Merc Direct Charge

[petlun]

Herrman Meier designed the "Direct Charge" version of the cross flow scavenge system for Mercury in the late sixties.

The US patent number is 3 494 335 and the paper can be had as a pdf-file with a free of charge log in from www.freeepatentsonline.com.

The key feature is on the transfer side with the C-shaped piston deflector, the shape of the main transfer ports and the dividers/splitters in the transfer port covers/channels. The system reduced short circuiting of fresh gases to the exhaust (improved "retaining and trapping efficiency") compared to the conventional cross flows. And it could still be used within the compact cylinder to cylinder spacing of an ordinary cross flow.

The Direct Charge system was introduced on the new 66ci 4cyl Merc800 in 1969. It was also used on the 1250 and 1000 Super BP´s.

In 1970 the new 1350 and 1150 were Direct Charged as well as the new 33ci 2cyl Merc400. In 1972, the new 50ci 3cyl Merc650 was also a Direct Charge engine. All DC engines share the same 2 7/8"/2 9/16" bore to stroke combination, except the oddball short stroke 1000 Super BP.

In 1973 the "Power Port" was introduced on the 1500, 850 and 650 (which was still rated at 65hp though, perhaps in need of a bit more power to compete with OMC loopers ?). The PP was one of a few different booster port variants suggested as would be additions by Meier in the paper.

When the 4cyl 80hp Mercury was introduced in 69, it was considered (at least here) to be a compact, sleek, rather lightweight and VERY fuel efficient engine. Competition at the time in this hp-range was OMC V-4´s and Chryslers.

Herrman Meier had a background mainly with European motor cycle manufacturers and their racing efforts such as Ariel of UK in the late fifties to early sixties, Lube of Spain in the early sixties and Royal Enfield of UK thereafter. Meier is mentioned by Gordon Jennings in his "Two-Stroke Tuners Handbook" (pg 120 in my copy) for a transfer port solution he came up with for the Royal Enfield 250cc GP racer.

In the mid seventies Meier was hired by Volvo Penta who recently had accuired the remaining Swedish outboard production (Archimedes/Penta/Monark/Crescent). With Volvo he was responsible for the design of the powerheads for a series of new small engines, the P-series; ranging from 7 to 20 hp. Despite a rather long history of loop charged two strokes here (in motorcycles and mopeds, outboard engines as well as Saab car engines up to 1966!), Meier did nevertheless convince Volvo to use a modified cross flow design for their new engines. Christened the "T-Loop" charge, the system was actually much like taking the Mercury Direct Charge system one step further. The US patent is 4 174 685.

Seventy pre-production engines were made for field tests, spread to dealers and selected customers in Sweden and W. Germany, with good results. However, mainly in fear of the "Japanese Invasion", Volvo pulled the plug and stopped all of their outboard production in 1979.

Peter L.

[mk30h]

very good summary Peter. I remeber when the merc 800 was introduced, I loved the look of that engine with the red stripe.

Question the merc 650 4cly of 1969 was 62 cu, while the 800 at 66 cu produced 80 hp. Was the 62 cu underrated or was the 800 overrated? Or did DC really produce 15 more hp with only a 4 cu increase? Did it really produce that much of an increase over the cross flow 65 hp?

[Mark75H]

Thanks Peter, that was great!

The 62ci 4 is a dog. Internally it is based on the old 93 ci 110. The jump from 65 to 80 is almost the same jump from 110 to 135. Direct Charge was not the only difference. Like the 135, the 80 had 10 reeds per cylinder ... the 65 like the 110 only had 4 per. I bet the 80 had exhaust like the 135 too.

[bearclaw]

Mark75H, how would a '68 1000 compare in this group? I had a chance to buy a nice one, short shaft, recently for next to nothing. Just to play around with it, I was trying to figure out what to do with it or what it would do performance wise.

[Mark75H]

The '68 1000 is pretty much the same 89ci motor as it was back when it came out in '62, just with some updates like solid state ignition. Its a lot more motor in every way than the 80 or 85, but no match for its 99ci sisters.

A solid workhorse, but nothing special

[mk30h]

Thanks Sam
Your explantion explained a lot of issues that I had wondered about over the years. Makes sense.

I wonder did Merc have a prototype 800 with the new reed design of the Twister or the 650 XS? Would have seem to be a logical extension, but I guess there was no class advantage at the time for such a departure.

[Raceman]

Looks like I blew it on this one. I'd have bet the farm that the '69 800 was the old crossflow, BUT I talked to my old retired Merc buddy that remembers EVERYTHING from late 50's through '70's and he said that the '69 Merc 800's were DEFINATELY direct charge. Glad I didn't have a farm to bet.

[ironlake2]

This is great all this discussion. Now am I correct in thinking then that the 1st direct charge was like 75h,s photo without the pistion port and then later the port was added. Would this be the reason the 80 increased to 85 hp.

[Mark75H]

I think you are correct

[CrayzKirk]

I can speak from fairly recent experience: An 1100 is no match for a 1350. With the same boat and load, a 7 mph increase in top end and very noticable increase in power. A 1000 of similar vintage is a nice piece of history however there is no comparison. It's like comparing a 1350 to a 135 v6 IMO.

Kirk S.

[mk30h]

Sam,
How would a 66 cu. 6cly Merc 700 compare stacked up against a 4 cly Merc 650 60 or 62 cu, a 3 cly Merc 650 49cu or finally the direct charge 4cly 800 66 cu?
I know there is a 10 year difference between the 700 and 800 but I thought the cubes are similar and the 700 might rev a bit higher.
Steve

[Mark75H]

Too many variables. Some boats will like one, others another ... prop selection would probably mean more than anything else.

[Mark75H]

Herrnan Meier designed the "Direct Charge" version of the cross flow scavenge system for Mercury in the late sixties.

The US patent number is 3 494 335 and the paper can be had as a pdf-file with a free of charge log in from www.freeepatentsonline.com.

The key feature is on the transfer side with the C-shaped pistin deflector, the shape of the main transfer ports and the dividers/splitters in the transfer port covers/channels. The system reduced short circuiting of fresh gases to the exhaust (improved "retaining and trapping efficiency") compared to the conventional cross flows. And it could still be used within the compact cylinder to cylinder spacing of an ordinary cross flow.

I just took the time to look this up ... that patent specifically applies to the split intake stream and uses a W shaped deflector that Merc did not use. O.F. Christner set up a looper design using Merc's regular cylinder spacing around 1962, so it was behind on getting an advanced porting "within the compact cylinder to cylinder spacing of an ordinary cross flow"

[petlun]

I agree on that the "patent specifically applies to the split intake stream". (And some related features for that matter.)

However I am not sure what you mean by saing it "uses a W shaped deflector that Merc did not use".

I guess you refer to the deflector style shown in fig. 10 and 11 in the paper, which as far as I know never was used, at least not by Mercury. And so was not the variants shown in fig. 4, 5, 12, 13, 14 and 15 either.

But the figures 1, 2, 3, 6, 7, 8 and 9 shows exactly (on a sketch level of course) how it went into production, marketed as the Direct Charge system.

Number 18 in fig. 6 and 7 shows the Power Port booster port version (although with a somewhat deep and narrow duct in fig. 7) and number 20 in fig. 8 and 9 shows the booster ports close to the exhaust ports, as used in the 700X (right?) and maybe a few T II´s before that. In fig. 3 you find the transfer channel divider as it was cast into the transfer covers of the ordinary DC engines. And the piston deflector with its C or "single eyebrow" shape, is shown in fig. 1, 2, 6, 7, 8 and 9.

The paper says the features "distinguish the invention from the commercially feasible engines of the past". The system was far from unique in its close cylinder to cylinder spacing. But it of course had to be done in a production friendly way, possible to mass produce at limited costs, and one that could also be easily packed within the limits of Mercury´s existing line of engines.

For instance, the transfer ports could be done in production with an end mill cutter that was applied at an angle, about as simple as drilling out the ports in an ordinary cross flow. (Mercury actually took a patent also on the transfer port machining method, see 3 542 000 !)

I think the Direct Charge system should be seen just as an attemt to improve on the ordinary cross flow system. It pretty much retained the advantages of the ordinary cross flows, like good idle and low speed characteristics and low manufacturing costs, but in reality still was a bit short on power and efficiency potential compared to a loop charged engine.


It would have been legal to post the patent paper here as it comes from an "open" source, wouldn´t it? Anyway I tried to do so with my earlier post, but with no success. My posting skills are not what they should be. (Probably I should learn and try the Tinypic route to see if that helps.)

Peter L

[Mike Davis]

Very fascinating read . Thx. guys.