I assembled the top end on my '72 125 Penton this weekend and installed a NOS ELKO piston. I checked the Squish clearance and found only 0.011". Visual check of piston/deck height showed that the top OD of piston is flush with top of cylinder. I used std. head and base gaskets. What should squish clearnace be? Small squish prevents detonation –right? If piston does not make contact with head under worst case conditions, is minimizing squish clearance desirable for max performance? What are the down sides of minimum squish clearance?
Also noted that this ELKO piston (marked 1170a1) had a steep taper machined starting at OD and going about ½ way across corresponding squish band in head. If you measure from piston OD the "taper" width is 0.195 inches, then "normal" squish width is 0.230" for a total squish band width of 0.445". Could this be a high compression piston? Thanks,
Ernie P.
Chattanooga, TN
Hi Ernie,
Minimum squish is ideal in all cases. The squish area is trapped (wasted) gas and your right about preventing detonantion.
However striking the head is catastrophic.
I seem to recall from my Two Stroke Tuning" book squish should be held to .040".
I'll look it up tonight and check myself.
You may consider a thicker or extra base gasket.
RonW
Ernie,
What was the compression reading or did you install the head?
Ron Carbaugh
Ron W. The "tuners" book may suggest 0.040" min. Do you recall what your hi-performance engine squish clearance is? You can use a piece of soft solder (lead) through the spark plug hole to check. I'm thinking about thicker/additional gasket ... if needed.
Ron C. Yes, I assembled but did not check compression. Will check tonight and report back. Thanks,
Ernie P.
Chattanooga, TN
Ernie,
Lead is fine, I use clay....give me a call if I can help.
Ron Carbaugh
Huh, a shop owner on the board looking for what he should already know, what a concept!
Quote: Thomas Jefferson, We are all born ignorant, some work to remain that way.
Quote:Merlin, "it is impossible to teach those that wish not to be taught".
Better to ask a question than to ruin valuable Sachs parts eh Merlin?
Brian
'72 Six Day (on loan from Ernie P.)
Ernie,
If you would like to see what Ron has given you in print, go the the Vintage Monark sight and look under the magazine articles. The last one on the list is titled Super Power Sachs Secrets. You can try this link.
//www.vintagemonark.com/magazine.htm
Hi Ernie,
This is straight out of Performance Tuning in Theory & Practice, by A.Graham Bell.
"If you are willing to measure the squish clearance each time you do a rebuild, and then compensate for inadequate clearances by fitting a thicker barrel base gasket or a thicker head gasket, you can reduce the squish clearance down to the amount shown"
50 - 80cc .6 - .8mm / .024"-.032"
100 - 125cc .7 - .9mm / .028"-.035"
175 - 250cc .1.0 -1.4mm / .039"-.055"
300 - 500cc .1.1 -1.5mm / .043"-.059"
Hope this helps you.
RonW
Thank you for sharing your knowledge and experience.
Cranking pressure with ELKO: 160 psig - new, never run
2 other stock engines with considerable hours: 120 & 130 psig
I'm going to dig back into the ELKO engine and see if I can identify exactly where the differences are. I'll target 0.028" mim. squish. Thanks again,
Ernie P.
Chattanooga, TN
Ernie,
I have 2 125 pistons like you described. If you have a piston ( the old one or one that has the groves just below the bottom ring ,its a Mahle ) try and get the profile off the crown. We have a pattern maker that will do this. Its used in sheet metal work. Its a bar with many small metal dowels in line.
You can rest it against the piston crown then transfer that profile shape to a piece of paper. Do the same with the Elko piston. You can compare the difference between the two.
I think we will try and rig up a holder for the lathe and reshape ours when it comes time to use them.
hope this helps some,
John D.
Hey, are these Elko pistons forged? I need a forged one to replace this cast Wiseco. thanks,TTP