Cyl/piston/rings tolerences EC 300 2009

[TheEfterbliven]

Hello!

New to the forum, hoping for some help.

Bought myself a 2009 EC 300 Racing. Doing her ready for the spring.
So disassembled the jug so i could see what parts to be ordered, but ran into some questions.

I got a A cylinder and A piston(71.93 mm).

Measured the ring gap to be 0.3 and 0.4 mm, manual says 0.5 mm and a maximum of 0.8 mm.

So i put the piston in the cylinder and saw that the upper part of piston seemed to be smaller than the lower part, is that normal?

Used a feeler gauge and got 0.25 mm play on upper part, and 0.05 on the lower.

If i turn the piston up side down i get the same readings (top of piston in bottom of cylinder and vice versa)
So the piston seemed to be like a cone.

Now, both piston and cyl looks very nice, ordered a piston from spain but got insecure in case i need to cancel that order.

Ordered a C? 71.95 mm piston. Have a feeling that the bike itself have atleast a couple of hundred hours on it.

So, do you guys Think i need A, B or C piston?

 

[(F5)]

I've had to gently file a little bit from ends of ring. Have to be super careful in vice so ends supported.
Piston is shaped like that so when at operating temperature the top part which gets a fire lit next to it and has bulk of the material expands to same size as the bottom.
To be precise you really need to measure with a bore gauge and know how to use it.
But largely the difference is real small and another A would be fine. Might get away with a B.
Best would be to Diamond hone from a specialist and get them to measure but plenty of people don't bother.

 

[TheEfterbliven]

Thanks for the reply!

I Think i`ll stick with the order i did. Done some more research so Think It will be fine.

File the rings, is that common procedure? Thought that it just was slapping Everything together.

 

[(F5)]

People do just throw stuff together and often get away with it, but tight ring gap can cause damage and bad sealing until it wears a bit, or if unlucky seize.
On a well used bore getting it honed will aid sealing but can't just use old fashioned hones on plated. Again most people don't bother and bike still runs OK.

Spend some time cleaning the PV system.

 

[TheEfterbliven]

Yep, will check ring gap on new piston kit for sure. I got no glazing and can still see hones.

PV cleaned and new bearings ordered, cleaned every part and screw from back to steering head so far, and ordered parts for 1000 euros. Will be fresh looking bike when im done.

 

[motopsycho87]

Use KTM tolerances. Gasgas is huge, I don't understand where they got it from...

 

[TheEfterbliven]

Use KTM tolerances. Gasgas is huge, I don't understand where they got it from...

Do you wanna share KTM tolerance? Maybe go for between GG and KTM.

Saw something about squish in your signature, is that the distance from top edge of piston to top cylinder?
Recommended tolerances of that would be great to have!

 

[(F5)]

Read this thread. It goes on a bit but tells you what you need to know about squish and how you can't just close it up to a ideal value without consideration.
http:// gasgasrider.org/forum/showthread.php?t=16560

Strangely searching for this I found an old thread I'd forgotten about. . concerning ring clearances. . .

http:// gasgasrider.org/forum/showthread.php?t=12530

 

[TheEfterbliven]

Thanks for your time.

I`ll just leave squish for what it is, too advanced for me at the time being.

However i had two base gaskets when i tore apart, one thin and one thicker.

 

[(F5)]

Comes like that usually. I pulled thin one off. Will marginally aid bottom end power through lower ports - not much change. Will increase compression marginally and as long as you don't have pigs swill as gas should be fine.

Getting rid of the std N1EF needle will make far more change. Do search on jetting section.