Saito 72 problem
 

Last night after flying my WM Cap 232 w/Saito 72 in it, I decided to remove the cowl and wipe down some of the oil that had accumulated inside the cowl and the firewall. While I had it apart, I figured I'd check the valve clearances (first time I've done it...motor secondhand). When I removed the cover, all the oil contained in the cap of course ran out, I readjusted the valves (using gauge) and reassembled.

Fast forward to tonight. Got home from work, grabbed the plane and headed outside. Right off it didn't run right. Had to turn the needle in an extra 1/4 turn, just to get rpm's I should get. Bottom line, it doesn't run worth a crap, and when I shut it off I can hear what I'm assuming is oil sizzling in the engine. Probably because I had to have the needle to 1 turn out just to get it to run. Head temp (infrared) showed 210 F. Needless to say I didn't fly it or run it long, but Sunday's a'commin.

I did try to run rich for a tank, but it didn't help. I've gone through everything I can think of. Everything is tight, no air leaks, just doesn't want to run correctly. Throw out some ideas for me to try. I went through Bill R's Saito notes, but if it's there I didn't catch it.

RE: Saito 72 problem
 

reincarnate,

If it ran fine before you adjusted the valves and now it runs like crap after adjusting the valves you might want to recheck the valves again just to be on the safe side and make sure you didn't get them to tight. It's always worth checking to make sure.

RE: Saito 72 problem
 

I have never used the guage tool that comes with the engines. I use a feeler gauge set from Sears. I always use the .003 one.

You are probably going to be getting all kinds of readings from the temp gauge. I wouldn't use it.

RE: Saito 72 problem
 

Just included the part about the temp gauge to relate approximate engine temp, since I stated it sounded like oil sizzling, just to show I wasn't sitting at 500 degrees or something.

I've never seen a case where a slight misadjustment of the valve can have that much of an effect on the overall performance. Not saying I didn't screw something up, just haven't experienced it.

More diagnostics: Engine runs rough with greatly reduced power. At previous "good" needle settings, it almost seems to be set extremely rich, and like I said I have to dial the needle down so far, it worries me I'm leaning it out too far. Going to tear it down again Saturday.

Anyone else have any idea's or similar experience?

RE: Saito 72 problem
 

Same thing happened to mine.Then engine locked up. Connecting rod was stuck on crank shaft. This engine had very little time on it. Bought engine NEW and broke it in correctly. We have two at our club with the same problem ,except the rod in the other engine broke . There are no connecting rods available at the present time. Have had one on order for over a month. Crank shafts are available ,but no rods. BE CAREFUL!!!!!!!!!

RE: Saito 72 problem
 

Recheck to see that you have the piston at top dead center on the power stroke when you adjusted the valves. It sounds to me like you have the exhaust valve on a short stroke. (Not opening enough.) If that is the case, you should be able to find a crank position where there is way to much clearance on the rocker when moving the crank around.

RE: Saito 72 problem
 

You hit it brokenprop. Fixed it Saturday, flew it Sunday, and had much better performance than I've had all year. The engine is older, and TDC isn't as defined as it used to be!:)

RE: Saito 72 problem
 

You can see TDC if you pull the glowplug and put a toothpick down on top of the piston.

RE: Saito 72 problem
 

Indeed the way I got it, but I used a wood dowel.

RE: Saito 72 problem
 

You can have one valve fully open and be assured the other valve will be in the correct position for setting the clearance

RE: Saito 72 problem
 

The absolute best way to adjust valves....

The cam turns at 1/2 speed to the crank.... so it takes 2 turns of the crank to make the cam complete 1 turn. At one turn of the crank your cam has turned 1/2 turn.

The object is to find the heel of the cam as the toe (where it opens the valve to it's fullest) is 1/2 turn away from the heel.

OK... take your glow plug out and your valve cover off. Watch one of your rockers.. when it is at it's highest point either make a mental note of where your prop is or make a mark on the case and the thrust washer. Turn the crank exactly one turn... your cam has made 1/2 turn and is on the heel. Thats where you adjust your valve at .002". Repeat for the other rocker and your done.

RE: Saito 72 problem
 

Good advice!

David

RE: Saito 72 problem
 

You guys an your jacking around at top dead center to set valves. Hah Use toothpick HAH pull glow plug HAH

Just spin engine till one valve opens fully and set the other valve. Then spin engine till other valve opens fully and set that valve. If you do this I will gar-ran-tee the valve you set will have no chance of being on the ramp or starting to open.

RE: Saito 72 problem
 

Well, the way race engine guys usually set valves on 4 stroke engines... Probably not nearly as critical on a mild airplane engine camsaft, but extremely critical on big race engine cams.
When the intake valve "rocks" (meaning goes to full valve lift and just starts to close) adjust the exhaust. When the exhaust valve just starts to open, set the intake. This works on all four stroke engines that I know of.
On big camshafts (again, probably not our engines) it is easy to imporperly adjust valves if using the TDC method. Exhaust valve starts to open so soon after TDC, it can throw people off.
Next time, take alook at the rockers while rotating the engine. It is pretty obvious.
Just a tip from a drag boat guy.
Wags

RE: Saito 72 problem
 

Wags, and Jim,


The most accurate way to adjust the valve-lash is to adjust the lash of each valve, while completely disregarding the position of the other valve...

Just find the position of full-lift for the valve you want to adjust and from there, turn the crankshaft exactly one complete revolution.
Since the camshaft(s) turn at 1/2 the rate of the crankshaft, it has turned 180° and the tappet/cam-follower/lifter of that valve is now on the middle of the base-circle.


Notwithstanding production tolerances and errors, this is the most accurate position, at which valve-lash should be measured, or adjusted.
There is absolutely no other position that anyone can show to be more accurate; just that it may still be good enough...


With one valve at full-lift, with a very 'hot' camshaft, the other valve could already be on the on/off ramp of its own cam...

RE: Saito 72 problem
 

That is effectively what you are doing by this method. But if I were you I would discount what countless race engine bulders do (remember a four stroke engine is a four stroke engine) and go by whatever makes you happy. Also, make sure you are not open to others suggestions, as it is obvious you know all.
Just a dumb race engine guy trying to simplify some things.
Wags

RE: Saito 72 problem
 

Oh, and BTW, with the exhaust at full lift, the intake is most ceretainly off the base circle.
Wags

RE: Saito 72 problem
 

Wags,


What could be simpler than 'one full turn from full lift' on the same valve??

Using the position of another valve, just makes it more complicated; not simpler...


And... When adjusting a valve's lash you want that valve's lifter/tappet/cam-follower on the base-circle; not off it!

Any and all adjustment techniques assume this is so.


I am not a 'know-it-all' but there are some 'absolute facts' that I state.

While in all techniques the valve's lifter/tappet/cam-follower is somewhere on the base-circle, my method puts it dead in the center of that base-circle.

Are you saying that taking the measurement with the valve's lifter/tappet/cam-follower still on the base-circle, but just off a ramp, is better than doing it in the middle of the base circle??? I don't think so...

If the base circle is perfectly round and concentric with the camshaft (can you trust that?), it may be 'just as good as' in the center.


But 'just as good as' is certainly not synonymous with 'better than'...

RE: Saito 72 problem
 

No, we must be speaking different languages. I am saying adjust on the base circle. I am saying how to get on the base circle. The one full revolution works just fine whan working on a 1 cylinder, prop as a marker engine. Try it on a v-8, rotating with a starter, no absolute maker for each cylinder. Or on any "conventional" if you will enigne. It would take you hours to adjust valves instead of minutes. As I said, probably best to disregard what works for me. I am not an airplane engine expert. Just a backyard hack.
Wags

RE: Saito 72 problem
 

I'm sure if it is how the Nextel cup guys and the NHRA guys do it, it is probably is not high tech enough for a model airplane engine.
Wags

RE: Saito 72 problem
 

Wags,


We are speaking the same language...

Only on this forum we are talking about four-stroke engines, ~98% of which have only one cylinder and most of the remaining 2% have no more than 2...

So, it is very easy to turn the crankshaft one complete turn from fully open...

As to being a back-yard 'grease monkey', I am also one... at least I was.


In a Chevy V8, with a firing order of 1-8-4-3-6-5-7-2, you adjust I1 with I6 at full lift; E7 with E3 at full lift and so forth...
And I am sure you had noticed, each valve adjusted has its 'twin' (the one in the cylinder that fires in the same sequence, on the next revolution), at full lift.

You would need to turn the crankshaft two complete revolutions, in order to adjust the valve-lash for all the valves.
You just need to follow the sequence, to know which valve it is that will be reaching full lift next...

Some guides specify four stops per revolution, at each of which one intake and one exhaust valve is approaching, or just past full lift and then both corresponding twins' valve-lash is adjusted.

At the adjustment points, each adjusted valve is ±10° from its cam's base-circle.

This is much more accurate than relating to some valve's point of just rocking/on the ramp, Etc.

RE: Saito 72 problem
 

Dar,
I never adjusted a 4-stroke, can you tell me how you know when the one vavle is at full lift?
Thanks,
Frank

RE: Saito 72 problem
 

That is pretty easy, Frank.

You do it by visually following the intended rocker as you turn the prop.

The rocker opens the valve further and further, until at some point it 'dwells' and then begins to close the valve.

The middle of that 'dwell' period is full lift.

Exactly one complete crankshaft revolution from that point, the lifter is on the center of the base-circle, after the camshaft has made one-half a revolution.

RE: Saito 72 problem
 

Dar,
Okay I think I understand, watch the valve stem reach its highest point then rotate 180 and set only that valve? I have been trying to watch the rockers which are not as easy to follow.
Frank

RE: Saito 72 problem
 

I give...your method is much simpler. Remembering the firing order, which ones you have set, the valve that is 180 different than the current one. I agree. Your method is much better. There is no way to miss a valve with your SBC method. I am wrong.
Your ap engie way is simple, fast and cool. I was trying to shed some light on engines outside our little world.
Everyone, put your blinders on...airplane one cylinder engines are the only ones that exist.
Wags
Sorry for trying to elighten some as to another way to skin a cat. I will not try to explain the relations between intake and exhaust cycles. Appearantly the two valve cycles are not related (except to be on the same cam, same cylinder, same engine, but NOT other than that).
I give.
This horse has been beat to death. The best way to adjust valves is the one you are most comfortable and accurate with. Figure out that for yourself. I will not try and help anyone with engines in the future.