402 Clearances, specs info needed. (technical)
 

Hey guys,

I'm rebuilding a 402 for my '71 Camaro, and as these have the same engines, I was hoping some of you may have some info I need.

According to my book it says that the piston to cylinder clearance is .0035" MAX.

Now after measuring what I have, it is sitting at .005" Now do you really think the extra .0015" is going to make a huge difference? This isn't a race engine, and I plan on buying file to fit rings to the gaps will be perfect. And I do plan on the very occasional SMALL shot of NOS. I was thinking that the extra clearance may help in a juiced situation? I don't want to have excess piston slap/noise so I am just being sure. This block is already sitting at .060 over the stock 402 size. (4.157" now)


Any info or thoughts on this?

My info shows .0018 to .0026 for factory pistons - you didnt state what kind of pistons you are going to use - forged or cast - the forged grow more and take more clearance - if your using cast pistons I would take it easy with the juice as they will not last very long. HTH:::::::::CB

.015 is the difference between life and death in a motor. they have reccomended clearances for a reason and like he said if your using cast pistons ya better go real easy on the giggle juice or your going to need a lot more than just a rebuild. have it bored and have the pistons fitted to the bore any good machinist will do this

The pistons are not forged, but again the NOS isn't my worry. Its the piston slap that may occur.

The reason I am worried about this is because nobody makes a piston for bigger than .060 over the stock 402 size. I would have to get custom pistons, and that means lots of cash. :whine:

juice
 

talking about the juice, when i built my first 383 i got ready to put it in and the motor in the el camino was still running good and i couldn't see taking a good motor out, so i hooked up a 200hp nos kit and had some fun. stock motor nothing fancy, 10- 10lbs bottles of juice later finally popped a piston skirt. LOL... :metal: it was alot of fun :)
Dwayne

Well sounds like you are going to have to run what you got - I just went thru a 454 for my 72 and the bores were looser than I would have wanted but it runs fine and no slap that I can tell - I used sealed power pistons in mine and they have a teflon coating on the skirts which helps with the piston slap - GM has had slap problems with alot of their new engines because of bad QC and that was one of their fixes was to use pistons with coated skirts. With file to fit rings you should do OK. Instead of custom pistons,if I had to do it I would have the bores sleeved back to std. size - just something to think about. Let us know how she turns out.::::::::CB

Ahhhhhh.......you made a good point. I know people here that do the piston coating. I wonder how thick that stuff is? I may look into this as a cheap alternative to what I need. May help a bit I hope!!

Thanks!

Reid

When you buy hypereutectic pistons with the coating already on it reduces the piston to bore by one thou. Essentially they are at Zero with the coating. If they are hypers they will not expand at all! A band aid solution is the have the piston skirts knurled. It will take up the clearance but won't last long and is really a poor band aid even at that.

If your going to use file to fit rings, make sure the cylinder bores have NO taper.