OMC 260 spark plugs for reading

[floattest]

I'm tuning up my 1979 OMC 260 and would like to share some pictures for the pros.

I've run 2 full seasons on these plugs (maybe too long?) after they were installed with a new mallory breakerless and CDI ESA.

The boat has run flawless since then, shifts smooth and idle is very predictable.

I'm not sure what the white crystals are on the plugs. Most of the plugs look good to my eye, with the brown colored insulator and generally clean electrodes.

I'm wondering if these pictures tell stories I don't have the experience to read.

thanks
FT

 

[Reinell-BRXL-191]

Re: OMC 260 spark plugs for reading

Unfortunately, that is detonation.. it's slight, but still exists.

You are either running too advanced on your timing,

Or you are running poor quality gas, or under jetted / carb issue...

also, it can be spark plugs with a improper heat range or gap

 

[Bondo]

Re: OMC 260 spark plugs for reading

Unfortunately, that is detonation.. it's slight, but still exists, you are either running too advanced on your timing, or you are running poor quality gas, or under jetted / carb issue...

Ayuh,.... Or water in the fuel....

 

[floattest]

Re: OMC 260 spark plugs for reading

Hey thanks guys.

Oh, should have mentioned, the motor hadn't been run for about 7 weeks. Not sure if that would affect the look of the plugs.

So in general it sounds as though maybe too far advance from stock. Which is 10 degrees.

Is that correct? When you say too advanced it means MORE before TDC than spec?

And it may be lean as well?

Does 10 degrees still work for E10 fuel? Or is there a compensation that should be made?

Could this engine be running good relativiely even with these conditions?

Oh, and how "unfortunatley" we talking here.

If it isn't pinging can it still do permanent damage?

I'm doing my year end maintenance, going to get this thing right before layup.

Thanks for the help.

 

[floattest]

Re: OMC 260 spark plugs for reading

Well, you are correct, reinell. Too far advanced. I got a decent timing light and determined the timing was set at about 14 degrees. My bad for not getting that right when the new distributor went in.

Now it's at 10 degrees. I used AC plugs this time for no other reason than they are the stock part.

Do you think it will run cooler now because of the timing adjustment?

I replaced the rotor and cap and just an fyi on the sierra rotor for this distributor. It's junk, I wouldn't put it on my lawnmower, cleaned up the old mallory part and reused it, it's only two years old. I don't care about brand names but you can tell a good part from junk sometimes just by looking at it, sorry sierra, in their defense many of their parts I've purchased are just fine.

When I get a chance to pull a couple plugs after a good run I will post the pics so we can all see the difference. Still three weeks of Dungeness season so I'm looking for an opening in the weather, haha.

One question nobody answered was about timing adjustments for E10 gas. Just set it at the spec or can you adjust a couple degrees one way or another to accommodate the alcohol gas on the market?

Thanks for the help

 

[muc]

Re: OMC 260 spark plugs for reading

If I remember right.
OMC put out a service bulletin in the late 80’s changing the spec to 8 degrees BTDC.
Because of the new gas.

 

[bruceb58]

Re: OMC 260 spark plugs for reading

Do you think it will run cooler now because of the timing adjustment?

No. When an engine is run too retarded it will actually run hotter.

The amount of alcohol in the fuel affects the octane rating, actually increasing it. However, you set your timing to what the octane is, not the amount of alcohol.

OMC changed the timing setting because the octane rating of fuel became lower since the original engines were produced and had nothing to do with alcohol content, only octane.

 

[Reinell-BRXL-191]

Re: OMC 260 spark plugs for reading

Correct, if the timing is retarded, the cylinder is firing after the optimal point, and the heat is not transferred in to power as efficiently as it is supposed to be, this causes more heat in the cylinders, and causes hot exhaust and cylinder heads... Unless you are running premium fuel in your boat, I would go down to the recommended 8 degrees, on a hot day with a bad batch of gas, you could still be seeing knock - If you are running 91 or above all the time, then you will probably be safe at the old 10 degree spec... as far as E10, they adjust the octane rating of the gas portion of the mixture, so the alcohol does nothing to effect the total octane rating... 91(93) is 91(93), 87 is 87... don't chase timing based on who made it or what is claimed to be the the fuel...

 

[floattest]

Re: OMC 260 spark plugs for reading

Well, I'm not exactly sure if it is nailed yet but I will share my observations.

The weather broke a bit so I got to go crabbing on Sunday. Sorry to tell tales of adventures on the sea if you are snowbound.

35 degrees at launch and light fog, with partly sunny clearing later. It got up to a balmy 39. No wind, waves less that 1 foot. Beautiful day on Puget Sound. We fished the west and south side of Hat Island.

Observations:
1. It started harder than it used to. (could be the conditions)
2. After it warmed up, about 5 minutes or more, it idled all day whenever asked and never stalled. about 650 rpms, Easy in and out of gear all day dropping and pulling pots.
3. The go-fast runs we took was where I noticed a faint gas-exhaust smell when accelerating hard up to 4500. It was smooth power and got on plane pretty quick. Again, no pinging and the secondaries opened up and lots of power available. My friend thinks it's rich on the carb adjustments. I'm not convinced it needs to be changed.
4. 4500 rpm runs at about 30-32 mph.
5. The engine feels like there is a lot left and I have never had it pegged and wound up to WOT. I've had the tach up near 5 lots of times but I'm reluctant to take it past 5, so I usually back it down and run anywhere from 3700 to 4500 when making time.
6. There was no difference in running temp from before. It runs about 10 degrees hotter after a long 4500 pull, stays steady though, then it cools back down, I guess the guage stays around 175-180.
7. The picture of the plugs is just the first four I pulled. I didn't pull them all for the pic. They look good though. For an old engine it seems to be running real good.
8. We got 2 limits of dungeness

 

[bruceb58]

Re: OMC 260 spark plugs for reading

My friend thinks it's rich on the carb adjustments. I'm not convinced it needs to be changed.

I would not listen to your friend. There are no adjustments you can make. Only jet change would affect mixture when you are running at speeds other than idle.

175-180 is a bit on the hot side. You should verify using an IR gauge. When was the last time you changed the impeller?

 

[floattest]

Re: OMC 260 spark plugs for reading

I agree it seems to run a little warm. Impeller is new. Actually much of the outdrive is new. I have full confidence in the drive. If there is anything that I suspect might be letting it get warm it would be the efficiency of the heat exchanger, I don't know how old it is. Or a restriction at the ps oil cooler. I'm considering on just replacing the ps cooler anyway. I flushed the exchanger and replaced the big rubber cap and the zinc last spring.

It stays within a comfortable range all the time, but like I said I wish it ran a little cooler.

I used an infared thermo on the engine a few months back when I was out on the water and it was quite interesting.

After a while of taking temps I figured everything was fine in that the temps I got at the intake manifold and around the temp sender were in the 170 range.

But if you pointed it around the exhaust manifolds close to the head you could get reading around 200. The risers were warm, not hot, like 140 or so depending on what part of it you shoot.

I've been meaning to do a real good mapping of the heat on this thing after a good pull on the motor and post it for everyone. Of course the weather again. Not sure when she'll hit the water next.

all I have now is pictures of spark plugs, and engine, haha sorry.

In the meantime, I think instead of leaving it at 8 degrees where it is I'm going to use my advance light and try to get the advance curve on the new distributor to closely match the curve spec in the factory manual. With an emphasis on getting idle at 9 degrees plus or minus 1 degree.

After that, run again and read all 8 plugs, if it does'nt indicate a rich or lean condition or detonation, leave it there and sail it.

thanks everybody,

spring is right aground the corner, days are getting longer

 

[Maclin]

Re: OMC 260 spark plugs for reading

With closed cooling that temp seems ok depending on what thermostat you put in.

 

[bruceb58]

Re: OMC 260 spark plugs for reading

With closed cooling that temp seems ok depending on what thermostat you put in.

I agree. Didn't know it was closed cooling either.

All of the temps measured seem very normal.

 

[floattest]

Re: OMC 260 spark plugs for reading

I guess I have come to learn over the last few years that it's normal for it to run these temps.

When I first got it I changed the waterpump and eventually the manifolds. Overheating hasn't been a problem since,

What about the 4 plugs from last Sunday? Look pretty good, like new almost. This was about 6 hours of operation with most of the time being at 1500 RPM or below.

Thanks

 

[bruceb58]

Re: OMC 260 spark plugs for reading

They look perfect from what I can see.

 

[floattest]

Re: OMC 260 spark plugs for reading

Here is the OMC advance curve from the 1982 factory manual.

Since it's too cold to work on her I just want to get my plan straight and see what you think.

Reading the chart which oddly gives the limits of the curve instead of a one line curve on the grid, I see that it's base is 10. total advance is 31 degrees.

For me I think that if I start at 8, it won't show any additional advance until about 1000 rpms.

I presume though, that the way to do this is get the base at whatever it is, 8, 10 or other, zero the light. Then measure advance at selected rpms.

I'll be looking for:
1500: 7 degrees
2500: 16 degrees
3000: 21 degrees

Do I compensate for the 2 degrees retarded?

Does this work ok out of the water, you would think that the best measure would be under load, maybe tough to do though.

Thanks,
FT

 

[bruceb58]

Re: OMC 260 spark plugs for reading

You can do it in your driveway. Distributor doesn't know anything about load.

 

[floattest]

Re: OMC 260 spark plugs for reading

Got a chance to work on the boat in the driveway marina. Here is what I learned.

My new timing light is awesome. My tach is way off.

Got base timing at 8 Degrees.

It's very difficult to adjust just 1 degree. The timing seems to move about 1 degree when the clamp is fully tightened.

I bounced around 8-11 for about half an hour. Trying to loosen just enough so I could turn the dizzy while it was idling and then tighten it down.

Anyway, settled on 8 degrees, at idle.

Then I checked 3 additional RPMs with the light set at various advance numbers.

Base 8 degrees; 600 RPM
Base plus 3; 1250
Base plus 11; 1700
Base plus 16; 2150.

waddya think

On the last setting the tach on the dash was reading over 3K. what the heck. It could be one reason I have never had her at full WOT for any extended period. When my dash tack reads 4500 I'm going about 32 and it is fast enough for me. So I have always worried about winding it up where the dash tach reads over 5K because that is past the recommended WOT RPM.

I thought it was either prop slip or something else that was allowing it to rev so high. So I just didn't do it.

Now I'm thinking that I was never really winding it up that much because the tach was fooling me.

So I'm looking forward to the next outing to see how it runs at the real actual WOT. yikes.

 

[bruceb58]

Re: OMC 260 spark plugs for reading

You may have mentioned if it is or not, do you still have points in your distributor?

 

[Reinell-BRXL-191]

Re: OMC 260 spark plugs for reading

You may have mentioned if it is or not, do you still have points in your distributor?

I will bet he does.. I see a dwell meter purchase in his near future....

Also OP... look for a switch on the back of the onboard tach... sometimes there will be one that allows you to change from 4-6-8 - sounds to me like it is set for another engine...