Aluminium Engine Block "Alignment/Twist/Straight"

[flymo351]

Hi all; was hoping that somebody could advise on the following;

I will try to explain, but you may find my inexperience in describing what I am trying to find out, a little confusing, sorry

There is always a lot of discussion on the effects of Torque Plate Twist on cylinder bores.

What effect to the alignment of the Block has the various parts of an aluminium based engine block under torque loading.

If I have a bare Aluminium engine block, took measurements of Cranshaft Centre Line, Deck Height, Cylinder Alignment, etc, what would you expect to see compared to the same measurements on a completely built engine under torque load.

What effects would you expect to the alignment of the Block when the motor is running and under load, how much distortion would be seen.

Is it possible to machine the Block in such a manner that, when not under Torque loading the measurements may look incorrect or completely out of alignment, but when the Block is Built and under torque loading from usage, that the Block would effectively straighten up, measurements would be correct and come into alignment.

Hope you all get what I am trying to find out, many thanks for you assistance in advance

 

[patprimmer]

This has been done at length before without specifying aluminium, but the effect is the same, just the degree changes.

You cannot correct for distortion from load as it changes continuously as the engine runs at different rpm and load and temperature gradient.

Regards

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[patprimmer]

The main purpose of a torque plate is to replicate local distortion of the bores due to radial strain caused by the load from the stud threads as the studs (or bolts) are tightened. This is to improve ring seal by keeping the bore as round as possible without these little bumps that will lift the ings from the rest of the bore. I don't think it has much effect on bore axis alignment. I also dont think minor deviations in axis alignment are all that important.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[flymo351]

Many thanks for the updates.

As you can tell I have an Alloy Block; which recently had some major work completed by a "recognised engineer" and I need to understand why some measurements appear to suggest that the work done is not correct.

I understand that all engine blocks, whether Cast Iron or Alloy are subject to the effects of distortion/alignment, from Bolts/Stud Torque and Torque loading from usage.

The Alloy Block in question ia a V8, and has had a Full Cylinder Bore Liner replacement x8 new Crankshaft main caps, reduction in Main Bearing diameter to reduce friction by using fabricated smaller diameter saddles placed in the Main Bearing Block saddle. The Deck height has been modified/machined when fitting the new Liners.

When taking measurements from the Crankshaft centreline, it appears that there is some differences in measurements across the block, for instance (looking from above the deck with an imaginary horizontal line centred on the centre of each cylinder bore left to right) starting at the first cylinder on one bank of four, there appears to be a variation in height along the horizontal from one side of the bore to the other of between 0.005" +- 0.002" so one edge of the liner has a different height from the Crankshaft than the edge that adjoins the next cylinder, and this appears true of every cylinder on both banks, with a maximum variation in height recorded at 0.010"

There are a number of other measurements that appear incorrect but, my gut tells me that the differences in measurement could actually dissappear/reduce once all the Torque loadings for Crank Main Cap Studs, Head Studs, etc are in place, but I am not sure and also have the feeling that a mistake has been made in the engineering process.

Thanks

 

[RossABQ]

Are you saying that each cylinder liner is low towards one end of the block and high towards the other? Sounds like a milling or surfacing operation that progressed from one end to the other, with the liner getting hotter as it went across each cylinder liner, or some such issue. I would not expect torque'ing the main caps to affect the deck at all.

 

[dicer]

No matter what "expert" you have work on something, it maybe his/her employee that does the work. They could be having one of those days etc. To properly check the deck height to crankshaft center line you would at the minimum need a large micrometer and either a pin or anvil ball to accomplish it. But that only gets end to end parallelizim.
It takes a person that knows how to do precision inspection to check it all correctly. And no one is going to machine in unaccuracys for distortion other than what is standard pratice. And another note, if you reduced bearing clearances that is a bad thing on an Al blocked engine for performance, as the block gives and distorts more than iron.

 

[macquari]

This sounds like a set up problem with either the tunnel bore or the boring.
You said there were saddles fitted which I'm presuming by 351! is reducing from 3" to 2.750" mains and new caps fitted this would require a line bore/hone and if not set parallel to deck heights could cause your error, this may also create problems with timing chain or worse if a gear drive is fitted.Check the distance between cam and main tunnel centres allowing for different diameter cam tunnel sizes (your cam tunnel should still be original) (note that caps would be tensioned before tunnel bore so tensioning wont fix it).
The other problem could be the machinist not checking deck height before boring out for sleeves or not checking both support bar if used and original deck height was parrallel to machine bed before boring, again check your deck height from end to end to both you cam and main tunnels.
If the variation is across the block it means the tilt was wrong when set up so as the bore centres weren't sitting at 90 degrees vertical above the tunnel when either bored or milled.
A torque plate will only correct ovality not deck heights.





































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[flymo351]

Many thanks for the info;

Yes each cylinder liner is low at one side and taller at the other, from the Crank Shaft Centre Line, we are only talking about 0.005" to 0.010" I think Mac is right about the deck heights of each liner, and the tilt when boring.
The Mains have been reduced from 2.749 to 2.249
I understand the Block was "Hot" Bored, align boring done with block at operating temperature with Torque Plates etc.

Understanding that any Block will twist in or out of alignment under loading. Torquing of Studs/bolts of around 110 ftlbs will also pull the Cylinders and Main Journals into their respective shapes. I was wondering if the "HOT" boring is one of the ways attempted to lessen the affect of this problem, and could result in the alignment being out when cold?

Is the 0.005" to 0.010" going to make that much difference, obviously no guarantees that any engine used in racing is going to survive. The short block assembly all built and torqued, with correct bearing clearances, spins over by hand smoothly without any bind, and it can be rotated by hand by spinning the Damper not the flex plate.
To me this is great, I have built other short blocks of the same model which have been tighter than this, and have run perfectly into the mid eights without any damage.

I think I am going to give it a test, as the cost of doing all the work again is too much.

Thanks again

 

[patprimmer]

I would have thought the cost of correcting the mistake would be zero to you. Your machinist really stuffed up.

He hones the bock hot to get some imagined infinitesimal extra accuracy, but misaligns the whole thing by 0.005 to 0.010".

If he was careful to get everything within 0.001" instead of chasing the last bit of imagined fairy dust, you would both be a lot happier.

I guess there is some argument to support hot machining on an aluminium block with cast iron sleeves due to differential expansion of the metals

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[izzmus]

"I would not expect torque'ing the main caps to affect the deck at all. "

I'm told that, on a Ford 302, you can measure the distortion in the mains resulting from torquing the intake manifold. I've never bothered to measure it myself, but that engine is as close to a latticework of bolt holes and journals held together by a skin of iron as any I've seen.


The service procedure for Ford's 4.0 SOHC V6 (evolution of a 50 year old pushrod V4) has you first removing the mains girdle (caps) before removing the cylinder heads, or permanent block distortion will result. In practice, they are thrown away and replaced as assembly, since nobody wants to touch them if they have such a scary-edge design.

 

[tbuelna]

There are machining tolerance spec's published by all of the OEM's for rework of factory components (like blocks, heads, rods, etc.) or their aftermarket duplicates. You can get those from any factory service manual.

In general, blocks are "decked" in a fixture that locates off of the main bearing saddles. Getting the deck surface at a uniform height relative to the crank centerline, as well as normal to the bore axis, is important because it can alter compression ratio and valvetrain geometry/timing from one cylinder to the next.

The purpose for using a torque plate when boring/honing cylinder bores is to simulate the block/liner strains resulting from bolting the cylinder head into place. The bore should be round and cylindrical at room temp. The piston skirt is machined with a very precise cam, barrel and taper shape so that it fits nicely in that cylindrical bore at operating temps and loads.

Finally, I would expect that an aluminum block will have looser main bearing clearances at operating temps and will distort more under load than an iron block, since aluminum has a CTE double that of iron or steel and its MoE is only about 1/2 that of ductile iron.

 

[Tmoose]

Can you use the variation in block deck height to your advantage ? Maybe swapping pistons or rods around (within the piston clearance variations) to create more nearly equal piston-deck clearance and ultimately more uniform squish/quench clearance?

Squish clearance greater than ~ 0.04 inch is reported to be kind of ineffective anyhow.