valve lapping

So I started working on the 4x4 dakota I bought in November finally. Long story short the guy I bought it from wasn't smart enough to check the air cleaner after it had sat for a year or so, and it sucked mouse nest through the engine. Ran with a miss, narrowed it down to number 6 (3.9 v6). Pulled the heads a couple weeks ago and no surprise number six has a burned intake valve.

I have a couple options here.

A) take the heads to the machine shop and let them clean them do a valve job and put new seals in.

or

B) pull the springs, put new seals in, and lap the no. 6 intake valve.

The most important thing here is I don't want to do this again. I need this engine to last 1-1.5 yrs until it gets a 318 put in.

So what says the braintrust? Should I pony up the $$ I don't really have or suck it up and buy some valve grinding compound (which I already did)? If I DIY it what is a good process to use?

What about option C: used head from junkyard?

Around me that's $50 plus hg and vc gaskets, which you need anyways, and that engine is not exactly rare.

option A and C require me to actually get some time to go to either the machine shop or junkyard. C is cheaper but not as cheap as B. I already have a full gasket set so I can replace all the leaky gaskets while I'm at it.

I build cylinder heads. It's what I do.

Lap in the new intake valve, and while replacing seals, have a look at everything else. Reassemble, and call it a day.

If it only needs to live another year, and the valve seals aren't terrible, I would just lap it, replacing the valve if its really bad, along with its seal and put it back together.

I would lap it. As a matter of fact, if the head is out i would lap all the valves and make sure they are all sealing properly. Harbor freight has one of those sticks with a suction cup that is pretty cheap and makes it a breeze.

BEFORE you lap the valve in... check and make sure the valve seat isn't burned... often seats will burn with the valve. If the seat is burned... no amount of lapping will get it to seal

I was just going to say that.

I can't recall ever seeing a modern head with a burnt seat, and I've replaced hundreds of burnt valves.

I find it weirdish that the truck has a burnt intake valve. Not unheard of... just not run of the mill normal...

Guy I bought it from said it was his neighbor's. It say for awhile because it needed a rear main. He is a "mechanic" so he did the rear main, on the test drive after it sucked part of a mouse nest inside the air cleaner into the engine.

Mouse's final thoughts: "The whole world sucks."

Just trying to imagine what part of a mouse nest would cause a burnt intake valve.
If it hangs in the intake or exhaust port, then no compression = no ignition = no fire to burn anything.

I smell a 'mouse'.

Maybe this 'mouse' was more like a loose bolt or air cleaner wingnut ;)

Little twig or piece of grass, at high RPM, it would light off.

There was still remnants of the nest in the air cleaner when I bought it. It looked like fiberglass insulation was the main component. I thought it was strange also, but there doesn't seem to be any physical damage or evidence of anything metal going through the intake. All the other valves seem ok, but maybe I'll just do them all.

Any how to advice on hand lapping?

moparman76_69 wrote: There was still remnants of the nest in the air cleaner when I bought it. It looked like fiberglass insulation was the main component. I thought it was strange also, but there doesn't seem to be any physical damage or evidence of anything metal going through the intake. All the other valves seem ok, but maybe I'll just do them all. Any how to advice on hand lapping?

Buy the suction cup thing from HF it will save your wrists.

I bought my suction thing and lapping paste at the local Napa, IIRC it was about 8 bucks total.

The method I used is to rotate it three or so times then lift the valve out and tap it a couple times against the seat so the paste stays distributed on both seating surfaces. You don't have to push down real hard while rotating the tool.

Also I took a Sharpie and marked both seating surfaces completely. That way when I was done I knew I didn't have any funny spots in the finished product.

Optional is enjoying a few cold beverages during the process.

But I don't do this for a living, so others may have better advice.

Just remembered too- make sure you clean all the residual paste off when you are done so they don't continue to lap themselves while the engine is running. Pretty sure I used carb cleaner or the like.

moparman76_69 wrote: There was still remnants of the nest in the air cleaner when I bought it. It looked like fiberglass insulation was the main component. I thought it was strange also, but there doesn't seem to be any physical damage or evidence of anything metal going through the intake. All the other valves seem ok, but maybe I'll just do them all. Any how to advice on hand lapping?

So I have a problem. Either:

A) I really suck at this

B) all the valves are bent

C) the seats are burnt

I did basically what is described above, and watched a couple of videos before I started. The one video showed pouring gas down the intake ports to make sure they were sealed. I lapped all the valves because I determined that more than just one leaking. After lapping all but one leak including the ones that didn't before. I did determine I had one bent valve and I might have at least one more. Guess I'm taking a half day to drop them off at the machine shop after ponying up for at least a couple of valves.

valves don't just bend..... they usually need some kind of contact.

here is an idea of before/after valve lapping..

before

after

Are the guides tight?

Well as I said before solid objects went through the engine. At this rate I can buy a 318 for 30-40 bucks more than I can buy another 3.9 which is about 50-60 more than buying a pair of heads out of the junkyard would be. Buying junkyard heads is cheaper than new valve+machine shop at this point. I've pretty much talked myself into doing the swap now rather than later.