Plastigage Question???
Plastigage Question??? Before everyone jumps all over me for using plastigage I know it is not as accurate as micrometers and bore gauges but I still thought it would be more accurate than what I am seeing. If I measure use the green plastigage specified for clearance ranges from .001-.003 I get a reading of .002 but if I use the red plasigage specified for clearances from .002-.006 I get right about .003 if not a hair under. Anyone else ever seen this?
Makes sense....you have a larger window of measurement, and plastigauge will only get you close.
Think about it as trying to measure the length of say a city block with a yard stick....now measure the same with a tape measure....the tape measure will be more accurate because of the smaller increments.
Think about it as trying to measure the length of say a city block with a yard stick....now measure the same with a tape measure....the tape measure will be more accurate because of the smaller increments.
I originally used the red because there is a greater window between .002 and .003 on the spec card to estimate where the reading is in between. Just out of curiosity I ran it with green also and was surprised to come up with .001 difference. The difference between clearances of .002 and .003 pretty much determine weather or not I need to start playing with bearing sizes.
On The Tree
Joined: Mar 2012
Posts: 131
Likes: 2
Are you leasuring rod or main bearings? When doing rods, you need to take out side clearances with feeler guages. This comming from a guy who only uses mics and dial bore guages (used Plastigage when I was young and stupid.)
Both. Rods came out to be .00021 when I ran them with the red plastigage but now due to the inconsistencies between both color gauge I am not sure what anything really is. Rods with red are .003 & .002 with green.
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Verdad Gallardo so if you did measure your bearing clearances with feeler gauges in place and called tech support and still have no answer the only thing left to do it take one apart and measure it with the correct tools. then we will know for sure which is closer. I assume the green is closer and thats why it is the recommended plastigage for measuring LS1 rods and mains. But i would still like to know how close Plasti actually gets to the real numbers
I would trust the green over the red. You are smack in the middle of the green's recommended measurement range but on the fringe of the red stuff. Tighter range should have better resolution and I'd expect better accuracy for the green.
Has anyone compared their bore/mic clearances with their plastigage measurements?
Has anyone compared their bore/mic clearances with their plastigage measurements?
I think you added a zero there, but also this doesn't agree with your following statement:
Did you place the plastigage on the piston side of the bearing, not the cap side? Did you use feeler gages as suggested?
How many have you measured so far?
Did you place the plastigage on the piston side of the bearing, not the cap side? Did you use feeler gages as suggested?
How many have you measured so far?
On The Tree
Joined: Mar 2012
Posts: 131
Likes: 2
To be really honest, I think if your building a hydraulic cammed LS motor, your fine. Main bearing clearances are more critical especially if your building an aaluminum block LS. 0.002" should be fine for rod clearance on a motor running to 7K RPM, if your drag racing your GTG, if your going to run extended duration high RPM races (road racing, mile racing) you might want buy a 1/2 set of 0.001" larger bearings and put a 0.001" larger bearing insert into each rod to give yourself an additional 0.0005" clearance.
Thank you everyone for your responses. I got sick of all of the problems with the plastigage and went out and bought a dial bore gauge to do it the right way. Let me first start out by saying I will never use plastigage again, it sucks. Maybe I got a bad batch or something but after using the correct tools to measure a, I get drastically different results which brings me to my next question. According to my measurements my off the shelf Dragonslayer crank with Ultra rods and standard Clevite rod bearings I get a -.001 clearance. Has anyone ever seen a negative clearance before when using standard bearing?
