[Speargun]

When should a torque plate be used when boring a Pontiac engine?

I was talking with my machinist about an upcoming engine build and we got on to the topic of torque plates and when one is needed. Since I'm his only Pontiac customer, I would have to buy one for him and he will do the first couple of bore jobs in trade.

I know that it would most likely be better to use one on every build, but at what performance level does it become necessary?

[leeklm]

Subscribing... my last build was supposed to have been torque plated, but I found out later it was not (Bill found this out when balancing a new rotating assembly for me). Since the bores were good, we left it alone, installed the new assembly and has been running like a champ ever since putting out ~600hp to the crank.

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[hurryinhoosier62]

Boring with a torque plate CAN be a good idea; honing with a torque plate is a requirement.

[Formulajones]

ALWAYS as far as I'm concerned.

If you've seen one finish honed without, and then took it back and had it finish honed with a torque plate, it's a real eye opener when you see how out of round the cylinders are and how the first past doesn't even touch large portions of the cylinders at all.

Ran into this with a 455 I recently did, which was just redone by another shop. Paul torque plate honed it and the first pass was just absolutely horrible looking. Had to take another .002 to .003" off just to get the cylinders as best as possible without the need for new pistons, but there were still small areas the hone didn't touch. It became apparent right away the first rebuild was not torque plate honed.

[mgarblik]

I bore without a plate and ALWAYS hone with a plate. I leave .005-.007" for honing depending on the job. My boring mill makes using a plate very difficult and not really necessary if you leave enough material to hone. Also, one less operation which would save the customer about $100.00.

[Formulas]

When you can afford it along with a place within a reasonable distance that can do it proper

[Lee]

Years ago, a guy brought me an engine that only had a few hundred miles on it. It was overheating and just not running well.

The bores were in spec for the pistons, but we decided to add new rings and re-hone. The shop used a plate when honing it. There were four VERY obvious oblong circular areas where the hone did not touch, where the cylinder wall was pulled outward by the bolts used on the plate.

[Schurkey]

Originally Posted by Lee

Years ago, a guy brought me an engine that only had a few hundred miles on it. It was overheating and just not running well.

The bores were in spec for the pistons, but we decided to add new rings and re-hone. The shop used a plate when honing it. There were four VERY obvious oblong circular areas where the hone did not touch, where the cylinder wall was pulled outward by the bolts used on the plate.

So you re-honed without a plate?

You proved how much the cylinders move around when the bolts are tightened. The cylinders were probably round in-use, and now they won't be.

[242177P]

Originally Posted by Schurkey

So you re-honed without a plate?

Believe Lee meant "The shop used a plate when REhoning it"?
Or at least that's the way how I read it. HTH.

[Lee]

Originally Posted by 242177P

Believe Lee meant "The shop used a plate when REhoning it"?
Or at least that's the way how I read it. HTH.

Correct, thank you!

1st shop honed w/o a plate, motor was run for a few hundred miles - long enough to smooth out the cross-hatch and add some vertical lines to the bore.

2nd shop RE-honed WITH torque plate. The previous "vertical" marks were obliterated by the new cross-hatch - EXCEPT around the areas where the bolts ended, where there were circular areas that still had the vertical marks.

I wish I had a photo.

[Steve C.]

There is a Tampa chapter of the Pontiac Oakland GMC club. Worth a try to contact them and see if a member knows of where you might borrow one.


.

[PontiacJim1959]

My 2 cents. I think a torque plate is overkill for a street engine.

OK, so you use the plate, but think of all the variables that can get that precise perfectly round cylinder out of round.

Heat & expansion. Heaven forbid some of your cylinders don't run even temps and one runs hotter/colder and it expands differently. Are all cylinders the same temperature from top to bottom, left bank to right bank, front of the block and back of the block?

What if the intake is not perfectly matched to the heads and one head is .010" less on the intake side than the other and you torque it down and the bolts draw the head in, pulling on the head bolts, pulling on that one bank of cylinders. OMG, distortion.

How much block distortion do you get when the engine torques over against the motor mounts? Or the twist applied to the back of the engine via the rubber trans mount as the driveshaft loads up the posi unit and sends it to the wide tires that dig in and twist the frame.

For a drag race only engine, I can see the benefits where every ounce of HP can make the difference between win & lose. Blueprinted assembly, hard block fill to stiffen the casting, front/rear engine plates, roll bars to stiffen/eliminate frame twist, etc.. But for a street engine, I can't see it and have never used one. That's why engines have tolerances.

[hurryinhoosier62]

Originally Posted by PontiacJim1959

My 2 cents. I think a torque plate is overkill for a street engine.

OK, so you use the plate, but think of all the variables that can get that precise perfectly round cylinder out of round.

Heat & expansion. Heaven forbid some of your cylinders don't run even temps and one runs hotter/colder and it expands differently. Are all cylinders the same temperature from top to bottom, left bank to right bank, front of the block and back of the block?

What if the intake is not perfectly matched to the heads and one head is .010" less on the intake side than the other and you torque it down and the bolts draw the head in, pulling on the head bolts, pulling on that one bank of cylinders. OMG, distortion.

How much block distortion do you get when the engine torques over against the motor mounts? Or the twist applied to the back of the engine via the rubber trans mount as the driveshaft loads up the posi unit and sends it to the wide tires that dig in and twist the frame.

For a drag race only engine, I can see the benefits where every ounce of HP can make the difference between win & lose. Blueprinted assembly, hard block fill to stiffen the casting, front/rear engine plates, roll bars to stiffen/eliminate frame twist, etc.. But for a street engine, I can't see it and have never used one. That's why engines have tolerances.

I would respectfully disagree. Having machined as many blocks as I have, I have personally seen the difference torque plate honing makes in regards to cylinder sealing in both gasoline and diesel applications. We witnessed faster break-ins and better cylinder sealing with blocks that were torque plate honed verses non torque plate honed. In 6.2/6.5 GM diesels the difference was nearly stunning. Cummins recommends torque plate honing for ALL of its mid range diesel engines.

[mgarblik]

As hard as it may be to believe, torque plate honing is worth 8%-10% in peak HP on an engine dyno. It has been proven time and time again. On a 400 HP street engine, that's 32-40 HP. That's not just on a Pontiac, but typical for American V-8 engines. If the goal of the rebuild is to cruise around on a Sunday afternoon from one car show to another, or drive the car in a parade, I agree torque plate honing is not necessary. I have run a ball hone through many, many engines and put the old pistons right back in and away they went. But there is real HP just sitting out there waiting to be had and it's a fairly inexpensive up-grade to an engine rebuild. My rule of thumb is, if the engine is getting new pistons, it's getting torque plate honed. This includes even 5 HP Briggs and Stratton engines for say a Jr. Dragster. It makes a huge difference in those little engines. Joe Mondello was under contract with Briggs and Stratton to develop machining practices for their Jr. Dragster engine. Torque plate was worth 2 HP on a 20 HP Jr. Dragster engine. Same 10%. Verified on the little dyno.

I would like to add that PontiacJim 1959 made some good points about the many variables of heat cycles, uneven heating of different cylinders, and external forces on the block from mounts, and even the intake. Huge money has been spent trying to duplicate those forces while honing. I have honed blocks with the mounts on the block, the bellhousing attached and used a hot hone that circulated 180 degree honing oil through the block while honing. Believe it or not, going through all that aggravation on different blocks, Chevy, Mopar and Pontiac, it didn't show much on the dyno. Possibly a few HP, but not enough to really verify. So we discontinued the process. Some cup teams and Pro Stock still hone that way.

[Schurkey]

Thanks for that. I guess I misunderstood what order things were happening in.

[Dragncar]

Pontiac distort .004 right under each head bolt about 1/2". I had long conversations with Dan Whittmore on this. He told me you not only need to hone it with a tq plate you need to bore it with one "if you want your bore to be ROUND". That is a direct quote. The guy was anal about such things.
Its not like a sbc where you can bore them .004 under without and hone with and you are fine. Some shops can not bore and hone with a plate because of their equipment. My last 400 was done in a shop where he could not do as I wanted. So he bored it .010 under and ridged honed it to spec (.006 clearance since it is hard blocked) .
I paid Dan extra to do one of his tq plate bore and hone jobs. He passed before he got it done.
So when I got the block and had to have it finished by a local guy he checked out everything with a fine tooth comb. Dan fit the billet splayed caps, got that part done. When the guy inspected it he said he was impressed with the caps. Said the main bores were dead on the nuts. Asked who did it and I said some guy back east. You can see remnants of the factory main hone barely viable, just kissed the block.
I expect a very good ring seal on this engine. Dan hard blocked it and used a tq plate for the cure, it matters with that guy. It cured for 3-4 MONTHS on each side with the same type gasket I am using, 1016.

OPs original question ? I say all tq plate the time. I mean, on a typical daily driver why would it matter. But Pontiac these days are anything but daily drivers. They are our "babies". Make it run sweet, crisp.

[Speargun]

Thanks for the replies.

Where can I buy a torque plate or find the specs to have one made?

[mgarblik]

Originally Posted by Speargun

Thanks for the replies.

Where can I buy a torque plate or find the specs to have one made?

BHJ and Sunnen are the two suppliers I use, but their are others as well. IMO, the BHJ plates are a little nicer.

[hurryinhoosier62]

Originally Posted by mgarblik

BHJ and Sunnen are the two suppliers I use, but their are others as well. IMO, the BHJ plates are a little nicer.

Mike, I wasn't aware that Sunnen made torque plates for Pontiacs. We made our own, but we had access to TONS of 1 inch steel plate and a tool and die department.

[mgarblik]

Originally Posted by hurryinhoosier62

Mike, I wasn't aware that Sunnen made torque plates for Pontiacs. We made our own, but we had access to TONS of 1 inch steel plate and a tool and die department.

I can't swear if Sunnen actually makes the plates themselves or buys them from someone else and paints their name on them. When we bought a bunch of equipment for my college from Sunnen, we were able to get some "accessories" for the new equipment as part of the package deal. I was able to pick 6 torque plates and of course a Pontiac V-8 was one of the 6. Since that purchase, I bored the plate for large bore IA II blocks. 4.425". So now it's too big for typical 400-455 stick blocks. That's when I bought a BHJ plate for the smaller bore Pontiacs. After using both, the BHJ one is just a little nicer because it has counterbores for the fasteners that work nicer with spacers when running studs. Either will get the job done. We made our own plate for a student with a Jeep 4.0 L inline 6 and another one for a student racing a Studebaker 289 RIII. It's allot of work to make one IMO.