OMC 3 cylinder "loopers"

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amuller
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OMC 3 cylinder "loopers"

Postby amuller » Thu Oct 12, 2017 4:24 pm

Can anybody point me to a rundown of the evolution of these motors and the differences between them? I've had a look at a 60 hp, 1971, which appears to be set up like my '72 V4. Electric/hydraulic gearcase, mounts on slip-in brackets, complex ignition system with both electronic box and mechanical distributor, points, etc. There is not much negative said about this line of motors anywhere I've looked. I see there is a C model and an E model taking different prop shafts. Are they all 20" or was there a short (15") version also?

Thanks.

outbdnut2
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Re: OMC 3 cylinder "loopers"

Postby outbdnut2 » Thu Oct 12, 2017 7:26 pm

I've towed a number of the early 3 cylinder models off my lake that had bad ignition boxes - this was back in the 1970s. One guy said he had replaced the ignition module 3 times in two years. I would think that any one of them today would have had these replaced with a good box by now.

The electric shift gears work fine as long as water stays out and the proper OMC gear oil is used.
Dave

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twostroke
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Re: OMC 3 cylinder "loopers"

Postby twostroke » Thu Oct 12, 2017 7:32 pm

Ditto. My folks had one when I was in high school.....and every time you looked at it cross-eyed, it ran on two cylinders and wanted a new CDI box. It was pretty good at turning mixed gas into noise, also.

Jim
I say "Pardon Me" a lot. I had a 20H with a toilet bowl, then raced open mod sleds. :D

fleetwin
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Re: OMC 3 cylinder "loopers"

Postby fleetwin » Thu Oct 12, 2017 7:44 pm

Yes, the 71 60hp has battery CD and the hydro-electric gearcase like your 85hp.
So, I would recommend looking for a mid 70s-mid 80s 3cylinder, which has the simpler/more reliable magCD ignition and the plain mechanical shift gearcase. 78 and later models are set up to accept the nice integral power trim/tilt unit as well. These three cylinder engines have a great balance between power and fuel economy, they are much lighter than the V4s as well...

FrankR
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Re: OMC 3 cylinder "loopers"

Postby FrankR » Thu Oct 12, 2017 8:12 pm

The 1970/71 60hp motors about drove me crazy until I found out they need L77JC4 spark plugs. They ran terrible with the surface gap plugs they came with. I'll bet at least half of those "defective" amplifiers were not bad at all, but were replaced under the "it's always the black box" mentality.

fleetwin
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Re: OMC 3 cylinder "loopers"

Postby fleetwin » Thu Oct 12, 2017 8:42 pm

FrankR wrote:The 1970/71 60hp motors about drove me crazy until I found out they need L77JC4 spark plugs. They ran terrible with the surface gap plugs they came with. I'll bet at least half of those "defective" amplifiers were not bad at all, but were replaced under the "it's always the black box" mentality.

That mentality is still popular today!

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Phil B
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Re: OMC 3 cylinder "loopers"

Postby Phil B » Thu Oct 12, 2017 9:21 pm

I seem to recall there were two different versions of the three cyl engines, one with 49 cubic inches and one version (maybe two?) with a 56ci block, and that some prefer the 49ci version (more durable, smoother idle?)

I always think it's funny when I read the article (in the "inner sanctum") about different configurations Mercury tried out and rejected early on (big twin, inline-3, V-4, V-6), and then Mercury later made and sold.....
[the Aerocraft & OMC boat guy; formerly "Silver Bay"]

amuller
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Re: OMC 3 cylinder "loopers"

Postby amuller » Thu Oct 12, 2017 9:41 pm

(I wrote this once before and the site ate it:)

I'm interested in this motor because it has the same hydro-electric gearcase and strange ignition system as my V4, and mounts with the same drop-in brackets, so it could be fairly trivial to change it out and the comparison would be interesting. And I've already struggled through learning these systems with much help here. Opinions of these 3-cylinder loopers seems generally high, with some criticism of idling and midrange power. The price is near-free and, assuming nobody in the past 45 years has forgotten to mix the oil, or run it with a bad impeller, it might be fine....

What's special about the L77JC4 plugs? Just curious, they are readily available.

I'm really convinced that big outboards need power tilt and preferably trim also. Tilting the V4 is not a relaxing way to end the day.

fleetwin
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Location: Rhode Island

Re: OMC 3 cylinder "loopers"

Postby fleetwin » Fri Oct 13, 2017 8:05 am

OK, understand now....
Like you say, you have experience with this set up now....
The 3cylinder engines have unique running qualities, you can not really compare them to other models in the line up. The do idle "differently", which some might interpret as a "bad idle". These engines are surely not going to have the mid range power of the V4s, but might outrun them at WOT in some cases. A lack of midrange power would only be a complaint of a boat that squats or is hard to plane off, but V4s would have the same struggles due to their extra weight. This series of 3cylinder engines does not have tilt shock absorbers, so it is relatively easy to tilt up, but don't let it drop on its own when you tilt it down.
The original plugs for these engines were "surface gap", they did tend to foul easily at lower speeds. The j gapped L77jc4 plugs solve this problem. The surface gap plug will outlast the j gap plugs if used for extended high speed running though, such as racing or a hydroplane.
I'm hoping the gear lube is clean and you have good spark on this engine....

FrankR
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Re: OMC 3 cylinder "loopers"

Postby FrankR » Fri Oct 13, 2017 8:50 am

The surface gap plugs do not have any extended tip at all, so they are ultimate "cold" plug. I guess one could say they have no heat range at all. Since they do not burn off the deposits, they rely on the very fast high voltage spark to fire them at all. The conventional gap L77JC4 has a very short tip, so they are still a very "cold" plug, while being more tolerant of spark conditions. In later years the L77JC4 was modified to QL77JC4, the Q meaning it has an inductive RF suppressor so it does not cause noise and static on your electronics.


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