why are block cylinders tapered

[DanielRobert]

Wondering why engine block cylinders are tapered. What is the effect of this and what is lost or gained by boring straight. This would be a good reason to not bore a low mileage block?

[John_Kunkel]

Used block cylinders are tapered at the top because pressures exerted at the top of the ring travel and at the thrust and non-thrust surfaces is highest near the top of the bore. This taper causes the rings to lose their sealing ability and this lowers compression; lower compression means lower power.

If you're not looking for maximum performance and lowest oil consumption, simply reaming the cylinder ridge and glaze breaking the cylinders will save the overbore for another day.

[BSB67]

Wondering why engine block cylinders are tapered.

They're not made that way, they wear that way.  Usually used blocks are both tapered and out of round.  How much depends on its past life and mileage.

What is the effect of this and what is lost or gained by boring straight.

Taper = less power and more oil consumption.  
Straight bore = A lot less money in you wallet

This would be a good reason to not bore a low mileage block?

It is always best to have round, straight bores.  Here are the three things you need to decide: 1) exactly how tapered and out of round are the bores, 2) What is your goal is for the engine/car, and 3)  What is your budget.

[DanielRobert]

Thanks guys,
I thought they came that way   Good to know. Leaning towards machine shop work at this point. Two different places quoted me $1000 starting price for the block. Cleaned/magnafluxed/bored/honed and line bored

[birdsandbees]

They come that way in some aircraft engines... but the other way around, tighter at the top !! Called "choke" cylinders.

[BLK 68 R/T]

Thanks guys,
I thought they came that way   Good to know. Leaning towards machine shop work at this point. Two different places quoted me $1000 starting price for the block. Cleaned/magnafluxed/bored/honed and line bored

Do they have a torque plate for the bore and bone process?

[DanielRobert]

Not sure if the use torque plate....they better for that price

[BLK 68 R/T]

No idea what the average rate is for block machining these days. But IMO if they are a quality shop then they should have a torque plate. Or have one they can borrow/rent/use as needed. Ask what there machining process involves and go from there based on what they say. If they don't mention even using a torque plate...move onto another shop 

[John_Kunkel]

Two different places quoted me $1000 starting price for the block. Cleaned/magnafluxed/bored/honed and line bored

Wow!! Less than $500 around here.

[c00nhunterjoe]

Two different places quoted me $1000 starting price for the block. Cleaned/magnafluxed/bored/honed and line bored

Wow!! Less than $500 around here.

Same here. 1000 is high.

[Challenger340]

Two different places quoted me $1000 starting price for the block. Cleaned/magnafluxed/bored/honed and line bored

The above completely misses Decking/Milling the Block to "square" it up ? and provide adequate sealing finish for today's gaskets.

Oh well....
As a Shop Owner who PAYS someone to do work on Engines, here is my opinion as to what should be acceptable "Time-wise" for those competent people tasked with: providing quality Machine work performed to specifications, that I will accept leaving my Shop. I will provide those "Acceptable Specs" at the end... which I personally Inspect BEFORE it leaves.
I do NOT want anyone "rushing" just to make money, nor will I accept or PAY for inferior product leaving ?
therefore,
these are only BASE time expectations, beyond which very simply informing me of a "problem" requiring extra time to remedy, is always allowable, and MUCH desired, versus, something potentially sub-par slipping through !

And to clarify the "type" of work referenced below, this is "GENERIC" style machining fine for the average Hot-Rod build.... NOT to be confused with Engine BLUE-PRINTING procedures typically performed on High Performance or Racing applications, and take FAR longer !

Below is just acceptable "general" machining.


Cleaned:
* Involves removing the Cam Bearings, Frost Plugs, and all threaded Oil Gallery Plugs(usually more than one will strip and require a spot weld to remove)
20 minutes
* Place the Block in a caustic Hot Tank or jet wash, overnight or until all grease/oil buildup is removed, then remove and wash thoroughly with Hot Water to remove caustic, then Blow-Dry the Block thoroughly so the now bare metal Block does not begin rusting(Threaded Bolt Holes especially must be DRY)
30-40 minutes Labor washing/blow drying thoroughly etc. No time while sitting in Hot Tank or Jet Wash.

Magnaflux:
* If using a powdered Mag Kit, some touch up on Decks etc can be warranted to remove leftover caked on gskt material, then get block up on a well lit table, magnetize across all critical areas and apply mag powder looking for cracks, Main Webs, Decks, Cylinder Bottoms & Tops, Mounting ears. De-Mag Block and remove Mag Powder(Brake Clean, etc.)
45 minutes

Bored:
* If performing BOTH Boring & Honing, good idea at this point to Mic all 8 Pistons & record sizings(Yes, they can be up to .001" different within a set of 8, and usually within .0005" even on the best Forged units). Check/Adjust Mic to be used to std, MIc Pistons and record, Set-up Bore Gauge to targeted overbore sizing, then Bore Gauge ALL 8 Cylinders to determine if they will accept Bore target. Set-up Boring Head to desired Bore Target and clamp Engine Block in Boring Machine/Center/Reference..... Bore 8 Cylinders to target.  Remove then "Bored" Engine Block, re-check satisfactory with Bore gauge, Blow out iron cuttings.  
1 Hr 15 minutes

Honing:
* Clean/Lube Main Caps Bolts, and Torque Main Caps on Block to spec. Put Block in Honing Machine/Clamp/Set-up Heights/Stroke/Speeds for cross hatch by Bore dimension. Thread Chase all Block Deck Bolt Holes for T/Plate(15 minutes by itself), Set-up Dial Bore Gauge to FINAL Sizing for desired Piston to Wall clearance as determined from prior Piston readings, apply Torque-Plate at Rec Torque.
30 Minutes
* Begin Cylinder Sizing/Honing with 220 grit(if NOT using Diamond Head) on 4 Cylinders(one bank) to within .002 of Final @ High Load.
20 minutes
* Remove T-Plate to allow Cylinders to cool on that Bank and install T/Plate on other Cylinder Bank, rough out to within .002" of final @ High Load, remove T/Plate and allow Block to cool.
25 minutes (walk away go do something else)
* Re-apply T/Plate @ Torque, check repeat, re-hone/correct cylinders back straight and round from cooling, on/off T/Plate BOTH sides, Hone to within .0005" of Final monitoring Block temps with infrared so as NOT to apply excessive friction Heat that will distort as it cools....
1 Hour
walk away and go do something else again, allow Block to stabilize really well.
* Come back, Re-apply T/Plate @ Torque each side, Hone last .0005" @ High Load to Final, Changes Stones @ 4 strokes only Low Load, Changes Stones again 4 Strokes only @ low Load = Plateau Finish(BOTH SIDE and T/Plate On & Off again for repeat)
1 Hour

Line Honing:
* Machine all 5 Main Caps .003", Clean/Lube and install @ Torque, Install Block in Line Hone, Clamp Block, Set-up mandrel Height/Length of Stroke, Set-up Dial Bore gauge  
45 minutes
* Stroke Mains .001" Vertical at a time, Bore Gauging as you go, turn Block end for end and re-clamp in machine every .001", UN-Torque'ing Cracking, and re-Torque'ing Main Caps each time for repeat, to within .0005" of Final
1 Hour
walk away and go do something else to allow cooling
* Come back, Re-Torque Caps again & check, Stroke Mains to Final
15 Minutes  

Final Washing, Installation of Cam Bearings/Frost & Oil Gallery Plugs:
*  washing/brushing all Oil galleries and de-carbon/abrasive removal from Cylinder cross-hatch, dry & thoroughly inspect Block, includes installation and "fitting" of Cam Bearings, Frost & Gallery Plugs, Lube/Torque Main Caps, Bag CLEAN and ready to assemble Block.
2 Hours

Total 10.25 Shop Labor Hours
at such Rate for the demographic area to reflect decent Employee Wage(who are competent) so they can actually EAT and Pay rent/mtg and actually still show up for work/retain, Shop Bldg Rent, Business Taxes, Power, Heating, Accounting, Light Bulbs & repairs, Employee Benefits Health/Dental & 401K and on and on and on
with added
3.5% Shop Supplies as a general standard of labor performed to account for consumables ie: Honing Stones/Honing Oils/Lubricants/Sealers/Cutter wear/rags/cleaners/hand cleaners/employee PPE/machine maintenance
3.0% Environmental for such things as sump containment and paying for removal/exemptions/permits to dispose etc.


Expected machining tolerances:
* Cylinders must be within .0005" Straight & Round at desired Piston to Wall clearance with the T/Plate installed.... usually more like .0002' to .0003" (2 to 3 ten-Thousandths), correct Ra/plateau finish for ringset specified
* Line Honed Mains Final should be within specs, no more than .0005" Straight & Round, repeatable under UN & RE-Torque with Lube specified.
* Block and Cylinders must be perfectly CLEAN, white glove wipe anywhere = free of Carbon/Carburendum or Caustic residues
* Cam Bearings must exhibit no drag, able to turn Camshaft with fingers only under light oiling.
* Written report provided, all Pistons numbered as measured and fit to their Bores with all Final Cylinder Sizings/Clearances, Final Main Cap Dimensions @ Trq,  

So long story short here.....
To perform the above at our Shop.... to the specifications posted.... takes us at least 10 Hours !
and,
While it is very true that SHIT will RUN.... I have a hard time believing anyone any good, can do the above... SAME-SAME... for $500 Bucks and still keep the lights on ?
If it is $500 ?
it is either NOT the same-same... you got one helluva DEAL.... or... like I said before... SHIT will RUN ?
Your Call !

[66FBCharger]

Very informative.
Can you please explain the process of fitting cam bearings?

[DanielRobert]

wow! Thats great  info. I don't have a problem with the $1000 for machining. I used to be self employed(upholsterer) and I know how much time is spent on doing things the right way and how much time is spent doing things your NOT getting paid for. Valve jobs start in this area(Detroit) at around $400 so, I expect the block to be a lot more.
Thanks
Dan

[Bronzedodge]

Nice detail in that write up, Challenger 340.  Especially the part regarding what it takes to run a successful business.   

[John_Kunkel]

it is either NOT the same-same... you got one helluva DEAL.... or... like I said before... SHIT will RUN ?

OR, some shops don't waste time on operations that don't amount to 1% improvement in performance/reliability.

[c00nhunterjoe]

Im not taking anything away from any shop or person on this site. This is a quote i was given today by one of my local areas major machine shops who is well known and very reputable in the car industry in our tri state area. They do mild to wild engines. While i admit, my under 500 quote is now dated, it wasnt that far off.

[John_Kunkel]

Hmmm, if the mains aren't "out" why do anything? Are torque plates really of that much value if the block isn't heated to operating temperature?

http://www.hotrod.com/articles/cylinder-block-honing/

IOW, is the expense/hassle of trying to attain that last few tenths of a thousand precession really worth it for what's likely just a street motor?

[c00nhunterjoe]

I just got the quote based on the origonal posters question of paying 1,000 for the work. Im not arguing what is, or is not needed on a street motor vs race. There are things i could argue all day long in race applications that i wont do anymore based on my personal experiences, but thats a different subject.

[Challenger340]

Hmmm, if the mains aren't "out" why do anything? Are torque plates really of that much value if the block isn't heated to operating temperature?

http://www.hotrod.com/articles/cylinder-block-honing/

IOW, is the expense/hassle of trying to attain that last few tenths of a thousand precession really worth it for what's likely just a street motor?

Got to love the "comic Books" LOL !

The reason you do Mains is to SET Bearing Clearance and Bearing Eccentricity ? Which changes according to "crush" and Highside versus Lowside Cranks.
Next Time you have an Engine Bearing in your hand ? Measure it's thickness in the middle, then over as you move closer to the parting lines ?
Anyone wish to quote "spec" for a P Bearing Eccentricity 500 hp 440 from the "Book" ?
Oh wait,..... can't find the BOOK with Bearing Eccentricity ""spec" for 500 hp ? or 600 HP ? How about same on an "H" eccentricity Bearing ?
or maybe because Chrysler maybe never MADE a 500 hp 440 huh ?

"Stock" clearances/eccentricities work for awhile... and as I said "poop WILL run", but to answer your question about being precise and showing pride in your machining, the difference is LONGEVITY ! and YES...even on just a street engine

The threaded Head Bolt distortions at the TOP of the Cylinder change very little from Hot to Cold... and mostly if not ALL concentrated in the top 1" to 1 1/2" of the Cylinders and ring travel, the MOST important part for power production as that's where the peak combustion pressure and sealing is most critical, which the rest of the Cylinder pales in comparison....ask me I know.... as we used to run a heater in ours, and yes with the Blocks at 180*F 

[Challenger340]

it is either NOT the same-same... you got one helluva DEAL.... or... like I said before... SHIT will RUN ?

OR, some shops don't waste time on operations that don't amount to 1% improvement in performance/reliability.

OR, some people would NEVER recognize, NOR know the difference anyway ?

[John_Kunkel]

If you were a car salesman you'd be selling A/C in Antarctica.

[Challenger340]

And if you were an art critic, it would be for marvel comics.

[John_Kunkel]

Totally non-sequitur but I'll give you a touché out of pity.

[DanielRobert]

Found a cheaper machine shop that didn't use torque plates for boring and when I asked why? he said it's only if you want to squeeze the most hp you can from a motor. He didn't seam too concerned about not using them.  BTW I'm not building a bracket racing motor , but don't want a shop thats not paying attention to the thousandths  of an inch that blow motors.

[Challenger340]

Ridiculous, straight and round is straight and round, and sealing efficiency is sealing efficiency, and it matters Not Race or Street... it is done for longevity.
just say'in...
IMO, BEST rings for a NON-Torque Plate Bore job, is just a plain "Cast Iron" set ?