rw200
Member
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.
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.
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