Valve replacement

[Bulldozer]

Currently rebuilding a 49N engine.

Wondering what is the criteron for decision to either resurface valve or replace with new valves.

What is criteron on valve stems?

Valves cost ~ $10
 

[TheOldHokie]

[Bulldozer]

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.
 

[TheOldHokie]

[Bulldozer]

Thank you for your response!
 

[William Fissell]

I had the valves ground and the seats ground for about $45 at my local machine shop. I cannot for the life of me see any reason to do otherwise.
 

[TheOldHokie]

[ZANE]

If you take the valves out of their holes and mix them up then you will have to either regrind them and the seats or replace them with new and regrind the seats.

I've done many re-ring jobs without touching the valves and they are all still running good sometimes 20 years later.

Zane
 

[ASEguy]

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
 

[Hobo,NC]

No margin: The margin of the valve will get pounded away in time. If the margin is to thin the valve will heat up and burn prematurely... I am not sure of the discard measurement of the Margin I ditch them if they look to thin/sharp... I venture to say its 1/32... Its rare I run into a seat are a valve in a 60 year old engine I would reuse...



http://www.freeasestudyguides.com/engine-valves.html


http://www.briggsandstratton.com/support/frequently-asked-questions/Servicing%20the%20valves/
 

[Bulldozer]

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
 

[ASEguy]

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
 

[Bulldozer]

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.
 

[Ken(Ark)]

[Greg 2N (TX)]

Rebuilt my 49 front mount too....

Just wanted to mention that I also did the free-rotating exhaust valves while I had the chance.

Something to think about if you would.

Regards

Greg