Generally speaking, is a torque plate used when boring/honing Y-block cylinders? When does distortion become a concern?

I prefer to use torque plates for cylinder wall honing on most engines regardless of their intended use.  That makes for an expensive collection of torque plates especially considering that some of them are for the same family of engines but are bore size specific.  By using torque plates, the rings do seat in quicker with fewer break-in issues.  But on my end, most engines have the thinner piston rings which are sensitive to cylinder wall finish.  The newer Mahle pistons for street applications are now using the 1mm rings which are 0.039” thick versus the old 3/32” rings found in some of the Ford Y’s that were 0.094” thick.

The use of torque plates for cylinder wall honing becomes increasingly more important as the cylinders become thinner as a result of over boring and also when using the thinner metric piston rings.  Either one of those scenarios makes the use of torque plates recommended.  Engines with blind head bolt holes like the Ford Y tend to have less distortion at the decks due to head bolt torque but there is still some measurable distortion regardless.

Expect to pay more for torque plate honed cylinders versus not being torque plate honed.  For the Ford Y, not very many shops have the torque plates which means you either have to select a shop with that capability or furnish the torque plates to the shop doing the honing.  To get the most out of torque plate honing, it’s always best to use the same head bolts and head gaskets as being intended for use on the finished engine.  Even the amount of thread penetration of the head bolts into the deck is a player.  There is obviously more to this than just bolting a torque plate to the block and honing.

Lorena, Texas (South of Waco)

Thanks, Ted, I'm glad I asked. Should the torque plate be the exact diameter of the finished bore size?

There has to be enough space to clear the stones so that you don't damage them.  Most used head gaskets are slightly larger than the bore.  If you had the torque plate the finished size of the bore, then you would need dozens of torque plates for each individual engine you honed.  Some shops keep two each and torque both in place to simulate a better finish.  Other shops use hot oil circulating to near 200* to simulate operating temperatures.  The list of possible scenarios is endless.  The torque plate and bolts/studs used simulate the bore distortion with a head torqued in place.  The torque plate needs to be thick enough so it will not flex when torqued to the upper torque value of the heads.   Joe-JDC

JDC

At what stage would one consider using torque plates now? Common rebuild or HP?

I know in the olden days it was mainly for a competition engine.

____________________________

The use of a torque plate helps to reduce the head bolt distortion that occurs if honing the cylinders without a plate.  It simply boils down to how good you want those cylinders to be when first cranking up the engine.  Torque plate honed cylinders simply seat the rings in very quickly as compared to non- torque plate honed cylinders.  Those engines with thin cylinder walls and/or non-blind head bolt holes in the decks will obviously distort more than those engines that are built beefier or more robust.

To add to what Joe said, the head gasket sealing ring must be fully incapsulated by the installed torque plate.  That small detail makes using the same style of head gasket as is being used on the engine extremely important to the torque plate honing operation.

I recently honed the cylinders on a Dart block with a 4.600” bore and used a torque plate that would accommodate up to a 4.660” bore.  With still over 3/8” thickness for the cylinder walls and having blind head bolt holes in that Dart block, the bores still distorted up to 0.0007” when the torque plates were removed.  A major part of the distortion was occurring at the head bolt hole locations.  I have seen up to 0.0015” of cylinder wall distortion on some Ford Y engines when the torque plates were removed, so Yes, using torque plates raises the bar on having truly round cylinders when the heads are bolted in place.

Lorena, Texas (South of Waco)

THANX! Again ...

So nowadays, it is considered that boring and honing is to be done with a plate as normal/quality procedure?

____________________________

Just depends upon the shop and what quality of work is dictated by the either the shop or the customer.  It’s definitely more expensive to torque plate hone the cylinders which originates from the perspective of buying the necessary plates, gaskets, and fasteners but also from the perspective that it takes more time to do cylinder honing with plates versus not.

I cringe when someone tells me “It’s good enough” as that suggests that some quality was left on the table.  Torque plate honing just adds another level of getting the machine work closer to perfect.  The same thing goes for balance work where 0.5 oz/in is considered acceptable but in reality, most performance work calls for 0.1 oz/in or better.  Don't get me started on that thought process that says performance engines should be built to a higher standard than stock engines as I personally think they should all be built to a higher standard.

Lorena, Texas (South of Waco)

'Don't get me started on that thought process that says performance engines should be built to a higher standard than stock engines as I personally think they should all be built to a higher standard.'

I understand that fully. I know someone else like that ...

____________________________

The hard part is finding someone with the skills and integrity to do it right.