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dudeX

10+ Year Contributor
126
12
Jun 14, 2011
Surprise, Arizona
Hello, I recently had a 6 bolt block bored and honed .020" oversize and after installing the pistons I noticed that there was a bit of movement in them. Is this movement normal? I called the machine shop and they said this was normal but I want some opinions. The ptw clearance was set at .004 so i figure the movement shouldnt even be noticeable. Thoughts?
 
Yes it is normal.

if you did not have that bit of rocking, then you should be worried that it was too tight.
 
I hope reviving this thread isnt against some rule somewhere so apologies.

I have in the last year put about 2k miles on this motor in between other catastrophes (trans exploded) and have an issue I feel may be related to the piston movement question I had a year ago.

Do you think the piston movement would cause me to have 100psi compression in all cylinders but idle fine and run strong? Ideas?

From what I've heard low compression like this should be making the car run rough but it doesnt.

Also as a side note I went with 8.3 to 1 compression versus the stock 7.8 to 1. Something doesnt seem right.
 
Sounds more like your timing is off. If it is the same in all 4 cylinders. That or the compression gauge is out of calibration.

Also if you have aftermarket cams, can drop the compression some, if you have a fair amount of over lap
 
Another thing to remember is that pistons are tapered. The PTW clearance is not measured at the crown of the pistons (where I assume you were rocking them). You're going to need to do a leak down test to determine where you're losing compression.
 
I have stock cams for now so that shouldn't be the issue. I will check the timing this weekend and see if that is the problem. I'll keep posting back when I find more and let you guys know what I find. Thanks for the suggestions so far.
 
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