MDavis28

SrTelemaster150

In order to fix this you have to find what is casing the problem, not what the symptoms (cylinder base failure) are.

Any side stress on the cylinders bases should be in the direction of rotation as the piston will rock somewhat in the bore as it is forced downward.. Cylinders failing like what you have experienced points to something causing stress perpendicular the what the normal forces would generate.

If it was my engine I would check the rod angle in line with the crank against the surface on the crank case where the cylinders bolt on. Your most recent failure has a piston severely misaligned with the longitudinal access for whatever reason. If you find a similar pattern on all of your pistons I would suspect something in the way the case is machined for the cylinders bases or perhaps the master rod in flipped backwards . Also check the crank bearings to make sure there is no radial play in the crankshaft.

IMO I would run methanol instead of gas anyway. I have been running glow fuel (methanol with some nitro) with CDI (spark ignition) since 1997 on all of my Saito engines. Methanol runs much cooler than gas, does not pose a much fire hazard, doesn't have the objectionable smell, is just as user friendly and makes about 20% more HP than a similar size gas engine. The only draw back is fuel consumption, but eliminating the nitro, and reducing the oil content will help. If you live near a large city or race track, methanol is about $2 a gallon if you buy it from bulk into your own container. To convert a gas Saito you would need a glow fuel carburetor and advance the ignition timing about 8 degree more. Saito engines were not originally designed for gasoline use.

SrTelemaster150

Here is how to check your rod alignment.

Attachment 2260427

Have someone measure the diameter of the FG60R3 wrist pin and make a longer version that will hang over the edges of the case opening.

When you get it made, I can walk you through the procedure. You can check for both straight misalignment or twisted misalignment.

BobH

My Feedback: (2)

So the wrist pin bearing is installed incorrectly? It's pressed into the connecting rod at some wrong angle? Or the lower end bearing is mis-installed?
All I can say is WOW. I worked for a small engine mfg for near 10 years. Saw about a bazillion engines come through our shop. I don't ever recall ever seeing a mis-aligned wrist pin.
That's a new one on me.

SrTelemaster150

How many forked rod (Harley Davidson) or linked rod (radial) engines have you worked on?

It isn't likely the wrist pin itself that is misaligned. That is merely where any misalignment can be conveniently measured. Since, as you pointed out, it is unlikely that the wrist pin bore itself is the culprit, it is the most accurate place to do so.

On Harley Davidson engines it is usually a tolerance stack-up of the various components on the big end of the connecting rod. (roller bearing races, race bores, crank pin, etc) In this case, it could be any of a number of reasons. if the pistons of all three cylinders show the same wear pattern, there is something amiss with the master rod alignment and/or case machining..

The first step is to check to see if there is indeed misalignment since it would be quite easy to make a tool and use some thin paper strips to check. All three pistons/rods should be checked at this point.

I am basing my assumption that the piston in the picture has never been installed in another cylinder that failed completely at the base causing the severe signs of misalignment.

Since the cylinder pictured doesn't appear to have failed to the point of becoming misaligned with the case itself and IF that piston spent its entire life to this point in that particular cylinder, it definitely points to something below the piston/cylinder causing the misalignment.

If I had the engine in question in my hands, with an alignment gauge pin, I could could find out what is causing that misalignment (if indeed there is misalignment) in a few hours time with common mechanics gauges and measuring devices.

757jonp

My Feedback: (48)

I've got my doubts about any kind of serious misalignment in Davis's engine. I'm more prone to believe you had some pre ignition going on due to high temps which caused the jug failure. (the jug being the weakest part) JMHO
I'm in agreement with Telemaster in that this engine just doesn't have the cooling ability to run on gas dependably... it needs some serious fins on those cylinders and quit dickin around dammit!
For the helluva it I bought a couple carb gasket sets and I've got one set immersed in glow fuel right now just to see if they're compatible with methanol. I'll leave the parts alone for a day or two and see what happens.

SrTelemaster150

How could pre ignition force the piston sideways enough for the ring land, which is .1 mm smaller in diameter, to rub the cylinder wall? Perpendicular to the rotational axis no less,

Checking rod/deck alignment would take just a few minutes with the elongated wrist pin and some paper strips. It would be the easiest factor to eliminate and THAT is the 1st rule of trouble shooting.

Just adapt a carburetor from an FA-125 to run on methanol..

757jonp

My Feedback: (48)

I'm not seeing where the ring land was in contact with the bore... I am seeing an area where chunks of carbon probably flaked off and got down between the cylinder and piston ring and caused some scuffing.

Granted, checking rod alignment is easy... ONCE you have a elongated wrist pin in your grubby little hands.

If able I want to use the stock carb if it'll handle glow fuel... no adapter needed. (it's basically a glow carb with a pump)

SrTelemaster150

Your kidding me right? The land is polished on the rear side and you can see the radius wear pattern on the oil residue band on the ring land about 1/3 of the way towards the front. Not to mention the cocked contact pattern on the skirt.


Yeah, I noticed that looking at Horizon's part page.

If you end up running methanol, you'll get the mist efficiency if you crank the ignition timing to about 35 degrees BTDC.

757jonp

My Feedback: (48)

I'm seeing a normal clean land on the left...not polished, and excessive carbon on the right, which matches the pattern in the cylinder head. I'm seeing your uneven wear pattern on the skirt, but not terribly concerned about it. Air cooled engine, fairly loose tolerance... short skirt... piston is going to rock right to left of crank especially until it gets up to temperature. Consider the piston or bore may be out of round also for all we know, or uneven temps adding to the problem. Consider also if that land was in contact with the bore you'd see aluminum deposits on the ring in short order.

The thing I don't like is the carbon buildup on one side and not the other. I would expect it to be more uniform. Poor swirl pattern? Possible detonation cleaning off one side? I've seen many Briggs and Stratton's look better than that!

I'm aware of the timing. I may have to drill a couple new holes in the crankcase to get it or come up with some other method.

I checked the carb parts, they looking good so far. The valve plate is made out of clear acetate (?). For awhile I couln't find it in the glass jar and thought it disintegrated. Turned out to be just nearly invisible..no damage.

SrTelemaster150

Here is a normal piston contact pattern from a 12.7:1 Compression FA-180 running glow fuel with spark ignition. I ran this on a test stand for many hours, at least 10 hours @ WOT doing prototype tests.

Attachment 2260430

Attachment 2260431

SrTelemaster150

Here is a normal piston contact pattern from a 12.7:1 Compression FA-180 running glow fuel with spark ignition. I ran this on a test stand for many hours, at least 10 hours @ WOT doing prototype tests.

757jonp

My Feedback: (48)

Looks great! And I think MDavis's piston was on it's way there if he'd gotten enough time on it. Chances are your piston looked just like MDavis's before it got fully bedded in... were talking microns here.

Considering the temps that were posted on this engine I'm surprised the piston looks as good as it does.

What are your thoughts about the carbon buildup and pattern?

aquaskiman

My Feedback: (46)

Did you guys ever consider just maybe that odd wear happened after the cylinder cracked???? I think with all the cracked cylinders maybe the rod angle is wrong, putting to much stress on the side of the cylinder.

BobH

My Feedback: (2)

Ya know putting a piston design into a cylinder isn't rocket science lol. Normally everything is Square and normal to the plane.
Why that isn't the case in some of these engines is beyond me. Standard engineering and Mfg. No tricks here for sure.
I have one of these engines that has been broken in but not flown in my Corsair yet. Hopefully I'll dodge some of these issues.

SrTelemaster150

Hard to believe that piston came out of an engine that pushed the rear ball bearing through the bottom of the case isn't it.

SrTelemaster150

The top arrow points to the line of demarcation where cylinder contact due to misalignment rubbed off the oil residue (not carbon in this case) to the left of the arrow, yet adequate clearance to the right of the arrow allowed that same oil residue to remain. Looks like a smoking gun to me. .

The bottom arrow shows the uneven contact pattern on the skirt due to the same misalignment. To the the left of that bottom arrow there was no cylinder wall contact as there would have been with a properly aligned piston.




Indeed we are talking microns here and that top ring land should be .002" away from the cylinder wall. That far exceeds any specification for piston/cylinder clearance on such a small bore.



I would say that the carbon build up would be caused by excessive oil and/or higher than normal operating temperatures.

ForcesR

Just a thought, would the damage shown in the photos be the result of a missing Master Rod Retainer (Crank Pin Plug) that was not installed during factory assembly? Removing the rear cover will confirm if the plug is installed or not installed. I checked my FG60R3 and the plug is installed

SrTelemaster150

That, or a master rod installed backwards could cause misalignment..

SrTelemaster150

That is why I qualified my assumption on that piston never being installed in a cylinder that failed completely. The hairline crack in the cylinder pictured in the original pst would not have flexed enough to cause the misalignment. Cast aluminum is brittle and would break or open up the crack before deforming enough to cause significant misalignment..

In other words, the misalignment caused the crack, not vica versa.

757jonp

My Feedback: (48)

In my opinion... (for what it's worth LOL) I thing the actual failure of the cylinder was cause by detonation. I base that on the pictures of the inside of the cylinder in which it shows an unusual carbon pattern. Observe the area surrounding the valves, quite a bit of hard caked on carbon (cooked on oil due to high temp?), but on the other side almost clean. IMHO I think your seeing evidence of pre ignition which literally blasted off the carbon off the clean side just like you hit it with a hammer. I've replaced my fair share of pistons and head gaskets and even a head or two in engines that failed due to pre ignition. In this engine the weak spot just happens to be the jug.

And yes, the hotter it runs, the more prone it is to pre ignition. Excessive carbon buildup will also contribute to pre ignition tendencies. We've all heard pre ignition in automotive engine, but I doubt you'd even realize this thing is doing it (couldn't hear it).

This is the whole reason that I used 100LL AVGAS in mine right from the start. Again... just my .02 cents worth!

BTW I just checked that gasket set that been sitting in glow fuel overnight. No weird stuff going on with the o rings, gaskets, or valve plates. Therefore I don't see any reason why not this carb could be used with glow fuel if you wanted to. The only remaining question is will it flow enough to handle glow and develop full power without leaning out.

SrTelemaster150

And what about the uneven pattern on the skirt?

Never mind the fact that the "blasted" portion of the combustion chamber is on the front while the "blasted" portion of the ring land is at the rear. I would love to hear your explanation for that







Yes, detonation probably contributed somewhat to the failure but not as much as the misalignment which directed the majority of the stress to the rear portion of the cylinder base.

757jonp

My Feedback: (48)

If it was misaligned to the extent it would "rock" the jug to the point of breaking it I'd expect to see a lot more damage to the piston and cylinder. Overheated just south of destruction and pre ignition finished it off!

I think I can speak for myself and bunch of others that we'd love to know what the reason for these failures are. I wish Saito would get involved in it as their name and my pocketbook are on the line with these engines.

SrTelemaster150

I'm still waiting for your explanation of the detonation blasting carbon from the front of the chamber and then the back of the piston ring land.

757jonp

My Feedback: (48)

I didn't say I could explain it, but I think it's pretty clear something unusual is occurring to create that carbon pattern. Wouldn't you expect it to be pretty much uniform across the head? Especially with a semi-hemispherical combustion chamber? It's possible that the carbon never built up on that side, hence the clean ring land. Question still remains... how come?

I think if we had a pic of the piston crown one side would be carboned up and the other side clean to match the CC.

It almost looks like one side of the combustion chamber was considerably hotter than the other the other side. I know, that makes no sense and I've never seen anything like it, nor do I have an explanation for it.