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TDI Power Enhancements Discussions about increasing the power of your TDI engine. i.e. chips, injectors, powerboxes, clutches, etc. Handling, suspensions, wheels, type discussion should be put into the "Upgrades (non TDI Engine related)" forum. Non TDI vehicle related postings will be moved or removed. Please note the Performance Disclaimer.

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Old September 21st, 2019, 18:29   #1
rw200
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Default Torque plate needed? - Took some measurements!

The topic is whether a torque or honing plate should be used when honing cylinders, to better simulate the loads a block actually sees with the head bolted onto it, with the goal of getting the most round cylinders possible.

Building up an AHU to put into a MK2. Stymied by whether I really needed to use a torque plate as many suggest; but that apparently VW does not use in manufacture. So I decided to measure the bore distortion from head studs.
The block was cleaned up and dingle-ball honed. The head was installed snug, the block flipped over and measurements taken at 1" down the bore from the head (used a wood block to make this repeatable). Then the head was torqued (ARP's, oil, 120 lb-ft in 3 steps), and measurements repeated.
Measurements in 3 directions; "A" - short axis of block, long axis of car "B" - 45 degrees to that "C" - long axis of block, short axis of car.
Used a Fowler bore gauge that can read in tenths. Numbers are relative to piston dia; in mils (thousandths of an inch). Measurements were repeatable within one tenth; I was surprised at the results and checked several times.
Sorry for ****ty format, don't know how to insert a table..
cylinder 1 2 3 4
A-snug 2.5 2.5 2.3 2.7
A-Torqued 3.2 2.8 2.7 3.1
B-Snug 2.4 2.3 2.2 2.7
B-Torqued 3.1 2.8 3 3.5
C-Snug 1.9 2.2 2.2 2
C-Torqued 1.5 2.2 2.2 1.8
So it seems like a pretty big effect. The bores don't change much in the long axis of the block ("C") but do quite a bit in the other axes (like up to 0.8 mils). So it looks like I'll be buying, renting, or making a torque plate to use while honing my cylinder bores out round. Then maybe I'll try the abradable piston coating stuff to build up my pistons, or buy new and then hone to fit. Have some prior experience with a good Lisle hone that I used to hone up to the next oversize (with the block and crank still installed!) on the 1.6 TD presently powering the MK2 Jetta mentioned earlier. Tech tip - If you want to remove a lot of material with a hone do it dry. Doing it with the crank in is really hard, you have to contour the stones to get the bottom of the bore.
Oh, just being able to see crosshatching doesn't mean jack. These bores on the AHU cleaned up nice but with ~230k on the engine they were significantly worn (range of 1.9 to 2.7 mils without head torqued on). Need to measure to know whats going on.

Last edited by rw200; September 21st, 2019 at 20:45.
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Old September 21st, 2019, 18:31   #2
rw200
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should have mentioned the block was decked and the head was skimmed. Should have been a pretty good test. I think
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Old September 21st, 2019, 21:51   #3
Mongler98
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You cant just skim the head of an ahu, it must be torqued in a heater box by a pro, and torqued to straitened it out. When these heads warp, like all heads, the head is fully warped, not just the surface. You will trash the cam and the head if it was warped and resurfaced to flat.
Been there, regret that!
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Old September 21st, 2019, 22:08   #4
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the head didnt seem warped, took off only a very small amount. hopefully it'll hold up.
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Old September 22nd, 2019, 14:18   #5
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Quote:
Originally Posted by rw200 View Post
the head didnt seem warped, took off only a very small amount. hopefully it'll hold up.
If you torque it to the block with the cam out, a straight edge across the cam journals should tell if it will be an issue
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Old September 22nd, 2019, 16:55   #6
rw200
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Or see if the cam rocks in the bearings. I think the head's ok, but I'll check it.
The amount of cylinder deformation was the eye-opener for me. I'll be sourcing a torque plate; unfortunately it seems like it might be needed both to hone bores and install a tight-fit coated piston. That kind of takes it out of just renting, from a time perspective.
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Old September 23rd, 2019, 01:45   #7
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Quote:
Originally Posted by Mongler98 View Post
You cant just skim the head of an ahu, it must be torqued in a heater box by a pro, and torqued to straitened it out. When these heads warp, like all heads, the head is fully warped, not just the surface. You will trash the cam and the head if it was warped and resurfaced to flat.
Been there, regret that!
We have skimmed many heads and not had trouble.
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Old September 23rd, 2019, 02:54   #8
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Skimming a good head, yes, a warped head no.
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Old September 23rd, 2019, 03:01   #9
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Quote:
Originally Posted by jmodge View Post
If you torque it to the block with the cam out, a straight edge across the cam journals should tell if it will be an issue
Well, a good lapped strait edge and a set of feeler gauges, there is not a lot of wiggle room on the ahu cam, rides right on the aluminum bore and if it's off by I think no more than 0.004 from strait, it wont get its proper oil flow, I'm not 100% on the measurement but it's really small.
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Old September 25th, 2019, 16:42   #10
rw200
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Using a machinists ground straightedge there was less than a sheet of notebook paper's thickness difference on the cam journals. That's about 2.5 mils so I think its OK.
Thinking of getting a slab of cold-rolled steel 1.5 or 1.75 thick, then plasma cut and maybe ground after for the torque plate.
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Old September 27th, 2019, 00:35   #11
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Paper? Get some feeler gauges.........
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