Spark plugs this marine store sold me.

[LAC_STS]

When I bought my new engine (5.7 OMC) a couple months ago it came with autolite 25 plugs.

I have been wanting to change them out to NGK plugs but when I go to NGK's site it shows that I need they're UR4 plug.

I havent been able to find these anywhere locally so I have to order them and I havent gotten around to it yet.

Well I went to a local marine store and they didnt have the UR4 either but they told me that the ones I really need are the BR6FS. When I look on the cross reference tables that are online the Autolite 25 comes up crossed to the UR4 also.

So I ended up getting the BR6FS plugs from this marine store and when I took one of the Autolites out to compare them this is what I found. (attached images)


From where they seat in the head is the same length but the rest of the plug is shorter than the Autolite 25.

Whats the deal with this? Are these the plugs I need or should I get the UR4 like NGK's site says?



Thanks

 

[Gary H NC]

Re: Spark plugs this marine store sold me.

That engine came out of the factory with AC plugs. Usually AC-MR43T on the OMC engines if it is the 5.7.

 

[LAC_STS]

Re: Spark plugs this marine store sold me.

I dont think this engine came out of any OMC factory.



When I just crossed that # it came up with this.

Convert from AC_DELCO MR43T.

NGK P/N: BR6FS
NGK STK: 4323
Accel: 263
Autolite: 3265
Champion P/N: RV12C6
Champion STK: 35
Denso P/N: T20R-U
Denso STK: 5038
GM OEM NR: 5613438
Motorcraft P/N: ASF4C
Motorcraft STK: 10
NGK TYPE: MARINE
Thread size: 14MM
Hex size: 0,81
Reach: 0,75
Seat type: TAPERED
Projected tip: NO



When I search UR4 it says:

NGK STK: 6630
Accel: 274
AC Delco: 2
Autolite: 26
Beck Arnley: 176-5179
Bosch P/N: HR10BC
Bosch STK: 7585
Champion P/N: RV17YC
Champion STK: 25
Denso P/N: T16PR-U
Denso STK: 5025
GM OEM NR: 25164640
Mopar: 4289155
Splitfire: SM002E
Valley Forge: 23R
NGK TYPE: AUTOM.
Thread size: 14MM
Hex size: 0,63
Reach: 0,46
Seat type: TAPERED
Projected tip: YES


So whats the "projected tip"? NGKs site tells me to use UR4. What do your guys think? I think the difference is the projected tip.

 

[John_S]

Re: Spark plugs this marine store sold me.

That engine came out of the factory with AC plugs. Usually AC-MR43T on the OMC engines if it is the 5.7.

and the NGK you have should be the cross to that AC.

Nice crack in that Autolite.

 

[LAC_STS]

Re: Spark plugs this marine store sold me.

Yes the AC # you gave me crosses to the BR6FS I got from the marine store.

But it doesnt cross to the Autolite 25 that is in the engine now nor does it to the UR4 that the NGK site tells me to use.

Only difference I see on the specs it that the UR4 has a projected tip. What is that?

 

[John_S]

Re: Spark plugs this marine store sold me.

Yes the AC # you gave me crosses to the BR6FS I got from the marine store.

But it doesnt cross to the Autolite 25 that is in the engine now nor does it to the UR4 that the NGK site tells me to use.

Only difference I see on the specs it that the UR4 has a projected tip. What is that?

Why put ford plugs in a chevy?

On a projected tip, the tip extends slightly more into the chamber. If there is clearance in the head, they usually run a little better than standard plug. Less fowling, etc. The standard plug for vortec heads has an extended tip. I ran NGK BPR6FS on the standard heads before switching to vortec. I can't say there was a very noticeable difference, but seemed to run slightly better on long no-wake zones.

 

[TilliamWe]

Re: Spark plugs this marine store sold me.

Why does everyone make this so hard? If it's 5.7 made before Vortec heads (meaning 1995 and older, but also some after 1995 for a couple years) then it should have MR43T spark plugs.
If it's got Vortec heads, it needs MR43LTS.
Done.

 

[sethjon]

Re: Spark plugs this marine store sold me.

When I bought my new engine (5.7 OMC) a couple months ago it came with autolite 25 plugs.

I have been wanting to change them out to NGK plugs but when I go to NGK's site it shows that I need they're UR4 plug.

I havent been able to find these anywhere locally so I have to order them and I havent gotten around to it yet.

Well I went to a local marine store and they didnt have the UR4 either but they told me that the ones I really need are the BR6FS. When I look on the cross reference tables that are online the Autolite 25 comes up crossed to the UR4 also.

So I ended up getting the BR6FS plugs from this marine store and when I took one of the Autolites out to compare them this is what I found. (attached images)


From where they seat in the head is the same length but the rest of the plug is shorter than the Autolite 25.

Whats the deal with this? Are these the plugs I need or should I get the UR4 like NGK's site says?



Thanks

Although unusual, its the lower half that counts. To ease your mind make sure the temp range is the same.

 

[John_S]

Re: Spark plugs this marine store sold me.

Why does everyone make this so hard? If it's 5.7 made before Vortec heads (meaning 1995 and older, but also some after 1995 for a couple years) then it should have MR43T spark plugs.
If it's got Vortec heads, it needs MR43LTS.
Done.

While AC's are fine, why should he throw away a perfectly good set of the NGK's?

 

[LAC_STS]

Re: Spark plugs this marine store sold me.

While AC's are fine, why should he throw away a perfectly good set of the NGK's?

I can return / exchange the NGK's. I thought (maybe wrong) on a marine engine NGK's were a better plug.

 

[LAC_STS]

Re: Spark plugs this marine store sold me.

Oh yea.

The MR43T that Tilliam said cross ref to the NGK's I have now.

 

[wire2]

Re: Spark plugs this marine store sold me.

My '84 OMC 5.7 came from the factory with BR6FS's, I've been using them ever since, no issues. The Autolites being taller above the sealing flange means nothing.

 

[Aloysius]

Re: Spark plugs this marine store sold me.

I like Autolites. Had an interesting thing happen in my boat, though. The unplated automotive threaded base rusted, causing a couple of plugs to leak compression past the insulator. The insulators are aluminum oxide, and unforgiving of the force of expansion from oxidation. "Marine" plugs have a rust resistant base.

 

[EddiePetty]

Re: Spark plugs this marine store sold me.

.......From where they seat in the head is the same length but the rest of the plug is shorter than the Autolite 25.

....I believe that cracked Autolite is a resistor plug, thus the extended porcelain length.

 

[LAC_STS]

Re: Spark plugs this marine store sold me.

So is the BR6FS NGK plug that I have pictured next to it.