Blue ET3

[tzsteve]

well got a few bits so time to make a start

the crankshaft had dalready been ground by someone else.



i like to keep the inlet to about 195 Deg for road use i find that the inlet makes a tremendous deference to the power output but if it`s too big the engine can be a bit peaky.
so after splitting the crank i had a top lambretta man weld up part of the inlet so that i could reduce the timing a little.






the welding  from all sides

then its into the lathe to get remove the excess weld





this shows where the weld was placed and cleaned up



the inlet cut away was then ground to give the inlet opening point that i want

the crank parts are then put in place and then pressed i used a crank pin from
bike as a drift ( i could not get the ram of my press to fit into the recess on the vespa crank





after pressing the parts together the crank is then put in the lathe on centers so that i can
check the alignement with a DTI



then check the clearance on the side of the big end



the finished crank

[Hugoagogo]

Very impressive!

[gav]

Nice job ste

[eean]

Cool are you an engineer by trade?

[tzsteve]

yup

[nickj]

Nice stuff...wish I could do that!

[tzsteve]

Honestly it`s all easy stuff, its just having the toys and a little practice (it helps if you know a top lambretta man who can weld)

[potatopl]

Great job. How do you divide those 195^o before/after TDC?

[scooterfreak]

its all good practice for when i give you my spare engine mate

[eean]

Excellent, can you machine cases too then?

[tzsteve]

I dont have a miiling machine

[vinrouge]

Nice work, very impressive

[tzsteve]

so a little playingaround before goimg to work.
crank in the casing and measured the amount of piston sticking out of the barrel at TDC 6.8mm i need a packing piece of 7.8mm to give me the normal squish of 1mm. not much i can do untill that has been cut and ground to thickness.

so with a bit of time on my hands i decide to cut some copper for a copper axhaust gasket, this is handy as its a make once use for ever one, as its solid it also helps with blending the exhaust port (this will be done much further down the line).

started with a piece of 22mm pipe cut a slit in it length ways


cut this pice off the pipe and heated it on the gas ring till it turned a blood red colour quenched it in cold water. this softens the copper so it can then be easily opened out and flattened, i used the press but it becomes so soft that it can mostly be done by hand and finished in a vice




this shows how flat you can get the copper.
it`s now a piece of copper sheet.  i will now leave this untouched for a couple of weeks as copper becomes harder with age, that will help when i come to drilling, cutting out and blending the gasket.

i still had more time to kill before work so i worked out the port heights that i will need,.
i reckon that the franz exhaust that i have has a tuned length of about 35 to 36 inches as i am only doing a mild tune i want the peak power at about 7500 RPM so:
exhaust timing of about 170- 175 degrees will be enough.
and if i keep the transferes to about 126 main and 130 boost ports,
that should give a broad spread of power if i can get the transfers wide enough.
i `ll consider the porting in greater depth later.

[tzsteve]

did a few more sums using the rod and stroke that i have opted for.
the rings (1mm thick) will limit the engine rev to about 8700 rpm and the piston will be ok upto about 11000rpm.

im only aiming for les than 8000 rpm so there is no problem with the ring speed limit as long as i can get enough torque.
i could always change the piston for one with thinner rings at a later date if needed.

rewound the stator for 12 volts dc.if i get the time i will do the cylinder head in the next couple of days.

[tzsteve]

a little more done today.
made a some progress with the cylinder head.
the first thing is working out the radius of the squish ban and the profile of the cutting tool
here`s the maths for the radius of the cuttimg tool

and how i work out the profile of the tool

a rough check with the piston and a drawing of my cutting tool radius


now the cylinder head and how its mounted on the lathe


and the work holding with a mandril

from another angle

this pic also shows the form tool ready for use
first cut is straight across the gasket face to provide a flat suface that i can measure across when cutting the squish band

second cut is the recessing of the squish band

third cut is to fully machine the gasket face



and the head now looks like this after i removed the little bit of carbon with 400 wet and dry


i will be coming back to this head at a later date to port out the combustion chamber.

there are many differant aproaches to profiling cylinder heads.
I ussualy go for a squish band that matches the piston profile  with a clearance of 1mm for about 7-8 mm and slightly increase this clearance for the next few mm to give a clearance of about 1.5mm at the edge of the combustion chamber, and then work on the actual combustion chamber width and volume to give the compresion ratio that i want 
.

I hope that makes some sort of sense and that i havn`t lost track of what i was trying to put in this post.

currently waiting on some bearings and other little bits, with a bit of luck ill be able to do some more work on the engine soon

[unclechufty]

Can't tell from the pictures. What holds the head to the spigots on your mandrel?

cheers, UNCLE CHUFTY

[tzsteve]

four  3/8 unf bolts tapped into the stud holes with a big fat spacer.
i dont have the time to make a faceplate/mandril this is how they ware all done in the 80`s.
these days its done with a cnc lathe and i dont have one of those either

[tzsteve]

more fun this morning putting some small dowels into the bottom of the barrel to locate the packing piece and engine case
so that everything lines up when the engine is assembled
I started by roughing out the packing piece and making all the standard holes that you find in a base gasket, the hole for the barrel spiggot is about 0.25 mm bigger than the barrel spiggot.

next i drilled two holes 3.0mm dia through the packing piece at opersite sides these are one at the back and one at the front of the engine case, one in each half of the case.

next this was put on the bottom of the barrel so that i could make two drill holes in the bottom gasket face of the barrel that
would hold the two dowels into the barrel.
to keep the packing piece in place while drilling i dropped a couple of allen screws into the stud holes

next to make sure that these holes in the barrel and packing piece all line up with the holes that i drilled in the case.
the barrel, packing piece and one dowel (a piece of drill bit) were put in position on the case and the barrel given a good tap with a nylon mallet.
this left a little mark on the gasket face of the case where the first dowel hole had to be drilled,
to make sure the hole was in the right place i left the packing in situ and sighted through the packing to line up the mark on the case
after drilling this hole the a dowel was placed in this first hole and then the second hole drilled.
these holes are about 5mm deep


here you can see one of the dowels this one is at the back of the engine.

this little bit of work will help to keep everyting  lined up when i come to blend the bottom of the barrel and then when i assemble the engine.

next something similar was done to the cylinder head

first i drilled two 5mm holes into the head as far apart as possible one at the back one at the front
and get the head central to the barrel and lock it in position with a coupl of studs

you can see here that the head is still a little of center.

when sattisfied that all is in the correct position drill though the holes in the head into the top 3 fins of the barrel




when the head is being fitted i will put a small piece of 5mm drill into each hole to make sure that the head is sitting central as it is bolted down.

again i hope i have not lost the thread of what i am trying to explain.
and i know that to many this stuff is common practice
.

[tzsteve]

made a little more progress
tackeled the exhaust gasket no comments for the first couple of pics as i think they are self explanitory







when i put the gasket on the barrel i noticed that the gasket and exhaust would get caught on one of the fins and a fair amount of rough casting on the gasket face so out with the big file


after the filing

then i put a small nick in the gasket and the barrel  so that i wouldnt get the gasket the wrong way round while blending

it looks as if the walls on the exhaust port may be a bit thin after the blending.
just keep my fingers crossed and try to avoid the need for welding.

I made a small rubbing of the barrel so that i could see just how bad the port shaping was.
it looks like i will need to get the ports a little more even than they are at the moment

the boost ports have dropped with the 2mm over bore, and are a little uneven and it looks like i can make the exhaust port somewhat wider, also i think that i could do a little work on the main transferes inorder to get them to enter the barrel a bit squarer

[tzsteve]

come to a standstill,

bearings etc are in the post, (thanks mate)
also still looking for a late type 4 speed box

any offers gents ? not too pricey please