco MR43LTS while the Gen 2 used the smaller reach plug MR43T.

The following link is where you can see the two heads and valve covers used/mentioned, item number/S 1, 5 23... http://www.marineengine.com/parts/mercury_marine_parts/sn/0F595397/443L100HU/1599_130

While the spark plug you were running (CR43TS) may not been the exact number called for it was close enough that it would not cause any damage to the engine.
http://www.acdelco.com/auto-parts/spark-plugs/snowblower-lawn-mower-spark-plugs.html
Here's the Marine plug info, http://www.acdelco.com/auto-parts/spark-plugs/marine-spark-plugs.html

The quickest way to know what head design you may have between the two is try counting the intake manifold bolts. The Gen+ should have 8 bolts while the non Gen+ (GEN 2)< should have 12.

Gen+, http://www.boatfix.com/merc/bullet/97/97_01.PDF
Item numbers 2 = 12, http://www.mercruiserparts.com/bam/subassembly/31484/1619/160

Here's your engine Specifications, http://www.boatfix.com/merc/bullet/91/91_17.PDF

User Notes: 0F595397 is an MERCRUISER 1995 4.3LX Model number 443L100HU...Parts guide part number 90-801874 93... https://www.perfprotech.com/mercury-marine-parts-catalog/umodel/20861
http://www.marineengine.com/parts/mercury_marine_parts/sn/0F595397

Hope this helps, good luck.
 
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