Lapping using a drill

There are quiet a few videos out there with guys lapping pitted and damaged seats and valves with a power drill. The valve basically becomes a grinding tool.

I am thinking you really want the seat and valve to be conical and smooth. This should accomodate for the valve and seat heat expanding at different rates. I can imagine these radial lines that often form on the surfaces aggravating that problem.

What else can be said about this? I know people will rage about this But lets try and be objective. Would be interesting if anyone had key indicator measurements of some sort, e.g. compression, power etc. I suppose any cold measurements taken directly after the operation will show premium values. I assume drawbacks come long term or during actual operation?

Here is one example, a bit extreme though:

 

I have done it with the drill on a few heads over the last 30 years and never had an issue. I just chuck the drill right to the valve stem. I change directions often and pickup the valve off the seat several times while the valve is turning. Works fine and they seal up great. Now of course ideally in that guy's situation they were pretty rough and the right thing to do would be a valve job, but for low budget, on an engine that will not get a ton of miles on it, as something recreational, I don't see an issue. Those grooves will smooth out on their own from running. Especially if the guides are kind of worn like they likely are on those heads. They will be wobbling around and centering into the cone of the seat every time they open and close. We have to consider the situation. Does this guy and even myself know the correct way to refurbish things? Of course. But just because it is not done back to full rebuild spec and perfection, it does not mean this budget rebuild he is doing won't run just fine for his intended recreational needs of burning some tires in an old car. I have personally been a trained mechanic for decades and I know how to it should be. I fully support a guy putting something together like this for himself to have fun. Sometimes these budget rebuilds work pretty damned good. Will they last, likely not, but who cares. This guy will be out having fun with his Trans Am build while others will have a car torn apart in their garage for decades.
Greg

 

The problem with lapping valves is the seat surface becomes too large. When using an actual cutter the goal is to have the sealing surface around 1/16". Usually after lapping that area is way too large.

 

For sure that is a concern. The seat area on the valves in that video are huge. They are not ideal but they will seal and that thing will run.
Greg

 

Yes, done is better than perfect! Cannot say I am not tempted to try this backyard method... All workshops around have long waiting times, and Neway cutters are weeks away. This guy has had the car apart for 5 years now though it seems by the video dates but that is besides the point Interesting to hear that this method worked out for you! Did you happen to take any measurements or was it more the experience that the engines performed well in general?

And the reason for that seems to be that a too wide seat promotes carbon buildup and the seating pressure can become too low?

 

Permatex sells "Valve Grinding Compound" in squeeze-tubes, available in most auto parts stores. It's like sandbox sand in a grease carrier.

I think that crap is useless.

I bought 400-grit Valve Lapping Compound, and if I had it to do again, I'd have bought 600-grit or even finer.

Grinding the valve against the seat is a hack-job. Lapping is for the final polish of valve faces and valve seats that are already in decent condition.

 

I have to agree with Schurkey here. All my experience with machining valve seats when I was a Navy Machinery Repairman in the machine shop.
Navy high pressure valves don't get a 3 angle cut for first thing.

You first machine a 45 degree seat. Then a 45 degree on the valve.
You try to get the best and most accurate valve angles and surface you can obtain.

The final step is the lapping process. Blue in your seat and lap with the proper tool that reciprocates in a back and forth motion. Obtaining a good machining finish makes the lapping process go much faster.

You want to ensure that you get a very good seal.
Using a drill gun and switching it back and forth to try and mimic the lapping motion is really a hack job at best.

If you are going to put work effort into a engine job, do it correctly or not at all. Spending the time to do it right pays off in the long run.

 

I have done this on a every day street motor so as to get another 20K miles out of it.
Depending on how bad the seat looks I might start off with a course lapping compound, but then switch to a
fine grit fuel pro / clove lapping compound.

I make a sleeve out of a Aluminum soda can to go around the valve stem to keep the guide from getting nicked up from the drill chuck.

I lube the valve stem well and run the drill in both directions while applying some good pressure.

I wipe off the compound offten and apply new compound to have sharp cutting edges on the grit.

When going for a final smooth finish that has some polish to it only spin the drill in one direction.

Does it make the seat wider and sink the valve some YES to that , does it help or hinder air flow ?
I can't say as I never took the time to plop the head on my flow bench afterwards.

What I do know for certain is that once you get the two sealing sufaces to mate up nice you can pour rubbing alcohol into he runners and it will not leak out, and that is what flat out matters first and foremost.

A beautiful multi angle valve job and a new valve that will not seal up and bleeds off 25 psi of cylinder pressure will knock off way more power then a seat that you made .006" wider by lapping, and even more power will be lost if it's a Intake valve that's leaking and sending strong compression pulses back up the Intake runner and into the plenum.

 

I expected to get this opinion, but what are the objective reasons for that? Lost control of the valve seat width is one, but other than that?

 

For one issue, the Navy is not making high performance race engines.
All of the high pressure valves I worked on are either high pressure steam valve or submarine ballast valves.
So has much valve seat surface you can get is optimal to maintain any leakage.

 

It's obvious you have a good technique for lapping valves with a drill gun.
I for one have never tried your method.
I've been trained to do it the Machinist way.

I have to say, I don't get the 3 angle method. I want as much valve surface contact to the seat as possible. Just as you pointed out. More surface contact less likely that leaks will occur.

One of the reasons Prussian blueing is used to see and verify you have a good surface contact area for valve and seat contact.

My problem is, every time I take a short cut, it ends up biting me in the ass. Have to do it all over a again, wast money and labor time. So I stick to what I know works best for me. LoL

 

Reading around it seems you dont want to large seating area either, as that reduces pressure on the contact area. That can also promote leak in an engine application. Then on the other hand we want some area to promote heat transfer. But then, I am literally trying to learn this as we speak

I tried using a drill for lapping valves on a dirt bike once. That was a nicked hard metal seal. Took forever and I called it prematurely. Compression measured just fine afterwards though. Other than that I have no experience with this.

 

Doing something is better than doing nothing.
That process will work in a pinch.

 

“I think” it’s the other way around.
The wider the seal, whatever kind of seal it may be, they’ll be less pressure on the seal to contact area to help seal.

 

Ok, I'm good with that. LoL
Just no leaks please. Vet

 

I always hand lapped after cutting. Rubber hose and a hose clamp on the stem.... You don't need blue on these as the seat area will turn a uniform grey when done.

 

Prussian bluing during the lapping process is my machining Naval training. Just can't get away from it. LoL VET (Navy)

 

Just had to go out and try the drill method. If this doesn't come with imminent adverse effects it seems pretty promising... In 2 minutes a really pitted cast iron seat was already almost cleaned up.

 

I believe if you're using a drill you are well beyond anything that should be lapped. A wide seat is not good for longevity, and cleaning up that much pitting means the geometry is off and the springs should be shimmed. A seat cut with carbide along with a valve that has been properly cut won't need lapping and will seal just fine.

 

"Three Angle" (seat) valve jobs are bragged-up as if they're something special. In fact, they're the ABSOLUTE MINIMUM needed for a proper valve seat job. EVERY "valve seat" should have at least three angles.

The seat angle is where the sealing occurs. There's a top cut and a bottom cut that set the final position, and the final width of the seat angle. If the seat is too wide, and too low on the valve face, the "bottom cut" narrows the seat, leaving the upper part to do the sealing. If the seat is too wide and too high on the valve face, the top cut narrows the seating surface, and brings the contact area down on the valve. The seat angle needs to be wide enough to have an adequate service life--too narrow and they don't transfer heat well, and the contact pressure is too high. Too wide, and the contact pressure is too low, carbon can build-up preventing sealing--and then the high-pressure, hot combustion gas blows-by, "blowtorching" the seat and valve.

A narrow seat tends to flow better than a wide seat. For awhile, folks building race engines played around with "radius" valve seats--a continuous curve rather than three or more discrete angles. I think that's gone away now, but I haven't kept up with that sort of research.

Yes. I'll admit that for immediate results, "grinding compound and a drill" on the valves/seats is better than pitting. The engine could run better afterwards than before.

Long-term results are likely to be very poor.

Yes. I own a real, live, Military-Surplus "ZIM valve lapping machine", a hand-held deal that has a crank handle on the side, you spin the crank handle and it wiggles the valve back and forth, but turning one direction a little more than the other so the valve head oscillates back and forth--but will eventually turn a full circle. I don't use it.


I use a plain ol' suction-cup-on-a-stick, spun back and forth with the palms of my hands.


Spin the valve with a drill, and I'd expect that the rotational speed of the valve head will fling the grinding/lapping compound off the valve due to centrifugal force. But I haven't tried that, and have no plans to begin...so don't listen to me. Maybe you guys can control the speed so that isn't a problem.

Perhaps. Depends on how much metal is actually removed. I'd be more concerned about the increase in seat width, seat surface roughness, and reduction in flow due to "improper valve job angles" than the loss of valve spring pressure.

As said...an improper valve job that seals will still run better than a pitted valve job that doesn't.

I don't have experience with carbide cutters. I know that any "Professional" is going to use a "Seat and Guide Machine" that has the cutters, and clearly they work well--and QUICKLY. "Time is money".

I have seen leaky valve jobs done with cutters, that sealed nicely after being "kissed" with a stone. And any of the seats I've refurbished--and that's very few--have been done with stones.

I have no equipment to replace valve guides, and if the guides are worn...I can't grind the seats with adequate precision. So I'm limited to home-brew valve jobs only on cylinder heads that are already in decent condition in terms of valve guides. (i.e., "not many")

There has been some discussion on SpeedTalk.com about lapping compound getting "stuck in the pores" of the metal, it can't be completely cleaned-out, and leads to abrasive wear of the valve and seat. I can't say that I've ever noticed a problem with that, but then I don't build Indy/NASCAR/Top Fuel engines, either. I have no concerns about that on my engines.