GasGas Riders Club Forum  

Go Back   GasGas Riders Club Forum > GasGas Enduro Technical Forums > Enduro Engine - 2 stroke

Enduro Engine - 2 stroke Cylinder, Piston, Tranny, Bearings, Clutch, Pipes & Silencers, etc.


Reply
 
Thread Tools Display Modes
  #1  
Old 09-05-2018, 06:25 PM
Thompo Thompo is offline
Member
 
Join Date: Aug 2017
Location: Northern Ireland
Posts: 86
Default Squish and port timing..

Hi folks

Putting a whole new top end on my mates 03 300. New pistion replated barrel of unknown year, exchange service.

Last top end on a 2t i done was a beta trials bike when i was 14 around 20 years ago lol. I was happy it worked and knew nothing of squish and port timing etc.

Roll on today and i want to do this right...
Ive fitted a single 0.5mm base gasket.
Pistion is around 1.0mm above the exhaust port at bdc.

Squish measures 1.8mm at cylinder wall increasing to 2.7mm, 12.5mm from cylinder wall.

Squish seems a bit large from my reading.

Reducing the base gasket to 0.3mm should help but will lower the exhaust port further.

Whats best compromise?

Hes new to offroad riding (in at the deep end on a 300 2t lol) so peak power isnt going to be an issue. Cutting the head isnt a option for a few months.

Cheers
Attached Images
File Type: jpg 20180905_230753.jpg (124.8 KB, 12 views)
File Type: jpg 20180905_225758.jpg (126.2 KB, 14 views)


Reply With Quote


  #2  
Old 09-05-2018, 06:29 PM
Jakobi's Avatar
Jakobi Jakobi is offline
Super Moderator
 
Join Date: Oct 2010
Location: Australia
Posts: 7,655
Default

I'd be whacking 2 x 0.5mm base gaskets in there to get the piston only 0.5mm above the base of the exhaust port. Then you'll have a nice big squish clearance; send the head to milled down to 1.3mm and have the compression ratio adjusted through chamber volume.
Reply With Quote
  #3  
Old 09-05-2018, 07:34 PM
Zman's Avatar
Zman Zman is online now
Platinum Level Site Supporter
 
Join Date: Apr 2010
Location: Burbs of Chicago
Posts: 1,342
Default

You can run the 0.3mm base gasket now if you do not have a ridge on the cylinder and get the head cut later. The piston spends so little time at the bottom of the stroke that the piston overhang does not matter too much for flow but the port timing change will move the power band to the lower rpms. Some people prefer that while others like the stronger top end.
Reply With Quote
  #4  
Old 09-05-2018, 11:04 PM
Jakobi's Avatar
Jakobi Jakobi is offline
Super Moderator
 
Join Date: Oct 2010
Location: Australia
Posts: 7,655
Default

True that Zman!

Personally I find a 300 with the power curve moved down can become a bit snatchy and responsive to small throttle inputs.. Then again, everyone knows I prefer the delivery of a 250 as well.

Was the pan to cut the head, or just find your best compromise working with what you have?
Reply With Quote
  #5  
Old 09-06-2018, 01:45 AM
Thompo Thompo is offline
Member
 
Join Date: Aug 2017
Location: Northern Ireland
Posts: 86
Talking

Possibly will cut the head in the future but for now i just want to get him riding before winter hits.

I think id want to aim for as mellow a power delivery as possible especially off the bottom end to keep him out of trouble, he is unlikely to use the power band off road for a good while yet.

With that in mind i should raise the port at expense of squish to keep the hit up the revs a bit?

Thanks
Reply With Quote
  #6  
Old 09-06-2018, 02:34 AM
Jakobi's Avatar
Jakobi Jakobi is offline
Super Moderator
 
Join Date: Oct 2010
Location: Australia
Posts: 7,655
Default

Given what you have said,

I'd run the single 0.5mm gasket, 1.8mm squish clearance, jet it the best you can and then let em at it.

Most stock bikes have squish clearances in this range. It's not ideal but also not necessarily excessive.

It won't be too wild and if it is you can always gear some snap out of it or retard the timing a touch.
Reply With Quote
Reply



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
2015 ec250 squish and port timing ljdb Enduro Engine - 2 stroke 1 05-02-2018 07:55 AM
'13 300 S3 head and port timing TorbenS40 Enduro Engine - 2 stroke 8 12-24-2015 09:43 AM
Port Timing farmerj Enduro Engine - 2 stroke 8 08-15-2012 07:44 PM
MC 250 port timing... rpduc Enduro Engine - 2 stroke 17 07-04-2012 09:29 PM
Port Timing PEB Enduro Engine - 2 stroke 2 03-15-2012 12:36 AM




All times are GMT -5. The time now is 09:34 AM.


Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2009 - GasGasRider.org