Porting and lapping Pt 2: Valve Seats

[jackrides]

Mixture flow across a valve seat is really important to performance considering that valves are only partially open a lot of the time. Back when they were in black and white it was thought that a 3 angle seat was 99% as good as it gets.  (The final 1% is for the top .01% of machinists, so let's not go there.) The center angle, typically 45 +- 1 D (degrees) is the contact area for the valve and its placement is critical. It's found by putting machinists dye (Dykem or perm black magic marker) on the surfaces and rotating the valve on it to see where they touch. 
The placement of this contact ring is then adjusted by very minor cutting of angles on the port side and on the chamber side. These cuts both size and place the contact ring in the right place. Now, these cuts also ease the transition of the flow around this corner as they blend into the port and the chamber.  These cuts are kept precise by anchoring the cutter  or stone into the valve guide. So, finally, here are  the questions: Anyone have experience with grinding stones for valve seats? Kwik-Way cutters are the top of the line but quite expensive. Anyone know of shops that can handle seats as small as our 50cc scoots?  
 

[90GTVert]

There are Neway cutters too. I watched a vid long ago with someone cutting a Briggs head with one IIRC.
www.newaymfg.com/parts/cutters_small

I never looked for head work on my little 4Ts, but in general most local machinists wanted little to do with anything beyond basics like milling for small engines. I met 1 guy that another machinist referred me to that would take on any task I asked about, but he passed away last year. Now there's no one local that would give a damn about a 49cc enough to work with anyone beyond those basic tasks that they can knock out quick and easy. That guy actually enjoyed the work because it was different and he wanted to make anything and everything fast.

[jackrides]

Thanks for the info!

[lilpinny]

Drowsports does race ports and polishes, one of them is Tier II: Head Porting & Polish, Sniper Cut Valve Guide, Radius Valve Job

Mostly on bigger engines, at least on their site. You might shoot them an email and see what they think about a 50cc job.

[GrumpyUnk]

I would expect that the only places that would do head work on small cycles would be either a small engine repair shop or a motorcycle shop that did machine work.
The investment in the seat and valve machining equipment would have a long payback in most cases. For small engines, most repairs would either replace the valves, lap them, and send it on its way. Some would have valve grinding and refacing equipment. Possibly re-installing a valve seat ring that has come loose from its normal position, and peening the edges to retain it, and then lapping the valves would be done if cost or availability was a factor. No such thing, normally, as a 'performance valve job' on a lawn tractor engine.
Motorcycle shops that did machine work would be more likely to have the equipment. They would want to be paid well for their service, and they have shop overhead that must be covered by even the smallest of jobs.
Most times, the 'setup' for the machine work on a small engine makes it economically unfeasible to do the work and keep the doors open. Setting up for a 50cc head is the same, except for the size & weight, as that for a diesel truck cylinder head. Everything must be squared, leveled, and clamped before anything else can be done. Once set up, the cutting part is quicker, but that's done by the machine while the operator goes to the break room for a cup of coffee.
The 'kits' that NEWAY makes are over $500, closer to $1k, individual cutting heads being around $100 each, based on size range. Spending that much for tools would require deep pockets or a lot of enthusiasm.
tom

[90GTVert]

For the most part, all of this port related work for 50s requires a lot of enthusiasm at least. Anyone that's ever tried to get tools into the tiny stock head knows that. It makes far more sense for most to go BBK and try to find a decent quality BVH, like Taiwan made or at least for a while Scrappy had a machine shop in the US working heads over for them.

To be really good at head work on any engine it requires a whole lot of "enthusiasm". If it were as simple as making the port smooth and then kicking a lot of ass, there wouldn't be people with college educations testing on flowbenches for their careers and auto manufacturers running extremely complex computational fluid dynamics to design new intakes and heads. That's not to say that the average Joe can't see gains, but don't be fooled into thinking any of this is easy or can always be taken at face value.

[acvw74]

When I burned the valve on mine, I was lucky enough to work with a guy that use to be heavy into Garden Tractor Pulling.

He made several suggestions including carving a groove into the top of the piston to enhance the flow.
I wish I had written everything down - It seems that most of these folks don't share much of that information because it is considered a competitive advantage.

However...if you can find someone they know a lot of trick to get more power out of a small engine.

[joeesquire]

As I remember, a fellow named Dave Vizard, an English engineer, who used to write for British magazine Cars and Car Conversions, was an enthusiast, and always tested his ideas and theories on small ford motors. I had a subscription to the magazine, and years later was shocked to see his name and his Camaro on the cover of Hot Rod.

Actually, it was his 16 year old daughter's car. She had complained that, when she hit the nitrous button at under 60, the rear end always broke loose. Bad for a girl's composure, so Daddy came up with the first 3 stage nitrous system. At lower speeds, it only allowed a small percentage flow, then at higher speeds, a larger percentage, and finally, 100%.

Easy Peasy, as the Brits say. I found that he had been living in So. Cal for 20+ years prior.

Anyhoo, he always had a way for the home mechanic to DIY, as they still like to say it. One of his books on mods was describing the "modern" poppet valve in pretty derisive terms, as just a compromise that evolved due to it's original cheapness and ease of manufacture.

The way he described that magical 3 angle cut was again a compromise, but one that simply approximates a radius. You need a certain amount of seat width, which varies, depending upon whether you are racing, or driving to the store every day. That is for heat transfer, and preventing particulate buildup.

His solution to cutting seats was quite simple. The radius required on a valve seat is related to the valve diameter, but is not a critical item. What he did was to fashion a cutter holder, like say, a face cutter, with a center pilot shaft, which fits into the (new! clean!) valve guide. That's got to be accurately sized.

Now making your radius cutter started with a piece of brass rod, maybe 12 inches long, cut on a lathe to give your radius. Next, in a drill press, or better, a lathe, you coat the brass with grinding compound over it's entire length.

Next, your soon-to-be cutter, which is just plain tool steel, is run back and forth over the brass rod, until the radius is worn into the cutter. You can actually rough cut the shape on a table grinder first, then finish on the brass. The length of the brass really prevents the rod from wearing excessively.

I think that this is simplicity itself, and can actually be applied to any seat size; just grind a suitable cutter.

All this was 20+ years ago, and in the People's Republik, we do not encourage modifications, nor even doing it yourself, unless you are a certficated congresscritter. "It's for the ENVIRONMENT!" Did I scream that loud enuf? HA!

Personally, I love the new way cutters. A quick light twist of the wrist, and you're done! Effortless.

Well, your mileage may vary. Caveat Lector

[GrumpyUnk]

I am having a hard time imagining the cutter. If you start with a 12" length of brass stock, I figure a cylinder, and use a lathe to cut the diameter to the desired valve radius, ummh.. I don't understand the rest.
A "'soon-to-be-cutter' of plain tool steel...run back and forth over the brass rod". Shaped like what? Rod, bar, cutting blade...
I doan geddit. You run the 'cutter' over the brass rod to wear into the cutter? Wouldn't steel wear into the brass? Confused.
tom

[joeesquire]

Feb 5, 2018 10:00:13 GMT -5 GrumpyUnk said:

I am having a hard time imagining the cutter. If you start with a 12" length of brass stock, I figure a cylinder, and use a lathe to cut the diameter to the desired valve radius, ummh.. I don't understand the rest.
A "'soon-to-be-cutter' of plain tool steel...run back and forth over the brass rod". Shaped like what? Rod, bar, cutting blade...
I doan geddit. You run the 'cutter' over the brass rod to wear into the cutter? Wouldn't steel wear into the brass? Confused.
tom

Tom, I think that you actually do get it.

Plain old tool steel is really a joy to use on a lathe, compared to carbide, the high-priced spread.

Tool steel, round square or other can be shaped on a grinder into an infinite variety of shapes quite easily. It can be re-sharpened indefinitely; good, because it does wear.

So, after you have most of the desired radius ground into your tool, you finish grind it on the coarse lapping compound-coated brass rod, running it back and forth along the rod, to equalize the wear. Yeah, I guess that you could also cut a steel rod instead.

In these situations, you might be surprised at how much more the harder metal wears, compared to the soft ones. Look at heavily loaded babbit bearings on your crank shaft. In good designs, the softer bearings can outlast the crank, unless it's nitrided.

Anyhoo, As far as finishing your seats, there used to be a rotating, reciprocating lapping tool in the JC Whitney catalog. It was 10 or 12 bucks, and came with lots of attachments, some of which I never figured out, like one valve rotating thingee (technical term!) with pins sticking straight up. Turns out it was for Model A ford valves, which had indentations on the top, just for this purpose. Whoda thunk? When turning the handle, the head reciprocates back and forth about a quarter inch, but then....it also advances every few turns, to spread the lapping compound around, to equalize the grinding. Quite the clever, effective tool.

If still offered, these little gems are collectable and usefull; steel gears in a grease-filled steel case, with real wood grips, like your grandad's manual hand drill. Made in Chicago, US of A. If you're desperate and patient, many a valve job has been performed with these tools. They included suction cups, spring to maintain even pressure, even sandpaper discs, for those burned seats. Quite the package, and yes, applicable to tiny motors. Might even see if still available, even though I'm a new 2 smoke addict, I still have my post WW2 bikes. No sidecars, though- that would be sick. Hah!

keep it shiny side up

[GrumpyUnk]

Ummh... I have one of the hand cranked valve grinder things. Used a long time ago when I was a teen. It had the 'spade' thing with the two 'teeth', and I didn't know what it fit, but figured it must fit valves with notches. I got pretty good at smearing a bit of compound on the valve seat, installing with spring to assist when I would lift the crank tool, and inspecting the parting line of the compound. FWIW, I don't think a lot of people look at the way the residual compound separates from the seat/valve interface. If you get a good, even separation of the compound between the two, that means they are 'congruent', and seated to each other all the way around. It's just a visual reinforcement of the appearance of the seat & valve after you clean the compound.
Does the steel cutter end up being a piece of rod with a curve ground into it?{via wear on the brass cylinder?]

How does it bear against the inner diameter of the valve inlet?
tom

[james82nd]

I recently upgraded from 50mm to 52mmBBK you are right scrappydogscooters has a Taida racing head with three angle valve seats and larger valves. I think I gained at least double the power from stock 3.5

more like 7.5HP to * according to this program I have and everything upgraded to the max except that expensive HIT clutch

plus up hill I can go 50MPH with the new racing head and 52mm BBK compared to the 50mm and small valve head at 45MPH uphill with blue/yellow torque spring



bye the way my stock 41.4mm crank shaft has 5000km on it and still running strong with the upgraded 52mm BBK.

[dexameth]

I lapped my valves once... with an electric drill and the original valve. Pulled the springs and retainer off, but leave the valve in the head, put some lapping compound on the valve seat, then attach the drill to the valve and while you spin the valve like a drill bit slightly seat the valve over and over, pulling the valve up into it's seat.

I was getting blow by into the intake port, and after I did this little trick it never happened again.