SOHC 750-4 for the New Millenium

[Fire-medic]

When the Honda 750-4 SOHC was released in 1968, as a 1969 model, it set the standard for performance and that includes the engine design and the bike's braking equipment. The BSA Rocket III and Triumph Trident 3 cylinder 750's had been released a few months before, and good as they were, the Honda eclipsed them in-terms of its specifications. A disc brake! Whoever saw a disc brake on a street bike from the factory? The astute aficionado of things Italian will be able to claim, "well, what-about the MV Agusta? That had a disc brake!" Yes, a cable-operated disc brake!

If you're a British bike enthusiast, then you were really happy in the summer of 1968 with the release of the Triumph Trident and the BSA Rocket III. The 2-valve/cylinder OHV triples had one carburetor/cylinder, huge drum brakes, and body lines that screamed 'built to perform.' They were not-without controversy: the BSA Rocket III had Flash Gordon 'ray-gun'-style mufflers! These were almost universally-despised for their form, but their function couldn't be denied, owners who removed them and replaced them ended-up with less horsepower than stock. It seems the factory did a great job of engineering the exhaust.



You earn points if you can I.D. the very-famous person riding his personal Rocket III to the filming of a movie which became part-of one of the most popular and successful series in movie history.

BSA Rocket 3 (classic-british-motorcycles.com)

The SOHC Honda 750-4 was not-without some issues. Failure to pay-attention to chain maintenance could and did cause broken chains or chains which jumped-off the sprocket, often causing broken engine cases. Also, it was heavier than anything short of a Harley hog, and the British 750's were way-ahead of the Japanese in bike handling. Indeed, the Rickmans soon developed a brazed chro-moly frame kit for the Honda 750-4, which greatly-improved its handling, and made it into a proper cafe-racer. Yours-truly is the happy possessor of one, awaiting its turn in the queue.

This bike is something of a retro-mod, Keihin CR carbs, mag wheels, and more-displacement than stock. Japauto in France, a Paris Honda dealer well-known for its endurance racers featuring big Honda 750-4 engines, back in the day, at the Bol d'Or, which it won in 1969, 1972, and 1973 is the basis for this build. Look carefully at the jugs on the Japauto "750-4" which as you can see from the side cover insignia, has tipped its hat to what lies inside as it's re-named the 1000 Quatre VX. Dig the dual-disc front end with its ventilated rotors, a delirious fantasy for a rider back-then, unless you dialed-up Japauto. The otherwise stock appearance of the SOHC bike belies its true potential, much to the chagrin of those who might choose to challenge one on the street. A 'Q-ship.' The Long Blue Line: USS Big Horn – the Coast Guard’s “Q-Ship” « Coast Guard COAST GUARD COMPASS (dodlive.mil)

Japauto's engine work was well-received, and famous bike builders like Egli and Dresda used the Japauto big-bore components to make low-production bikes capable of for the time, astonishing performance both in a straight-line and through the curves. The Honda disc brake was such a game-changer that it was homologated for use on other manufacturers' bikes in the interests of safety and parity in racing.

http://earlysuperbike.com/earlysuperbikereportage/japauto.aspx

 

[Radioguylogs]

Fire-medic:

I enjoyed reading your interesting and informative post, like many before.

BTW, Rider is George Lazenby ; Agent 007.

 

[Fire-medic]

Yes that is the rider.

 

[Jerry Klay]

1st bike was a Honda CL175... next step was a 1974 (pretty sure) 750 Honda. Wow! What an experience that was.. 68 HP! Holy Crap!. I did put K&N individual filters on it. Never ran worth a crap. Original air box ran great every day. Never did the velocity stacks, didn't have the extra $$ back then.

Great Bike..

 

[tinman22]

local speed shop picked this up at auction in mi.

I tried to get him off of it. He won't sell yet...yet.

 

[Fire-medic]

Looks like a lot of RC Engineering stuff on it. And notice the steering damper, a subject of discussion on the forum recently. Terry Vance and Byron Hines worked for Russ Collins before going out on their own.

Looks like the induction system uses Lake Fuel Injectors besides the Roots-type vane supercharger, 'blow-thru' style. Like the Shelby Paxton supercharged V8's had in the 1960's. The entire carburetion system was encased inside a plenum box. The supercharger blew to the box.

Russ Collins developed a magneto system for the SOHC Honda 750 so he could burn the blended fuel he was running, with whatever induction system. Then he added engines: one, two,... or, three.

 

[tinman22]

webber carb hiding behind the oil tank. some rc stuff. bike really isn't finished. tank is shot and nothing is hooked up. as it sits its more of a decoration.

old guy died while working on it in his basement. apperently he had been at it for several years.

some old stuff some new. but certainly should be in my shop.

 

[Fire-medic]

So the vertical gold band assembly in-front of the jugs is just a manifold/plenum? Is it configured as a "log-style?" Or does it have individual spider tunnels headed to each intake cylinder head port?



L to R: Ford, Solex, Weber



Lycoming aviation spider manifold (L); Continental (R)

 

[tinman22]

common plenum from the charger to the boots is three pieces with the gold piece in the middle.

I thought i had a shot of the other side. It came with a vintage set of wheelie bars.

reciepts for an ape ultra crank,carrillo rods, varey large big bore,

 

[Fire-medic]

JapAuto, the Paris France Honda endurance/roadracing dealership, tried the 1,000cc builds, but found better reliability dialing-back the displacement a bit (an earlier post in this thread).

 

[tinman22]

there are a couple of companies that go really big.

I have seen them as big as 1300+ depending on bore 1200 ish is pretty common.

Its a money pit for sure. But arent they all to some level.

r.p.e. racing has a couple of youtube vids. 145hp for the 1200 and a 1340 version

 

[user 16790]

that's the true meaning of drilled discs

 

[desert_max]

Now THAT is a Super Sport and a serious piece of old-school engineering. Wonder what he did with the bottom end - the most important part?

 

[tinman22]

reciepts for carrillo rods and an ape ultra crank came with it.
not sure what else is in there.