New exhaust valves?

Should I replace the valves ? And if so, if the seats look ok can I just lap new ones in? Should I do the intake too?

 

Depends. If you take the head/block to a machine shop to have the valves ground, they will tell you if you need new valves. There's a spec for how thin the edge of the valve can be after grinding. I'd say there's no point in replacing the valves if you don't grind the seats to match.

 

Do it all! A rebuild ain't a rebuild unless you rebuild it! JMHO.

 

It's just that I keep hearing about how unleaded gas burns the old exhaust valves. so it would be the block taken to the machine shop and I can just see the money pit doors opening.

 

I wouldn't make a special thing out of this, I have the hardened seats in my heads on my 225 now, but I wouldn't have done it had my whole engine not needed rebuilt. I had a bucket load of miles on my 71 model when I rebuilt it, somewhere around 165,000-170,000 miles. The engine was tired and needed rebuilt so I installed them then. If your engine runs decent I wouldn't make a big deal out of these unitl you really need a rebuild. My .02¢

 

RonDog has the right idea, IMO- For the same amount of effort in removing heads and all of that why not just be done with it and do it all

Mark

 

That's the way I was taught back in the stone age, anyway. If you go to the trouble to pull a motor out and tear it apart just to clean it up, do everything to it that you can while you have the chance. Why risk future problems if you can prevent them in the first place? And why wait until later if you've got the parts out now? Again, JMHO.

 

Am I missing something here, no one mentioned anything about pulling the motor or a rebuild, he asked if he should replace the exhaust valves due to unleaded fuel.

 

I don't know the details Mike, but I remember Clay saying he'd just picked up an F-head from Kodiak, so I was assuming he was cleaning up that motor.

 

I don't see any mention of using unleaded fuel :twisted:

clean 'em up good
check for out of round/warpage/burnt spots
replace if necc
touch up the seats and the valve faces
run 'em

 

Jim if I was you I would have your eyes checked.:twisted:

 

by golly miss molly
Mike is correct !!!
I have my eyes checked once a year, not due till next year thank you !

If they (the valves) check okay, run em as mentioned !

 

All that I'm saying is that were I to go to pains to replace the exhaust valves, I'd rework the entire head. If I were not willing to do that, I would run it until I did need to rework them. JMO- Afterall, it is a 30+ (or more) year old engine- :stout:

M

 

It's not the head it's the block with the exhaust valves. and the difference is a little under a 100 to a little under a 1000. I did just get the engine from kodiak and he said it was a runner. I was just doing some leak prevention when I thought of the valve problem.

 

they make a dye or marking compund that you can apply to the seats or valves
then pop the valves in and turn by hand
you can check the seating of each valve in each seat this way
clean them up good first
then inspect both the valves and the seats
check the seats closely for cracks
if no problems found and the dye marks look good, light lapping and your good to go
a good shop could do this for you
personally, I wouldn't worry about the unleaded gas problem
ymmv

 

A tube of prussian blue is what you need, should be able to get it at the flaps. Then I would follow Jims advice.

 

Ah, prussian blue....takes me back to my old machinist days. Had lots of fun putting that stuff on each others machine handles and tools!R)

 

Oh- I assumed :v6: . I see this question a bit more clearly now..

My advise: What they said....

Mark

 

A couple more comments, if I may...

Your question was whether you should replace the exhaust valves. The usual criteria are condition of the face of the valve and seat, the thickness of the edge of the valve, and the diameter of the valve stem.

If you have any cracks or pitting on the face of the valve, replacement is obvious. Exhaust valves are much more at risk than intakes, because they run at a higher temperature due to the exhaust gases. If you have a big crack in the valve, you'll probably have some erosion on the seat too - unlikely a new valve will seal in that case.

For exhaust valves, the edge of the valve should be at least 1/32" thick. Any thinner, and it will heat up too much. The intakes should be at least 1/64".

You can measure the thickness of the valve stem with a micrometer. Valve guides have a diameter of 5/16", 11/32", or 3/8" typically, with a stem-to-guide clearance of about 1-4 thou. Anything more than about 5-thou is excessive.

Regarding lapping, it's not typically done today when valves are ground. You can use lapping as a check to see if the valves will seal, but if there's a problem with the seat, lapping probably can't remove enough material to make a difference. Personally I don't think it's worth your time if you can check with blueing. If the seat is eroded, you'll have to have it ground.

Even if you're going to keep the valves, I'd be inclined to replace the springs and retainers. Both will fatigue with time, and strong springs will help the valves to seal.

$1000 to grind the seats in the block is robbery. All you need is the stones and the right pilot - same process as grinding the head.

I don't think unleaded gas is an issue with an F134, considering the low compression ratio.

hth!