My machine shop bored out my block .020 this weekend for my Arias pistons from the group buy. My machinist noted a couple of interesting things. He said that the bore material was quite soft when compared to others he has done. Also he noted that my motor with only 6000 miles had some taper at the top of the bores....most likely from the short stroke of out motors design. Maybe the AEBS stroker kit with new sleeves and longer stroke wouldn't be such a bad idea after all

 

Good to know!

 

it's not the stroke that causes the out of roundness, it's the open deck block. the short stroke/long rod actually reduces piston side loading.

 

good post...and another good reason that all blocks should be bored out .020 when building them up.

 

Tapering is going to happen to all engines even one with 6K on the clock...What I would be interested in knowing is how much tapering had occured?

 

What's the deal with tapering? Is it good or bad?

 

If you looked at this block you would see that it is not a true open deck like in a Honda.....the open deck only goes down about 2.5" from the top of the bore...not all the way down.
He mentioned that the amount of taper he found was equivalent to some of the Honda's he has done with over 100,000 miles. I looked at the bearings though and they were almost perfect....so the car had a few oil changes in the first 6000 miles.

 

Taper is cause from excessive ring wear right at the top of the bore. .....so the bore gets wider as you go from bottom to top of the bore. Excessive taper is bad...but a little is normal.

 

i know what the block looks like. what you don't understand is that you have to support the cylinder walls where the piston side load has the most leverage, that is the top of the cylinder. the lip in the middle of the water jacket has it's advantages and disadvantages. yes it provides a little extra support, but it also means the forging die can't forge the block all the way down the bore, which is important for having a block of uniform strength.

 

royce - why would the piston side load be greatest at the top of the stroke? the rod is vertical at that point, isn't it? wouldn't the greatest side load be mid-stroke, when the crank journal is perpendicular to up/down, creating the largest angle between vertical and the rod?

not trying to be difficult, just don't understand...

ahm

 

Have you seen how thick the stock sleeves are....and this motor was naturally aspirated....no boost yet.

 

The greatest inertial loads on the rod and wrist pin/piston is when the piston is at TDC and BDC. The "rocking" of the piston within the bore would be with the piston is at BDC...right? As mentioned, when the piston as at the top, the rod is fully extended, and it would seem that the side loads would be minimal at that point.

 

i worded that badly. yes, force against the cylinder wall is greatest at 90 deg. of crankshaft rotation or halfway down the bore. but the as the the piston pushes against the cylinder wall the top will see the most movement simply because it's farthest from the crank centerline. it's like a building that sways in the wind, the top floor will move side to side a lot more than the lower floors, regardless of where the wind hits it. or if you wanted to topple over a granite block, you'd try to push it at the very top, cause that's where the least amount of perpendicular force will tip it over. with a free floating cylinder wall, no matter where the piston pushes against it, the top will walk the most and lose concentricity the most. that's why you see taper vs. say ballooning in the middle of the bore.

 

Interesting...maybe a reason to at least pin the deck.

 

I think the vq35 was a poor resdesign of the 3.0 liter engine. end of discussion?

 

Those are good points royce, but i just wanted to point out that those analogies are missing something. There is nothing pushing down on the building yet there is a head and gasket torqued down on the sleeves. What im wondering is, how much force is being pushed down on the sleeves and how much side loads are being exerted on the sleeves by our pistons.

 

Most engine designers will tell you that the VQ motor is superior in almost every way....for its intended purpose.

Yes, the rods and pistons are a tad weak...but not for N/A applications.