Author Topic: Query on squish clearance  (Read 189 times)

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  • Scooter
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on: June 18, 2021, 01:43:14 pm
Hi all,

I took my cylinder head off the other day and looking at the deposits on the piston crown concerned me a bit (see the red arrows on the attached photos)

I've used a base gasket to give me 0.9 - 1.0mm squish on the 2 squish bands which i measured with solder. But i'm worried about the clearance at the piston crown on the inlet side because there are no combustion deposits at all. Makes me worry that it almost hits.

The bike runs well but i just want to make sure its not going to be an issue later on.

I can't measure the clearance to the cylinder head at the section highlighted because the normal play from the piston / cylinder clearance means i will get a false reading. Left to right the axis of the gudgeon pin means there is no play in that direction so the solder gives me true reading.

Has anybody else have any clean sections like this with no deposits? Should i be worried?

Would be grateful for any input or advice on this. I dont want to increase the squish clearance unless its necessary as i believe it should be 0.7mm-1.0mm.

Note : The second squish band is something i've added as an experiment. Normally just has a squish band on one side. But that shouldnt effect the area that im concerned about.


  • Grease Monkey
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Reply #1 on: June 18, 2021, 07:09:15 pm
Just a bit fuel wash from the shape of the inlet port.
Looks to be running a little rich.
Off route, recalculate?


  • Scooter
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Reply #2 on: June 18, 2021, 09:07:38 pm
Thanks Haggis,

That would make sense because that area is right next to the inlet port.

That's put my mind at rest. I couldn't think why it was like that.

  • Grand Gearhead
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Reply #3 on: June 21, 2021, 02:16:27 pm
No worries. It should look like that.
Correct squish distance also provides "quench" which mostly prevents combustion in the squish area. This reduces the likelihood of knock.
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