Engine disassembly quiz

[Duke W.]

You are disassembling your engine for a blueprint/overhaul to OE specs or are only doing internal modifications to improve performance without affecting idle characteristics or normal driving opeating behavior. (You want it to pass a PV.)

Once the heads are removed, what is the next operation?
Hint: It is NOT removing another part.

Duke

[John H.]

Re: Engine disassembly quiz

You are disassembling your engine for a blueprint/overhaul to OE specs or are only doing internal modifications to improve performance without affecting idle characteristics or normal driving opeating behavior. (You want it to pass a PV.)

Once the heads are removed, what is the next operation?
Hint: It is NOT removing another part.

Duke

Duke -

Measure the deck to down-in-the-hole piston clearance (for all 8 cylinders) so you know what you're dealing with as a baseline.

[Michael W.]

Re: Engine disassembly quiz

Massage the heads.

[Jeff P.]

Re: Engine disassembly quiz

Men; the next step is to find top dead center (TDC) and check the timing mark on the harmonic balancer.

[Larry B.]

Re: Engine disassembly quiz

I,ve never been convenced that measuring deck heights using stock cranks,rods and piston deck heights meant much as they all vary some.When measuring you must also be sure you measure to the piston at pin center line because of piston rock caused by piston clearnce.

[Duke W.]

Re: Engine disassembly quiz

John H. had the correct answer - measure the deck clearances of all eight cylinders at TDC - the distance from the piston crown to the block deck - before you you proceed with pulling out the pistons and rods.

Now, the next question is: Why is this important?

Duke

[Gene M.]

Re: Engine disassembly quiz

You are disassembling your engine for a blueprint/overhaul to OE specs or are only doing internal modifications to improve performance without affecting idle characteristics or normal driving opeating behavior. (You want it to pass a PV.)

Once the heads are removed, what is the next operation?
Hint: It is NOT removing another part.

Duke

Not enough information provided. Is engine total degreased and on an engine stand or still in the car? Is this block assembly verified original and not a stamper. Was it never taken apart previously? Are the casting numbers real? If it is a stamper stick the heads back on and get rid of car. Figure on trashing everything except head and block castings, crank, timing cover, oil pan, balancer, distributor, intake and exhaust manifolds, starter, water pump, pulleys, and possibily rods.

I just don't see your point.........

[Jeff P.]

Re: Engine disassembly quiz

I'm not sold on this checking all the pistons to deck TDC. I like the Idea of cleaning the deck surface,and checking for warpage on the deck surface. j/s

[John D.]

Re: Engine disassembly quiz

Get a Summit catalog ?

[Gene M.]

Re: Engine disassembly quiz

I'm not sold on this checking all the pistons to deck TDC. I like the Idea of cleaning the deck surface,and checking for warpage on the deck surface. j/s

Now Jeff that makes sense. The old stuff deck height will mean nothing. Rebuild will have new bore, pistons, reconditioned rods or new rods along with new bearings and turned crank. So deck height measured on the old engine will have nothing to do with the new parts and machining. Hope the deck is flat so numbers pad are not touched since it is an original block.

[Duke W.]

Re: Engine disassembly quiz

Measuring deck height prior to disassembly (and you can assume this is done on an engine stand since the engine will be completely rebuilt) tells you two things.

First, it tells you if the block decks are high or low relative to OE spec, and this dimension can vary considerably from engine to engine and even side to side on the same engine. It accounts for most of the deviation in CR from OE spec. You then use deck clearance along with other data you measure or obtain from tech specs to determine what the CR actually is for EACH cylinder, and if the engine did not detonate prior to the rebuild it can run at least as high CR as you determine from the measurements.

Second, this this data tells you is if the block decks are parallel to crankshaft centerline. Usually they are within a couple of thou, which is okay.

With the known deck heights you can now do "what-ifs" with a compression ratio calculator using different piston (and not all replacement pistons have the same compression height as OE pistons) and head gaskets to achieve your target CR range.

When the block is assembled you again measure deck clearance of all eight cylinders (it can change due to pistons with different compression height and "rod resizing", which shortens the rods a few thou.

With the final measured deck clearances and piston and combustion chamber volume data you can now pick a head gasket thickness that hits your target CR.

Deck clearance is one of the most critical dimensions in determining the actual compression ratio of the engine, which, unfortunately, most guys don't pay any attention to - including so-called "engine builders". You can buy a set of 11:1 pistons, but if the decks are high and you use a thick head gasket you will probably end up closer to 10:1, if that. A small change in clearance volume - a couple of cc head volume or a .010" high deck or the same increase in head gasket thickness can have a signficant impact on the actual true compression ratio of the assembled engines.

The point is to maximize the CR for premium fuel in order to achieve maximum across the range torque/power and fuel economy, and I've stated many times, including in my San Diego presentation, my maximum recommended (measured, true) CR for various OE or mildly modified OE engine configurations.

All the details along with photos are in the Fall 2009 Corvette Restorer article "Compression Ratio Explained" that I co-authored with John McRae.

Duke

[Duke W.]

Re: Engine disassembly quiz

The point is to maximize the CR for premium fuel in order to achieve maximum across the range torque/power and fuel economy,...

The Car and Driver Web site has some very interesting interviews conducted by Csaba Csere (pronounced "Chubba Chedda" - it's Hungarian) with key people behind the C7. The GM Powertrain engineer said exactly the same thing, so if you don't believe me..., and it applies to vintage engines the same as modern engines.

Duke

[Joe C.]

Re: Engine disassembly quiz

I've had many interesting conversations with Don Sherman and Patrick Bedard who were both Technical Editors of C/D long before Csabe came on board.

One of the most intuitive aspects of engine design is to build with near maximum dynamic compression for fuel detonation resistance while permitting the most aggressive spark advance program tolerated. If either of these is to be sacrificed in favor of the other, than SCR/DCR is of lesser importance.

Very few people understand this essential principle.

[Larry B.]

Re: Engine disassembly quiz

You are using a stock crank [which varys in stroke] stock rods ,even reconed {which vary in length} a piston that you at Summit and a block that you can't surface {because of the numbers} and your about a tenth or two in compression.Get real. The heads vary alot to. Decking the block will increase compression faster than surfacing heads but we have to save the numbers.Summit piston will have a flat top or a 11 to one.Not a lot of choice. You can have piston made to anything you want. For example just a two valve relief instead of four take out about 5 cc in the formula. I do this all the time and i have a Rottler F65 CNC that measures in tenth of thousanths.

[Jeff P.]

Re: Engine disassembly quiz

Men; The topic was DISASSEMBLE. We just talked about spending hours cleaning the deck surface and decarboning the tops of the pistons. We depth mic the distance from the deck to the top of pistons and recorded the Data. Are we ready to take apart something now ? The labor charge is going thru to roof. Or do we want to degree the camshaft to record the data? We are still taking this mill apart ?