Correct plugs

[justright1998]

I have twin 1998 7.4 mercruiser inboards. L29 Generation 6 ( I believe). When I went to buy new plugs, I was told (by the marine store) that I have had the incorrect spark plugs installed after I got my last tune up. When I asked the mechanic who installed them about this , he stated that he just replaced what was already in them. (I bought the boat used and don't have a clue who maintained it) Would anybody know which AC Delco plugs are the correct ones? Extended reach or "shorter reach" ? If I try to install the long reach and they are incorrect, would they not screw all the way in etc? I have rebuilt them from the heads up, and dont want to screw up now. TNX in advance.

 

[mkast]

Re: Correct plugs

Someone will ask you for the serial numbers off the engines to verify the year of the engines.

 

[justright1998]

Re: Correct plugs

tnx for the quick response. I provided the serial number to the marine store which told me I should have the onger raech plugs and the boat yard that recently installed the shorter reach plugs would/should have had access to that information as well.... which is why I am kind of lost with this one. Two places giving me differant information. I jst thought that maybe thier would be something "visual" to be looking for etc. Legnth of threads or if the long reach would not completely screw in.

 

[justright1998]

Re: Correct plugs

sorry for the typos

 

[Don S]

Re: Correct plugs

I provided the serial number to the marine store which told me I should have the onger raech plugs

How about providing US with the SN, then we have a place to start.

 

[justright1998]

Re: Correct plugs

OLOO3434 ( I would believe that the O's would be alphabetical) TNX

 

[1980Coronado]

Re: Correct plugs

My 1980 Mercruiser inboard (MIE 330) 454 cid has a sticker on the valve cover with the serial number, that also gives the point gap, dwell, and spark plug information with the proper gap. I have no idea if the newer engines list the plug information, but it's worth a look. Obviously you don't have points to worry about.

FWIW......I also recently replaced my plugs, and found that the previous owner (or whom ever did the work) did not install plugs that matched the numbers given in the manual and the gap was set .010 too big.

 

[justright1998]

Re: Correct plugs

I never saw any information regarding the plugs........just the Engine serial number OLOO3434. I am not currently at the boat but I don't recall seeing much else.

 

[Don S]

Re: Correct plugs

OLOO3434 ( I would believe that the O's would be alphabetical) TNX

They are not O (letters), they are numbers 0. Your serial number is 0L003434 which is a MIE 7.4L MPI.
The engine is a MIE 7.4L MPI, which uses the long reach plug NGK BPR6EFS, or AC MR43LTS. The MIE 454 Mag Horizon (Which you don't have) used the shorter MR43T

Here is from the Mercruiser dealer program parts catalog.

Here is a page from the service manual. I highlighted your engine in yellow.

 

[justright1998]

Re: Correct plugs

TNX Again. Yes they are the MPI's. I guess whoever serviced this in the past didn't pay too much attention to "detail" Well at least I don't have to run back to the marine store who suggested the long reach plugs TNX for the attachment.