Timing the ignition and Valves

Hi All,
As I learn more about my "new" 15 HP IHC engine it becomes even more clear to me that these old engines are ALL female! And as it is with exploring the beauty and potential of a "new" women, so it is with exploring the beauty and potential of a "new" engine! Each secret uncovered, each success achieved, even each failure brings with it an awe and appreciation that only comes with a "hands on" learning experience! So it has been with my IHC, and so it will continue to be for some time into the future.

The intake valve was stuck when I brought the engine home. No big deal there. I removed the rocker arm support (the intake valve is inside it) and a light tap with a hammer loosened it right up. A bit of Gibbs and it worked just fine. However, the engine would not hold compression after the first/second time over. I could move the valves by hand and get compression, but one/two time(s) over and NO COMPRESSION. So off with the head to see what the hell was wrong. Some crud in the cylinder and intake chamber, so that was cleaned out. The valves looked pretty good, but while I was inside her that far I decided to lap them.

Put the head back on--same thing, loss of compression after the second/third time over! I then took the intake damper (I think that is what it was) off the intake valve and that seemed to help some, but still a loss of compression from time to time.

Arnie came over on Saturday to pick up some oak for a cart he is building for his Robertsonville. While we were looking at the IHC and talking about the loss of compression we decided to give her a spin.

Second time over and BANG. She then ran for about 10 minutes before blowing an ignitor gasket! (All female, YES! Admit it, you have all been there and done that. Just about the time you are at your wits end with that "new" chick you are seeing she is so damn impressive in front of your best friend that all is forgiven and you are in LOVE all over again--or are you just in "heat?") Sunday it was back to square one. After making a new ignitor gasket, NO COMPRESSION after two or three times over. I then put the intake "damper" back on the valve and BINGO--compression every time it should be there! I have no idea why there is now compression, but as I said earlier--they are all female. And when things are working right DON'T ASK WHY, JUST BE GLAD!

Now I remember this engine from when a former Club member owned it. (No Reg, we didn't kick him out because he let someone come in behind the ropes--he simply died!) It was ALWAYS hard to start and ALWAYS ran too fast. Therefore, on Monday I decided to check the valve timing. Perhaps there are marks somewhere in this engine, but I couldn't find them if they are there. So I set up a temporary tram and marked the flywheels at OC and IC. I then marked a permanent tram on the engine. After that I located where the exhaust valve SHOULD be opening and closing. The valve timing was off by 15-17 degrees! No damn wonder it was hard to start and run slowly!

Yesterday I cleaned the cam gear well to see if there were any timing marks on it and sure as hell there were prick punches. Two in the cam gear and one in the crank gear. They meshed PERFECTLY! HOWEVER, the punch marks in the cam gear looked "homemade" and the one in the crank gear looked as if it was perfect. A bit more cleaning and I found a timing mark on the cam gear one tooth off from where the prick punches were AND in the proper direction that I needed to go to correct the valve timing!

Apparently some idiot that had been "with" this engine sometime in the past had prick punched this old gal in the wrong place. (Again, I call your attention to all these old engines being female! I'll not go into detail since this is a family List and women and children might be reading this post. USE YOUR IMAGINATION!)

I CAREFULLY removed the cam gear (after all, you must keep in mind that this was my first time with this old gal) and moved the gear to the proper location. A check of the timing then verified that the exhaust valve was now opening and closing w/in several degrees of where it should! I tightened everything up and Mike (my youngest son) and I spun the flywheels several times and it ran well--BUT FAST! Checking things over a bit it became evident that the governor springs were too heavy and would need to be replaced.

This morning I installed lighter governor springs and after playing with the engine for several hours was finally able to start it by myself--ONCE. (I finally figured out the compression release! What a "doGsend" that was!) This evening Mike and I played around with the old gal a bit and FINALLY figured out how to get her "turned on." Gas open 2/3 turn, 1/3 choke, slight prime, compression release and the second or third time over--BANG!

Then backing the gas off to 1/3 she runs happily at about 80 RPM's. We started her several times that way and then I let her run for about an hour just listening to the music that she produced. As darkness closed in I just sat there and took in ALL that she had to offer. The sight of her doing her thing, her smell and her sound were all that anyone could ask for. I let her "do her thing" for an hour, or so. Tomorrow is another day and I'm sure that the old gal will teach me how to get her to go down to 70 RPM's--perhaps 69!

Dave

General Rule

F.B. Wright, in his _The Small Single-Cylinder Gas Engine_ (published, originally, I would guess in the '20's and available from Hit and Miss for about $8.00) says that the "average engine" timing should be EX close 10 degrees afrer IC and open 40 degrees before OC. He also recommends that the IGN. should be set to fire 20 degreed before IC.

Is Wright right? Well, he is probably w/in reason, but every engine manufacture had their own ideas. Most that I've come across are w/in 10 degrees of each other. If you can get the engine manufacture's specks use them, if not Wright, at least, gives you a starting point.

Dave

Hi Dave, it sounds like you have "Her" under control, though I am sure you will agree that is a delusion that most men are victim of. :)

As to the timing marks, just for general information, I am sure that most of us have heard the old saw about an engine only needing 4 things to run, those being fuel, compression, spark and all at the right time.

Also seen as SSBD Suck, Squeeze, Bang, Blow

These are truths and are absolute, another absolute truth in reference to 4 stroke internal combustion engines, is that the exhaust stroke, can not encroach on the intake stroke, EVER!

The exhaust valve must be closed at or very near Top Dead Center ( also known as Inner Dead Center) some engine may over lap 5 degrees or so but not much more than that.

Some engines designs will, when the valve is set to close at TDC or very near, will open the exhaust valve at 35 to 40 degrees before Bottom Dead Center ( outer dead center ) and some will not open the valve till 15 or 20 degrees before BDC, and others may have some other point at which the valve opens. Regardless of when the valve opens, they will all close the valve before the engine begins the intake stroke.

The point of this is that as long as you know this TRUTH, you can always figure out the valve timing on a 4 stroke engine without any timing marks. Just turn the engine to TDC before the intake stroke and see when the valve closes, some adjustment is usually given in the push rod, but many times you will have to move the timing (Cam) gear.

Ted Brookover

All this talk on timing reminds me of a question... I know how I work out how many degrees we're talking about - I do it by the position of the conrod as compared to horizontal (or vertical for vertical engines). How do you do it?

Paul

Hi Paul, I'm not sure exactly what you are asking, so this may be more than you want--but I'll give it a try. First you must fine IC and OC (TDC and BDC for a vertical engine) and mark them on the flywheel.

On an open crank engine it's easier to fine OC and work from there. To do this move the flywheels until the piston skirt is even with the open end of the cylinder. (At this point the crank will be either above, or below, horizontal.) Using some determined point on the engine (which point will become your permanent tram) or a temporary tram, mark that point on the flywheel in some TEMPORARY manor. (I used masking tape for this on the IHC.) Now rotate the flywheel until the crank passes OC and the piston skirt is again even with the open end of the cylinder. Using your tram temporally mark that point. OC (BDC) is the midpoint between these two marks and can now be permanently marked on your flywheel. IC (TDC) is, of course EXACTLY opposite (ie half way around the flywheel) from OC and can simply be measured with a tape and permanently marked. (If, for example, the circumference of your flywheel is 90 inches, measure 45 inches around the flywheel and that's IC.

To determine degrees do the following. Again, let's say that the circumference of your flywheel is 90 inches. Given that there are 360 degrees around your flywheel simply divide 360 by 90 and you have determined that there are 4 degrees in every inch around the flywheel. (The circumference of the IHC flywheel was 199 inches. Thus 360 divided by 198 equaled 1.8181818181. Thus 1.8181818181 degrees to an inch. I rounded that off to 1.8, since my eyes are not good enough to see "those little marks" any longer!)

Not sure this is what you were asking, but perhaps it will help someone.

Dave

Paul:

Since these engines aren't that high-tech, you can use approximations for crank angle.

There are several ways to figure crank angle. The one I used when I was doing the initial tests of my Solid-State Ignition System circuit with my ZC-52 was as follows:

First, I found Top Dead Center (TDC) by making a pointer for the rim of a flywheel. I then turned the engine just a little before TDC and made a mark on the flywheel at the pointer. Taking a depth gauge, I carefully measured the depth of the piston. Turning the crank to the same piston depth after TDC, I made another mark on the flywheel. I used a tape and carefully measured the distance between the two marks, divided this number by two and made a mark at the halfway mark. This was TDC.

Next, I measured the circumference of the flywheel. I then divided the circumference by 360 (degrees per revolution). That gave me inches per degree. I used my CAD program to make a degree stick that I could print. Gluing this to the rim of the flywheel gave me a -mostly- accurate way to check timing.

In most cases, what you can do is to glue a piece of paper on the flywheel (masking tape?). Now, after transferring the TDC mark to the paper, measure off and mark the degrees.

I tried to use my el cheapo timing light to check spark when the engine was running but the engine was so slow and the light was so dim, I couldn't see where I was.

As for the ZC-52, it runs best at full speed with almost 20 degrees of lead. For best starting (a very slow pull on the flywheel), I can adjust the pickup so the engine fires at about 5 degrees after TDC.

I hope this wasn't more than you needed to know about Alaska! :-)

Take care - Elden

A few definitions from this article...

Timing Marks - these are marks - usually indentations, but sometimes horizontal lines or arrows which show where the timing gear(s) should line up with the gear on the crank shaft for correct valve timing. Before taking an engine apart you should clean these gears and see if they are marked. If they are not marked, or you just want to be safe you should make your own mark. A sharp metal punch is the best way because the indentation won't be lost during cleaning.

Piston skirt - this is the end of the piston where the conrod (the rod which connects the crank shaft to the piston) enters the piston body - it is the open end.

Tram - in this context this is just a mark on the engine where the timing is taken from each time you do it. It does not matter that much where it is as long as you can easilly compare the mark with the flyhweels. For example on a Rosebery type C vertical there is a raised V on the side of the block, the flywheel has marks for the spark and valves. The raised V is the tram.