Hi, first post
I purchased a used Saito 150 that seemed to be in pretty good condition. I replaced the bearings, set the valve timing and valve lash
per the book. I am confident these are correct. The engine has good compression and runs reasonably well. It seems to have a sort of knocking sound especially at idle and at certain speeds seems to rattle. Sometimes reminds me of pre ignition. At idle I hear this BAM, BAM, BAM hard hitting sound. BTW I can't get a reliable idle below about 2900 rpm. I am using Cool Power 15%, 18X6 wood prop well balanced. Last night I removed the back plate to take a real close look at the rod bearing fit on the crank shaft journal. At TOC on non compression stroke by wobbling the prop back and forth I could see some play in the rod bearing fit. I know there is a oil clearance on this fit. Just don't have the expereince to know if this fit is to loose and causing the knocking. Any help or suggestions would be greatly appreciated. Don't want to buy a lot of unnecessary parts and end up with same problem.
Thanks, Don

You may have just a little too much prop. A 16-8 is the usual prop for casual flying

I've experienced this knocking sound at idle. The last episodes were with some fuel that had experienced too much light.

Enjoy,

Jim

Don't understand what you mean by fuel with to much light.

Old fuel runs unstable. It will cause the little sputters at idle you are hearing, it was cause unexplained quitting and unstable mixture settings.

Fuel was fresh, tried a friends 20% no difference. Had the test mount mounted to side of my shop and when I went inside with the engine running. There was a gosh awful vibration - knocking sound inside the shop. My friend has a 150 and it idles and runs smooth, low vibration. Ticks over smoothly at idle, mine sound as thought the airframe is coming apart from the beating it is taking.
courious!!

That eleminates the fuel.

My Saito 150 runs as smooth as silk also.

The next thing is the idle mixture. Is it too rich?

If you have a metal throttle arm, the idle needle should be flush. If the plastic arm, it should be slightly below flush.

Metal arm, idle screw slightly below flush. I set idle using the pinch test and it seems about right. No setting of mixture eliminates or reduces the problem. It sounds like, especially at idle, a series of explosions going off, like I said BAM, BAM, BAM with vibration. I know that combustion engines are a series of explosions, but this thing is really noisy, not smooth sounding at all. I just don't have the experience to know what a rod knocking in rc engines sounds like, or if one can look at the rod bearing fit and tell if it is to loose.

I don't think it is a rod knocking.

I have experienced this on different brands of four strokes in the past.

Are you running a OS "F" or Saito "SS" or Hanger 9 "Super Four Stroke Plug", or Y-S plug?

The Fox Miracle could be too cold for right now?

Enjoy,

Jim

ddotson:

Quote:

Fuel was fresh, tried a friends 20%... awful vibration - knocking sound...

Quote:

That eleminates the fuel.

Remember "Sportin' Life in Porgy and Bess? "It Aint Necessarily so."

It could well be you made the problem worse by going to the 20% nitro. Depending on the age of your FA-150 you might have one of the "High Compression" versions, they can be really critical on nitro percentage. Try using some fuel with zero nitro, or at most 5% and see what happens.

Also, reset your valve clearance to 0.0015" at most - that helps too. And yes, that is one and one half thousandths inch, not fifteen.

Bill.

>>EDIT to add picture. wr.

This is an older engine, manual choke and all, and boy does it have compression. I never knew Saito made engines designed to run on 5% or less. Is there any way to tell if this is a high compression engine other than feel? Have you ran into many saitos with rod bearing knocking, if so out of courisity what does it sound like.
I appreciate all the help!!
Don

Jim, OS F plug new.

It is not uncommon for a Saito to knock at low speeds when the LS needle is too rich, this would also explain the inability to idle lower than 2,900. The high compression Saito 1.50 will idle at 2,000 with a prop that has a little weight to it.

Just talked to a friend that sort of knows the history of owership of this engine. He said it was at least 8 years old and probably older.
Mabe this will help the experts find a solution.
Again thanks, Don

The older higher compression 150's would most likely have a "A" stamped on top of the right engine mounting lug.

Don:

Given reasonable treatment, it's just about impossible to wear a Saito out. Prolonged running with preignition and/or detonation (not the same thing) can damage the rear crank bearing, and eventually loosen the rod fit on the crank pin. Looking in the back of the case if all you see is oil squeezing out of the rod bearing it's OK. If you see an open gap inside the big end of the rod, replace it. I can't say I've ever heard a rod knock in a Saito, just too much other noise.

High or low compression? With the rocker cover off, look at the top of the cylinder around the valve spring. If you do not see a brass ring it's high compression. The cylinder fins - if they are too big to get the cam cover out without pulling the cylinder, it's high compression. These both show it's the ABC version instead of the later AAC engine. Actually has a choke, probably high compression.

The early AAC engines were also high compression, so lack of the ABC cylinder does not mean your engine is low compression, but there were very few HC engines with the AAC cylinder.

The 18x6 prop might be a little much, as Jim said, it's right on the high end of the permissible range.

Pictures:
1) Comparison of ABC and AAC spring pockets, AAC on the left.
2) Cylinder fins over cam box, ABC
3) Smaller fins, AAC.

Bill.

Don:

Forgot to say try the low nitro fuel. Wont hurt anything, and might cure all your problems. Besides, it's cheaper, and will give you more flying time on the same amount. Double savings.

Bill.

Oops. Forgot you can't see the top of the spring pocket on the FA-150 without removing the roker pedestal. Ignore the part about the brass ring on your engine.

Bill.

Jim:

I have three of the high compression big block engines. Two of them are stamped "E" and the third is stamped "K" on the lug. And they are all the same size engine.

What's worse, the two with the "E" code have different size rear bearings on the crank. I don't pay much attention to the letter codes.

Bill.

At work don't have engine to look at, but from pics and info, I am certain it is high compression. Fin arrangement over cam cover etc.
If so, then this engine was not desigined to run on 15% nitro, right? Would explain a lot. Just courious, if I had the original instructions for this engine what would the MFG reccomend as a fuel. Have some 5% Wildcat, will try it on this blend tonight and let all know the result.
Don

One other thing I noticed looking at Pics, the intake manifold screws into cylinder just like the exhaust manifold on mine, if this tells anything about this engine.
Don

Don:

With a prop in the smaller end of the acceptable range, and the valves set at minimum, the HC engines will accept 15% nitro, but they are still touchy on it.

As I recall, the instructions didn't say much about nitro percentage, it was just something we users had to learn for ourselves.

The American market is Saito's biggest customer, Americans like high nitro, Saito modified the engines to suit the market.

All but a very few of the "Big Block" Saito engines have the screw in intake pipe. The one in the picture was a very limited production version of the FA-120, high compression, wild cam, free exhaust. The one in the picture is the very first of the big block "S" type engines, possibly no more than a couple hundred made.

Bill.

More on the cylinders and intake pipes.

All the FA-150 and FA-180 engines have the cast intake with screw-in attachment. Only the short run of the first version FA-120S had the curved pipe.

This picture shows the ABC FA-120 cylinder on the left, and the first production FA-120 AAC on the right, it's the FA-120S.

Bill.

>>EDIT: This also shows how much larger the fins of the ABC cylinder are. wr.

Bill , mine is the style on the left with the cast intake manifold. Getting kind of confusing. I guess, bottom line is what engine do I have and what fuel should I use.
Don

The pictures of Bill's engines I think are 120's and not 150's.

I havn't seen a 150 with a tubular manifold.

That was not the point of of Bill posting the pictures. He wanted you to look at the valve spring pockets and the valve guides.

Enjoy,

Jim

I have a 120S-DP. The Dp stands for duel glow plug. does anyone know anything about this engine? What was the purpose for the duel glow plugs? Is this thing worth hanging on an airframe?