Gunfreak25

My 455 has never been rebuilt, poorly maintained. Time for a rebuild. Tore it down and now am undecided as to what to do. I'm going to take it down to the shop in a couple days to get them all properly measured since I don't have a bore gauge. If I wanted to reuse my stock pistons, what the maximum allowable bore diameter before a proper machine shop hone/oversized pistons is needed? The skirts on my stock pistons have a little wear but still have much of the tooling marks still intact, can feel them with my thumbnail. If I can reuse the stock pistons that would be great, i'll just throw on a set of .010+ rings and make sure they gap correctly.

So, maximum bore specs before I have to ditch the original pistons?

rustyroger

More than 005" wear on the bores and it needs a rebore, rule of thumb(nail); if there is a ridge near the top of the bores you can feel with your fingernail it needs machining.
Don't regap +010" rings as they will not fit properly.

While it is all apart get everything else measured for wear and do the whole job properly, it will be the most cost effective way in the long term.

Roger.

joe_padavano

It's not bore that's the issue, it's piston-to-wall clearance. You need to mic both the pistons and the cylinders to determine the current clearance.

Gunfreak25

Roger that, i'll just have it bored then. Shop wants $190 for a bore, hone, hot dip and new cam bearings. Shweet! They still do real genuine hot dips here too, not a booth. I am finding good deals on pistons right now so I see no reason not to do it properly. Thanks all!

Assuming I leave everything stock as far as replacement parts go, which i'll be doing, can I run 87 octane with high comp pistons or will I get pinging?

ah64pilot

If you run high compression pistons you're going to have to run 93...

if you run the thickest head gasket you can find you have a better chance...but it won't guarantee you can use 87. I would stick with lower compression pistons and a thick head gasket to make sure your compression is low enough to run 87. If it is going in the deuce and a half or whatever it is you have, lower compression won't hurt you much for torque. You won't be spinning high rpm or make instant power anyway with the low gear / big wheel combination.

Gunfreak25

I'll stick with low comps then, just thought i'd make sure before spending the money on hi comp pistons which i'm finding at the same price as low comps. Thanks! And yes, it's going in my deuce and a half. I'm aiming for 8mpg with those 40" rubbers!!!!

ah64pilot

TRW makes a forged "10.25:1" piston that is actually around 9.5:1 w/ a .040" gasket. If you don't deck the block, and run a .040" or greater gasket you can run 93 with not problem but you will be hard pressed to run 87 when you're demanding that it move a 40" tire carrying a huge truck. If you really need it to run on 87 you will have to go the lower "advertised" compression route. If the engine ran fine before, it may be a good idea to have the machine shop measure the piston dish & find something comparable. Make sure they have all of the parts before they do machine work, cylinder bores are matched to pistons...everything is machined to work together. Good luck!

Gunfreak25

So it's advisable to have the pistons WITH the block when I take it in to the shop? I know I want it bored .030 over, but I guess depending on the initial cylinder wear the final bore diameter can vary greatly, correct?

ah64pilot

Correct. The piston may be .030" bigger than stock, but the block will need to be machined enough to give you proper piston to wall clearance. Since different types of pistons require different wall clearance (cast, forged, etc) its a good idea to have them on hand when they machine for them. Also, its a good idea to have the pistons there to be measured because what may say .030" over may actually be .029 or .032 etc. You want to make sure, do it right one time...its cheaper than doing it all over again.

Gunfreak25

Thanks for the tip! Guess the first thing on my list are the pistons then. I am seeing sets of low compression/oversized pistons go for $250 to $300. I don't need anything fancy. Any brand or certain thing to avoid? Keeping in mind the application of course. Less than perfect vehicle that was not designed to drive more than 55mph. It will be my "town car". LOL

My budget for pistons will be in that price range.

Junkman

No need for forged pistons in this application in my opinion. I would just go for the cast pistons. This is what was in the engine originally, and they gave good service. Only reason to go forged would be if you are building a performance engine.

Gunfreak25

Tis what I figured, would anybody know of somebody selling a set of 30 to 40+ low comps? I'll more than likely get them off Egay but it's always nice to take something off somebody else's hands, especially if it's priced right! LOL