TOPIC: OMC looper tripple differences 55hp - 75hp ?

I'm short on knowledge about the OMC tripple loopers. I'm hoping someone here can give me some info on the differences between the 1968-69 Triumph 55hp and the later 70-75hp loopers. I hope Scott Stewart chimes in, as I bet he knows. I have seen old OMC advertisements for high compression heads for the tripples - could this be the difference? Port timing?

What can be done to the 55 to wring out more power? How well do the tripples respond to mods?

Thanks

Bruce

Thanks

The 68 / 69 ----55 HP had 2 intake ports.

---

The 70 / 71

---

60 HP had 3 intake ports ( better scavenging )

---

the 72 / 73---65 HP and up also had a different exhaust manifold.

---

The 74 ---- 70 HP had a different cylinder head.

Thanks Professor! I've located a 1969 Triumph shorty that I want. I'm waiting for the owner to give me some compression numbers. I'm guessing that the head and exhaust manifold would swap over - but of course I don't really know. I had no idea that the first generation engines had just 2 ports - wow. Of course they were pioneering the the design.

Thanks

The heads will swap out.

---

The 72 exhaust manifold will not fit on the earlier blocks , not a chance !!

---

The early trouble some / battery CD ignition may not fit on the newer 72 block that had the " magflash ignition ".

---

The early motors all had thin wall/ skirt pistons and many cracked.The result would be a hole in the block / crankcase.

---

So if you are going to run one hard you need to fit the newer thick skirt pistons. They are / were a good performing motor at the time.

Bruce,

As the Prof said, the early 55s were kinda the odd ducklings of the lot. There were a lot of small, refining changes done in the 30 odd years they built that configuration. In my opinion, they finally got it "right" by the late 1970s when they had the heavier pistons, beefier rods, better ignition, better carbs, better lower unit.

Fortunately, there is a fair bit of compatibility between years and some retro-upgrades are possible. The heavier rods and pistons can be used in earlier models, carbs can be swapped around to experiment, and some folks have retrofitted CD ignitions in place of the earlier battery fired ignitions.

I've got a set of 1970-71 60hp carbs here if you're interested...

- Scott

I do believe the later (up to 1985 ) 75 HP powerhead will fit inside the 68 / 69 covers.

---

The controls get interesting.

---

68 thru 71 had the black plug

---

72 had the yellow plug

---

73 and later had the red plug.

---

If you know wiring it can be done.

Thanks again guys. I'm still waiting to hear back from the seller of the Triumph shorty. He was supposed to call me 2 days ago & needed the $ in a bad way. Who knows, maybe it does indeed have a few extra holes in the crank case.....

I mainly want it because it's a shorty, & they are very hard to come by out here - and the bring top $. I know of some 75 powerheads that need a little TLC, so a transplant would make the most sense. I'm not going to race or anything, just want some options apart from the V4s that I'm always finding.

Bruce

Short shaft motors 50 HP and up are indeed harder to come by.

---

Have a few triples scattered about in my shop.----Also a 66 ---100 HP Johnson short shaft.

Well,

I ended up with the '69 Triumph Shorty,with a boat attached. I brought my own trailer, I had to drive clear over to Carson City Nevada to get the thing, which is a 250 mile trip, one way. Trailer lights failed & I got pulled over, but the cop was a nice guy & let me drive to the next town for temporary lights. 25 degrees & out in the middle of nowhere working on wiring I thought to myself, what the hell am I doing here....I'm getting too old for this crap. Fortunately, I have a good buddy who lives in Reno, I got to visit he and his wife for one night. The motor was attached to a Reinell runabout (no fins) and because it was a Nevada boat, the hardware was excellent. All of the Chrome will be transplanted on to my Reinell Jetflite. That is really why I wanted the boat & motor.

The engine is indeed a 1969 shorty, compression 120 on each hole. Top sparkplug hole stripped 1/2 way. I found a 1975 75hp head for cheap, so I'm wanting to bolt it on. All the wiring is toast, the CDI pack is gone. Decent stainless cup propeller, a chunk out of the skeg, oil in LU not milky.

So, I'm wondering - will this thing fly apart if I run it with the newer head? Can I run it a full tilt as lons as I keep the RPM below rated max? I'm not going to race it, it's going on a family classic. If the pistons & rods are really a serious problem, then maybe a powerhead swap is best.

All advice welcomed. Thanks again,

Bruce

Helicoil can be installed without removing the head.---The early ones did have thin wall piston skirts !

---

There were many failures !

---

They tried various mods to beef up the skirt ( 72 / 73 / 74 )and in the end just went with a thick wall skirt.--No more problems with them.Your decision on what to do with it.

Understood...

I have the Save-a-thread tools and inserts, and I may just fix the #1 hole & call it good. I bought a nice 75 HP cylinder head for 15 bucks & had just intended to replace the head for a little more poop. But, seeing as this engine only has 2 ports and won't accept the later exhaust plates, I probably will just find a fixable 70/75 power head & use that on the shorty tower & lower unit. This has the large hydro electric L/U which I've always felt were pretty reliable. It's in good shape, and since this motor won't be used for racing, I'd imagine that it will be fine. But, maybe not??

Bruce

The hydro-electric shift is indeed a very reliable unit.

---

Often messed up by water in the lower unit and careless wrenches.