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| Author: | DR.DETROIT [ Fri Jul 20, 2018 12:56 am ] |
| Post subject: | cylinder block |
Is there a spec for amount you can take off the block deck for surfacing ? |
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| Author: | rancherman [ Fri Jul 20, 2018 10:00 am ] |
| Post subject: | Re: cylinder block |
DR.DETROIT wrote: Is there a spec for amount you can take off the block deck for surfacing ? It varies from engine to engine. Piston protrusion is the factor. The more you mill off the deck, the closer the valves sit to the piston. Which head gasket is currently run on your engine? 'no hole, 1 hole, or 2 hole?' Each variation is .004 inch thicker. No hole is thinnest, 2 hole is thickest. Then, the more you take off the deck, this also lessens the depth of the pocket the liner sits in. Shims come in sets of 5 to choose from. Mine measured .005, .006, .007, .008, .009 inch. After the deck is milled say, .005 inch, put the next thicker head gasket, and THAT part will be good. Then you'll have to choose a thinner shim to get the LINER protrusion set, ( 0.00 to .002 above deck height) If you can't get the thinnest shim to get the liner down far enough.. you'll have to machine the 'step' in the block. I lucked out, I'm in the middle of rebuilding mine, and needed to take some off the deck for 'clean up' purposes. (corrosion) I got the 2 hole gasket to replace the 1 hole gasket. ( that takes care of the material removed from the block) Then since all my liners were either level-to-sunk in the block; After taking off .005 from block. Liners would've stuck out .004- .005. with the .008 shim that was installed. Not good! So, using the .005 shim, I got the desirable .001-.002 Liner protrusion (positive height), and using the 2 hole gasket, I maintained my piston to valve clearance. Also maintained was combustion chamber volume.. ratio, etc. If you are already running a 2 hole, for what ever reason, you better measure actual piston stick-out, do the math, and calculate what the actual piston clearance currently is. Seems like most original engines came with a 'no hole' gasket, Some, however, came with 1 or even 2.. Mine happened to be a '1'. I've seen guys claim they've removed up to .010 inch. Going from a 'no hole' to a 2 hole gasket would, for all practical purposes, take care of the difference. Making up the difference in liner protrusion (shims) will definitely need to be addressed. ( more machine work to deepen the 'step') Let me clean this up some; You should be able to take off .005 off the deck, but certainly will have to use thinner shims to 'set' the liner height. They'll stick out way too far. If for some reason the shims are already the thin ones, then you'll have to have an extra procedure done to deepen the liner pockets. Going with the next thicker gasket will then be needed to restore the piston to head clearance. My shim kit has 5 shims to choose from, ranging from .0055, .0065, .0075. .0085, and .0095. If you currently are running a no hole gasket, you could take off almost .010, and run a 2 hole gasket. This will maintain your piston to head clearance... but for sure you'll need to deepen step the liner sits in, and choose the proper shim to set the final height. I'd think these days, most machine shops would have the tooling to cut new lands. |
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