Substitute piston/rings for 66cc/80cc China engine (47mm bore)

[butre]

Between my fat ass and my bike's fat ass my little engine is only pushing around 270 pounds. You're carrying twice what I do uphill on a good day before even calculating in the weight of you and your bike

 

[Frankenstein]

Jesus Christmas I thought I wrote too much but this thread is giving me a headache and I'm only on the first page, damn.

 

[6blueoval9]

Need some Tylenol?

 

[Stoneman]

Jesus Christmas I thought I wrote too much but this thread is giving me a headache and I'm only on the first page, damn.

you must be a slow reader the last post was 2014 haha

 

[Philandra Chambliss]

Here is a good substitute piston/rings: Hoca Minarelli 47mm piston and rings $30
Why change out the stock one? 2 main reasons:
1) the stock rings are 2mm thick and have a lot of spring tension which wears the cylinder lining
quicker than normal.
2) the stock rings have 3 times the normal ring end gap which allows too much blowby which reduces
engine efficiency and reduces compression, thus reducing power.

With the stock piston for the Dax/Speed-demon engines (the most common, the "low wrist pin" engines) the wrist
pin is 21mm from crown edge to upper pin edge, and the piston for the Grubee engines (higher wrist pin
version) is 16mm from piston crown edge to wrist pin edge. The Hoca Minarelli Piston has already been
tested for this application. It has a 46.8mm diameter and has dual 1mm thick rings. When tested
in two cylinders the chrome plating of the cylinder got scraped off by, we assume, the chrome rings so
non-chrome rings are needed if the assumption is correct. The Hoca piston from the skirt to crown is
48mm, ours is 47mm. Once installed you need to double check that it doesnt hit the crank wheels at
the bottom of the stroke. The 10mm wrist pin on the Hoca Minarelli was reported by the person testing to
be 21mm from piston crown but the web site shows it as 20mm from the crown. If 20mm it will lower
cylinder pressure which is already too low on the stock engine. You should buy a tester to verify the
cranking pressure. Concerning the weight, which affects engine balance and vibration, the Minarelli
piston is 112 grams (5 grams heavier than our piston) and the wrist pin is 5 grams heavier than
our wrist pins (20g), so a lighter wrist pin such as a titanium one will need to be used although you may
have to shorten it a little by grinding down one end. ($19 here)

At 1977mopeds.com there is a 47mm non-chrome 1mm thick ring for $15. It is the Motobecane Airsal Piston Ring.
When I emailed them the above info they replied: "That ring (Motobecane) is not chrome plated.
Normally chrome plated rings are to be used in aluminum lined cylinders. Those motorized bicycle
cylinders are normally lined with nikasil (a very hard very thin coating). Uncoated rings like the
Motobecane are normally used with cast iron cylinders (uncoated). That is not to say that it
will not work and is probably worth a shot. However it might not be the piston rings that are the issue
in this situation but it might be a cheap coating on the cylinders that is the cause of the issues."

Every China girl cylinder I have owned has lost some cylinder plating so I know that their coating process is not
completely correct. But both of the two cylinders tested lost a large portion of chrome during the
first tests so we have to suspect that a non-chrome ring needs to be used. If I had a 66cc engine I
would definitely try the Minarelli piston and Motobecane rings. Also I recommend using a synthetic
or semi-synthetic engine oil for better lubrication and less possibility of cylinder chrome flaking off
due to friction.

You do know our MOD quality parts are inbetween minarelli, tomos, and ouch right?

We can use Minarelli heads puchs, heads which is also Pw50 which is pretty much a high CR HEAD without feeding RSE and BBR TUNINGS POCKETS RIGHT?

Relli also shares ring and piston sizes, as well for that if one wanted a real head go to malosi or polini.

 

[Frankenstein]

you must be a slow reader the last post was 2014 haha

There are threads from 2009 too, I decided on replying to this one. At least I find joy in reading about the history of this hobby lol.. also yes, I did notice the date, but I don't mind digging up corpses too much, in fact my name almost implies that reviving the dead is somewhat of a pastime.

You do know our MOD quality parts are inbetween minarelli, tomos, and ouch right?

We can use Minarelli heads puchs, heads which is also Pw50 which is pretty much a high CR HEAD without feeding RSE and BBR TUNINGS POCKETS RIGHT?

Relli also shares ring and piston sizes, as well for that if one wanted a real head go to malosi or polini.

This however is an example of not noticing the dates nor reading the complete thread before posting (both of which I usually try to do, if it counts for anything.)

 

[Stoneman]

It got me interested as I just ordered some after market rings

I noticed you been pulling up some interesting threads.

 

[Stoneman]

I’m going to check these out, worth a try I guessed

https://www.ebay.com.au/itm/172051853596

 

[FurryOnTheInside]

I’m going to check these out, worth a try I guessed

https://www.ebay.com.au/itm/172051853596

Nice find!
Doesn't seem to say if they're non chromed, though. Oh well, you'll be the guinea pig; I'll add them to my watched items and wait for your findings hehe.

 

[Frankenstein]

It got me interested as I just ordered some after market rings

I noticed you been pulling up some interesting threads.

There's plenty of interesting threads here, the one mentioning about using pool drain hose as a tire liner would be beneficial to lots of people, flats are just no fun, and can be dangerous at speed too so yeah.. worth digging up lol, hopefully it helps somebody, I know Im going to give it a shot.