OMG! DIY Cylinder Honing
12-18-2010, 04:53 PM
#46
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I believe he wasn't using a torque plate because he was lapping, not honing, and the lapping process removes such a small amount of material that it does not meaningfully change the dimensions of the cylinder.
12-18-2010, 05:35 PM
#47
12-18-2010, 05:46 PM
#49
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I'm not posting again in this thread....I just have one piece of advice for anyone wishing to do this on their own - read the factory service manual, look at the clearances listed, converse with a machinist who has experience with alusil blocks and ask him how much the bore size will change and whether it's a good idea.
12-18-2010, 05:57 PM
#50
12-18-2010, 06:29 PM
#51
The general idea behind a torque plate is that you want to simulate the cylinder head being bolted on. The block distorts some amount with all that tension in the head studs, therefore, in the interest of making the bore round under these conditions, machining is done in this stressed state. As to why you would need a torque plate on a 4 but not on a V-8, for honing isn't clear. I suspect it is something learned by doing.
12-18-2010, 07:02 PM
#52
Race Car
I've been under the impression that, in the case of alusil, that lapping and honing are different. The final stage of lapping is simply a surface treatment. These two are being tossed around interchangebly in this forum - myself included. lapping appearently removes a .5 micron of material and simply allows the rings to seat and the walls to retain a thin oil film. All the while having little or no effect on piston clearance. This is encouraging for the DIYer that wants to simply rering the existing pistons, or install good pistons of the correct size in a different block.
12-18-2010, 08:42 PM
#53
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absolutely correct whalebird.
I can tell you one thing for certain. Neither honing or lapping requires the use of a torque plate. I have built a many of engine over the years and never once was a torque plate used in the honing process (or in this case, lapping). Honing, when done correctly changes the bore dimensions very very little. Nearly every one of the honing heads i have seen allows for flex in the stones as to not take too much material off of the bore and only leave a good cross hatch. Since the stones are allowed to flex, it contours to the bore and does not change the bore dimensions. In this instance where a felt pad is used with a lapping cream, the felt pads give and allow for the variances and therefore the torque plate is not necessary.
As for the statement of using a plate on a I4 vs a V8.... well, let me say, you must have never really built any performance engines. Any reputable machinist building a high quality motor will use a torque plate when boring (not honing or lapping) the cylinders when overboring the block. The same geometrical effects and torsional deflection are not any different on a I4 vs a V8.
Oh, and this is not my first I4, I have built a many of turbo 2.3 engines in my time and the Porsche 2.5 is no more mysterious than any of them...
I can tell you one thing for certain. Neither honing or lapping requires the use of a torque plate. I have built a many of engine over the years and never once was a torque plate used in the honing process (or in this case, lapping). Honing, when done correctly changes the bore dimensions very very little. Nearly every one of the honing heads i have seen allows for flex in the stones as to not take too much material off of the bore and only leave a good cross hatch. Since the stones are allowed to flex, it contours to the bore and does not change the bore dimensions. In this instance where a felt pad is used with a lapping cream, the felt pads give and allow for the variances and therefore the torque plate is not necessary.
As for the statement of using a plate on a I4 vs a V8.... well, let me say, you must have never really built any performance engines. Any reputable machinist building a high quality motor will use a torque plate when boring (not honing or lapping) the cylinders when overboring the block. The same geometrical effects and torsional deflection are not any different on a I4 vs a V8.
Oh, and this is not my first I4, I have built a many of turbo 2.3 engines in my time and the Porsche 2.5 is no more mysterious than any of them...
12-18-2010, 09:44 PM
#54
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While I don't know a lot about this, I would be worried about galling after a hone job if you do not use new pistons. I imagine some of the gliding metal from the piston skits transfers to the bore upon break-in and if you try to run in an engine without it, it might gall.
12-19-2010, 05:32 AM
#55
RL Community Team
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I thought about that too. Considering the cost of new pistons, and the typical worth of a 944 engine, I would think it's worth at least trying the old pistons first, unless of course you're building some beautiful 500hp turbo motor. Even if the cylinders get damaged, oh well you just take it to the machinist, and now you have 2 reasons for new pistons so you buy them. Then again, I'm someone who has large blocks of free time now and then.
12-19-2010, 11:14 AM
#56
Race Car
While I don't know a lot about this, I would be worried about galling after a hone job if you do not use new pistons. I imagine some of the gliding metal from the piston skits transfers to the bore upon break-in and if you try to run in an engine without it, it might gall.
