66cc rebuild hurdle =piston contacts head

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djase10

Guest
Yeah

struck a couple of hurdles during my 66cc rebuild ,

1st problem =Gudgeon Bush to big for conrod
No worries..
rotated over a file & sandpaper.
had to take off about 0.75 mm
took a while , but got it done.

2nd problem
is a concern!!
the top of piston
is making contact
with base of head,
by a good 2mm
stopping rotation.



As a quick solution,
Using the old PITTED head,
i've ground out possible contact points,
using a grinding stone on a drill ..

not the prettiest of milling jobs
but
might just work..

pictures of the scene so far.
not finished grinding as yet

Jase
 

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Joined
Jun 4, 2008
Messages
216
Jase .

You are one determined Man..

Any thoughts on getting or making a thicker head gasket. Also you may want to use some clay on the top of the piston to view clearance to the head. Also putting a small chamfer on the ends of the bushing wouldn't hurt as well.

You are one great example of ingenuity at its best.

good luck.
cheers

Bob
 
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djase10

Guest
Gday bluecollar,
Yep tried two head gaskets, no good.



I may try to cut a slither off the top of an old barrel to make a
"thick head gasket" to get the gap i need.

keeping it leak proof may be a drama,
but may also-- just do the trick.

if i try the slither trick , i'll be smoothing out the barrel before i cut.

It is strange to see this miss match of parts???

cyas.
jase
 

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djase10

Guest
After quick discussion on the matter with WANGER during our ride today,
I think the BASE is the part to play with..
That is ..
(If the head trick is a no go??)..
thanks guys..
jase
 
Joined
Jun 4, 2008
Messages
216
After quick discussion on the matter with WANGER during our ride today,
I think the BASE is the part to play with..
That is ..
(If the head trick is a no go??)..
thanks guys..
jase

I would agree as well.
As you know by moving the combustion chamber up ( jug and head ) You may reduce the chance of leaks.

But you would need to keep the ring clearance in mind.

It seems you got a handle on this and I'm anticipating your Outcome.

I have a feeling your going to Succeed no matter what .


cheers

Bob:)

BlueCollarBike
 
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djase10

Guest
revolution= removed 6 grams from head..

Hi Guys & girls

Thanks Bob for your words of encouragement,

I persisted with the slow process of grinding the inner head , and i won..

I used texta color to find contact points, done this about 5 times,
& removed a total of around 6 grams of ALLOY from inner head , before revolution was had..

Still lots of meat there to hold up to combustion forces ( my nuts hope!!)

i havnt fitted/started
it as yet, but im pretty confident all will be cool.

I will update this once its running.


Jase
 

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Joined
Jun 3, 2008
Messages
59
You've done a neat job, I'm not trying to be a smart arse but theres a couple of things you need to consider.

1st you have made the circumference of the head larger than the top of the cylinder so a portion of the head gasket is going to be exposed in the combustion chamber and it will burn and cause detenation and melt a hole in the piston.

2nd you will find you have shortened the length and amount of time the exhaust and transfer ports are open which will limit performance.
 
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djase10

Guest
Keeping a close eye on the head gasket.

Cheers phil,
yeah i'll be keeping a close eye on that head gasket, ,
&

if exhaust is over restricted, i'll have to do a slight grind on the top of exhaust port.

heres the interesting stuff!!

For those that may be wondering why this even happened??,
it's to do with a different gauge GUDGEON PIN.

my original was a tiny 9.5mm

and the new piston kit is 11.5mm

there are two sizes of bush to cater for each one.

be aware of your pin size
before ordering a replacement bush.

Jase
.
 
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