Topic: Modifying the SOHC4 motor, is this possible??? Reverse facing head.

[Soos]

Don't ask.
It just came to me while reading another post....



Why are the carbs on the motor facing the rider, but the exhaust exits away from the rider and has to bend 180 degrees to exit at the back of the bike behind the rider?
 


Why aren't carbs facing INTO the wind(in front of the motor) and the exhaust coming out the back of the motor?

You would have shorter exhausts(less weight) and the possibility of taking advantage of the carbs in front of the bike. And the front might look funny, but the exhaust could be done well IMO.


Could a stocker motor work setup like this??
Would a new camshaft gear need made with appropriate timing for the mount holes?

Am I just nutz?



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l8r

[mkramer1121]

cycle world did a write up on this....just for why they don't manufacture bikes this way, I'll see if I can find the article and scan it...

[FunJimmy]

Cannondale produced dirtbikes with that configuration.

FJ

[mlinder]

MV Augusta had that design when they were first coming back to the market with the f4. They went back to standard design.

One problem will be carbs and an airbox sticking out way in front of the frame, perfect for the dront end to hit a lot. Remember, carbs and airbox are like a foot long or more. Pipes come out less than half that.

[cafe750]

One of the biggest reasons for putting the exhaust on the front of the motor, especially in an air-cooled application, is the exhaust valve and seat need good cool air passing over then to properly dissapate heat. Where better than on the front of the motor?Besides, four exhaust pipes look niftier than four carbies poking out the front, I think.

[mlinder]

Also, the exhaust and intake ports are very different. I don't think they would work well reversed. Would have to do a complete redesign of the ports. And valves. Valves are different sizes. Exhaust valve is smaller by a fair bit, IIRC.
Also the cam. You'd need one made that is the reverse of the stock one.

Unless you just turn the head around.. which would be a total #$%* and require a boat-load of fabrication and modification...

[Soos]

Unless you just turn the head around.. which would be a total #$%* and require a boat-load of fabrication and modification...

Thats what I was thinking.
I'm really good at removal of metal, but a welder I am not.
Machining a few new passages, o-ring spot faces, or new bolt holes is not a problem...as long as no real damage is done, IE the head is functional when done and will not self destruct in like 5 miles.
I would even consider external plumbing for the oil lines if I attempt this, just to avoid oil passage mis-alignment.

l8r

[Soos]

I think 4 carbs with ram tunnels on them, say 3-4 inches long....
Or if not that, 1 oval filter per 2 carbs.
Mabey 4 tapered cone individual pod filters...
Airbox?? No I would (if anything) make a SCOOP! force some air into those carbs.

And the carb setup(internally) don't know if it would work well with this style of carbs or not....
Mabey something like a V-max set of carbs? Aren't they forced air systems on those?

Yeah i'm sure this would entail an insane setup and many mods to make run... but who has their head on backwards?
I've been told mine is many an occasion.
Mabey my bike should match?
(another thing on the crazy project list to measure up....)



l8r

[Soos]

Also, the exhaust and intake ports are very different. I don't think they would work well reversed. Would have to do a complete redesign of the ports. And valves. Valves are different sizes. Exhaust valve is smaller by a fair bit, IIRC.
Also the cam. You'd need one made that is the reverse of the stock one.

Unless you just turn the head around.. which would be a total #$%* and require a boat-load of fabrication and modification...

If I turn the head around, is the firing order going to make the motor spin in reverse?

[MRieck]

Elmer Trett (RIP) did it.

[cafe750]

Also, the exhaust and intake ports are very different. I don't think they would work well reversed. Would have to do a complete redesign of the ports. And valves. Valves are different sizes. Exhaust valve is smaller by a fair bit, IIRC.
Also the cam. You'd need one made that is the reverse of the stock one.

Unless you just turn the head around.. which would be a total #$%* and require a boat-load of fabrication and modification...

If I turn the head around, is the firing order going to make the motor spin in reverse?

Not if you flip the cam around, or have one reverse ground...

[mlinder]

First off, I don't think you can 'turn the head' around. The sohc head is nowhere near front-to-back symetrical enough to get #$%* to line up properly.
I thought about whether it would have to run backwards as well, but can't make up my mind. On the surface of the subject, it would seem to make sense, but as I build the engine in my head, it seems plausible that you could make it run forward. This may still require a reversed cam though.... I have to think about it some more.

[jonbuoy]

Ever tried to breathe while sticking your head out of a car window? 

[Maxacceleration]

Elmer Trett (RIP) did it.

Didn't Russ Collins try it also some 30 years ago?

[TwoTired]

Careful with "ram air" on the stock carbs.

If you pressurize the carb throats, it pushes fuel (or air) BACKWARDS through the fuel jets.  This is because the float bowl area is vented to atmospheric pressure (which normally pushes the fuel into the vacuum of the carb throat. )  You can ram air the carb vents too.  But, it has to be the same pressure as the carb inlet, and not subject to the vacuum that can be created there (particularly with filters ahead of the carbs).  Of course, the ram air pressure changes with head winds and vehicle speed.  So, the vent and inlet have to be balanced or equal in pressure under all conditions.

Exhausts get hot.  Putting them in the breeze removes a lot of heat to the passing air.  Putting them in the calm, stagnating air behind the head, allows any air there to just rise in temperature, without getting rapidly replaced with cooler air.  This area is also normally close to the rider's "package".  So, this approach could also be an aid to birth control. 

Cheers,

[Soos]

Elmer Trett (RIP) did it.

http://www.youtube.com/watch?v=S9_kn7cRIWQ

THATS WICKED!
What DOHC inline 4 is that thing???


l8r

[mlinder]

You  might consider trying to turn the jugs and head around together. That may be easier than trying to get the head to fit on backwards.

[Soos]

And to answer myself....

On Sept. 5, 1983, Trett made what was arguably the most significant pass of his career when he rode his nitro-burning Kawasaki to a 7.16, 201.30, recording the first 200-mph motorcycle run.

Yeah, I think facing the jugs backwards might be needed actually, the cam chain tensioner needs to be on the slack side of the chain.
no.... it would have to stay, the motor would still turn the same direction, keeping the slack side on the same side of the motor....
The jugs could be turned, but would need machined to accept the tensioner adjustment bolt and nut on the other side.



This is fascinating.



l8r

[MRieck]

Elmer Trett (RIP) did it.

http://www.youtube.com/watch?v=S9_kn7cRIWQ

THATS WICKED!
What DOHC inline 4 is that thing???


l8r

That looks like an old Z head. Elmer's engine was all billet (except for the cylinders which were aftermarket) in the end.

[paulages]

first of all...the engine can't possibly run backwards. final drive chain direction aside (i suppose one could make an idler gear that would reverse the direction of the final drive), the cam tensioner, starter motor, timing advance, kick starter, etc. all need the engine to turn in the right direction.

if you flip the head around, you would have to have a reverse ground cam. no matter what, vacuum is produced when the piston is traveling down, etc. without changing the crank timing as well, the firing order- or piston sequence at least- will stay the same. if the cam was symmetrical in regards to the tach gear and chain sprocket mount, you could just flip it around. i don't think it would be all that hard otherwise, stud placement aside.

on that note: the cb750 studs are far from symmetrical as seen here:


the 550/650 look somewhat symmetrical though... i'm assuming Soos is talking about a 650 as that's his passion:

mill out the grooves for the cam tensioner and it might work?

[ghost]

interesting idea. but wouldn't the cam rotate in the wrong direction if you simply rotated the head. if you need some welding done pm me, i'm sure arrangements can be made

[MRieck]

interesting idea. but wouldn't the cam rotate in the wrong direction if you simply rotated the head. if you need some welding done pm me, I'm sure arrangements can be made

The cam will always rotate in the same direction. All you have basically done is change the orientation of the intake/exhaust valves. Paul is right....you need reverse cams to open and close the valves in the correct sequence. Build a billet head and all problems with stud placement etc are solved.

[ghost]

interesting idea. but wouldn't the cam rotate in the wrong direction if you simply rotated the head. if you need some welding done pm me, I'm sure arrangements can be made

The cam will always rotate in the same direction. All you have basically done is change the orientation of the intake/exhaust valves. Paul is right....you need reverse cams to open and close the valves in the correct sequence. Build a billet head and all problems with stud placement etc are solved.

    i ment relative to the orientation. but i think we're all on the same track

[paulages]

interesting idea. but wouldn't the cam rotate in the wrong direction if you simply rotated the head. if you need some welding done pm me, I'm sure arrangements can be made

The cam will always rotate in the same direction. All you have basically done is change the orientation of the intake/exhaust valves. Paul is right....you need reverse cams to open and close the valves in the correct sequence. Build a billet head and all problems with stud placement etc are solved.

just checked a 550 head/cylinders, and the studs are not symmetrical front to rear. mike's right: either go billet, or weld shut the original stud holes and re-drill.

[754]

You wood be OK on a 754 if you had a raised port head...


 Without that or tipping the motor the intakes would be running uphill ...hard to find carbs to angle THAT way...