Mercruiser Alpha One 3.0 LX

[IntelBoater]

I purchased a 1997 Bayliner 1954 with the Mercruiser Alpha One 3.0 LX. On the top of the flame arrestor it has the AC-MR42LTS spark plugs gapped at .035. The individual who i purchased from had Champion RVI5YC4 plugs and its been idling very rough. So i figured lets just swap out the plugs.

Looking online, i found that the AC-MR42LTS plugs are no longer able to be purchased. I found the following thread but had my doubts about the plugs being recommended as an alternative (http://forums.iboats.com/showthread.php?t=549396)

With some more research i ended up getting NGK #BPR6EFS. Today i put them in and started up the boat and had nothing but issues. When i did get it running for a bit, it ran VERY rough. I decided to check out the plugs and when i took out one of the plugs nothing but smoke came out of the hole. My guess is that cylinder wasn't even firing as the end of the spark plug looked new as heck. I replaced that plug with another of same since i bought extras, attempted to start again this time it would only turn over for a short time then always die.

I decided for the hell of it, lets put the old plugs in. So i put the old plugs in and it started up after 3rd time with no issues. Idled a little hard again but at least stayed running.

So my question is, what plugs are an alternative to the AC-MR42LTS? Should i get the MR43LTS? I understand since i have the LX model of engine i need to get the longer reach ones since my head is longer. If i research right, the current champions the previous owner put in, RVI5YC4, are not even the longer type nor marine. Plus i've heard nothing bad about the champions with blow out issues.

Are there any mechanics that know which plug i should be using? Let me know if you need more information. Hoping this thread can finally solve the debate as it looks like I'm not the only one with the question. Thanks everyone!

 

[ktbarrentine]

Re: Mercruiser Alpha One 3.0 LX

IMHO...Champions are good for lawn mowers... that's about it. As for the rough running, I am assuming you've triple checked the firing order and wiring (and timing)? Are you sure it is plug related, and not fuel related?

 

[Bt Doctur]

Re: Mercruiser Alpha One 3.0 LX

Possible spark plugs:NGK: TR5AC Delco: MR43LTSAutolite: 103Beck Arnley: 176-5180Denso: T20EPR-U
Details about your spark plug:Type: MIL.Thread size: 14mm (0.55118 inches)Hex size: 0,63 inches (16.002 mm)Reach: 0,71 inches (18.034 mm)Seat type: TAPEREDProjected tip:

 

[IntelBoater]

Re: Mercruiser Alpha One 3.0 LX

IMHO...Champions are good for lawn mowers... that's about it. As for the rough running, I am assuming you've triple checked the firing order and wiring (and timing)? Are you sure it is plug related, and not fuel related?

Unfortunetly I do not have the tools or the knowledge for timing. I plan on taking it in to shop this fall to have everything looked over but wanted to replace the plugs which i "thought" would be simple enough.

The rough idle isn't too bad but at times idling on the lake, the motor will just die. Can always start it back up. I did notice when i put the old spark plugs back in, i checked the gaps on each one prior and had to make some adjustments. It did seem to run a little smoother after making those adjustments. Boat just needs a really good tune up. Since i don't know what the prior owner all did, probably best to have a good mechanic look it over.

As for the fuel, this has also been one my thoughts. I've been running sea foam through it since i got it and i don't belive i've used a full take yet so some old gas may be present. We will be camping in coming weeks and should have no problem using it all up then.

Possible spark plugs:NGK: TR5AC Delco: MR43LTSAutolite: 103Beck Arnley: 176-5180Denso: T20EPR-U
Details about your spark plug:Type: MIL.Thread size: 14mm (0.55118 inches)Hex size: 0,63 inches (16.002 mm)Reach: 0,71 inches (18.034 mm)Seat type: TAPEREDProjected tip:

So it looks like the AC-MR43LTS will work and is the replacement for the AC-MR42LTS plugs? . Whats intersting if you cross reference AC-R42LTS you get all those along with the NGK-BPR6EFS. But if you cross reference the MR43LTS, the BPR6EFS doesn't even show up. Very odd.

 

[ktbarrentine]

Re: Mercruiser Alpha One 3.0 LX

43 is just one notch hotter in heat range than 42... 43 is typically what I am seeing in most boats these days. I just went down from a 44 to a 43 (in my 5.0l) with no noticable difference (but more confidence in the higher RPM range). I am sure there is more 3.0 experience out here to draw from.
Have you inspected your fuel/water separator? (if you have one).

 

[IntelBoater]

Re: Mercruiser Alpha One 3.0 LX

43 is just one notch hotter in heat range than 42... 43 is typically what I am seeing in most boats these days. I just went down from a 44 to a 43 (in my 5.0l) with no noticable difference (but more confidence in the higher RPM range). I am sure there is more 3.0 experience out here to draw from.
Have you inspected your fuel/water separator? (if you have one).

Thanks, I just put my order in from rockauto for the 43's. Will give them a try. As for the fuel/water separator, i have not checked. If i did have one, where would it be located roughly?

 

[ktbarrentine]

Re: Mercruiser Alpha One 3.0 LX

Thanks, I just put my order in from rockauto for the 43's. Will give them a try. As for the fuel/water separator, i have not checked. If i did have one, where would it be located roughly?

between the fuel tank and the fuel pump. Mine is mounted to the fwd stbd side of my motor and is hard piped to the fuel pump.