Hello everyone, This may seem like a simple question but I get really confused every time I build a motor and wind up having a friend reading clearances using plastigage. I have a 76 462 buick that i am the process of building. I am in the process of measuring rod bearing clearances. I talked to ta performance some months back and they said that the clearances I think was .00025 to .002 would be okay. Don't hold me to that as it has been some time back. I maybe misquoting them. What I would like to know in the most simplified manner is this: What measurement readings do these listed below stand for? 1. First reading= . 001, is this in tenths, hundreths or thousands? 2. Second reading= .0015 same as above. 3. Third reading= .002 same as above. 4. Fourth reading= .003 same as above. Lastly, if a measurment calls for .0025 to .003 how would it look on the plastigage since there is no .0025 mark on the plastigage wrapper? I know this is a pretty basic question but it confuses me no end and I don't want to make a mistake. By the way if anyone knows what should be the correct rod clearance should be please let me know as I maybe misquoting ta performance. Please keep it simple guys. Thank you very much Jon Thomas jthomas1248@satx.rr.com
Plastigauge is really simple. First cut a piece about 3/4"-1" long. Place it on the journal you're going to measure. Now carefully place the bearings and cap. Correctly torque the bolts/nuts down to proper torque. You now remove the cap and bearing carefully and measure the piece of plastigauge that is on the journal. .001 is one thousandth .0015 is fiften ten-thousandths .002 is two thousandths .0025 is twenty five ten-thousandths .003 is three thousandths etc, etc, etc. The wider plastigauge is, the smaller the clearance. In the above chart, .001 would would produce the widest piece of plastigauge as it is the one the is "crushed" the most. The .003 would be the narrowest as it was "crushed" the least. The .0025 is merely in between the .002 and .003 on the pastgauge ruler. Buicks like tighter tollerences than most other engines. Probably because of their inherent weakness in the oiling systems. Don't let anyone tell you that .004 is fine on your crank. That may be great for a Chevy, but NOT a Buick. Steven Dove's book and T/A are both good sources for proper clearances on everything for the Buick motor. Good luck. Phil
Not trying to be nit-picking here (and don't know if it is different for plastigauge), but... .0015 is "fifteen ten-thousandths" (aka, "1-1/2 thousandths") .015 would be "fifteen thousandths" ditto for .0025, etc. "fifteen ten-thousandths" is the midpoint between "one thousandth" and "two thousandths". Regards, Ira
Your correct Ira, but I think Jon got the jist of it. Actually, the terminology most widley used would be "One and Five tenths", for .0015. A tenth being .001, split 10 times. That's how the mics/dial bore gauges read. Rod bearing clearance has a whole lot less of an effect on a 455's oil pressure, than Main bearing clearance does. But Specs in that range should be fine. For reference, I run mild stuff at .0015-.002 mains and rods. That's my preference. That's for up to 475-500 HP. Above that, we will start to loosen them up in increments, as the motors get more powerful. JW
Know what I find confuses people? calling 0.020" 20 "mils". Even in industry, I found that confused people because they started thinking in metric terms instead of 20 thousandths.
cam degreeing Thank you guys for the info. on plastigage. I've got another one for you that I think that I am okay on. I purchased the ta 413 camshaft for my big block. The card says it should be installed (or checked) at 109 degrees intake centerline. Using the stock crank gear I was around four degrees retard. I have read articals that these gears can cause this variance. I bought the 9 degree crank gear from ta performance. My original intake centerline reading on the first pass with the old gear was almost 112 degrees. Long story short, I finally got a reading at 108.5 so I feel like .5 of degree is acceptable. But I had to move the keyway over to the +6 degree mark in order to accomplish this. I started out by moving the keyway (advancing) from 2 and 4 degree and the results brought it closer to 109 degrees but not quite there i.e. 110.5. + The #6 crank gear position did it. Is this because the original crank gear was around four degrees retarded? I matched the stock gear with the new gear where the dots would line up at t.d.c. and there was a noticable difference. thanks for all of the help. Jon Thomas jthomas1248@satx.rr.com
Maybe we were stupid, but years ago, I helped a buddy build a SBC and we used plastic gauge. Where we ran into a problem at was the rebuild kit had the wrong size rod bearings. Instead of the .010" bearings we needed, we got .020". Here is where the funny part comes in. We used plastic gauge and it read just right on all 8 rods when we were setting the engine up. Being that this was the first motor experience we each had, we were in for a big surprize when we went to crank it over. Needless to say, I became a believer in having the journals and bearings mic'd out vice using plastic gauge. Maybe it is one of those lessons that I learned the hard way that I do not want to experience again. Mike
Yes... No... Maybe.. The gear may be different than the orginal, but I do a lot of this stuff, and can tell you there is not any real standard here. Things vary.. the crank, cam, degree wheel zeroing, t-chain set, and measuring techiniques.. That's why you went thru the degreeing process. Good job! Run it! JW
Now you know why those of us that build these things as part of making our living at it... mic everything out. JW
