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Thread: Merc Direct Charge
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02-24-2010, 03:46 PM #46
I haven´t so far. But I do indeed consider it for my next rebuild.
There is a variant in Meier´s paper (No. 26 in Fig. 15) that seems to adress the same problem. Namely the gas stream(s) coming in with an upward direction, passing over the deflector and "short circuiting" to the exhaust.
Which one would be the way to go, I don´t know. Meier´s smooth curve or Lanpheer´s sharp edge/hook ?
On the small "auxiliary" ports shown and described in Lanpheer´s paper, I think they might be done if you use two-ringed semi key stone pistons. The locator pins/ring gaps on these are on the sides of the deflector with some little bias to the transfer side.
I did not have the pictures I thought I had. These pics of a 3 cyl. version (650XS or 700X ?) is probably from here or maybe from e-bay.
PL
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02-28-2010, 09:04 PM #47
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04-30-2019, 03:47 AM #48Screaming And Flying!
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old thread
but makes you wonder that Merc and OMC both stuck to their own piston design for all those years with barely a change.
The OMC deflector being convex to the inlet and the Merc concave. Anybody know why that was?
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04-30-2019, 05:22 PM #49
The OMC was cheap and reliable for a fishing motor. Made Charlie Strang very rich.
For the answer to the Merc piston, got to post #1 and re-read this entire thread.
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04-30-2019, 06:02 PM #50Screaming And Flying!
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04-30-2019, 06:28 PM #51
I thought your question was why OMC stuck with it
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04-30-2019, 06:46 PM #526000 RPM
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I remember testing the first DC 6-cyl Merc at OMC. Fuel flow was 6 gal/hr richer than optimum. We found out why when we leaned it out. It burned the deflector off the pistons. However, I don't recall fuel consumption being of particular interest in the late '60's/early '70"s. Gasoline was under $.30/gal at the time. It was all about HP.
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04-30-2019, 06:49 PM #53Screaming And Flying!
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04-30-2019, 06:52 PM #54
one is less expensive, the other makes more power.
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04-30-2019, 07:48 PM #55Screaming And Flying!
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04-30-2019, 08:10 PM #56Screaming And Flying!
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Something of interest, OMC style was close to the Chryslers. When Merc redesigned the Force 120 and triples with the new deflector and chamber as well as rods etc they had a clean drawing board and could have gone to the earlier inline designs but didn't.
Perhaps it's limiting by bore size and expansion shape of the deflector.Last edited by FMP; 04-30-2019 at 08:14 PM.
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05-01-2019, 06:04 PM #577000 RPM
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I ran both the 500s with the old crossflow design and the later dc 650s and 850s. The older design was more forgiving of mixture and timing errors. The dc motors were easier to hurt by tuning. I found myself very close to factory specs after a lot of testing. The 500s responded to careful timing and jetting but it was tedious work for a little gain. That being said it was usually worth the trouble.