4 stroke squish.

tzmike
Profile picture for user tzmike
Posts
444
Joined
2/22/2014
Location
Warwick, NY US
tzmike
In the throws of modding a 18 yz250f. Looking for squish specs and valve pocket clearances. Anyone ?
|
slipdog
Profile picture for user slipdog
Posts
10044
Joined
7/25/2009
Location
Nor Cal, CA US
slipdog 12/28/2019 7:06am
12/28/2019 7:06am
You will always get differing opinions from different builders but my rule of thumb was .040" squish, .060" intake, .080" exhaust.
Momus
Profile picture for user Momus
Posts
441
Joined
12/9/2019
Location
CD
Momus 12/28/2019 10:47am
12/28/2019 10:47am
Twenty thou (or less) squish depending on component rigidity might be enough- intake to pocket can be run with very little vertical clearance-maybe 010". Some highly developed engines have incipient intake to piston contact- valve following the piston down is 'safe'. Lateral clearance in the pocket would need to be set in relation to piston rock. Exhaust.vertical clearance to piston, if good valve control on a known cam/spring might only be 020" at the end of development. Get your pistons machined with the thinnest rings as far up the piston as you can.

To do this with real precision, like an OE, you will probably need CAD drawings and CMM info. Otherwise, in my experience on 15000 + rpm 2 valve Hondas, be willing to do several top end tear down inspections and adjustments and have pistons available..
tzmike
Profile picture for user tzmike
Posts
444
Joined
2/22/2014
Location
Warwick, NY US
tzmike 12/28/2019 12:12pm
12/28/2019 12:12pm
I spoke to Woo from Honda this morning and granted it's a Honda and a 450 for KR, he told me .8mm to 1mm on squish. I'm using a JE piston so that is another variable from HRC spec. He also mentioned his pocket clearances, again Honda spec, was 2mil on intake and 1.5 on exhaust. So the 4 bangers are way more clearance happy than was my TZ250 gp bike
I, as always, appreciate everyone's thoughts on this. And I'm sure others will use the above info from all in their builds. Happy new year all ! C'mon Jan 4th ! Jones's for A1.
Momus
Profile picture for user Momus
Posts
441
Joined
12/9/2019
Location
CD
Momus 12/28/2019 9:16pm
12/28/2019 9:16pm
tzmike wrote:
I spoke to Woo from Honda this morning and granted it's a Honda and a 450 for KR, he told me .8mm to 1mm on squish...
I spoke to Woo from Honda this morning and granted it's a Honda and a 450 for KR, he told me .8mm to 1mm on squish. I'm using a JE piston so that is another variable from HRC spec. He also mentioned his pocket clearances, again Honda spec, was 2mil on intake and 1.5 on exhaust. So the 4 bangers are way more clearance happy than was my TZ250 gp bike
I, as always, appreciate everyone's thoughts on this. And I'm sure others will use the above info from all in their builds. Happy new year all ! C'mon Jan 4th ! Jones's for A1.
Lazy ol 450 with about 150 hp per litre versus 250's wanting 200 plus.

The Shop

See All »
Momus
Profile picture for user Momus
Posts
441
Joined
12/9/2019
Location
CD
Momus 12/28/2019 9:20pm
12/28/2019 9:20pm Edited Date/Time 12/28/2019 9:20pm
Not easy to get 16:1 comp with those wide clearances. Tight clearances are not about detto, but burning the max mixture and powa.

Post a reply to: 4 stroke squish.