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Lire boring/Line honing

Engine Building Fundamentals

Relevant Module: Engine Machining Basics > Line Boring / Line Honing

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Discussion and questions related to the course Engine Building Fundamentals

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Hi, I didnt understand very well how aftermarket studs can affect the engine block... Did Andrew mean that fitting aftermarket studs or bolts with more clamping force in a tunnel that isnt aligned good will cause the engine to fail because there is more distorting because of the more clamping force? Or what others modifications are necesary to fit aftermarket studs like arp?The subaru example showed in the video in other words was that a aligned block with more clamping force was ideal to support the 2 halves of the block?

How do I know if the tunnel is aligned or not? Maybe measuring the bearing clearance?

Thanks in advance.

All materials will distort under a force, some more than others, with aluminium distorting more than cast iron.

This distortion, or deformation, will be either elestic, where it rebounds like squeezing a piece of rubber, or plastic/in-elastic, where it is permanent, like squeezing a piece of clay.

With an engine block, I'll use the main bearings in an alloy block as an example, as it's relatively common. When the fasteners (bolts or nuts on studs) are tightened they apply a clamping (squeezing) force between the cap and the block, which slightly distorts the main bearing bores in the block that hold the bearing shells, which in turn can change the shape of the inside of the shells slightly, and that affects the clearances between the shells and the crankshaft.

Usually the engine will have been build, and the main bearings align bored, for the 'squeeze' the standerd, OEM, fasteners applied.

The potential problem is when aftermarket studs are used, especially when higher torque is used, because they normally use a finer thread that applies a higher clamping force to the cap and block, even more when a higher torque is used. This greater 'squeeze' causes the block, and usually cap, to distort more, just like the rubber block would, and this changes the shape and clearances from what were correct for the standard fasteners.

Some engines are more seseptible to this than aothers, I believe the Subaru engine is especially so.

If this is for your rebuild, with factory fasteners, you shouldn't need to worry about it, as the factory usually does an good job, but you can have your machine shop check them with a "straight edge", a precision straight length of steel, while they check the deck (head gasket surface) of the block for flatness.

A double check can be done during the test build, or even final assembly. with the engine upside down, place the cleaned bearing halves into the clean block, with the thrusts if separate, apply a little oil to them and lower the crankshaft into place, it should rotate freely. Add the caps with bearings one at a time (I start with the one with the thrust), there should be a very slight increase in drag as each is fitted, and if there is a higher increase that suggests either the crankshaft is bent/re-ground incorrectly*, or there is an alignment problem with the bores.

*Usual basic check is to fit the end shells in the block, lightly oil them, then use a DTI (Digital Travel Indicator) on each of the main bearing journals ot check they are stright.

Hi Gord, If Im using aftermarket studs and I torque them to the manufacter apecs like ARP and this is more that the factory specs for reasons u explained. And the deformation was before with all oem just elastic, I upgrade from bolts to studs and now the deformation was plastic and permanent. Isnt always the problem to change the oil clearance but also can happen that the tunnel could be not aligned well because of an crank journal distorted right?

Doesnt care how many times I torque them if I dont torque more than the limit to pass from elastic to plastic deformation Im good?

It's still elastic, not permanent, just squeezed a bit harder so changed in shape slightly more.

Yes, the problem is that as the block changes shape slightly, it also changes the shape of the bores the bearings are fitted into slightly, and so can cause the oil clearance between the bearing and the crank journal to change very slightly.

Some engines are affected more than others.

Yes, so long as you use the correct torque you should be able to use them many, many times.

IMPORTANT - some OEM bolts are deliberately made to stretch and permanently deform, called TTY (Torque To Yield), and you can tell if your engine has them because it will have a torque value, then tell you to turn it through a certainl number of degrees, and sometimes through another set range of degrees. You MUST replace these bolts, if used, even if just tightened like that once, even if only for a few minutes, because they have been stretched beyond the elastic limit..

Hi gord thanks for the feedback, so whats the procedure u do when building an engine? If u choose to fit aftermarket studs and dont know if applying more torque than the oem specs (Because as u said manufacturers like arp tend to go more because of the fine thread) can go past elastic zone what do u do first? Maybe put bearings and crank, torque them, remove them and measure bearing clearance to see if it changed and a visual inspection plus the procedure u mentioned of put bearings with little of oil, crank and add one cap at time and see if there is a lot of drag or all of them and sending it to a machine shop? What experienced engine builders do in this case?

Gord has more knowledge on this than me, but I've had the block halves line bored and honed with the upgraded case bolts fitted and torqued, with the idea that this will make the mains round during normal operation (with the ARP case bolts similarly torqued). Gord please correct me if your experience says otherwise.

You have it Mike. If there is a risk of distortion, pre-loading the block/case with the aftermarket fasteners, torqued to those settings before machining will, hopefully, ensure they're round/correct on assembly.

This means when not torqued, and in their 'relaxed'state, they may now be spightly distorted, but that's OK,

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