I have an spx and I rebuilt the motor. After break in I was only able to attain 120 psi comp. So I tore it back down to see if I could determine what the problem was and re-ring it. It's bone stock but I went with WSM 1st over pistons. They now have maybe 1.5 hours on them. I was running a 4 hole base gasket.
That said this post isn't about the previous rebuild and what I may have done wrong or the present re-ring which I will be doing everything wright.
I want to ask some questions about squish. It's a very important measurement and I know the benefits of a proper or tight squish from my land toy motors I've built.
So, I want to test for squish clearance. I pulled the cylinders and pistons, removed the rings, looked every thing over, then I bolted the cylinders w/pistons back on with no base gasket. I am attempting a lead test to get a clear measurement. I glued a 3/8" piece of .125 lead to both sides of the piston against the cylinder wall and directly over the wrist pin. I then bolted the head on and turned the motor over hard by hand until it hit tdc and then rotated past. I removed the head and WOW, it worked better than I thought! All lead was between .059 - .061 I am disappointed at the thickness of the clearance but the test worked great!
Check the pics -
Ok, I really want a clearance of .045. I'm at about .060 with no base gasket. I have a 3 hole that's supposed to be .012 but it actually measures .010. So, my final squish is going to be around .071 - .073.
Questions:
Are these WSM pistons that far out of spec with the OEM pistons?
What squish clearance do these motors typically come out of the factory with? I believe this untouched motor originally had a 5 hole gasket in it
Will a squish clearance of .075 as opposed to .047 cause compression to be around 120 psi? when it should be 150
I realize tighter squish will increase compression but how much?
If I had a squish of around .045 would that raise compression to where I couldn't run 87 octane?
Actually, what is the limit in terms of compression where I can't run 87 anymore?
Obviously something's wrong if I'm using a .010 base gasket and still at .073 total squish?
Best way to increase squish? Deck top of cyl or flycut bottom of cylinder?
I see the squish band on these heads are slightly recessed into the head, so milling the head in this case, at least till it's flush would increase squish, yes? Or am I wrong? Typically you deck or flycut to alter squish clearance.
Is it better with these motors to cut the cyl or mill the head to take say .025 off???
Lastly and most important - Is there really going to be any noticeable difference between .047 and .075 clearance on this particular stock motor?
I'm sure I will have more questions that I'm forgetting but hopefully they will be answered in the course of this discussion
Thanks!
That said this post isn't about the previous rebuild and what I may have done wrong or the present re-ring which I will be doing everything wright.
I want to ask some questions about squish. It's a very important measurement and I know the benefits of a proper or tight squish from my land toy motors I've built.
So, I want to test for squish clearance. I pulled the cylinders and pistons, removed the rings, looked every thing over, then I bolted the cylinders w/pistons back on with no base gasket. I am attempting a lead test to get a clear measurement. I glued a 3/8" piece of .125 lead to both sides of the piston against the cylinder wall and directly over the wrist pin. I then bolted the head on and turned the motor over hard by hand until it hit tdc and then rotated past. I removed the head and WOW, it worked better than I thought! All lead was between .059 - .061 I am disappointed at the thickness of the clearance but the test worked great!
Check the pics -
Ok, I really want a clearance of .045. I'm at about .060 with no base gasket. I have a 3 hole that's supposed to be .012 but it actually measures .010. So, my final squish is going to be around .071 - .073.
Questions:
Are these WSM pistons that far out of spec with the OEM pistons?
What squish clearance do these motors typically come out of the factory with? I believe this untouched motor originally had a 5 hole gasket in it
Will a squish clearance of .075 as opposed to .047 cause compression to be around 120 psi? when it should be 150
I realize tighter squish will increase compression but how much?
If I had a squish of around .045 would that raise compression to where I couldn't run 87 octane?
Actually, what is the limit in terms of compression where I can't run 87 anymore?
Obviously something's wrong if I'm using a .010 base gasket and still at .073 total squish?
Best way to increase squish? Deck top of cyl or flycut bottom of cylinder?
I see the squish band on these heads are slightly recessed into the head, so milling the head in this case, at least till it's flush would increase squish, yes? Or am I wrong? Typically you deck or flycut to alter squish clearance.
Is it better with these motors to cut the cyl or mill the head to take say .025 off???
Lastly and most important - Is there really going to be any noticeable difference between .047 and .075 clearance on this particular stock motor?
I'm sure I will have more questions that I'm forgetting but hopefully they will be answered in the course of this discussion
Thanks!
My squish was .071" which I checked last instead of first LOL. I wasn't about the pull the top end over .008" and I figured WSM knew what they were doing. Compression check was 175. I'd give my higher number but it may have been a bit wet but I like em' tight. LOL Next top end I do, I'm gonna measure first then deck the cylinders.
