Reconditioning valve train components Knurling valve guides • For correcting worn guides • Mostly for integral guides • Use wear limit of .004” (Use.
Download ReportTranscript Reconditioning valve train components Knurling valve guides • For correcting worn guides • Mostly for integral guides • Use wear limit of .004” (Use.
Reconditioning valve train components Knurling valve guides • For correcting worn guides • Mostly for integral guides • Use wear limit of .004” (Use Go/No-Go) • Fixed arbor or roller Copyright 2003 Gary Lewis – Dave Capitolo Reconditioning valve train components Fixed arbor knurling • Cold forming tap with pilot • Produces a thread by deforming metal inward • Threads are formed, not cut Reconditioning valve train components Fixed arbor knurling • Standard domestic knurls are 5/16”, 11/32”, & 3/8” • Reamers are sized by thousandths of an inch Reconditioning valve train components Knurling procedure • Use extreme pressure lubrication • In guide/seat machine or with speed reduction drill • Clockwise direction only Reconditioning valve train components Knurling precautions • A 3/8” knurl will start in an 11/32” guide • Removable guides may break • Once knurl is started, don’t stop Reconditioning valve train components Reaming • • • • Increases inside diameter to proper clearance Pilot keeps reamer straight Clockwise direction only Shallow groove left in guide for longevity Reconditioning valve train components Reaming procedure • • • • Continuous flow of coolant to flush chips Select reamer Stem diameter + clearance When done, reamer should fall out of guide Counterclockwise rotation dulls reamer Reconditioning valve train components Measuring knurled & reamed guides • Measure knurled guides with bore gauge. Probe will span grooves • Set gauge to stem diameter & read clearance Reconditioning valve train components Roller knurling • Single roller used to knurl guide • Continuous flow of oil • Diamond hone used to finish guide Reconditioning valve train components Replacing guides • • • • Aluminum heads & some iron heads Usually removed & installed from port side Measure height above spring seat Heat head to 250ºF & add oil around guide Reconditioning valve train components Replacing guides • Tap guide & install cap screw to remove • Use cap screw technique for bronze guides • Core drill to create shoulder to drive on Reconditioning valve train components Replacing guides • Before installation, measure! • Heat head, oil guide & head • Install to specified height Reconditioning valve train components Oversized valve stems • • • • • For correcting wear in integral guides Sizes include .003”, .005”, .010”, & .015” oversize Engine manufacturers recommend oversize stems Economical when guides are worn Reaming is done incrementally Reconditioning valve train components Replacing integral guides • Valve guide bushing (false guides) • Allows for upgrading material to bronze • Replacement guides provide .0015” interference 5/16” guides 7/16” OD 11/32” guides 1/2” OD 3/8” guides 1/2” OD Reconditioning valve train components Replacing integral guides • Precision level is used to align guide to spindle • Level the guide in two directions • Core drill to within .025” of replacement guide Reconditioning valve train components Replacing integral guides • Ream to final size • Core drills and reamers follow the previous hole • Core drills and reamers use pilots Reconditioning valve train components Replacing integral guides • False guides are driven by air hammer & driver • Oil guide & bore for installation Reconditioning valve train components Replacing integral guides • Excess length can be trimmed off at either end • Ream guides after length has been cut Reconditioning valve train components Installing bronze liners • Thin bronze liner for reduced wear rates Reconditioning valve train components Installing bronze liners Production installation • Ream .030” oversize with coated reamer • Driven in place with installation tool • Liner is expanded & sized with burnishing tool • Excess length is trimmed • Brush type hone gives crosshatch Reconditioning valve train components Installing bronze liners Occasional installation • Bore guide using drill motor • Liner driven in using hammer & driver • Excess liner is removed • Knurling locks liner in place • Reamed to size Reconditioning valve train components Refacing valves and stems • To remove all pits from face & stem • Grinding sequence can be different between machines Reconditioning valve train components Refacing valves and stems • Interference – Thins margin less • Check for bent valves during machining Reconditioning valve train components Refacing valves and stems • Chamfer tips to 1/32” • Grind .003”- .005” from tip Reconditioning valve train components Refacing valves and stems • • • • Dress grinding wheel Use oil between wheel & valve Back & forth grinding action Back wheel off when done Reconditioning valve train components Grinding valve seats • Purposes: Remove pits Proper seat width Uniform seat width Seat position on face • Check seat inserts for looseness • Seats are machined concentric to guides • Guides serviced before seats Reconditioning valve train components Grinding valve seats • Seat width Too wide – Traps carbon & causes burning Too narrow – Insufficient heat transfer & causes burning • Seat width specs 2 valve heads - .060” to .090” smaller valve heads - .040” Contacts slightly above center on face Seat width must be uniform Reconditioning valve train components Grinding valve seats • Contact position on valve face Too high – Burning through thinnest part Too low – Poor sealing Reconditioning valve train components Seat grinding stones • • • • Stones should be 1/8” larger than valve head Select 30 º, 45º, & 60º stones 30 º stone that is too small forms a groove Roughing & finishing stones Reconditioning valve train components Seat grinding set up • Install correct size pilot, with pilot wrench Reconditioning valve train components Seat grinding procedure, method #1 If spring & stem height are a concern • 45º - Grind seat angle first to remove pits • Redress stone as needed for surface finish • 30º - Grind the top angle & check position Reconditioning valve train components Seat grinding procedure, method #1 • Make corrections with 45º & 30 º as needed • 60º - Grind bottom angle to narrow seat width & make seat width uniform Reconditioning valve train components Seat grinding procedure, method #2 For seats that require minimum machining • 30º - Grind top angle until seat angle narrows • 45º - Grind seat angle to clean up • Check position with Prussian Blue Reconditioning valve train components Seat grinding procedure, method #2 • 60º - Grind bottom angle to narrow seat • Check width with Prussian Blue Reconditioning valve train components Checking seat concentricity • Prussian Blue in a few places & do not rotate valve • Concentricity gauge Reconditioning valve train components Valve & seat wear • • • • • Poor lubrication with unleaded fuel CNG has less lube than unleaded Other engine parts wear less with CNG & unleaded Remove valve rotators in CNG engines Cobalt alloy seats & Inconel valves in CNG engines Reconditioning valve train components Cutting valve seats Adjustable carbide inserts • 30º then 45º for reduced chatter • Driven by hand or by low speed drive motor Reconditioning valve train components Cutting valve seats Three angle cutting system • Increased precision & productivity • Grinding stone may be used to touch up seat Reconditioning valve train components Cutting valve seats Three angle cutting system • Position pointer on valve face for contact point • Adjust cutter to same position • Seat width is determined by the cutter Reconditioning valve train components Cutting valve seats Three angle cutting system • Seat angles being cut in guide & seat machine Reconditioning valve train components Cutting valve seats CNC machine • Seat angles being cut in CNC machine Reconditioning valve train components Installing valve seats For crack repair & seat recession • If .060” shim can’t correct spring height • If stem height can’t be corrected by grinding tip Reconditioning valve train components Installing valve seats Seat selection • OEM seats may be induction hardened • Use hard seats with alloy valves for propane • Heavier duty seats for recession Reconditioning valve train components Installing valve seats Seat selection • Aftermarket seats listed by: OD ID Depth • Materials include: Cast Iron High-nickel chrome alloy Hard alloys Reconditioning valve train components Installing valve seats Seat selection • Interference = seat diameter – cutter diameter • For integral seats, select seats by application Reconditioning valve train components Installing valve seats Removing the original seat 1. Weld an old valve to seat & drive seat out 2. Weld a bead on the inside of the seat, cool, & remove Reconditioning valve train components Installing valve seats Removing the original seat 3. Bore old seat to a thin shell • Hard seats dull cutters! 4. Weld a bead on the inside of the seat, cool, & pry Reconditioning valve train components Installing valve seats Installing a replacement seat • • Inspect bore for damage & measure ID (Damaged bores cause unequal cooling) If bore is within specs, install new seat • If bore is out of specs, install oversize seat Reconditioning valve train components Installing valve seats Installing a replacement seat • • • • Clean bore & lubricate seat to prevent galling Install with chamfered edge down Aluminum heads may be heated Install with driver & hammer, using pilot as a guide Reconditioning valve train components Installing valve seats Replacing integral seats • • • Choose cutter for proper interference Set depth of cut to match the seat thickness Set spindle speed & bore Reconditioning valve train components Installing valve seats Replacing integral seats • • Grind seat angle to installed height Then grind top & bottom angles for position Reconditioning valve train components Fitting valve seals Types of valve seals • • • O-ring – Fixed to valve, lower groove, no sealing Umbrella – Fixed to valve, no sealing Positive – Fixed to valve guide, positive sealing Reconditioning valve train components Fitting valve seals O-ring installation • • • • Compress spring to expose lower groove Install seal Install keepers May have oil shield Reconditioning valve train components Fitting valve seals Umbrella installation • • • • Install seal onto valve stem Install spring Compress spring Install keepers Reconditioning valve train components Fitting valve seals Positive seal installation • • Machine top of guide to . . . - Reduce OD Leave 3/16” between top of - Reduce height guide & bottom of retainer - Chamfer top Reconditioning valve train components Fitting valve seals Positive seal installation • • • Use plastic sleeve for installation Use installation tool Adjust spring compressor to prevent seal damage Reconditioning valve train components Fitting valve seals Seal materials • • • Nitrile – OEM, 250ºF Polyacrylate - 350ºF Viton - 440ºF Reconditioning valve train components Replacing rocker arm studs Press fit studs • • Spacer & nut Hydraulic puller Reconditioning valve train components Replacing rocker arm studs Oversized studs • +.003” or larger • Ream to .001” to .003” press • Install to proper height Reconditioning valve train components Replacing rocker arm studs Threaded studs • Thread square to existing hole • Spot face top of hole Reconditioning valve train components Installed SPRING height • • Measure from spring seat to bottom of retainer Use shims to correct Reconditioning valve train components Installed SPRING height • • Use .030”, .060”, or no shim at all Goal is +/- .015” of specifications Reconditioning valve train components Spring warnings • Make sure spring compresses more than valve lift • Progressively wound springs - Reduce high frequency oscillations - Reduce valve float - Tight end faces down Reconditioning valve train components Installed STEM height • • • From spring seat to tip of stem Correct by facing tips in valve grinder to match ends If no specs, use measurements from disassembly Reconditioning valve train components Installed STEM height • • Shorter push rods can correct height Shim type OHC warning Reconditioning valve train components Refacing rocker arms • • Forged & cast rockers only Check rocker shafts clearance first Reconditioning valve train components Straightening Aluminum Heads • • Heads expand in all directions Heads warp upwards Reconditioning valve train components Straightening Aluminum Heads • • Straighten head based on the top side Check cam for binding Reconditioning valve train components Straightening Aluminum Heads • • Check seat-to-guide alignment Straightening heads: - Reduces surfacing - Improves seat alignment - Improves cam alignment Reconditioning valve train components Straightening Aluminum Heads Stress relieving • • • • Heat treating process to relieve stress caused by warp Requires 500ºF for 4 hours Slow cooling restores precipitation hardening Properly fitted seats should not fall out Reconditioning valve train components Straightening Aluminum Heads Stress relieving preparation – pushrod cylinder head • • • • Measure head warp on deck surface Use shims at each end equal to the amount of warp Torque nuts to no more than 25 lbs/ft This should bend head into alignment Reconditioning valve train components Straightening Aluminum Heads Stress relieving preparation – OHC cylinder head • • • Measure head warp in cam bore Use shims at each end equal to half this amount Torque nuts to no more than 25 lbs/ft Reconditioning valve train components Straightening Aluminum Heads Stress relieving preparation – OHC cylinder head (cont) • Recheck alignment & adjust shims as needed Reconditioning valve train components Straightening Aluminum Heads Stress relieving procedure – OHV & OHC • • Place head in oven for 4 hours Allow to cool slowly Reconditioning valve train components Straightening Aluminum Heads Stress relieving procedure – OHV & OHC (cont) • • OHV surfacing is minimal OHC surfacing may be more Reconditioning valve train components Correcting Overhead Cam Centerlines Removable bearing supports • • Top of the head can be surfaced Shims installed under supports Reconditioning valve train components Correcting Overhead Cam Centerlines Removable bearing caps • • • Can be line bored Caps are ground Housing bores are bored to standard or oversize Reconditioning valve train components Correcting Overhead Cam Centerlines Removable bearing caps • • • Minor wear – Fixed by polishing To reduce clearance – Lap bearing cap Plastigage on assembly Reconditioning valve train components Correcting Overhead Cam Centerlines Integral bores • • Can be line bored oversize Oversize cam journals or bearings Reconditioning valve train components Regrinding camshafts • Inspect: • Cam lobe wear • Fuel pump eccentric • Distributor drive gear Reconditioning valve train components Regrinding camshaft • Lift & duration can be maintained Reconditioning valve train components Regrinding camshaft, preparation • • • Check straightness Set up grinding masters Grind similar tapers, then opposite tapers Reconditioning valve train components Regrinding camshaft • • • Each lobe must be indexed Amount & direction of taper is ground into lobes Grind similar tapers, then opposite tapers Reconditioning valve train components Regrinding camshaft • • Scuff resistant coating is applied to cam Highly polished surface is preferred Reconditioning valve train components Lifter base grinding • Lifters & bucket followers can be reground