Will Sgarlat

I have a Madam X catamaran that was powered by an OPS 7.5cc inboard marine. The boat was awesome for sport running until two years into it, part of a cracked crankshaft bearing went up into the combustion chamber and kablooie...no more fun in the sun.

I bought the engine and pipe NIB for a hundred bucks when a local hobby shop was on its downward spiral. New parts and labor to get the engine back to running condition will cost perhaps 50 bucks more than a new K&B 7.5 cc, and a bunch more than I originally paid for the OPS.

The OPS was a mighty engine in its day. It was easy to start and well-mannered from slow running to near flying. I'd like the OPS to work again, but money is a factor and I'm not competing with the boat.

Does anyone have any glowing reports about their K&B 7.5 inboard?
Would the difference in performance between the two engines be all that noticeable?
Would the tuned pipe from the OPS work well with the K&B?
Thanks,
Will

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Will,

You should e-mail a member named Ron Olson. I think he was selling a 7.5 OPS new for cheap.

Will Sgarlat

Thanks Bigdaddy - Ron sold the engine the same day I wrote to him! Dang!!

Ron Olson

My Feedback: (1)

Sorry about that! About your other questions though. The older K&B has seemed to be a more reliable motor than their later ones. The newer version had problems with the carb falling apart and some of their machine work wasn't too good. The sleeve was not at a 90 degree angle to the crank and a lot of motors blew up the first time that they were fired! K&B was giving lame excuses like "maybe your prop is out of balance" so that they wouldn't have to cover the warantee.
The OPS pipe will work fine with the K&B or any other 7.5 motor. It is a popular pipe, I have one that I tried on my K-45 with good results.

Will Sgarlat

Ron, Thanks for the reply. That is not a "glowing" report on the new K&B 7.5 inboard. I think I'll hold off until a better opportunity knocks (once!).
My K&B 3.5 outboard with Octura 3-blade on a wooden Dumas Sprint just shrieks! I mean what a sound when the boat breaks free and dances on the last little bit of the sponsons! This engine is the newer one with the increased bore to the front rotor intake, and I would recommend one to a friend. I hope it wasn't just luck to get such a gem of an engine.
I'm the only known nitro speed boater in this neck of the woods and I don't get new info outside RC Boat Modeler. I'm so glad to have found you guys at this site!!

AltimaT

My Feedback: (4)

I had the old full circle crank 7.5 in a Sorcerer and it was bulletproof for many years. I also had a K&B .82 that grenaded 10 seconds after it was first fired. I'd get an OS for the quality, reliability, and the excellent carburetor. It may be down a little on power compared to some european engines but it will run well.

ggrc

my 7.5 K&B ran 80mph for three strong years, I have no complaints witht them, just make sure there is an RPM Rod in it and go balls out, thats what I always say. In case anyone was wondering, yes, I do use the O.S. backplate and Carberator on it.

sanecrazy1

My Feedback: (1)

I know this is reviving an old post but could you tell me who made the Madam x boat you had or still have as I have just bought one myself