66cc rebuild hurdle =piston contacts head

[djase10]

Thanks kidd,
after 24 hrs of thought, i will do the same ( thicker base gasket)..

my brides gonna freak out that all the grinding was for nothing .

the combustion forces wont be properly utilized, and blown head gaskets will be my new life..

kidd what material did you use for your base?
...................................................................
How does a rubber base gasket sound ??

( this stuff is heat - acid- & oil resistant industrial rubber mat),
==kindly sent to me by [fatboy67] -for sound deadening the sides of motor)

Thanks to all that have been of help, appreciated !

regards Jase

 

[Phil_McCracken]

Rubbers a poor sealer and you only have a surface around 6 -7 mm wide so trying to keep it in place when you tighten it down will be a issue, it will keep trying to push out of the join.
The best option would be to make a shim from bakelight or similar and glue a gasket to each side with contact adhesive.
You need to come up a fair bit by the look of it, you would get away with sticking 2 gaskets together with contact adhesive, more than 2 you may have problems sealing, any leaks and it won't run or cause it to run lean.

 

[KiDD]

I just used high density gasket material sourced from the local Kragen. Then I dressed it with some high temp RTV. One gasket was too thin, two was perfect.

 

[djase10]

shaved out head lack any torque or power.

I tried the rubber gasket and the material just squashed, and metal to metal contact remained.

I could'nt source base gaskets (late shipment)
************************************************
So i bolted on the "SHAVED OUT" head,

And gave it a test.

took a while to start (compression was high)

once running it
idles lumpy
lacks any torque (slightest hill & almost dies out)
minimum acceleration
struggles to reach 24km/h on flat ground with tail wind.
go against the wind & its more like 16-18km/h..
Embarrassing to ride..

Didnt blow the head gasket, and does'nt seem to be leaking pressure from it.

My thoughts are that the piston isn't getting the DIRECT push down it requires , and force is being lost in side way pressure within the head.

Just have to strip it down and wait for the shipment of base gaskets.

Had to try anyways..
jase

 

[Skyliner70cc]

Use factory gaskets and double up on them. Many of the HT engines have double gaskets on the base of the jug.

 

[Willy]

It seems as that you have a piston with an incorrect compression height, ( centerline of piston pin to top of piston). This will cause, in addition to piston to head contact, a detrimental change in port timing. You now have a very high compression motor that is not timed properly, hence the poor performance.

I know you have a lot of time into this project but I believe a new, proper piston with correct pin, bushing, and rings, as well as a new head will go a long way to setting things right again.

 

[djase10]

2mm or so makes SO much difference to timing!!

Spot on Willy,
it really is amazing how much timing difference that 2mm can make.

this was a strong motor before the (mismatched part) problems

Because of my motor being of old stock ,none of the newer parts match up properly, and my supplier carries none of the older parts.

Yep just gonna have to double or tripple the base gasket (shipment arrives soon, i'm told)
30 day shipments suck, but patience is a virtue.
Jase

 

[Willy]

Jase, not sure of the difference in piston shape, (skirt, shape, compression height) in relation to the old one. Try to keep port timing as close to stock as possible.

You will also be dealing with a lower compression head now that you have removed material to gain clearance. You may be able to regain some compression by using a thiner head gasket. I have used thin copper sheeting successfully in the past. It may take a little time to cut one out with tin snips and a file or grinder, but they do seal very effectively.

Don't forget to anneal the copper gasket when you are done making it as it does tend to work harden. Annealing it will leave it nice and soft so that it can conform to the mating surfaces. All you have to do is to get it red hot and then allow it to cool slowly and it will be dead soft.
Good Luck gettin the old girl running again.
Willy

 

[djase10]

Base gaskets, doubled & trippled

Ok ,
Received my parcel from zbox
containing
3 X 70cc base gaskests

also a pair of main seals for my 50cc =(blew the main seals, =in another thread)
& bearing chain roller &pin..
############################################

glued two gaskets together,
but i may need 3....

to elaborate on the problem=
the 2mm or so comes from the gudgeon pin size
old was 9mm
new is 11mm
piston height was identical as was the barrel height..

I hope that this brings the 70cc to its former glory..
Jase

 

[djase10]

Yes!Yes! Yes! 3 base gaskets does it >>

Yeah
# done it.. NO contact!!

Runs like it should, Great!!

A bit of a high pitch noise coming from somwhere, nI'll check it out further tomorrow..
But yeah ..
What a relief !! ..
Port timming seems perfect!!..

thanks for reading ALL...
. Regards Jase