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Thread: Fast Fred's Secrets of the OMC MOD50's Thread #1

  1. #491
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    Default Porosity?

    Hi John,

    I've never heard or seen such a thing, and have built dozens myself not including the untold numbers I worked on as a marine mechanic in the 70's. In it's original form (55 Triumph) it outstripped the very popular Merc500 and dominated the racing world. Is it possible Mercury lovers were just taking pot shots?

    Tim

  2. #492
    John (Taylor) Gabrowski
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    Default Now that is a vote of confidence.

    Tim: I have been and still am a Merc freak of the craziest variety. Coming from you with your Merc and OMC background well, that is confidence in OMC castings for people like me just getting in to them. Yes some people did put some notions in my ears but that is changing obviously. Its quite real that the OMC 45 2 cylinder racing engine is one way stronger motor than any Merc or Mariner 44 cube stock racer, that is why they put the 45SS into Formula E and 45SS tunnel boat racing right off. This OMC loop technology was superior to Mercs old style deflector/crossflow techologies that really didn't change much other than peripherals since the early 1950s.

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    Quote Originally Posted by Danny Pigott View Post
    Tim I can see what you mean.But why was the engine not built this way in the first place. An why are all inline motors built with the ex. on the right side.The Mark 58 merc. had in line wrist pins, they cause piston rattle. so merc off set them to stop this.
    Danny, the offset piston pin came into play because of the direct-reversing inline six (mk 75 and mk 78 engines ) aka 'dockbusters'.. These engines had no neutral and had a bi-directional starter. So to back up you cranked it up in reverse. With the center pins on the deflector pistons, the engine would rattle - customers were concerned. Carl was concerned. So they offset the pin to quiet things. The 58 & 78 used the same pistons.

    alex

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    Quote Originally Posted by John Taylor View Post
    How long are the diaphrams lasting with the present gasoline your using? What kind of gasoline in terms of brands, octanes etc? Would running aviation gasoline resolve the problem?
    John, the problem with "gasolines" now in most parts of the country is the introduction of ethanol. Without getting into all the technical crap too deeply, suffice it to say, it's un-stable $hit. Avgas on the other hand IS stable. The MilSpec says it's got to stay perfectly good in a 55 gal barrel for more than 10 years! Avgas, of the type you can find at most any little airport is of the 100 octane variety. It's referred to as 100LL, the LL being for low lead. It burns nicely, but you will see some deposit on your pistons or plugs tho not much. I always run it. However, I don't mix oil with it until I'm at the race site. Why? because I really don't know how it likes being mixed with TCW3.

    Alex

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    Sam Cullis Mark75H's Avatar
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    The storage spec for AV gas is 2 years

    I don't see any deposits on my plugs or pistons ... it stays mixed well with any oil. I often use gas mixed the previous summer in the spring the next year
    Since 1925, about 150 different racing outboards have been made.


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    Team Member 850cc racer's Avatar
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    hey guys quick question: i have a 56 cuber part number is 340899 i cant seem to find it on parts catalogs.. what would/should be the standard bore? it measure approx. 3.178 and it has one big oval exhaust port

    the other one i have 334474 measures 3.220 and has 2 exhaust ports

    any help appreciated

    850

  7. #497
    FFX-61
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    the oval port is newer, the oval exhaust port make of a more rounded power band. the split exhaust is the one, cuzz of the bridge it can be made bigger over all, you can incorporate the oval style in to the split port.

    standard bore is 3.187, 3.220 is a bit big for +.020 but small for +.030's

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    Also find a block without the idle bypass hole in front of the exhaust

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    okay, only that im going to use the block with the oval exhasut port, as the other block needs sleeving and 3 pistons, so i should be able to use 20 overs in the block that measures 3.178 app.

    also i was going to try Vertex pistons.. anyone used these before?

    thanks for the replys.. the block with the 2 piece exhaust port will be the one i build as a spare in the off season.. might even get some methanol burning in this one!!

  10. #500
    Team Member 850cc racer's Avatar
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    was just re-reading what fred posted and yeh it had +0.30 in it.. thats an approx measurement but wouldnt be that far out..

    what clearance do you run thare Fred?

    DW: ahh yes this one does have the idle relief hole too but much smaller then the motor i took off the boat, is this a real negative thing to have?

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