Author	[Modern View]
TheOldHokie 11-09-2012 06:47:07 108.8.5.192 Report to Moderator	Quoting Removed, click Modern View to see I wouldn't waste my time and money rebuilding any engine without doing a complete valve job - i.e. grind valves and recut the seats. Given current machine shop rates a complete new valve kit ($120 and includes new valves, springs, guides, etc) is probably cheaper than having old valves reground. JMO, TOH [Reply]   [No Email]
Bulldozer 11-09-2012 07:15:06 24.165.92.6 Report to Moderator	Re: Valve replacement in reply to TheOldHokie, 11-09-2012 06:47:07   So when are the valves too badly worn to be re surfaced? Suppose if the valve stems look smooth and with no sign of wear the valve is still good to go. [Reply]  [No Email]
ASEguy 11-09-2012 15:27:59 68.186.162.134 Report to Moderator	Re: Valve replacement in reply to Bulldozer, 11-09-2012 07:15:06   Sign of wear, in other words visual wear, is not enough. That's why TOH said to measure. Typical oil clearances are for proper lubrication and heat transfer in the stem/guide area. Margins should be checked for thickness before and after grinding/machining the valves. Check the margins for thickness, typical stem wear limit is .001 from stock diameter. Main issue there is oil clearance though, and line up all the valves and check for necking or stretching of the valve which should not be common in this engine. Mushrooming of the tips is somewhat common in older engines and nothing a file can't clean up. Hope this helps. Gerard [Reply]  [No Email]
Bulldozer 11-09-2012 19:58:45 24.165.92.6 Report to Moderator	Re: Valve replacement in reply to ASEguy, 11-09-2012 15:27:59   After TOH furnished the stem diameter specs measured al the valve stems with my B&S 1" micrometer. Have the type of valve with constant diameter stems and solid valve guide rather than the mushroom type with the split valve guide. The exhust valves were also non rotators. The valve stems seem to wear more at the top of the valve. All the valve stems were out of spec. and measured less than the allowable minimum diameter The intake valves have the most wear. The valve stems were worn on one side resulting in the valve stem not being round. One orientation measured within spec, Another orientation 90 degrees to the first showed the stem to be under spec diameter. The worst valve was .005" under minimum spec tolerance. The wear spot was noticable with a step worn on the stem This is the first time, have ever measured valve stems. All my other engine rebuilds were on 2 cycle outboard engines that have reed valves. Based on the valve stem specs furnished by TOH elected to replace all the valves. The top of the valves appeared to have sufficent material for resurfacing. However, believe one consideration on re surfacing is the valve cannot seat too deeply, otherwise there will no tappet adjustment. That is the adjusment screw on the tappet could be bottomed out and the valve is not yet seated. Another thing have experienced is the engine machinist is used to machining three angles on the valve and when you tell him that you want just a 45 degree cut, he looks at you cross eyed. Thank you all for all the advice [Reply]  [No Email]
ASEguy 11-09-2012 20:30:54 68.186.162.134 Report to Moderator	Re: Valve replacement in reply to Bulldozer, 11-09-2012 19:58:45   Stepped valve stems? That is considerable wear. In automotive use .001 isn't uncommon for older engines. Newer Stellite guides usually don't exibit much wear at all from my experience. With stem wear so high pay close attention to the valve guide wear. OHV engines usually show hourglass wear in the guide from rocker action. This translates into valves not seating concentric with the bore and flexing of the head which can lead to failure. There are ways to repair the guide if this will be a hard working tractor. Reaming and knurling will restore original size, but not original condition. Bronzewell guides are a great investment for a long term repair, but are pricey. Valve to guide oil clearance is very important, probably more so in automotive. Gerard [Reply]  [No Email]
Bulldozer 11-10-2012 05:11:05 24.165.92.6 Report to Moderator	Re: Valve replacement in reply to ASEguy, 11-09-2012 20:30:54   Yes, replacing all one piece valve guides with the all valves. Beleive the landscape has changed over the years with more imported parts. Once with high cost of machined USA manufactured parts and lower labor cost, more repair machining was performed. Now with lower cost import parts and higher USA labor costs, less repair machining is being performed to reduce total cost. Imports both affect USA manufacturing jobs and service jobs. [Reply]  [No Email]