Cylinder bore misalignment

[racear2865]

How much misalignment between the bore and the crank do you typically allow on say a sbc,
I'm not talking about the desaxe direction.

I dont worry too much about side to side misalignment as the rod will take care of that but I do worry about front to back alignment. I purchased a Starrett machinist square many years ago and I quickly check each motor to see how far they are off top to bottom using a feeler gage. Takes a couple minutes to check before I began any machine work. I too have a 4 inch probe to verify what is really there. Now to get to your question. The answer is two fold. You can have the piston running up and down the bore and rubbing on the skirts because of the misalignment. Also you have to remember if it is setting in a crooked bore then the rings are not square to the bore and may have blow by. Now a barrel shape ring will help the situation but still can leak slightly. The worst condition is a cast piston with, lets say .001 clearance, then it doesnt take much math to calculate when the piston will rub. Ive seen blocks with more than .005 misalignment top to bottom. You can see it on the skirt. Blow by is just what you want to live with. Is this what you were referring too.
reed

[englertracing]

How much misalignment between the bore and the crank do you typically allow on say a sbc,
I'm not talking about the desaxe direction.

I dont worry too much about side to side misalignment as the rod will take care of that but I do worry about front to back alignment. I purchased a Starrett machinist square many years ago and I quickly check each motor to see how far they are off top to bottom using a feeler gage. Takes a couple minutes to check before I began any machine work. I too have a 4 inch probe to verify what is really there. Now to get to your question. The answer is two fold. You can have the piston running up and down the bore and rubbing on the skirts because of the misalignment. Also you have to remember if it is setting in a crooked bore then the rings are not square to the bore and may have blow by. Now a barrel shape ring will help the situation but still can leak slightly. The worst condition is a cast piston with, lets say .001 clearance, then it doesnt take much math to calculate when the piston will rub. Ive seen blocks with more than .005 misalignment top to bottom. You can see it on the skirt. Blow by is just what you want to live with. Is this what you were referring too.
reed

okay we are closer now
so say you have all your finished shit sitting there,
bored honed, new pistons and rings

its 0.001" off, do you personally start over?
if its 0.002" do you start over?

[racear2865]

Too make your self comfortable. measure from top of top ring to bottom of skirt. That is the area you are only concerned with. You can calculate how much mislignment it will take before you mathematically have interference fit. .002 top to bottom of bore will not be a problem if cylinder is 6 inches long in my opinion if that is what you are asking, BUT I feel you have more misalignment than that with the amount of concern your exhibiting. What say??
reed

[englertracing]

best i can tell is 0.0015 on 4"

[racear2865]

what kind of piston, rings and clearance
reed

[englertracing]

well it is not a standard deal
3.150 bore
2.160 stroke

forged piston
nikasil wet liners
nitrided rings .8mm cmp
2mm oil

spins 6 or 8 to 13500 all the time

[modok]

Many blocks were bored from the deck surface, without checking if the deck was square or indicating the cylinder, and thus bored crooked, and worked ok. They already did the research for you!

The average factory engine, I'd say the cylinder is usually no more than .001 of center top to bottom, but the deck one end to the other of a 4 cylinder, honda perfect to .002,.002-.004(modern engines), .003-.006(old chevy). old Fords usually worst (.005+), but I got a chrysler once that rivaled the fords. It was so bad, set that thing up there, thought it was like a jeep or 235

[leahymtsps]

well it is not a standard deal
3.150 bore
2.160 stroke

forged piston
nikasil wet liners
nitrided rings .8mm cmp
2mm oil

spins 6 or 8 to 13500 all the time

Power sports engine ?
If so which direction is it out front - rear or left - right ?
If so how are you indicating it in from the top or bottom of the cyl.?

Tom

Tom

[racear2865]

well it is not a standard deal
3.150 bore
2.160 stroke

forged piston
nikasil wet liners
nitrided rings .8mm cmp
2mm oil

spins 6 or 8 to 13500 all the time

Run it.. Seen many worse than that. But let me tell you the real truth. Most people never check it so they will not know. If you dont do your on machine work, how will they check it. Yes I have a Starrett machinist square but how many do so also, you can bet many many have been built worse than that and they didnt even know it. If the block is not decked first, how will they correct unless something they have to correct. Yes Im lucky in that I do on a CNC but I did without for yeon years and that is why I installed set screws in the boring machine so I could move the block to get bore square but how many have never done that.
reee

[createaaron]

Boring a block of unknown history .0075 is probably not the best idea.
Personally I would have probed the deck surface and if it wasn't straight - level - parallel, I would use an indicator and sweep the cyl z axis on the major side and 90* to see how far the bore
might be tipped.
Dale has an RMC V40 he stole from an old lady who only used to drive to church on Sunday

Tom

I bored the block .015". I initially probe the deck and bores, then do my decking first. Boring second. Ill try that sometime using the indicator and sweeping the bore.

[leahymtsps]

Boring a block of unknown history .0075 is probably not the best idea.
Personally I would have probed the deck surface and if it wasn't straight - level - parallel, I would use an indicator and sweep the cyl z axis on the major side and 90* to see how far the bore
might be tipped.
Dale has an RMC V40 he stole from an old lady who only used to drive to church on Sunday

Tom

I bored the block .015". I initially probe the deck and bores, then do my decking first. Boring second. Ill try that sometime using the indicator and sweeping the bore.

My bad I meant .0075 per side

Tom

[createaaron]

My bad I meant .0075 per side

Tom

Im hearing ya now. Im gonna try sweeping the cylinder when I get another block in the CNC.

[createaaron]

Boring a block of unknown history .0075 is probably not the best idea.
Personally I would have probed the deck surface and if it wasn't straight - level - parallel, I would use an indicator and sweep the cyl z axis on the major side and 90* to see how far the bore
might be tipped.
Dale has an RMC V40 he stole from an old lady who only used to drive to church on Sunday

Just started to hone this block today. Went from 120 to 220 or 280. The bottom .200" or so of the cylinder on the major thrust side was already .002" over .060" over. So i basically had to hone the cylinder to the .002" its now within .0002" round and taper. Just need to finish it. My guess is that this block was unlevel when previously bored? And when i probed on location then bored to probe spec it didnt clean all the way..

[leahymtsps]

Boring a block of unknown history .0075 is probably not the best idea.
Personally I would have probed the deck surface and if it wasn't straight - level - parallel, I would use an indicator and sweep the cyl z axis on the major side and 90* to see how far the bore
might be tipped.
Dale has an RMC V40 he stole from an old lady who only used to drive to church on Sunday

Just started to hone this block today. Went from 120 to 220 or 280. The bottom .200" or so of the cylinder on the major thrust side was already .002" over .060" over. So i basically had to hone the cylinder to the .002" its now within .0002" round and taper. Just need to finish it. My guess is that this block was unlevel when previously bored? And when i probed on location then bored to probe spec it didnt clean all the way..

Honestly, just about nothing surprises me anymore with oe blocks or ones that were bored off the deck surface or pan rail. Sometimes it leaves you standing there
trying to figure out what that individual was thinking about.

Tom

[MotionMachine]

I've posted this before but it is relevant to the topic. It's probably the worst example of bores all over the place that exists. This was a BMW V12 that a previous shop had sleeved. And it's actually worse than the readout shows because in some cylinders, the hole in the block for the sleeve was offset in the opposite direction from where they bored the sleeve. The worst sleeve had a wall thickness that varied .035". I was able to somewhat correct the locations by going to larger sleeves but I couldn't bring it all the way back to the blueprint.

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