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06-12-2013, 09:35 AM #1
cylinder boring before block decking
I have my cylinder block out at a shop right now to be bored, and they are currently waiting on a torque plate to be delivered before moving forward with the bore
Then the thought occurred to me, I haven't decked the block yet...I was planning on doing it myself, taking off about .003-.004 to remove a slight warpage on the outer edges, and also some gouges made by the head gasket.
Will this be a problem for the bore if the deck surface will be different on the assembled engine then when it was bored? I would think that the block would flex differently with the freshly machined deck, wouldn't this throw off the bore?
I'm thinking of telling them to bore it without the plate, whats your opinion on this?
Obviously the best thing would be to deck it first, and bring it back, but the shop is not nearby, it would a ton of driving for such a small detail.
06-12-2013, 09:38 AM #2
06-12-2013, 09:51 AM #3
Maybe so, but I may win at a contest of engine longevity haha
I realize I'm splitting hairs with this, the main reason I'm asking is I already told the machinist to wait for the plate to arrive, but doing so will give me another week or so of downtime, I'm considering telling him to go ahead and bore it
06-12-2013, 10:02 AM #4
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I depends on what they are using to bore it with. If they are using the type of boring bar that mounts on the deck, yes, it should be decked first. If it is a machine that mounts and locates off of the main bearing bores, it does not matter. Using the torque plate is always a good step.
06-12-2013, 10:13 AM #5
What kind of engine? Some need plate honed and some don't. SB Chev. needs one, deck is no big deal as long as it is close. On a Chev. the bore distorts because the head bolt holes are so close to the bore. Even worse on a 4.125 bore block going out to 4.155. You don't use the plate to bore the cyl., you use it when you hone it to size. The NASCAR engine builders run 220* + coolant through the block as well as using a torque plate when they finish a cylinder.
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06-12-2013, 10:22 AM #6
It's a cast iron inline 6 from a Toyota Supra
06-12-2013, 10:39 AM #7
I was always taught that you assemble the shortblock and measure the height of every piston at TDC then you can plan out how you're going to deck the block to get the piston-head clearance you want. You can modify the rod lengths if needed.
Impossible to measure the piston heights if you can't install the pistons you are going to use.
06-12-2013, 11:31 AM #8
Are you planning on doing the final hone after a mock up ? ---Trevor
06-12-2013, 12:36 PM #9
06-12-2013, 02:50 PM #10
in the middle due to local forces acting on the liner/cylinder top....
Exceptions are those engines with liners where the compression forces of the head seal is directed against a flange at the top of the block...such as a Cosworth DFV.....
Point is the OP already ordered the plate....Use it, it won't hurt and might just give a better job.
Further the OP stated that he was going to surface the block himself...My question is what kind of machine will this be done on???
Doing this job on a knee mill will not give a flat deck. You really need a bed style machine. Gravity will make the knee shift as the table moves from right , to center to left giving a curved surface.
All knee mills will do this on a part as long and heavy as your in line 6.
My advice is get the automotive machine shop to surface the block ...he should have a dedicated bed style or rail guide surfacing setup. It will give a better deck and be flatter than a mill can make. (provided it is a knee style of course)
Once the block is decked, fit up the torque plate with the same kind of head gasket you will use on final assembly and finish hone the bores...(ask if your machinist understands and provides "Plateau Honing") ....
He should also have the pistons you are going to install and a sample ring set....Clearance values provided by the piston makers is a rough guide. A hone operator/ machinist worth his salt will chart the taper and cam of the piston and
arrive at a clearance he believes will work for your intended use.
06-12-2013, 06:56 PM #11
the block and cylinders are all one casted piece, no sleeves, not sure what a wet deck is
Even if I lock the set screws on the knee it will still move? I could always run a dial indicator on the table surface while the block is sitting on it to see how much of a problem this is.
06-12-2013, 08:10 PM #12
Wet deck means the tops of the cylinders are surrounded by waterjacket, they aren't connected to the deck.
Besides the obvious knee mill table sag, how much travel does it have, how long is the block and what's the minimum flycutter radius you need to cut the deck in one pass? I can't see an 8" diameter cutter clearing the ends of a 30" long block on a knee mill.
I don't know anything about the Supra motors, but I know the slightly larger 1FZ's and there's no way you're decking one of those on a Bridgeport.
06-13-2013, 05:45 AM #13
If you hang a dial indicator off the quill and run the table side to side it will show that the table runs pretty much true, however you should clamp a piece of material to the table and take a full travel cut. You will be amazed to see that you have machined a huge arc rather than a nice straight part. This is because the table is only supported in the center, If you run the table to one side it will droop as a tiny amount of clearance in the gibs is greatly magnified out at the end of the table.
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06-14-2013, 08:45 PM #14
With one of the newer "boring mill" setups, the boring bar locates off the mains and existing bores. It doesn't matter what the deck looks like.
With my old Van Norman boring bar, which mounts on the deck surface, the block should be decked square to the mains first if you want your cylinders to be the same way.
I deal mostly with 1960s-1980s American V8s. Ford and GM had some pretty loose specifications on bore and deck squareness.
06-14-2013, 09:38 PM #15
06-14-2013, 10:17 PM #16
If you are working with a 2JZG series or a 7M series engine, deck the block, and slow down and wait for the torque plate.
One week won't matter one whit, just take it easy, and get it done.
So many 7M series engines had blown head gaskets, you are almost forced to always deck them and then use a torque plate.
With the 2JZG's power potential, do the same for it, and you have will have far more stable, far truer base to whatever you build.
Cometic also makes the very best gaskets for these engines.
Bonus thoughts: Stay the heck away from Monkey Wrench Racing in Detroit
06-14-2013, 10:29 PM #17
I still have one that came from a Monte Carlo, and some poor misguided soul wanted it in a Jeepster Commando. I finally got him to accept the Buick 225 V6.