Boring, Torque Plate question

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Laecaon
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Hey guys, I just received some CP 84mm pistons and I realized they pretty much mandate a torque plate to be used with boring the block, by both suggesting it, and then stating it again in the chrome rings section.

So my question is, how critical is this really? I dont have plans for big power (going into a Datsun 510), at most a T28 and probably 250ish HP.

I work at a non automotive machine shop, so I do have some understanding of how metals behave, and what happens when metal is removed.

I guess really, a torque plate is kind of expensive for a one time use tool, and I am having troubles swallowing that down. I probably could borrow/rent one if I could find one, or just make my own (machine shop...). But it is all added expense still for a one time use item.

If you are wondering why I am boring out to 84mm, well the block I got happened to have coolant sitting in the cylinders... and it rusted the walls just a bit. My machinist was a little concerned if +.5mm would clear it up, but he was 100% positive +1mm would clean up. But also I have a weird fascination with 1.9L motors...

Thanks,
-Jacob


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float_6969
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My machinist said that the bores distored about .0015", and it wasn't concentric. That means that with the torque plate on, it was a round hole. With the torque plate off, it was shaped like a 4 leaf clover. It's not VISIBLY shaped that way, but it measures that way. The opposite is true if you bore without a torque plate. It's round when you bore it, and goes out of round when you bolt the head on. In normal cars, with cast pistons and softer rings, this isn't an issue because the thermal expansion of the piston is far less than a what you get from most forged pistons. They also use more conformable rings. What happens with a forged piston is that if you bore without a torque plate, your builder has to run the clearances on the loose side to accommodate for that distortion. That makes for a noisey engine that doesn't make as much power as it could have.

All of that being said, I had a torque plate built for my last build and am more than happy to rent it out for a reasonable price. I think $100 for a torque plate rental is fair compared to other torque plate rental prices. BUT, I HAVE to have a deposit up front. It cost me nearly $500 to have it made. I would want a deposit of $500 up front + shipping costs both ways. Once I have that, I ship the torque plate. Once I get it back in good condition (no dings or deep scratches), I refund $400. I have to do it this way to make sure someone doesn't just keep the torque plate, or if they do, so that I can make a new one. PM me if you're interested.

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sjbsuperman1425
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Jacob,

I'll put my neck out there for float_6969 (aka Ryan) and say he is a good, honest guy. Never met the man, but he is always willing to help people in need and I would trust him with $500+ to rent his torque plate and expect a refund once it's returned.

That is all,
Zak

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mdb4879
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So a question on torque plate alternatives. If you have a spare head that you're doing nothing with, could it be used as a torque plate if you don't care about scoring the combustion chamber?

tommey
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I would vote no unless you rent Float`s plate.
No need to get one made and it is not critical.
Yes it better, but not enough for you to spend alot of money on.

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Laecaon
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So pretty much, it would be very wise.

I could probably make one for under $200. All depends on my cost of the metal. Machining it would take $20 and convincing of a friend to stay after work for a minute.

I have no doubt that Float is a good guy, I have done my research over a long time in many threads, and he has been around for a long time and is always helping everyone.

My idea is to grab a chunk of 2.5" thick by 6"x17", machine the headbolt holes, machine out the bore holes to probably a little less of whatever a headgasket bore is, and then make up any high difference of the head studs to the block with spacers of sorts (because really 3" thick would be better, but also probably costs more). Ill talk to my boss to see about pricing.

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float_6969
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Most boring/honing operations can't be done from the bottom of the block, as the machines are designed to center off of the main bearings, so just using an old head won't work. I thought about taking a spare, ruined head and punching holes in it, but after finding a couple of people who tried it online, there was too little structural rigidity left and they gave up on it.

If you're going to make one yourself, do some research on materials. As you know, there are different types of aluminum. I don't have the info in front of me anymore, but there is one particular type of aluminum that doesn't distort very much from machining processes because it's made in such a way that the internal stresses are already relieved. This is the type of aluminum that you want to use. Secondly, you want the holes to be BIGGER than your bores. Not by much though. I made mine .5mm bigger then my bores (my bores are 84.5mm, so the bores of my torque plate are 85mm) You need to have room for the boring machine to go down inside the bores from the top and the machinist boring the block is NOT going to want his boring/honing stones that are designed for iron to be fouled up with aluminum. Lastly, make sure when you cut the spacers that the ends are perfectly parallel. This usually has to be done on a lathe to ensure that happens.

Oh, and this whole process is going to take a while. Cutting 4, 85mm holes in 2.5"-3" thick aluminum bar is going to take a while unless you have access to a badass waterjet/laser cutting machine.

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Laecaon
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Well lucky me, my shop just scrapped a 3"x6"x31" block of 6061 T651 (stressed relieved), from a drill breaking off in it. I plotted all the holes we put in it in Solid works, and then plotted the cylinders and head bolt holes over top and found that I can use it as no holes over lap.

So this could be almost free for me... yay...

So one more question. How big are the bores in the head gasket itself? I ask because I have read that you are supposed to use a head gasket when using the torque plate, and would like to figure out how to get somewhere in between...

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float_6969
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IIRC, the bore in a stock HG is 84mm, but you really should measure it. I've been told that your HG should always be .5mm bigger than your bore though. I was told it creates less bore distortion and keeps the fire ring cooler on the HG.

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Laecaon
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What about the Fel-Pro, is that 84mm as well?

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float_6969
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I'm pretty sure it's 84mm.

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Laecaon
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So I take it then, since I am boring out to 84mm, my only option for head gaskets are the MLS ones? I was trying to avoid that...

The last motor I built, I bored out 2mm, and the stock head gasket still had room, but that was an old L series Datsun motor, and of course no turbo.

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float_6969
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Yes, unless I'm wrong about the bore size on the Fel Pro, which is possible, but I'm pretty sure I'm not. I haven't measured one in a while though, so maybe somebody else can chime in.

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Laecaon
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Well I ordered a Beck/Arnley* gasket kit for a Pulsar. Ripped it open, pulled the head gasket out, and held the pistons to it. Clears effortlessly!

For reference this is a 84mm CP piston, and a Beck/Arnley head gasket.
Image


For those who are not aware, Beck/Arnley doenst make parts, they supply parts. I have gotten Tripple 5 tie rods inside both Beck/Arnley and Moog boxes. That said, 9 times out of 10, they are of the better quality options. Still, you are buying whatever they were able to source to put in the box that day.

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Laecaon
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Forgot to also post that I made a plate. In my research, I found people used all different thicknesses for making torque plates, So I concluded 1.5" will do well enough. Still need to clean it up a bit. This plate used to be the base plate in one of our Vertical mills.

Image

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mdb4879
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Man that's cool. I wanna make one now. If only I were a machinist, lol.

Yeah, iirc there are only about 3 different companies that make parts these days. I can't remember all of them, but I remember Federal Mogul is one in the mix.

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Laecaon
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Should I be using a head gasket between the torque plate and block when it gets bored?

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float_6969
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Yes. Ideally the exact HG that you're using with the build.


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