HunkaJunk

Shaggy,
The only reliable way to way to know when the valves need adjusting is to periodically check the clearance.

DarZeelon,
To quote the Saito manual "Valves must be in the compression stroke or closed position as shown in figure 2 below. When adjustment is completed, make sure you tighten the lock nut" a little vauge, I know. But there is nothing wrong with the TDC method, or the method you are promoting.

littlera

Checking valve clearance is so easy and quick (I can do it in under 3 minutes) that it is really a moot point to worry about how often to do it. It is part of regular maintenance on all four strokes, and should be done. Period. You will find, in most cases, that as things polish in in the first hour or two of operation that the valve clearances will open up enough that the .004 gauge will slide under, indicating the gap is out of tolerance. Once reset, often the valves will stay in tolerance for YEARS. Therefore, on most engines I check them once each flying season, usually not having to make adjustment.

I use the go - no - go gauges supplied with my first O.S. four stroke many years ago. The "go" is .005 mm and the "no-go" is .01 mm.

Regards,

Randy L

gkamysz

My Feedback: (19)

Dar, it doesn't matter because you don't know where the error of concentricity lies. It could be anywhere, so your method is not any more accurate than the other. If you wanted to be as accurate as you think you are suggesting, you'd have to put an dial indicator on it define the base circle and opening and closing angles of the cam and then decide how much clearance is required to get exactly what you want. You would really be setting clearance to obtain the specified timing rather than a defined clearance dimension.

In a multi cylinder engine with many valves your method method ensures that the follower is not on a ramp.

To introduce some real world figures I grabbed an OS FS-40 cam which is used in the FS-40S. FS48-S, FS-52S and FSa-56. I measured about .0004" TIR. I would say that for a .0015-.004" clearance this error is small enough to ignore. There is no chance of being on a ramp at TDC compression so the simple method is adequate and certainly not incorrect.

Campgems

Dar, .

You are splitting hairs. The engines today are CNC machined, and those dumb manufactures do have a clue how to setup their engines.

To tell the truth, I don't use feelers to check the lash. I can tell close enough that the lash is OKor needs checking just by wiggling the rockers on our engines. A guy that used to work for me kind of summed up your process."Measure it with a micrometer, mark it with chalk and cut it with a broad ax." The hardest part of adjusting the valves is getting the nut tight and not loosing the gap you have set. Most lash problems are probably due to guys not getting the nut tight, or not holding the adjustment when they do. If the lash is set close enough that the valves will fully close when hot, and it is not open enough to spit a push rod, there probably isn't going to be much difference in performance from one end to the other. I like to keep the lash around the 0.004" mark, a couple thousands either way isn't going to matter and it lets the valves close and is tight enough that things stay intact in running. Don't make a simple job dificult.

Don

gkamysz

My Feedback: (19)

That is the hard part. The way the jam nut is arranged it takes up the slop in the thread when you tighten it so the gap opens up. In OS and Saito this usually isn't much, but in the cheaper engines this can make it hard to set the clearance you want because the threads are not as tight. Also in the cheap engines the rockers wear at the valve stem interface. This makes a groove so a feeler gauge gives a false indication of clearance. Only an indicator will give an accurate reading, but I just go by feel. These are toy engines, it's not rocket science.

DarZeelon

Quote:

ORIGINAL: gkamysz

Dar, it doesn't matter because you don't know where the error of concentricity lies. It could be anywhere, so your method is not any more accurate than the other. If you wanted to be as accurate as you think you are suggesting, you'd have to put an dial indicator on it define the base circle and opening and closing angles of the cam and then decide how much clearance is required to get exactly what you want. You would really be setting clearance to obtain the specified timing rather than a defined clearance dimension.

In a multi-cylinder engine with many valves your method method ensures that the follower is not on a ramp.

Greg,


Finally, someone 'hit the nail on the head', so to speak.

I somehow guessed you'd be the one to do it. Thank you.


My point is that model engine camshafts are ground 'center-less', with nary a real 'base-circle' to speak of...
I believe they are now made with a CNC grinder...

If this is so, the zero-lift point would be diametrically opposite the point of maximum lift on the cam.


The only parts that are actually 'round', are the shaft-ends that engage into the bearings...
But then, only if both stages are continuous; i.e. without removing the 'in-work' camshaft from the 'CNC fixture', can one be sure that this stage is really is concentric with the "base-circle".

On this condition, my method would be more accurate than other 'off-the-ramp' methods.

gkamysz

My Feedback: (19)

Theorizing about how something is made and where the tolerances will end up is a waste of time. Especially if you think the cam is ground on a centerless machine because it certainly isn't. Cams are ground between centers on manual machines or CNC machines. Centerless machines are for cylindrical parts only.

Regardless, I measured actual TIR on the base circle of a cam. I suspect it was much less than you expected. Do you care to comment on how a ±.0002" tolerance will effect a clearance 10-20 times as large? BTW one cam was out like you said and the other was not. This is what one would expect when the they are ground on center and the error is relative to how the part is held rather than the position of the cams.

DarZeelon

Greg,


I believe a model engine camshaft is not 'center ground', but CNC fabricated, along with its gear.

Regarding full-size engine camshafts, the story could be quite different...


If you know otherwise, please send a couple of relevant links, to web pages, or to videos, that can help visualize this for all of us.
Much obliged!

Regarding the ±2 ten-thousandths tolerance you stated; it would obviously have a minuscule effect on clearance; but I am talking about greater misses.

ThumbSkull

My Feedback: (57)

I'll follow the MFG. recommendation to set the gap on the compression stroke which insures both valves are closed.
That is how they designed the timing on the engine to be set.

Spending an hour setting something that should be .003" with a +/-.001" tolerance is just wasting time and effort.
I get this done in under 5 minutes.

Just my $.02

gkamysz

My Feedback: (19)

Dar your suggestion that I forward proof that I know otherwise is out of line.

There must be a lack of communication in manufacturing processes. I don't understand the the process you are describing. I agree the cams are CNC machined. I think we agree that the bearing journal are being used to hold the workpiece. In this case they are ground on center, even though they don't use the outdated master cam and follower to generate the profile. Youtube turns up a quite a few hits if you care to look at the process. There is a good possibility they are not grinding blanks in multiple setups or operations. Chances are bar goes in one end of the machine and finished cams out the other. The OS cams having only one end center drilled very much supports this. If I was going to manufacture cams that's exactly how I would do it. Common machines exist that can do this and hold ±.0002" all week long if you're serious about what you are making.

DarZeelon

Greg,


Please note my language in post #33...

"I believe..."... "If you know otherwise, please..."....

I don't think it is 'out-of-line' to challenge a blank statement, but also the 'absolute truths' that you state.

I just want to know more and think it may be interesting for many of us.


Regarding the CNC machines I am talking about; it is a six-plane holding fixture, that can rotate a machinable part in all three axes; and also move it about in all directions, so that part can be ground it in virtually all its locations; even some non-line-of-sight places, using 'angled' attachments.
It can grind the cam lobes, but also the cam-gear teeth...

This machine can, of-course, change its grinding tool during the work process.

Here in [link=http://www.youtube.com/watch?v=EH4ZQvyC9Ns]one example[/link]. [link=http://www.youtube.com/watch?v=OIWyGtXEgR4]This one[/link] is much more simple.

gkamysz

My Feedback: (19)

So basically you have no support for your statements or the comments about data I posted.

This is more likely what the process looks like.

http://www.youtube.com/watch?v=E1Fj1...eature=related

ThumbSkull

My Feedback: (57)

You can only guess how they are made. If you have ever held a new Saito camshaft, they are made from 3 separate pieces of material. The bronze shaft tube with a gear and one lobe pressed on then the extra lobe is pressed on and a swage to lock the last lobe on. There are no machining marks on a new one either from a grinder or a lathe or any kind of multi-axis machine except the bore of the bronze shaft tube. Possibilities are that they are machined or could be cast from powdered metal or even forged. The finish looks similar to sandblasting.

I'll stick with the manufacturer's recommendations for their maintenance.

DarZeelon

Quote:

ORIGINAL: gkamysz

So basically you have no support for your statements or the comments about data I posted.

Greg,


An exhaust camshaft, from an old Enya, was the only one I measured, with simple vernier calipers, that had a dial.

I held the calipers across the cam, with the cam pointing out...
When I rocked the lobe with the caliper held with finger pressure, the needle showed a smaller diameter on either side, until a ramp was approached... And then it grew larger.

I don't remember the exact amount, but would suppose 1-2 tenths of a millimeter.

...Not exactly what I would call a 'Perfect Circle'...

gkamysz

My Feedback: (19)

That is simply not an accurate way of measuring the runout of the base circle. Ramps, as you know, take up the clearance before lifting the valve. Doing what you did in an attempt to measure the base circle accuracy probably involved the ramps in the the cam has them if not the actual lobe itself. I just tried and I can turn the cam maybe 20° before the lobe is acting on the caliper jaws. A simple measurement of diameter doesn't tell you if the cam is on center. Your .1-.2mm error is huge and 1-2 time the suggested clearance. The engine would never run correctly if it was that bad, unless clearance was at least twice what the manufacturer recommended. We often read about guys setting Saito clearance as tight as possible without issue.

I'm done. Enough information has been presented for readers to draw suitable conclusions about the accuracy of the described methods to set valve clearance.

ThumbSkull

My Feedback: (57)

Shaggy, hope you didn't get lost with these guys trying to be the smartest one in the room without actually answering your question.

It is just routine maintenance. Periodically pull the rocker covers and check them and adjust if necessary.
While I'm in there, I add some lube and I do this at the end of the season to help it last the winter storage.

shaggy48

Got the answer thumbskul.
thanks.
I know how sometimes what should be a simple question and a simple answer, can be made really complicated.

shaggy48

Well i checked the valves and sure enough they were loose. Not terriblely loose. But. Enough to warrant. Adjustment. Now the question I have is, after adjustment (tightened), will I need too re-tune the engine? Does a valve adjustment change the way the engine runs enough to require adjustments to the high or low speed needles.

Hobbsy

My Feedback: (102)

Nope.

Campgems

If the engine doesn't need to have the carb tuned again after the valve adjustment, it didn't need the valve adjustment to begin with.


Don

shaggy48

You know, that makes more sense to me. I'll bet it needs just a little tweaking after the valve adjustment. I should have left the cowl off after doing it but I just didn't think about it until long after I had everything back together. Guess I was looking forward to getting it ready to fly again this weekend. Last weekend was a blast! It was a little windy and it was on Sunday, so the fair weather flyers were too scared to fly and I'm guessing the rest were in church, so me and a friend had the field all to ourselves.

The Saito 100 is a sweet running engine. And a great match on the Aeroworks Yak 54. I don't think either of them knew the wind was gusting to 20 MPH or so, But I did. Cal, my friend is a great pilot, and I guess I was confident that if I got in trouble he'd be there bail me out. So we put two or three great flights on it before deciding that maybe we are fair weather flyers too and packed it up before our luck ran out. (Well to be honest I decided, as the wind was just getting stronger)

Anyway I may have to consider a way to access the needles without having to remove the cowl every time. Guess I was hoping that maybe it may not need to be adjusted, but I think Don is right. If it valves were loose, it stands to reason the carb will need some tweeking.

When the valves are loose does that tend to richen things or lean things? (lets not talk about the potential for damage) I'm just tying to get an idea of which way I should be looking to turn the needles when I start her up again, considering I just made the valve clearances tighter. I"m guessing I'll need to lean out the top end some and may see a rise in rpm as well if only a couple hundred.


Shaggy

Campgems

Shaggy, it is a good idea to have access to the needles without removing the cowl. One option is to put an extension on the high speed and and access hole for the idle mix. One other option is to tap the hole in the high speed needle and locktite a socket head screw in the end. Then use a ball end Allen driver to reach through the hole and adjust the high end. I've used the extensions, but when you see them flaying around, the socket head screw makes sense. I'll probably do that on future planes.

It's aways best totune the carbwith the plane dressed for flight. Air flow is different with the cowl off. Also, on one of my planes, the only way to get the cowl off is to remove the engine and cowl as one unit. More and more, I'm thinking a split cowl is the way to go. I"m probably going that route on my next cowled plane. You need access to the engine and fuel lines and filters without having to dismantle the whole front of the plane.My 1/4 scale Sukoi SU31 is a great example. It is a royal pain to get at any of the fuel lines or needles and each time you mount the engine back on the firewall, it is off just a tad from the last mounting. A split cowl would eliminate most if not all the problems with adjustments and normal maintenance of the engine and fuel system.

Don

DarZeelon

Shaggy,


A weather change; such as a rise in temperature, or a change in barometric pressure, or humidity; will require slight mixture tweaks...

This is truer; if your engine uses low-nitro fuel, which needs a more exact mixture setting for both the high and the low-speed needles.
If you use 15%, or more nitro, which can 'suit for' a wider range of mixture settings, without changing its running characteristics (- at the cost of paying more for the fuel and for more fuel), the required change can be so subtle; it can be overlooked.


A cowled-in engine installation must have access to both needles, incorporated into the structure, at the time of building.
Removal of the cowl, changes the running conditions of the engine to a great enough degree, to make it not worth the effort!

I have yet to see a scale judge, who will reduce a competitor's points score 'because the cowl has two 1/8" holes for fuel-adjustment access'...
...Yeah! The 'real' plane does not have these holes, so the scale effect is impaired; ain't it? ...


This is something you do while building your model; not just after you realize there's a problem...
The same goes for cooling-flow baffles installed inside the cowl... You construct them in anticipation of possible overheating - not just after your engine burns up...[&:]

EDIT: Language

Hobbsy

My Feedback: (102)

The Saito High Speed needles are all set up for an extension, so just stick a 2/56 screw in there tighten the grub screw and you're done.

blw

My Feedback: (3)

I use the small Allen wrenches that come with the engines.

Some Saitos seem less affected by weather changes. Others need tweaking more often.