Merc Direct Charge

[petlun]

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

[baldad45]

[powerabout]

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?

[Mark75H]

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.

[powerabout]

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.

OMC had that design before Charlie was there
They both went down their own roads very early re piston design

[Mark75H]

I thought your question was why OMC stuck with it

[Rotary John]

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.

[powerabout]

I thought your question was why OMC stuck with it

I was looking for the technical argument for either system

[Mark75H]

one is less expensive, the other makes more power.

[powerabout]

one is less expensive, the other makes more power.

I cant see where there is a cost advantage in either?
Merc piston is the cheapest to tool and the combustion chamber

[FMP]

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.

[2us70]

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.