Squish & cylinder packplates

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Mrnice71
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Fri Jan 18, 2019 12:16 pm

Hi fellas trying to set my squish on my TS1 if using a 2mm cylinder packer the squish is 0.93mm a bit close if l use a 2.5mm packer it will be 1.43 mm a bit excessive , wanted it at 1.2mm , any way around this ? Noboby sells a packer in-between these sizes .

Adam_Winstone
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Fri Jan 18, 2019 1:10 pm

With a typical recommended range of 1-1.5mm the 1.43 is ideal. Unless a head is perfectly machined (virtually never) and dowelled or spigot recessed, to ensure accurate alignment, then going much lower introduces risk. I've seen a number of instances where people have worked to a target of 1mm but found that the 1mm where measured was zero on the other side of the piston and ended up hitting when running (result of relying on poor alignment of cylinder studs + holes). With other heads the casting/machining of squish band is nothing like crown profile and the squish measurement can range from 1 to 3mm!

Basically, IMO, a target of no more than 1.5mm is a good working measurement for most builds.

holty
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Fri Jan 18, 2019 2:42 pm

good advice from adam, is you head dowelled ? this makes sure it is centrally lined up over the cylinder and helps with accurate measurement, also I always check the squish across the same path as the gudgeon pin to eliminate piston rock, or a suggestion I read the other day a feeler guage in the inlet port beween barrel and piston to stop rock, this will give a more accurate reading, I have turned down packers in my lathe to get the squish that I was after or you can buy very thin base gaskets to add to your packer, good luck,
holty

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garry inglis
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Fri Jan 18, 2019 2:49 pm

1.43 is spot on for a ts dont risk going smaller

Mrnice71
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Sat Jan 19, 2019 1:02 am

Thanks some good advice , does 0.5 mm difference alter the compression ratio at all

hendy
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Sat Jan 19, 2019 7:04 am

Mrnice71 wrote:
Sat Jan 19, 2019 1:02 am
Thanks some good advice , does 0.5 mm difference alter the compression ratio at all
Short answer is yes. But notnecessarily worse, just lower.

Typical compressed volume is around 20cc and 0.5 on a 70mm bore adds around 2cc, so about 10% lower.

Mrnice71
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Sun Jan 20, 2019 7:57 pm

hendy wrote:
Sat Jan 19, 2019 7:04 am
Mrnice71 wrote:
Sat Jan 19, 2019 1:02 am
Thanks some good advice , does 0.5 mm difference alter the compression ratio at all
Short answer is yes. But notnecessarily worse, just lower.

Typical compressed volume is around 20cc and 0.5 on a 70mm bore adds around 2cc, so about 10% lower.
Cheers Hendy :)

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