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all about torque plate

Engine Building Fundamentals

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Discussion and questions related to the course Engine Building Fundamentals

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how important to use the torque plate in ring gap.. it was mention in of the module that there is a need to use a torque plate but it was never show how? and why is necessary to use???

Ideally if you have had the engine torque plate bored/honed then you should also use the torque plate while set the ring end gaps since the torque plate can result in some distortion of the bores. It does really come down to how tight you're going with your ring gaps though. If you're really aiming for tight ring gaps then you should use a torque plate to ensure that the end gaps are where you need them to be under real operating conditions. If you're using the ring manufacturers recommendations then these are normally a little conservative so it's not in my opinion an essential step and I've set ring gaps multiple times without a torque plate fitted with no ill effects.

Andre i have always thought torque plates arnt the best method.

my concerns are: is the torque plate actually going to be the same stiffness as the cylinder head? if not wont your torque plate clearance be different than clearances with the head on? which is again different to clearances with nothing bolted on.

and also temperature, in an ideal world the head and block expand together at the same rate. this how ever isn't possible especially with an aluminum head on cast iron block. so again how accurate is the torque plate on a cold block going to be vs a hot block with a head that has a different rigidity?

I'm not saying a torque plate isn't better than no torque plate, I'm merely asking at what point is the torque plate going to give inaccurate clearances compared to real world?

The torque plate really replicates the distortion caused by the localised load from the fasteners so it's not strictly essential that the torque plate is identical to the head in terms of stiffness. It's definitely not a perfect world sadly and I've found that even with a torque plate the distortion will change a little bit every time you tighten the torque plate down. It is however a case of getting whatever improvements we can.

Taking the torque plate honing concept to the next level is having the engine block 'hot honed' where coolant is run through the block to take it to operating temperature. I think your last statement really nails it - A torque plate is undoubtedly imperfect but still going to give you a better bore finish than no torque plate at all.


When making a torque plate how thick should it be?

As Andre said, it's supposed to replicate the loads on the block and so it should match the cylinder head. However, unless you have some very good analytical tools that's beyond most of us.

Most seem to be made from an iron plate with around 50mm/2" thickness, but for an alloy head, an alloy plate may be a better option. You will also need to use the same fasteners, and they should be torqued to the same value as when the head is fitted to the block - it's common to use spacer tubes or even stacked washers to take up the height difference.

How critical a 'plate is is partly dependent on the engine design. Some have the fasteners very close to the cylinder walls, and this can definitely cause distortion - the old small block Ford is an example - and when pulling such engines down, you can sometimes see where the areas by the fastener holes are polished by wear, but the areas in between may still show honing marks. Some engines will use liners and an open deck surface that isolates the cylinder from the fastener loadings - this type of engine is very unlikely to see any gain from a plate.

Andre also mentioned hot honing, in theory this should also help, but from what I've read, even NASCAR engine builders aren't able to confirm it helps and it's also going to be a lot of hassle. But that might be them fudging things because they're concealing an advantage? If you were pushing for any potential advantage, such as a race class where advantages are gained in tiny percentages, it may be worth trying it - but I'm not sure it would be worth the hassle.

Something else, that many miss, is the bottom of the engine's cylinder bores will also suffer from distortion from the main bearing fasteners, and the caps, with girdle, if applicable, should be fitted and torqued to spec'. Again, some engines are more susceptible than others - you could check yours before sending it in, with the block bare, and with caps installed, and see how much variation there is?

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