HAWK 40 A 6.5~~ GLOW PLUGENGINE

by Australian reader G. Punter

Part I

THE HAWK 40 has been developed over the past fouryears and so far four engines have been made. Eachengine is slightly different from the others and takesabout 150 hours to make - this does not include themaking of the dies for casting. The first engine tookover four hundred hours from designing to workingengine.

SpecificationsEngine Type - Overhead valve four stroke.Bore - 7/8 in. Stroke - 1 l/16 in. Capacity - 6.5cc.Weight - 15ozs with oil tank, 14ozs without.Plug - Glow, any long reach without idle bar, (Couldbe adapted to spark).Oil - Castro1 M. Fuel - Shell A Methanol.Propellers - 10 x 4, 12 x 4.Carburettor - From O.S. 15.

28B

I

\

28A/

31/

32

30

4 - -

5 - -

2B 2B

1 5 10A

9

138/

1' 11 IiA

1390 MODEL ENGINEER 21 NOVEMBER 1980

View shwng back ofcrankcase with Pourings p o u t Plate removed

The Authors Hawk 40 engine

CrankcaseThe crankcase is a diecast light alloy part. It could

probably be made as a sand casting, but at the time Iwanted to experiment with this aspect of casting. Thedie started of as a block of mild steel 4 in. x 4 in. x1 1/4 in. and the crankcase was machined out in thenegative - plates were then bolted to the back, frontand top. These plates hold the mould together whencasting takes place. The main block was then cut upusing a piercing saw, each cut enabling a part of the

C R A N K C A S E

M0Ul n.

mould to be removed from the finished casting. Apouring tube was made up and likewise split down themiddle to enable it also to be removed - this tube wasattached to the split plate which was bolted on to the

Top plate removedPiece A lifts out at 45%eng,ne bearers8remams aftwhed to

back of the mould. Before casting, all rough edgeswere removed and the inside of the mould polished. Acoating of black from a candle flame was then appliedand the mould assembled - all holes and saw slitsbeing covered with metal strips to prevent the moltenmetal from escaping. Before any metal was cast, I didtry a casting using candle wax as a material - thisproved that the finished casting could be removedfrom the mould!

Another view of the completed Hawk 40.

The engine was designed so that the camshaft wouldrun in small ballraces, but on later engines both plainbearings and needle rollers have been used withsuccess. The early engines used the oil drain hole as areturn to the oil tank but later engines have used amodified backplate for the oil return and the oil drainhole is now blocked off with a4 BA screw. This shouldensure that some oil will be retained in the crankcase.When machining has been completed some hand workmay be needed to blend the area between the upperand lower crankcase to clear the connecting rod. Theballrace used came from Mr Whiston and was of theshouldered type. Plain bearings could be used but theballrace does help to reduce friction and also allows oilto flow freely to the gear case. The gear case was alsodiecast but could be made as a sand casting as analternative. The bearings are a press fit into the case.There is a space left between the two bearings so thatoil may collect and act as a reserve supply to the shaft.

CrankshaftI have used many methods of producing the crank-

shaft - all have been successful but some have takenlonger than others to produce. Methods used havebeen: turned from solid including the crank pin (thistakes many hours). Turned shaft and disc and pressedin pin was the second method used and lastly acompletely fabricated unit with shaft and disc silversoldered together and the crank pin pressed in. Loctiteis used both on the press fits and on the end stop screwthread - the latter have to be done on assembly. Thecrank pin is heat treated after all machining has beencompleted and before being pressed into the disc.

Continued

i0 INCL TAPER1.0

OIL HPLE CRANKSHAFT

*0625&a

ATCH CRANKWEB.

END STOP CRANK PIN

012 011PRESS FIT CRANK 8 PIN

CRANKSHAFT : steel

MODEL ENGINEER 21 NOVEMBER 1980 1393

HAWK 40 A 6.5 cc GLOW PLUG ENGINESUITABLE FOR AERO OR MARINE USE

by Australian reader G. Punter

Part II

Piston UnitBoth the piston and connecting rod are made from

Dural. Check the width of the piston rings used beforecutting the slots. The gudgeon pin is made from silversteel and is hardened and tempered and has bronze orDural pads on each end. A small hole could be drilledin the end of one of the pads to allow the air to escapewhen they are pressed in. Likewise oil holes could bedrilled in each end of the connecting rod.

Cylinder HeadThis part is machined from Dural stock bar. Each

head on each engine has been slightly different. Thefirst engine used a down-draught intake port and briefdetails of this are given on drawing No. 12. This typeof head, while being harder to make, does give a betterintake angle for the gas and does promote turbulence.The head shown on drawing no. 6 works well but maynot have quite as many revs as that on drawing no. 12.Various fin arrangements have been tried and all haveworked (photographs may show this). The undersideof the combustion chamber should have all sharp

/.1675b 6P I S T O N D U R A L

32

30

M A C H I N E G R O O V E S T O S U I T P I S T O N R I N G S

AO625

yx25u

From Page 1393

28A/

I

8 G U D G E O N P I N : S/S 9 P A D : B R O N Z E o r D U R A L7 f f

P I S T O N U N I T (X2)__

31/

Both ends ofco. rod couldb e b u s h e d i nw h i c h ,coseo p e n llttle e n dout to .250 bigend to .312$

m a k e sutobleb u s h e s

1510 MODEL ENGINEER 19 DECEMBER 1980

M A I N B E A R I N G SB r o n z e

.255

2BA---1

IO I L P I P E

II 2A

I 0I

IA

I i-CI

S E C T I O N C - C

2BA FOR OILP I P E

.500FROM 8

2 H O L E S .468wPC Rod.

A L L H O L E S 6BA C L E A R

GEARCASE : l o f f a l u m i n i u m(X2)

edges removed - I use a Dremel tool for this and find The valve guides are made from cast iron and arethat it is just the job. The exhaust port may be of two screwed into the cylinder head using a 3/8 in. x 40Tsizes depending on the type of exhaust pipe fitting thread. The valves are made from silver steel and use aused, these are given on drawing nos. 8 and 8B. small spring collet to retain the valve spring collar.

/ x D R I L L 8 T A PF I N S E S P A C E S xx40

REl.IEVE S I D E O F H E A D

C Y L I N D E R H E A D : loff a l u m i n i u m(X2)

MODEL ENGINEER 19 DECEMBER 1980 1511

FT- FINS AND SPACE-0625 EQUAL SIZE.

.12

PRESS FIT LINER INTO BARREL

3

i-01.1255 CYLINDER BARREL DURAL

1.75"

TWO HOLES&125

CYLINDER LINERCAST IRON

QUARTER SECTIoNS ON CENTRE LINES -663C Y L I N D E R U N I T : c.i. a l u m i n i u m (X21

Cylinder Barrel and LinerThe cylinder barrel is made from Dural stock bar. already well protected). The cylinder liner is machined

The fins could be made thinner and more of them but from cast iron and is made a press fit into the cylindercare will be needed. On some engines I have opened barrel. I lap the cylinder liners with a copper lap andout the push rod holes to 3/16 in. dia. and inserted feel that this is a very essential part of the procedure.short aluminium tubes - this looks good and it does Note: A 3/4 in. dia. bore gives an optional capacity ofoffer protection for the rods (mind you they are see. To be continued

VALVE GUIDE/ SEATC a s t Iron

VALVE COLLAR

Dura l

Ed @VALVE SPRING

V A L V E U N I T (X2)

1512 MODEL ENGINEER 19 DECEMBER 1980

HAWK 40A 6.5 cc GLOW PLUG ENGINE

Suitable for Aeroor Marine Use

by Australian reader G. Punter

Part III (Conclusion)

Rocker UnitThe rocker shaft is made from silver steel and is heat

treated. The ends have a 5BA thread cut on them forrocker retaining screws - these could be replaced bycirclips of a suitable size (if you can find any!) The camfollowers are also of silver steel and are left hard. Therecess in the end is for the push rod to fit in and is madeby centre drilling and then counter-sinking the hole.The rockers are made of mild steel and are fabricated.The end in contact with the valve stem is case hardenedand the tappet end is silver soldered on - care will beneeded when heat treating to prevent the soldered endfrom becoming too hot (shield this end). The rockerbearing is a tight press fit into the rocker. Make thetappet locknuts from 8BA nuts tapped 6BA. The pushrods are from piano wire of 16 or 17 s.w.g.Cam Unit

The camshaft is the lung of an engine and con-trols the breathing. The shaft blank is made from

Drawing No. 1

R O C K E R S H A F T : et stl. pushrod.

s

02 4 A R O C K E R P O S T : s t e e lM a k e t a p p e t l o c k n u t sf r o m t3 BA nuts topped 6BA

a p p o x 1.875

028B P U S H R O D .,R O C K E R U N I T

R O C K E R B E A R I N G : b r o n z e

Drawing No. 9

96 MODEL ENGINEER 16 JANUARY 1961

Ex. In.

CAMSHAFT BLANK

029

-254%Front Back

C A M S H A F T B E A R I N G S 3 10G E A R S 4 0 D.l?

1 - 25T1 - S O T

CAM UNIT : steel

S.H MUFFETTunbridge Wells -

silver steel and is heat treated after it has been shaped.The cam shapes shown are the ones I have used - butothers could be tried. To produce the cam shape I havemade a cam grinding jig which utilises an old foodmixer motor (3 speed type - again with Whistons!)but they could be made by the methods explained inother articles on the subject (Some backgroundreading may be needed here). There is sufficient roomin the crankcase to take plain, needle roller or smallball races on the camshaft, but check sizes beforemachining. The gears used came from S. H. Muffet

Drawing No. 10Ltd and are lightened as shown. The large gear is apress fit onto the camshaft (use Loctite) and use eitheran 8BA grub screw or a roll pin as a key. Assemble thegear on the shaft and drill the hole so that half the holeis in the shaft and half in the gear - thus forming atype of key. The small gear is located with a keywayand Woodruff key. Note that the back bearing isblind.Exhaust Pipe and Intake StubThe exhaust. pipe is made from thin brass tube and isbent to the shape shown. (Use drv sand packed in tight

I

PROP WASHERdurol PROP DRIVER

duroi

INTAKE STUB: dural

EXHAUST PIPE: full size

Drawing No; 8

M O D E L E N G I N E E R IGJANUARY 1981 9 7

25%

4 holes 8BA clear M5dPc.d.

drill &topZBA

013A

ENGINE BREATHER/ OIL RETURN PIPE

DRILL & TAP PORT

I -375DEEP-375~ 40 ME.

z --

q

I -\

t \cl0:\_ ,FLANGE s/solder to pipe

RETAINING NUT

ALTERNATIVE EXHAUST FITTING

BACKPLATE M O D : d u r a l Drawing No. 8b

to prevent distortion, and work in the flame).. If athread is to be used as shown in part no. 18, make thispart separate and silver solder onto the main pipe.Part 19 is an exhaust pipe steady and bolts onto thegear case front. The intake stub is made from Duraland is machined to take an 0.S.15 carburettor - theother end screws into the cylinder head with the fibrespacer in between to reduce heat transfer. Use Loctiteon assembly and the O.S. carburettor screws supplied.General Notes

Fabricate the oil tank from thin brass sheet - notethat the return pipe points up. Use fuel tube for the

sight glass and make the top from Dural bar.The water cooling unit, for boat applications, is

shown on drawing no. 12 and is a press fit over thecylinder liner. All pipes are silver soldered in - allparts being made of brass. A suitable flywheel couldbe made to replace the prop. driver.

Gaskets used have been of the silicon jelly type andhave been successful in operation.

The backplate has been modified and is shown ondrawing no. 8B. It now includes the oil return breatherand has therefore been thickened locally to take the2BA threaded pipe.

m PUSH ROD ANDWATER PIPES

ALL TUBES SILVER SOLDERED INTO BRASS BARREL

CYLINDER HEAD WITH 35DOWN DRAUGHTINLET PORT

CYLINDER HE4D MK2

See notes

Valve guides and seats will need tobe modified for this type of cylinderhead

NOTE - Glow Plugs are normally% in. x 32 t.p.i. and Cylinder Headshould be tapped to suit plug avail-able - see p. 1151.

WATERCOOLED CYLINDER BARREL Drawing No. 12

98 MODEL ENGINEER 16 JANUARY 1981

Hawk40-1aHawk40-2aHawk40-3a