<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">The theory about squish area in two strokes is that besides generating turbulence (thus mixing) and moving the majority of the mix to the middle of the head, that the relatively cool surfaces in close proximity to the mix slow the flame front headed for the cylinder wall and prevent detonation. If the squish band is too tight the gasses cool too much and don’t burn to the edges. The piston is still moving upwards at that point so partially burned gases push back into the non-squish area as well and screw up complete burning. One of the reasons that head and piston tops needed to be decarbonized was closing up the squish gap and losing horsepower. <div class=""><br class=""></div><div class="">At least that’s what Gordon Jennings said. I always believed him. </div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Aug 23, 2017, at 6:46 PM, Kas Kastner via Fot <<a href="mailto:fot@autox.team.net" class="">fot@autox.team.net</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">This is a very interesting subject. In the thousands of hours of <span class="" id=":ji.1" tabindex="-1" style="">dyno</span> testing I did in the 60's, the squish area clearance was never addressed with exception of making certain the piston did not hit the head. Off hand, when the clearance is too close it rather sounds like there is insufficient volume in the squish at <span class="" id=":ji.3" tabindex="-1" style="">TDC</span> to do its job of properly exciting the balance of fuel mixture when it squirts back into the combustion chamber thus making a better mixed and thus more powerful combustion moment. Or maybe something else :-)</div><div class="gmail_extra"><br clear="all" class=""><div class=""><div class="gmail_signature" data-smartmail="gmail_signature"><p class=""><strong class=""><font color="#000099" class="">Never be beaten by equipment.</font></strong></p></div></div>
<br class=""><div class="gmail_quote">On Wed, Aug 23, 2017 at 3:47 PM, John Hasty via Fot <span dir="ltr" class=""><<a href="mailto:fot@autox.team.net" target="_blank" class="">fot@autox.team.net</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div class="">Interesting... We found 1.5 mm in the 250 two strokes was the best....<br class="">
<br class="">
Sent from my iPhone</div><div class=""><div class="h5">
<div class=""><br class="">
On Aug 23, 2017, at 6:31 PM, "Chris Marx via Fot" <<a href="mailto:fot@autox.team.net" target="_blank" class="">fot@autox.team.net</a>> wrote:<br class="">
<br class="">
</div>
<blockquote type="cite" class="">
<div class="">
<div class="m_-1583056859754097110WordSection1"><p class="MsoNormal"><span lang="EN-US" class="">On dyno test we found a disturbing issue that lowers the power if the piston to head clearance is less than 0.039“.<u class=""></u><u class=""></u></span></p><p class="MsoNormal"><span lang="EN-US" class="">We didn’t find a cause for this but tested thoroughly clearances from 0.0236” upwards.<u class=""></u><u class=""></u></span></p><p class="MsoNormal"><span lang="EN-US" class="">Best power reading was with 0.0472”.<u class=""></u><u class=""></u></span></p><p class="MsoNormal"><span lang="EN-US" class=""><u class=""></u> <u class=""></u></span></p><p class="MsoNormal"><span lang="EN-US" class="">Cheers<u class=""></u><u class=""></u></span></p><p class="MsoNormal"><span lang="EN-US" class="">Chris<u class=""></u><u class=""></u></span></p><p class="MsoNormal"><span lang="EN-US" class=""><u class=""></u> <u class=""></u></span></p><p class="MsoNormal"><b class="">Von:</b> Fot [<a href="mailto:fot-bounces@autox.team.net" target="_blank" class="">mailto:fot-bounces@autox.<wbr class="">team.net</a>]
<b class="">Im Auftrag von </b>fubog1 via Fot<br class="">
<b class="">Gesendet:</b> Mittwoch, 23. August 2017 23:52<br class="">
<b class="">An:</b> <a href="mailto:timmmurphh@gmail.com" target="_blank" class="">timmmurphh@gmail.com</a>; <a href="mailto:fot@autox.team.net" target="_blank" class="">
fot@autox.team.net</a><br class="">
<b class="">Betreff:</b> Re: [Fot] FW: Grattan VSCDA next weekend? piston/head clearance<u class=""></u><u class=""></u></p><p class="MsoNormal"><u class=""></u> <u class=""></u></p><p class="MsoNormal"><span style="font-size: 10pt; font-family: Arial, sans-serif;" class="">With the good rods and reasonable rpm you have plenty of clearance.<br class="">
You don't want too much clearance either cuz then it lessens the "squish" effect.<br class="">
The idea is to have enough clearance for all running conditions, plus a few thou safety margin, and no more.<br class="">
Glen<u class=""></u><u class=""></u></span></p>
<div class=""><p class="MsoNormal"><span style="font-size: 10pt; font-family: Arial, sans-serif;" class=""><u class=""></u> <u class=""></u></span></p>
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<div class=""><p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size: 10pt; font-family: Arial, sans-serif;" class="">-----Original Message-----<br class="">
From: timmmurphh <<a href="mailto:timmmurphh@gmail.com" target="_blank" class="">timmmurphh@gmail.com</a>><br class="">
To: 'fubog1' <<a href="mailto:fubog1@aol.com" target="_blank" class="">fubog1@aol.com</a>>; fot <<a href="mailto:fot@autox.team.net" target="_blank" class="">fot@autox.team.net</a>><br class="">
Sent: Wed, Aug 23, 2017 3:38 pm<br class="">
Subject: RE: [Fot] FW: Grattan VSCDA next weekend? piston/head clearance<u class=""></u><u class=""></u></span></p>
<div id="m_-1583056859754097110AOLMsgPart_2_c9dd2094-052a-4e95-8dd2-24532eebf176" class="">
<div class="">
<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class="">The Payen head gasket last used was compressed to 0.055 at the fire ring. So, with the 0.010 pop-up that I have from the all efforts to deck the block, I will have 0.045 clearance. I have Carrillo
rods and we try to stay to under 6000 RPM for engine “longevity”. (Not sure “longevity” is a term that can be used with a race engine!) At the most we’ll hit 6200 or 6300 RPM briefly before upshifting. Therefore, I should be within the 0.030 clearance that
you recommended. It will be interesting to see what the top of the pistons looks like on the next rebuild with regard to carbon build up in the squish area.<u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class=""> <u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class="">Thanks for the advice and all the other comments on this subject. All much appreciated. Still a lot to learn</span><span lang="EN-US" style="font-family: 'Segoe UI Emoji', sans-serif;" class="">😊</span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
</div>
<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class=""> <u class=""></u><u class=""></u></span></p>
</div>
<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class="">Tim<u class=""></u><u class=""></u></span></p>
</div>
<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class=""> <u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class="">P.S. Finally got everything together on the engine and about ready to mate up to the transmission and put back in the car. Looking forward to ELVF next month. That will be the test.<u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><a name="m_-1583056859754097110_aolmail__MailEndCompose" class=""><span lang="EN-US" style="" class=""> </span></a><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
</div>
<div class=""><p class="MsoNormal"><a name="m_-1583056859754097110__MailEndCompose" class=""></a><b class=""><span lang="EN-US" style="" class="">From:</span></b><span lang="EN-US" style="" class=""> fubog1 [<a href="mailto:fubog1@aol.com" target="_blank" class="">mailto:fubog1@aol.com</a>]
<br class="">
<b class="">Sent:</b> Wednesday, August 16, 2017 5:27 PM<br class="">
<b class="">To:</b> <a href="mailto:timmmurphh@gmail.com" target="_blank" class="">timmmurphh@gmail.com</a>; <a href="mailto:fot@autox.team.net" target="_blank" class="">
fot@autox.team.net</a><br class="">
<b class="">Subject:</b> Re: [Fot] FW: Grattan VSCDA next weekend?<u class=""></u><u class=""></u></span></p>
</div>
<div class=""><p class="MsoNormal"><span lang="EN-US" style="" class=""> <u class=""></u><u class=""></u></span></p>
</div>
<div style="margin-bottom:12.0pt" class=""><p class="MsoNormal"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class="">Check the gasket thickness, it depends on what piston/wall clearance, rods, and RPM you use.<br class="">
You generally need around .030 piston/head with stock rods, so add that to your pop-up of .010 for minimum gasket thickness.<br class="">
If you run good rods you can run a little less before the pistons smack the head.<br class="">
It's perfect when there isn't any carbon build up on the piston tops under the squish area.<br class="">
When it's not right, it goes BRRRRRRRRRRRRR...<br class="">
HTH<br class="">
Glen</span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
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<div class="">
<div class=""><p class="MsoNormal"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class=""> </span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
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<div class="">
<blockquote style="border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 2.0pt;margin-top:5.0pt;margin-bottom:5.0pt" class="">
<div class=""><p class="MsoNormal"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class="">After all the machining to get the stick out<br class="">
right I now have the pistons sticking up about 0.010 above the tops of the<br class="">
liners. No problem with the composite Payen head gasket.</span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class=""> </span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class=""> </span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
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<div class=""><p class="MsoNormal"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class=""> </span><span lang="EN-US" style="" class=""><u class=""></u><u class=""></u></span></p>
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<div style="margin-bottom:12.0pt" class=""><p class="MsoNormal" style="margin-bottom:12.0pt"><span lang="EN-US" style="font-size: 10pt; font-family: Arial, sans-serif;" class="">-----Original Message-----<br class="">
From: timmmurphh--- via Fot <<a href="mailto:fot@autox.team.net" target="_blank" class="">fot@autox.team.net</a>><br class="">
To: fot <<a href="mailto:fot@autox.team.net" target="_blank" class="">fot@autox.team.net</a>><br class="">
Sent: Wed, Aug 16, 2017 5:48 pm<br class="">
Subject: [Fot] FW: Grattan VSCDA next weekend?<br class="">
<br class="">
<br class="">
<br class="">
-----Original Message-----<br class="">
From: <a href="mailto:timmmurphh@gmail.com" target="_blank" class="">timmmurphh@gmail.com</a> [<a href="mailto:timmmurphh@gmail.com" target="_blank" class="">mailto:timmmurphh@gmail.com</a>]
<br class="">
Sent: Monday, August 14, 2017 12:20 PM<br class="">
To: 'Tony Drews' <<a href="mailto:tony@tonydrews.com" target="_blank" class="">tony@tonydrews.com</a>><br class="">
Cc: <a href="mailto:ryan.murphy@fdlco.wi.gov" target="_blank" class="">ryan.murphy@fdlco.wi.gov</a>; Steve Yott <<a href="mailto:tr4@wi.rr.com" target="_blank" class="">tr4@wi.rr.com</a>><br class="">
Subject: RE: [Fot] Grattan VSCDA next weekend?<br class="">
<br class="">
Sadly, we won't be able to make it.<br class="">
<br class="">
I just got the block back from the machine shop last Tuesday. Not enough<br class="">
time to get everything together and in the car and ready to go by Thursday.<br class="">
The good news is the liner stick out is the 0.004 the machine shop said they<br class="">
machined the liner seats and deck to. It's still a bitch to measure, as the<br class="">
liners "wobble" on the seats and when you're looking for 0.004 it's a<br class="">
problem. I finally have a decent dial indicator gage setup to at least give<br class="">
repeatable readings. The figure 8's used was a set of copper ones I had<br class="">
that measured 0.016. The machining was done on a single setup on a Rottler<br class="">
floor type vertical 4-inch spindle milling/boring machine. These are<br class="">
special purpose machine tools built specifically to machine engine parts,<br class="">
such as blocks and heads. After all the machining to get the stick out<br class="">
right I now have the pistons sticking up about 0.010 above the tops of the<br class="">
liners. No problem with the composite Payen head gasket.<br class="">
<br class="">
Thanks for all the responses to the Figure 8 gasket question. I did<br class="">
eventually hear back from Moss UK. They said their steel fig. 8's are 0.016<br class="">
and their copper fig. 8's were 0.018. No explanation regarding the<br class="">
different thickness other that they have not had reported problems with the<br class="">
gaskets. I'm not sure where the 0.020 thick copper ones that I measured<br class="">
came from or for that matter, the 0.016 thick copper ones I'm using.<br class="">
<br class="">
Tim & Ryan Murphy<br class="">
1961 ('61, it is Comm. No. 511 and was built in 1961 per British Heritage)<br class="">
TR4 #317 BRG<br class="">
<br class="">
-----Original Message-----<br class="">
From: Fot [<a href="mailto:fot-bounces@autox.team.net" target="_blank" class="">mailto:fot-bounces@autox.<wbr class="">team.net</a>] On Behalf Of Tony Drews via<br class="">
Fot<br class="">
Sent: Saturday, August 12, 2017 6:21 PM<br class="">
To: <a href="mailto:fot@autox.team.net" target="_blank" class="">fot@autox.team.net</a><br class="">
Subject: [Fot] Grattan VSCDA next weekend?<br class="">
<br class="">
Anyone else going to Grattan next weekend?<br class="">
<br class="">
Vroom, vroom, Tony Drews<br class="">
<br class="">
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