81 srx piston ?

SRXfromHELL

SRXfromHELL

New member
Joined
Feb 5, 2005
Messages
107
Age
60
Location
Morris ,Pa.
I noticed that the windows in my piston skirt are 1/8 to 3/16 smaller than the ports in the cylinders should I cut this away and match it to the port ? It's bored and sleeved to 68.5 mm using 78-80srx pistons
 

hmm, the early srx is a 59.6mm stroke and the 81srx is a 64mm stroke, does the piston have the same compression height? if not they wont come all the way up to TDC or will come up too far?? maybe they are the same distance from the wristpin to the top o the piston edge??
 
pics

this is how the machine was set up when I got it ,the pistons do come all the way up and compression is good but the opening in the skirt is smaller than the port in the bottom of the jug should I cut the skirt to match the ports ?
 

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I wouldnt waste your time, wont be anything youd could tell riding the sled.
 
Thanks mrviper ,feel free to share any thoughts you may have . carbs are done went with 440 mains left 430 right 35 pilots and .05 air needles in 3rd clip try to get it back together this weekend . I keep reading about big pilots 90 etc what happens when you use these larger pilots ?
thanks
Kevin
 
mrviper700 said:
hmm, the early srx is a 59.6mm stroke and the 81srx is a 64mm stroke, does the piston have the same compression height? if not they wont come all the way up to TDC or will come up too far?? maybe they are the same distance from the wristpin to the top o the piston edge??
Click to expand...

They are the same. I agree. If it is a trail sled you won't know the difference. I did the opposite. I put '81 SRX pistons in '76-'80 cylinders. Worked fantastic!
 
just a thought but after reading the 488 phaser post wouldn't cutting the skirts basicly be doing the (sx piston skirt mod) ? I do have a midrange lean condition would opening these up help ?
 
Opening the sides of the pistons will give you some minimal gain which you will probably not notice, what you need to be careful of is if you cut the piston you have to make sure it is still wider than the exhaust and intake ports. Many people would match the side windows and forget on a piston port motor you have to cover the port.

What I would be worried about knowing the older motor had a shorter stroke, is whether or not the piston is long enough to keep the exhaust port closed at the bottom at TDC. Put the piston at TDC and look into the exhaust port, if it is open at the bottom you're just throwing HP away. Also, if the piston is too short, you'll have way too much intake timing and the motor will be gutless down low.

We used to take those cyls and the 540's, sleeve them, and put 570 EX pistons in them, that worked well because they were too long.

Also, in regards to your question on the PZ SX cut, you can't relate to that because it is a reed valve motor. You have a piston port, the piston is the valve, don't forget that. You cut the piston like an SX and put it in your engine it most likely won't start.
 
exhaust port coverage

I have the top end off the sled with the jugs still attached to the head when I place the pistons in the jugs resting against the head the exhaust port is covered but not by very much (1/8 inch) . given the fact that they are above TDC and the thichness of the base gasket will raise the jugs slightly . is that enough or should I consider thicker base gasket and how would that effect performance

anyone have a 81 piston laying around they could measure for me ? total length and bottom of pin to bottom of skirt
Thanks
Kevin
 
SRXfromHELL said:
I have the top end off the sled with the jugs still attached to the head when I place the pistons in the jugs resting against the head the exhaust port is covered but not by very much (1/8 inch) . given the fact that they are above TDC and the thichness of the base gasket will raise the jugs slightly . is that enough or should I consider thicker base gasket and how would that effect performance

anyone have a 81 piston laying around they could measure for me ? total length and bottom of pin to bottom of skirt
Thanks
Kevin
Click to expand...

You'll be fine on the exhaust port. An '81 piston is the same from the pin to the top but they are 3 mm longer from the pin down.
 
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