squish


6 replies to this topic
  • bluesbiker

Posted February 29, 2012 - 03:13 PM

#1

2001 wr 426 whats the standard squish to head area not valves

  • 2grimjim

Posted February 29, 2012 - 05:15 PM

#2

2001 wr 426 whats the standard squish to head area not valves


Are you refering to the quench percentage? i.e. the ratio of squish area to combustion chamber area?

  • GuyGraham

Posted March 01, 2012 - 04:49 AM

#3

bluesbiker - see reply in your other thread

Dont actually know std squish clearnace
Always worked on it being 1mm or less in a 2-stroke
Static sqish will be larger than when engine is running due to rod stretch

Normally its controled by thickness of head gasket as pistons normally finish flush with top deck of the cylinder, and the squish band on the head is flush with the gasket face
So, unless you've thinned down you head gasket or base gasket, or got a taller piston, squsih isn't going to change much

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  • bluesbiker

Posted March 01, 2012 - 05:27 AM

#4

yes guy thanks for the reply appreciated mate
i had the barrel and head skimmed at a local engineers about 3 weeks ago now he just said he took a lot off and if it were his to use two head gaskets bloody cowboy eh i didnt no any diffrent at the time,,,now some one says this could be my problem with the piston seizing,,, to close squish to hot detonation would destroy the piston if i could find out the correct length of a standard head and barrel jug i could make up a few base gaskets to take to normal size and spec

my other mate in a bike shop says valves would be a problem b4 detonation was a prob

  • 2grimjim

Posted March 01, 2012 - 08:43 AM

#5

yes guy thanks for the reply appreciated mate
i had the barrel and head skimmed at a local engineers about 3 weeks ago now he just said he took a lot off and if it were his to use two head gaskets bloody cowboy eh i didnt no any diffrent at the time,,,now some one says this could be my problem with the piston seizing,,, to close squish to hot detonation would destroy the piston if i could find out the correct length of a standard head and barrel jug i could make up a few base gaskets to take to normal size and spec

my other mate in a bike shop says valves would be a problem b4 detonation was a prob


Depending on how much material was removed, your valve timing will be upset a small ammount too. Removing material from the cylinder base, deck, or head will retard the cam timing on both cams.

Do a mockup with the cylinder and piston and turn the crank to TDC. If the top of the piston is flush or slightly below the deck surface you'll be fine. If the piston protrudes past the top of the cylinder, you will have to double stack the base gasket.

emoving material from the head isn't going to affect the quench (squish) clearance. The quench clearance is determined by the deck height of the piston and the thickness of the head gasket.

  • GuyGraham

Posted March 01, 2012 - 10:58 AM

#6

as said by 2grimjim, your squish wont have changed from the head machining, but will have been reduced if the top of the cylinder has been
of more concern is the raise in compresson ratio, which may cause detonation, and valve to piston clearance whcih will have been reduced by both the head machining and cylinder machining

you're gonna have to measure the squish and valve/piston clearance
squish is done with solder poked through the spark plug hole and the engine turned thru tdc and then measure the tickness of the solder
don't know the most accurate way for valve to piston - sorry

as regards squish clearance, the less the better, as it helps the combustion process and prevents detonation, by squeezing the mixture into the centre of the combustion chamber
it only becomes too little when the piston hits the head!
less squish clearnce means you can run more compression but there comes a point when when it will detonate due to the compression ratio being so high

Edited by GuyGraham, March 01, 2012 - 11:03 AM.


  • 2grimjim

Posted March 01, 2012 - 01:39 PM

#7

don't know the most accurate way for valve to piston - sorry


Plumbers putty, modeling clay, bubble gum. I've probably tried a half dozen different ways. As long as you have a good visual of where your valves in relation to the piston, you'll be okay. Sticking a piece of solder through the sparkplug hole is probably not going to work.

The proper way to do it is to remove the head and put some gobs of clay on top of the piston where the valve reliefs are cut. Reassemble and roll the engine over with a wrench, take it apart and check your clearance.

as regards squish clearance, the less the better, as it helps the combustion process and prevents detonation, by squeezing the mixture into the centre of the combustion chamber
it only becomes too little when the piston hits the head!
less squish clearnce means you can run more compression but there comes a point when when it will detonate due to the compression ratio being so high


Not always. The 450 has such a short piston skirt that when the piston bore clearance opens up from wear, the piston will rock enough to contact the head. Too much turbulence (from too littlel quench clearance) can hurt combustion effeciency. This is less of a problem if the quench area is reduced. Generally, increase the quench area and reducing the quench clearance help mid range power and torque delivery but doesn't necessarily help peak HP numbers.




 
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