Longboy's "BRATZ" Model Gas Engine.

[Longboy]

                                           "PREMIERING SOON"   

[b.lindsey]

I am sure it will be a good project Longboy. Don't happen to have a better picture of it do you. Hard to tell much from that one. 

Bill

[Longboy]

Of course I do Bill.....but I want to open up a new posting with a teaser photo of my latest! 

[crueby]

Of course I do Bill.....but I want to open up a new posting with a teaser photo of my latest! 

As long as we don't have to sit through the infomercial!!!   

[Longboy]

            .....I don't think anyone ever got more gray hairs during my presentations.

[Longboy]

   Twin cylinders, four cylinders....gotta be something in between. Coming back again from their forgettable intro in the automotive world in the 80-90's is the 3 cylinder engine. From Ford Fiesta and Mini Cooper as the latest offerings to Yamaha's biggest seller in large motorcycles, 3 cylinders are making headway in efficient, high output applications in small cars cutting the cost of driving. In the case of the BRATZ engine, it's a look back at historical means of power by 3 cyl. engines found in industrial and agricultural usage. After the single cylinder and excluding aviation radials, it is uncommon to find odd number cyl. engines being modeled.....let me show you my version!

[Longboy]

   BRATZ is the same design with some valvetrain changes as the BEST FRIEND engine. The crank is a heavier unit using .250in. throw pins in each pair of 1.75 in. dia. crank webs @ .50 in. height.



4 main bearings. Center brass and end Oilite bushings. Aluminum Parksy design cradle in black satin. Unit weighs just under 4 lbs.





10-32 set screws with blue Loctite hold the throw pins, upsized from #8's for a better grip in build progress.

[Longboy]

   A 6 in. long block receives some 1.125 in. bore DOM liners at a 2 in. bore spacing.



The block is relieved for the cam drive sprocket and the block hugger camshaft along its length to clear the lobes.

[Longboy]

   This is the lifter bar. Exhaust valves only. Brass guides are set screwed in. Bar screwed above camshaft into block.



   The lifters themselves are rivets found in the fastener bins over at ACE Hardware so I don't even bother making my own. The mushroom will be turned down to a smaller diameter to clear cam lobe set screws. A flat is milled on the mushroom dome to ride the cam lobe and the stem is drilled down into to take a piano wire push rod.

[Longboy]

   A 3/16 in. shaft with cam lobes of 3/8 in. CR. The drive is by MXL sprockets. Brass bearing on shaft end and a roller bearing in sprocket guard.



(Thats a funny looking brass lobe on there Longboy!  ) ..... I'll get to that next post.

[Longboy]

    A distributor at a right angle to camshaft is a change up from previous engines. Compact and close to block, its distributor cap is a 3/4 in. internal dia. PVC end cap.....



......while the rotor is Delrin, a #4-40 SS screw over a brass tab passes the coil voltage on to the spark plug leads.

[Longboy]

  The camshaft and lifter bar mounted to block.



Distributor just clears the lifter bar. Radiator fins relieved for the lifter guides.



The bevel gears are 24T at .5 modulus. Just the right scale! Knurled screws retain the distributor cap.

[simplyloco]

I'm really looking forward to seeing this thing running!
John

[Longboy]

   An intake valve block and manifold.



Delrin manifold has Traxxas carb on a pipe fitting angled out just enough for carb body to clear.



An O-ring around the valve guide makes the seal between the two pieces.

[Longboy]

   The head fining a tedious operation. By pattern to get around various holes and execution time. Eighteen rows @ two or three passes to get the depth. With shallow combustion chamber and a one inch height aluminum stock, the brass valve guides are near flush with the top of head.



On the exhaust side, a pair of ports are symmetrical for #2 & #3. but #1 had different ideas and went in another direction.....the black sheep of conformity.




Plenty of room in this chamber with a 1.125 bore. 10mm threads for CM-6 spark plugs and single ex. valve. The relief milled into the spark plug thread is for the intake port as the ports were above depth of combustion chamber. Tiered circles around chamber would be inner for cylinder liner seat and the outer tapered for the O-ring seal.