Do you need to have pistons on-hand when engine is bored ?

[AKcharger]

Hey engine experts, Can I get my engine bored say .030 then get pistons later or does the machinist need the new pistons at the time the engine is bored?
I Don't have time to do a complete rebuild now but wanted to get the block cleaned and mangna fluxed and thought hey why not get it bored... Suggestions?

[Blown70]

Hey engine experts, Can I get my engine bored say .030 then get pistons later or does the machinist need the new pistons at the time the engine is bored?
I Don't have time to do a complete rebuild now but wanted to get the block cleaned and mangna fluxed and thought hey why not get it bored... Suggestions?

They should not need them on hand.  Once you know the bore you can get what you need. So, you would order them .030  Over.

Tom

[is_it_EVER_done?]

The machinist absolutely needs the pistons in order to bore and hone to the correct clearance for the piston brand, and the fact that nearly all pistons will vary in diameter from each other by a bit and will be fitted to a specific cylinder (if your machinist is thorough). Plus you will need to know exactly what type of ring you will be using so that the block can be honed for the ring material.

Just make sure that your block will clean up at whatever overbore you plan on using, before you order pistons and rings.

[Blown70]

The machinist absolutely needs the pistons in order to bore and hone to the correct clearance for the piston brand, and the fact that nearly all pistons will vary in diameter from each other by a bit and will be fitted to a specific cylinder (if your machinist is thorough). Plus you will need to know exactly what type of ring you will be using so that the block can be honed for the ring material.

Just make sure that your block will clean up at whatever overbore you plan on using, before you order pistons and rings.

Must be different with different buliders then huh?

[8WHEELER]

The two machine shops I use and have used over the years, would prefer to have the pistons
when boring the block, some manufactures use different tolerance recommendations, depending
on applications and use of the engine's.

Dan

[chargerbr549]

In our machine shop we will measure the block first to see what oversize piston you will need and then get the pistons, measure them and bore block about .003" to .007" smaller than the piston depending on wether or not you are using a torque plate (which is highly recommended) when you hone the block. I would probably wait to bore it until you have everything ready. I have seen it many timeswhere people get stuff cleaned and freshly machined only to let it sit around for awhile till they get time or can afford to do more and it usually gets rusty or if they oil it down or WD 40 things to keep them from rusting it collects so much dust and dirt that they have to get it cleaned again, if it was up to me I would wait. Just my two cents worth.

Kevin

[firefighter3931]

Yep, have the pistons on hand so the machinist can get a mic on them before boreing the block. Cudaken had an engine meltdown because of sloppy machinework and a piston that was too tight for it's bore. The machinist should have caught this if he'd been on the ball. Don't leave anything to chance and i would request assembly notes with bore diameters, piston to wall clearances etc...

Ron

[sext7366]

I also agree with having the pistons, my machine shop said the same thing, especially when switching brands or going from cast to forged, then they usually want to have the pistons in order to measure precisely and get the rings to fit tight so you dont burn oil like some rebuilt engines do.

[AKcharger]

Copy All guys, I'll wait. I'm going to be moving so I was going to tear down the block and get started onthe rebuild but I'll just stand by. It's the #'s matching block for my '72...don't want to mess it up.

Thanks

[4402tuff4u]

My engine is currently being rebuild and the machinist told me that he would not bore the engine until he knew and saw what pistons I was going to go with. Once I dropped them off, he bored it 30 over followed by honing for perfect fit. He then sprayed this black graphite stuff on the new shiny pistons and installed them.

[Blown70]

Welll I never asked my engine guy.  So, I learn something guess I never thought of this but yea.... It would be a good idea to have them on hand.

Tom

[Chryco Psycho]

absolutly you must have the pistons on hand , you can rough bore the block but to fit the piston they have to be there , pistons have a tolerance in size & need to be fitted individually

[my69]

Great thread guys!
My engine guy told me the SAME thing  about the pistons and the rods. pretty much what this thread
is all about.   when he said that he also said in order to do this he'll need the $2,000.00 up font to start his process

So I now I need to start saving the dough 

Alls well in love and war.

[AKcharger]

Well I popped out my pistons on Saturday. I didn't need to reem the ridge out so pehaps the bore might still be good? Wich I had a good inside mic to check 'em

[MOPARHOUND!]

absolutly you must have the pistons on hand , you can rough bore the block but to fit the piston they have to be there , pistons have a tolerance in size & need to be fitted individually

The top shelf Ross Pistons in the 496 have two pistons undersized, .0015 or so.  Because the machinist had them on hand, they now occupy #7 and #8 cylinders, opposing each other.  If I re-did the math, the 496 might be a 495..............LOL.

[Sublime/Sixpack]

Well I popped out my pistons on Saturday. I didn't need to reem the ridge out so pehaps the bore might still be good? Wich I had a good inside mic to check 'em

Glad you didn't feel the need to use a ridge reemer. The machinists I patronize prefer that people not use them.

[Nacho-RT74]

Sorry to be some disagree with mostly of ppl here...
You DON'T NEED to have pistons in hand since machine shops have the books with all the info about measurements for all different kind, brands and sizes of engines, including cast part numbers and everything, in some cases includes some tolerances numbers.

HOWEVER...

Is BETTER to have the pistons, specially for used or aftermarket non stock parts, yes could it be better but NEED IT no, isn't true you NEED it.

[TylerCharger69]

If you are going to go with the overall stock type pistons AND rings.....it is NOT necessary to have the pistons on hand because it SHOULD automatically be known from the books what the tolerances are as far as bore to piston is concerned and as long as the machinest knows his s**t.....BUT   if you are going to go with....say....Keith Black, or Wiseco pistons, or any other aftermarket products....it IS necessary because the tolerances are different and heat displacement is different too.   If you choose cast, moly, or chrome rings....that makes a difference too.   The performance product should give you a sheet containing this information, including ring gaps, tolerances, etc.   I've run across a few issues with Wiseco pistons  as far as the balancing aspect was concerned  and when I weighed them out....I found a couple of the pistons were up to 4 grams off in weight, and had to "carve" accordingly.   As far as leaving a naked block on the shelf....well....either way, pistons or no...it's not a good idea.   You want to assemble that engine while it's fresh and clean.   If you remember back in 1970,  the Chevy 396 engine had a 402 version.  This was because of the blocks sitting on a shelf  and had to be bored to clean them up to be used because of rust  and pitting in the cylinder walls.  (I found this out the hard way during a 1970 El Camino restoration which was listed as a 396 on the tag, but sported a "402" engine)   Hope this helps  you in your decision!!

[is_it_EVER_done?]

To those that believe that you don't need your pistons before getting your block bored, I am shocked that you can find a machinist that would ever do this!

No book can provide current specs for any piston line, as the materials, expansion rates, hardness, coatings, diameters, etc., change all the time. That's why the manufacturers provide specifications with each set of pistons - even the cheap, cast versions.

If your machinist suggest this, find another right away. ANY shop/machinist that thinks this is an acceptable method is a hack! Can machining be done without knowing the pertinent specs of the pistons you plan on using? Yes, but it would have to be done at the largest specs possible -which is basically the same as a well worn out engine, which is probably why you are getting a rebuild anyway!

I offer this scenario. - Would you preffer laser eye surgery from a doctor that used your specific 'tested' results as a basis for the machine settings, or would you go with a Doc that used your previous eyeglass specs to set up the machine? I realize that an engine isn't as 'personally' critical as that example, but the principal and results are the same.

Sorry to say it, but if you are trying to do it right, there is ONLY one answer to this question!

[AKcharger]

...If you remember back in 1970,  the Chevy 396 engine had a 402 version.  This was because of the blocks sitting on a shelf  and had to be bored to clean them up to be used because of rust  and pitting in the cylinder walls.  (I found this out the hard way during a 1970 El Camino restoration which was listed as a 396 on the tag, but sported a "402" engine)   Hope this helps  you in your decision!!

Really? cool little factoid!

Well I disassembled everything and with my Chi-Com "re-education camp manufactured" Micrometer the cylinders and Crank looked OK so perhaps I can get away with a hot tanks, hone and re-ring?

[TylerCharger69]

well...what exactly is your caliper reading  as far as bore size....and.....how much ridge do you have showing on top of the cylinder walls???  Another question....has the engine ever been rebuilt before?  If there is  very minimal wear....just a hone would clean it up, but  I, myself  would  bore  with new pistons and rings.   Some people who prefer their engines with factory specs  have requested to me that they would rather resleeve to standard size  rather than bore....just another option

[deputycrawford]

AKcharger, You might want the machine shop measure the roundness of the bores also. They could look great but be slightly egg shaped. Just go into the rebuild with an open mind.

[max]

i always take the block to the machine shop and have them bore the worest cylinder and see what it takes to clean it up. for example if it cleans up at .025 then i buy .030 over pistons and take them to the shop and have the cylinders matched to the pistons i bought.

it is very possible to have clean looking cylinder bores but they could be tappered so it is best to have them checked the right way. 

[fourspd440]

Bill,
  Call Coleman's Machine Shop up in Glousester.  They seem to be very good.  I'm pretty sure that he will want the pistons on hand to fit them perfectly.

Stan

[GreenMachine]

i always take the block to the machine shop and have them bore the worest cylinder and see what it takes to clean it up. for example if it cleans up at .025 then i buy .030 over pistons and take them to the shop and have the cylinders matched to the pistons i bought.

it is very possible to have clean looking cylinder bores but they could be tappered so it is best to have them checked the right way. 

  I agree with Max, I had a std bore 400 that I estimated needed a .040 overbore. I bought the pistons and everything else and took them to the machine shop only to find out that when they bored the worst cylinder, it needed .060 pistons. So I had to send back the pistons and rings and pay a re-stocking fee, and wait several days for the .060 pistons and rings to arrive.
  My machine shop told me the best way to do it was bring the engine in for a cleaning and test bore. then, once you know the overbore size and that there aren't any cracks in the engine you can order you're parts. They do need the pistons when it comes to the honing.