main cap gaps - plasti gauge

[zooguy]

so i was having some trouble finding the exact gaps needed for each main cap .... i know that they need to be torqued to 77ft/lbs in three steps (i am going 35 than 55 and 77 last)

several friends and SBC guys i know say .0002-.0008 for all of them ... but i was wondering is that the same for us LTx guys?

[zooguy]

I found this ... but I don't know if I trust it 35214

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[Catmaigne]

http://shbox.com/1/engine_specs.jpg

Clearances depend on what you plan on doing with the motor. The stock ones are known for being tight. If you plan on spinning it high or loading it heavily then shoot for 20-25 on everything.

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[zooguy]

Well I got the main caps on ... here are the pics front to back

Front
http://uploads.tapatalk-cdn.com/20160225/d301628c8adaaa0ef6aa09ca3e1e12ff.jpg

#2
http://uploads.tapatalk-cdn.com/20160225/99a541d9b05b5eeb9a15a52e1eb6793f.jpg

#3
http://uploads.tapatalk-cdn.com/20160225/40c382769d9f2ce4e926ead1efca7e15.jpg

#4
http://uploads.tapatalk-cdn.com/20160225/6b9c818478d160e2e7367f062d2d572e.jpg

rear #5
http://uploads.tapatalk-cdn.com/20160225/f06b3853dfa952bab8646313410ac56d.jpg

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[BIG CAT]

I'm not a fan of pg! but seeing what you have i would get a set of x bearings. aka extra clearance. the give you a extra 0.001" clearance. street/strip motor. for the rods no less than 0.002" with 0.0025" being the target number. the mains you want to shoot for 0.003" with a low side of 0.0025"

also you can half shell with the x bearings. ie: use a std upper bearing and a x lower if you only want to open up the clearances 0.0005"

[Homerandabe69]

You should definitely be using a bore gauge for measuring clearances. I wouldn't trust plastigage with one of the most critical measurements in the engine.

On my 7k rpm engine I went with somewhere around .0025-.003 for mains and a little tighter for the rods.

Like Big Cat said, I had to use a few different bearing halves to get the right clearance.

[Tinbender59]

one thing to remember with the LT1 "if" you build the lower end to LT1 specs run "ONLY" synthetic oil after break in. this is a little known fact about our beloved LT's, if you are planning on running it harder than 5500r's, use vortec specs and then standard oil is fine. the problem is the specs are so tight that when they are wound up, (High rpm) the metal expansion of the crank makes the "gap" even tighter and standard oil cannot flow enough to keep it cool, which causes what is known as thermal runaway. (temp becomes unmanageable) then bearings cease up, the rest is history.

[Tinbender59]

I'm not a fan of pg! but seeing what you have i would get a set of x bearings. aka extra clearance. the give you a extra 0.001" clearance. street/strip motor. for the rods no less than 0.002" with 0.0025" being the target number. the mains you want to shoot for 0.003" with a low side of 0.0025"

also you can half shell with the x bearings. ie: use a std upper bearing and a x lower if you only want to open up the clearances 0.0005"

funny fact-I have "NEVER" checked clearances, I pay the machinist to do that, and tell him so when I drop the motor off at his shop. if it blows, he buy's me a new one. I don't have time to check his work, plus they generally like it when you "trust" them. and I'm not running down the track.

p.s. forget the catty remarks, I'm 56 and built my first motor at 15, I have a little experience with this sort of thing. Any way do you double check your accountants work. if you do why do you use him?