# Covered Short Block Sitting Outside



## chadd925 (Jun 5, 2016)

A local guy has a 400 short block that was rebuilt 7 years ago and never fired. He covered it and kept it under a overhang OUTSIDE. Would this be worth looking at? If so should I just run the pistons down and feel for a shelf? Any recommendations would be helpful. Photos attached.

- Note - Block is.030 over, crank is.010 under. Rods have been reconditioned. Has receipts for the machine work.


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## Pinion head (Jan 3, 2015)

As a special core provider, I have even wandered out & bought several never run rebuilt 428 & 455 shortblocks out of regional machineshops that customer could not pay the bill. Also kept one of the country's leading Pontiac crate engine builders in 400 Pontiac cores for over a decade, as had deals with mgrs of several large Pick-N-Pulls & crusher yards, buying Pontiac 400 & 455 & Caddy 472 longblocks at waaay under listed price. 

It amazes me that the pics show no surface rust in the cyl bores. I would think the Bay area would be far from a dry environment, I visited there in May many years ago on my honeymoon & it was cold & damp & we were very happy to fly down to SanDiego for 4 more days. Storing outside under a tarp, even if in a crate, typically just doesn't cut it. I've used a product by the name of Kano Products WeatherPruf on my own indoor stored longtime block & crank cores & keeper engine components. started buying it by the case when it was near $70 a case in the mid 90's. WeatherPruf leaves a hard amber colored coating whereever you spray it. After disassembling a shortblock & cleaning it in my solvent tank, or @ my machinists in his hot tank, if the components are not being machined, I'll let them air dry, then spray all the machined surfaces, including the block face with WeatherPruf. All of my blocks, heads, cranks, are inside UP off the concrete floor, but w/o the WeatherPruf, they tend to lightly surface rust. I can guarantee my climate is much less humid than the Bay area of Northern California. When it's time to have an engine machined, my machinist then does a short hot tank of the block & crank & it dissolves the amber colored protective coating. 

All I can see in the pics is what appears to be a '70-76 1/2 400 shortblock, which appears to be a rebuilt with cast pistons. Both cast 8 relief pistons, as well as bargain forged TRW/Sealed Power 400 pistons seem to set down in the hole about .020-.025. Personally, I prefer zero deck, so block has to be decked, but one typically doesn't get that in such bargain deals. Also see a double row roller timing chain & what appears to be a M54D Melling oil pump. The receipts, hopefully show a set of ARP rod bolts & resizing of the cast rods, as well as dynamic BALANCING. The parts & labor to recreate on your 400 block & crank, I would guesstimate at around $1200-1500 in my area. On the West Coast,I can imagine another 50+ %. The bottom line , is one shouldnt have to pay 50% of what the original bill was. If the engine was factory 4 bolt main capped '67-70 high performance coded 400 block, would be a totally different deal, as the block would be very desirable, & the original rebuilt price might be very good deal. Personally, I approach such deals very carefully, for last 25 years, have owned a Starrett brand set of inside micrometers that I roughly ck block cores with. Also have worn out an expensive dial caliper & am on another one today. On occasion, I've hauled blocks to a local SuperComp racer buddy's shop & ran his dial bore guage down the cyl bores. As long as machine work was dead nuts on, such bargain deals, can be truly a bargain. Hope this helps!


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## PontiacJim (Dec 29, 2012)

Looks like an engine for a basic application, ie stock, not high-performance. Cast pistons, cast rods are fine for about 5,200-,5,500 RPM's. The cam will dictate your torque/power curve whatever has been selected - which you can swap out easy enough. 

Those cast pistons don't look like the ones I had which also have a chamfer around the outer edge above the piston rings which lowers your compression further. Those type pistons will have an effect on your eventual compression ratio, so it is important to know what the cc's are of the tops of your pistons shown, which my guess is 12-14 cc's. 

PH mentioned decking the block. What you are after is a distance/space from the flat portion of the top of the piston to the corresponding flat areas under the head around the combustion chamber to be in a range from .040" - .045", called the "quench area." You could probably go a little tighter with cast pistons. This measured range helps the fuel burn better and you have less chance of detonation with optimum timing advance.

Some engine builders will "zero deck" the block which is machining off the tops of the cylinder deck/bores of the engine until the tops of the pistons are near even with the machined deck (some go less while some will have the piston protrude above the deck), thus leaving you with a "zero deck" height. The factory piston deck height is typically .020" down inside the cylinder bores. This space can be measured in cc's and becomes part of the formula in determining your overall compression. A 400CI bored .030" over has a diameter of 4.150" x .020" (our height above the piston OR down in the hole from the deck) = .270 cubic inches. Converting cubic inches to cubic centimeters (cc's), you get 4.4 cc's of volume above the piston. If we "zero deck" the block, there is no volume above the pistons, so no cc's to calculate.

Most head gaskets are typically .040" thick and I see compressed they appear to be advertised as .039" thick. If you "zero deck" the block and use the typical head gasket of .040", you wind up with the piston top being *.040"* below the head surface which puts the "quench area" right where most engine builders like to see it.

If you do not "zero deck" the block, you have the .040" head gasket plus the factory deck height of .020". This gives you a *.060"* "quench area" which is where most engine builders don't like to see it.

Obviously from the factory this was done, but keep in mind the gas was leaded and resisted detonation much better than today's ethanol gas. So engine builders like to see a tighter "quench area" which promotes a better flame in the combustion chamber and lessens the chance/effect of detonation.

However, my opinion is, I am not a fan of "zero decking" a block. It cuts down the block surface which in turn changes the geometry/fit of the those other parts that bolt to the block, ie the heads, intake, valley pan, and you also want to make sure your head bolts don't bottom out and crack your block. Additional milling of these mating surfaces adds up to more labor $$$. (Milling the heads to increase compression rather than a light clean-up pass will generally require the intake side to be milled as well, so I always go with just a clean-up pass)

What I did with my 455CI was to keep the factory .020" down in the hole piston height and use the Cometic head gaskets which I ordered at a .027" thickness versus the generic .040" thick head gaskets. (These gaskets are about $100 each, so not inexpensive) So I have a piston .020" down in the hole plus a .027" head gasket which gives me a measured .047" "quench area." I am using forged pistons which expand a little more when hot so the "quench area" will be slightly reduced by a few thousands. This will then put my "quench area" near .045" which is in the acceptable range for a good "quench area" _WITHOUT_ "zero decking" the block or having the need for additional $$$ machining done to my other parts. I will check my head bolt lengths to ensure none bottom out, but do not expect any problems.

I am also willing to accept the additional cc's found in the space above the piston tops being .020" when added to my gasket thickness of .027". The total cc's that this is, is added to the total cc's found in the valve reliefs on the top of my pistons, plus the total cc's of my combustion chambers found on my heads to give me all the numbers I need to calculate my engine's compression ratio which for my engine is about a 9.2 to 1 compression - which is where I want it to be to run pump gas. But for some, the extra 4 cc's or more can mean a lot in compression value and "zero decking" is one way to increase compression or blueprint the engine as allowed for example in NHRA Super Stock racing - which PH has more experience with.

OK, that all said and no doubt confusing you further, IF I bought the shortblock, I would bring it to my machinist to have it disassembled for inspection to ensure that none of the rings have gotten stuck which would cause me problems later, cylinders don't need a freshening up light hone job, verify all clearances, then re-assemble/re-torque everything down again, and go from there. So if you decide to buy it, cut a deal with your buddy allowing you to take it to a shop for disassembly & inspection (at your costs) before you buy it. 

You might also want to figure out what the cam specs are and what you are looking for in engine performances before putting back in the cam. :thumbsup:


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