I am building a 351W and am going to bring the block to the machine shop this week......

Anyway, I have a certain amount of money i can spend right now ($600)

I KNOW that the machine shop bill wont be over that (as i already have an estimate from them)

But i dont have the pistons yet and need to know if i the machine shop will need them or not?

I will be using a set made by Keith Black:
http://store.summitracing.com/partde...%2D8&view=2047

Lets say that I need the block bored to .30 over......They wouldnt need the pistons would they or do the sizes very a little bit?

Also, the piston pins are floating (i think) not pressed so will that work with my stock connecting rods which will be getting reconditioned?

Thanks

Nick~

 

They will tell you what size pistons to buy AFTER they have bored the block. You want them to do the smallest overbore possible that gives complete cleanup; that may be .010, .020 or .030. You gain NOTHING by going larger than necessary and you lose block strength.

 

A good machinist will want the piston up front. You can bore and hone to a nominal dimension , but what if the piston is a .001 small or large. You can and always should gap accordingly.
The piston manufacturer will specify what clearance to use for the intended application. To answer the ?, no the machine shop doesn't need the piston. the machinist will bore the block to what he normally bores them too not really to what the people who made it recommend. If it was my block and its likely the last bore it will ever see I would get the pistons to the machinist prior to bore and hone for the tightest possible fit.

 

Forgot the pin issue. No, stock 351 rods will not acept floating piston pins you have to have the machinist press in brass bushings then hone to fit the pin. Stock 351/302 rods are press fit.

 

Anyone who bores & hones a block without the pistons is "ASKING" for trouble.

 

I'm with Mark. The machinest tells you what overbore he wants, gets the pistons in hand, and finishes the job to fit the part.

 

If you are buying a quality set of pistons, and I would still classify KB's as "quality" the pistons won't vary more than a few ten thousandths of an inch. It should never be necessary to fit each piston to each bore if you are using decent parts. Also the clearance is usually built into the pistons by the manufacturer, meaning that a +.030 piston will be anywhere from +.026 to +.0285 so that if you finish size the bore to +.030 it will have the recommended clearance, go with manufacturers rec's on this clearance, they spend millions on product development and usually know the best clearance for each application. Any good shop will do a preliminary hone job just to see how bad the cylinders are before ordering the pistons. While it is nice to hone as little as possible when going oversize on the bores .030 over pistons and rings are readily available and inexpensive, and extreemely common. As long as the cylinders aren't trashed or super high mileage they should clean up nicely at .030.

 

My 400 with .02 over pistons is bored to 4.022. At 4.02 the pistons wouldn't even go in.

 

Well I am speaking from my own experience building race engines and using good parts. So far I have never had that problem.

 

The adage of "Measure twice, cut once" is impossible to adhere to if the acutal part to be used is not in hand to measure. Even though something has worked in the past does not mean it is the best possible practice.

 

My machinist will overbore first, but he wants the pistons in hand before he hones the cylinders. I think that is a good practice.

 

It is always good to measure the parts to verify that you have recieved the correct pistons but I have measured every set of pistons I have ever used from JE, Wiseco, Ross, CP, SRP, and even KB and have never seen more that .0001 to .0002 difference. If there was a piston found out of spec it would be sent back to the manufacturer and replaced. Telling a customer that you fit each bore to each piston sounds nice but is totally useless unless you just like mic'ing each piston and setting up a dial bore gauge each time when they won't be more than a couple ten thousandths different. We build anything from 500 to 1200 hp NA engines to 2200 hp turbo engines and have never found the need to individually fit each piston to its bore.

 

Now wait a minute, no one ever said anything about measuring one piston to another.

 

I rebuild engines myself and I agree that you would probably be safe with just boring and honing the engine to 30 over standard bore(or whatever size to clean the cylinders up).

However, on these newer motors, some engines require very tight piston to cylinder wall clearances, such as .001, or even tighter. Get it to tight, piston will seize. Set the clearance to loose, and you will have piston slap noise on cold startup. This is because the pistons are being designed shorter and shorter.

I still measure every piston and set the proper piston clearance to each cylinder hole on older engines. It's not that much more work.

Most pistons from manufacturers today are usually within .0001 to .0002.
But sometimes they vary as much as .0005, but there is nothing wrong with the pistons.

 

like I said