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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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
 
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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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
 
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
 
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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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.
 
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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