Saito 125 poor performance problem
 

Hi Guys,

I've just been running a new Saito 125 - I bought it a year ago but only just have a home for it.

It's had just over a gallon through it following usual Saito break in procedure. Plug is OS type F, prop APC 16x6, Hattori cooling header and muffler, fuel either 10% nitro 2% castor 15% ML70 or 20% nitro 18% EDL2 (tried both).

All went well until I started leaning it out after 1/2 gallon. It behaved normally as I progressively did this over two tanks of fuel, but when I finally had it correctly set it was only pulling 7700rpm. Didn't sound hard or tight, but just wasn't performing. Needle adjustments made it behave pro-forma, but didn't improve the performance. It will happily sit and burn through a complete 14oz tank like this without showing any signs of stress.

Whilst checking that it wasn't overheating, I discovered that if I let it cool down for 30 seconds or so by stopping it or just backing off to tickover, when I opened the throttle again it would belt out at 8800rpm for between 4 and 8 seconds before dying off over a few more seconds back to 7700rpm. This was completely repeatable and continued for another three tanks at which point I gave up.

During this time I tried a second new plug, swapped to the 20% fuel, removed the inlet venturi I'd added, checked all the engine bolts for tightness (its the first saito I've had that doesn't leak at least somewhere!) and let it cool right down to do the valve gaps. No change whatsoever.

I've not come across anything like this before. The only things I can think of are that it is either a piston ring problem (sticking? In upside down?) or a valve problem (valve not closing fully being tight in the guide?) which is being triggered by the temperature rise of full power.

Any thoughts?

HS

Ps My guess is that a run-in 125 on 20% nitro should swing an APC 16x6 at around 9000rpm.

RE: Saito 125 poor performance problem
 

I don't have any good ideas as to the loss in power; however, I can confirm 9000 RPW on a 16X6 with 10% nitro at sea leval (26' above to e exact :)).

Do you have any sense if it is going rich or lean? If it's leaning out, there could be an o-ring leak on the inlet manifold side. Or possibly an obstruction in the fuel tank, either pressure or suction side, like a collapsed clunk line. Perhaps try another complete tank assembly.

I think the sticky valve/ring issues are pretty remote and I'd try all the simpler things first.

John C

edit - I just reread your post and I am thinking you have a tank probem that resolves itself when you go to idle (air pressure in tank equalizes) and then reappears when you run for a time at full throttle (partial vaccuum pulled intank or lines).

JC

RE: Saito 125 poor performance problem
 

Try a APC 15x6 or 7. Mine is well broke in and wont swing the 16x6 more than 8000 rpm no matter how you tune it and the high speed needle is not very responsive with this prop. An APC 15x8 works a little better but it doesnt come to life until I used the 15x7. I have a 120 Saito that swings the 16x6 with no problem, I wonder what they did while they were shaving weight on this motor. Fuels used are 15 or 20%, never tried 10%

RE: Saito 125 poor performance problem
 

That sounds like a good thing to check but also check that your tank isn't foaming. Saitos can shake a lot and this will almost certainly induce fuel-foaming if you're not careful. Look for tiny bubbles in the fuel line to the carby they'll make the engine run lean.

It's also a good idea to change the plug after the first hour or so's running. It's not uncommon for them to be fouled by the microscopic metal particles that are liberated during the first hour or so's running.

_____
When I'm not here I'm at [link=http://rcmodelreviews.com]RCModelReviews[/link]

RE: Saito 125 poor performance problem
 

The fuel foaming problem is certainly a possibility along with suggestion about the prop size. I would also suspect excessive piston skirt expansion on what is a relatively new engine. If this is the case it will free up with additional running. You could pull the piston and look for scuffing or bright high spots on the piston skirt. If this is the case I would just continue to run it on at least 20% oil.

Bill

RE: Saito 125 poor performance problem
 

My Saito 125 peaks with a 16X6 at just under 9000 RPM at 500 ft. ASL, using 15% Wildcat Premium Xtra.

Have you tried switching to the stock muffler? I don't have any idea if it would help or not, but it CAN'T hurt!

RE: Saito 125 poor performance problem
 

Your numbers are a little low compared to mine and another 1.25 in my club. The 16x6APC never lets the motor unwind IMHO. I was getting in the low 8,000 on 15% Powermaster with 18% oil.I have switched to a MA Scimitar 16x6 and have gained 900 rpm and instant throttle response.

David

RE: Saito 125 poor performance problem
 

Try another prop

RE: Saito 125 poor performance problem
 

I did some searching for a Hattori muffler for a Saito 125. All I could find was one designed for a YS 63s, 91, 110FZ/120, 140Sport, and 160DZ. It's thread will also fit a Saito 125a, but you have to have some way of pressurizing the fuel system in order to use it with a Saito. If you aren't running pressure to your fuel tank, you might have found the trouble.

It would make sense that after your engine has run for a while, and you throttle up, your engine gets good fuel delivery for a period of time. Then, the suction isn't sufficient to supply enough fuel and your engine slows down.

I'd try the stock muffler, and run the exhaust pressure to your fuel tank.

RE: Saito 125 poor performance problem
 

If you read the Saito literature, Saito 4 strokes love 30% heli fuel, I only run Cool Power 30% Heli in all of my Saito's and I have to say they all run great, from my 72 all the way up to 182 twin. It is much more expensive and don't believe the stories of ruining the bearings, I have not had one motor die.

Good Luck

R/C Foolish

RE: Saito 125 poor performance problem
 

Hi Guys,

Thanks for all the input! :D

Firstly, the engine is on my standard test bench which I've used for running in/setting up tens of engines (last victim was a YS160DZ). It's definitely not fuel foaming (tank is well insulated and I can see its contents are fine). When it's running at 7700rpm I can adjust the needle to richen or lean it and it behaves accordingly; richening it lowers rpm, then it starts to 8-stroke a bit then a fully blown burble; leaning it causes it to start to go hard then a bit more stops it. So I question it being a fuel feed problem. But I take your points, and it's about time I replumbed my test stand so I will do this before running it again.

The Hattori system is as follows: Hatori #823 cooling header for YS 120 thro 170. This is the same thread size as the Saito head, but launches about 10 degrees off angle. I have turned a tapered spacer to correct this; I've actually had to do the same before when using on the intended YS because the header alignment isn't that great even on the intended engine! Hatori #822 header will also work and has less vertical offset.

http://www.centralhobbies.com/Exhaust/hatheadr.html

Muffler is the #725 version http://www.centralhobbies.com/Exhaust/hatori.html

When I get home I will post pictures, it really is a neat set-up and the tapered spacer is really easy to make.

You are absolutely right, although this system should outperform the standard I should go back and try the stock muffler (and include silencer pressure).

Finally, if it won't happily swing a 16x6 then that is disappointing, especially when the manual itself quotes upto a 17x6 or 16x8. The intended model is a YT Adrenaline which will weigh in at around 4.2kg, a 15" diameter prop isn't going to cut it in the static thrust stakes. But again you are all right, I will try a 15x6 to see if it persuades it to come "on cam".

Should have some time to put more fuel through it tomorrow, will post results!

HS


Ps. I've just given J D Haytree a call (UK service /repair). He suggested much the same things: check the tune, run a smaller prop for a while to get the rpm up and get some fuel through it in case it is just a tight example. He also suggested it could be a lack of piston ring gap, causing increased friction as the ring expands. Anyone know what the piston ring gap should be (order of magnitude)?

RE: Saito 125 poor performance problem
 

Try an APC 15x6 or 16x4w. You and your Saito125 will like them a whole lot better.

RE: Saito 125 poor performance problem
 

Hi All,

Today I had chance to put another 80oz of fuel through the 125. Fuel today was a YS mix, 20% nitro and 20% klotz techniplate. Here are the results:

Replumbing the test stand - couldn't find anything wrong with the original plumbing/tank, but replaced it all anyway (chance to fit a bigger tank). No change to engine performance.

Adjusting LS needle - engine behaved as expected in response to LS needle changes, no change to top end performance.

Revert to OEM muffler - no change to engine behaviour, rpm about the same as with the hatori system, just a lot noisier! No difference either between running with and without muffler pressure (apart from adjusting the HS needle accordingly).

Change to a smaller prop - Behaviour almost identical on a 15x8 APC (16x6 original). I then switched to a 14x8 APC (didn't have a 15x6). This increased the rpm but didn't change the pattern of behaviour. So after opening the throttle it would pull up to around 9800rpm for several seconds, then progressively die back to about 9100rpm. Once at 9100rpm, the HS needle could be richened or leaned and the motor would respond by going rich or lean, so I'm sure it isn't a fuel feed problem. Even 9800rpm for a 14x8 on 20% nitro seems a bit weak for a 125.

I then stopped tarting around, left the 14x8 on it and burnt through 60oz of fuel at full throttle and a "flight" needle setting. At the end of this, the motor was behaving identically at high speed (but the tickover has improved to a lovely smooth 2k).

At this point I decided King Henry was about right and "off with its head" was the next step. Photos below. Sorry for the quality, it's hard to get a representative photo of what the liner and piston surfaces look like. There is definitely some light scoring on the liner and high spots that have been polished. The piston is showing signs of wear at the edges and corners of the skirt. At this point my experience ends - I'm not sure what I should be seeing on such a new engine.

Any help appreciated!

Ps I popped the ring back into the bore and measured a ring gap of about 0.18mm (about 7.5 thousandths of an inch).

RE: Saito 125 poor performance problem
 

Finally, here are some photos of the hatori header/muffler and the tapered spacer to get it to fit.

RE: Saito 125 poor performance problem
 

9800rpm on a 14x8 is about right for this engine. Mine turned an APC 15x6 @ 9800rpm on 10% nitro. APC16x6 is ok for scale and slow bipe models flying mostly less than half trottle. On my UCD 60 APC15x6 and 16x4w pulled much better and worked better for hovering and 3D. I always have some castor oil in my fuel.

RE: Saito 125 poor performance problem
 

Forgot to say that I always set the idle needle slightly richer than what seem to be the optimum setting for idle. Saitos run and transition great with a slightly rich mixture setting and the larger ones should be able to idle at 1800rpm.

RE: Saito 125 poor performance problem
 

Thx Flyer95.

9800 on a 15x6 (or 14x8) wouldn't be so bad if the bloody thing would hold it for more than about 5 seconds! 9100 on a 14x8 sucks.

I'm beginning to think I should have gone with my heart and not my head. My heart said just get another YS110S and be done with it, whilst my brain said "no, try the Saito, it'll be cheaper to buy and cheaper to run and should only be slightly down on power".

:-)

RE: Saito 125 poor performance problem
 

You're right.The figures look rather low.I've found that the rpm figures do vary a bit from engine to engine in my collection.I had an engine with almost the same problem.turned out the piston/liner fit was off and when hot , compression was very light. Changed the jug and ring and solved the problem. I traced the problem to minor scoring and uneven wear.The piston showed marked scoring too.I don't know if improper running in with too big a load was the cause of my problem. I rerigged the camshaft when i did the change although I don't know if ithe timing was out from the factory.

RE: Saito 125 poor performance problem
 

The Saito 1.25 doesn't use a liner. The cylinder/cylinder head are one piece.

RE: Saito 125 poor performance problem
 

HighSide,


7,700 on a 16x6 APC is just 1.17 HP. Nice output for a Saito .72, perhaps, but not for your 1.25...


The only real clue we have as to what causes this low power, is the fact that you can momentarily get the engine up to full-power, before it bogs down...

This is not a problem related to fuel-foaming (Bruce), because if it was; richening would get RPM back up... and the leaning that would result from 'bubble ingestion', is very likely to cause a prop-throwing backfire, that does not seem to ever happen...

It is not related to the nice Hatori muffler, because others using it are getting full performance; and you had reported; a change to the normal Saito muffler produced the same phenomenon...

It is not the prop either (Mike, Flyer), because this reenacts itself with every prop you tried...


It is a result of a 'change' that happens inside the engine, as a result of running it full-bore and attempting to extract full power; a result of heat-soak altering a mechanical part...


It can possibly be the piston-ring having an insufficient gap, which causes the ring-ends to butt together, as it heats up; thus increasing its friction against the cylinder-walls and possibly buckling; causing massive blow-by... This could amount to a great power loss. A defective piston-ring could also heat-expand asymmetrically; causing the same...

The valves? ... I thought about it, but the only heat-induced leakage cause can be a distorted valve that heat-expands asymmetrically, causing a major hot compression leak that does not happen when it is a bit colder.


Because the surrounding aluminium head-cylinder unit would expand more than the steel valve, I do not think an incorrectly set valve-lash issue would cause this, but it will never hurt to check this too...
Perhaps the exhaust valve heats-up and expands so much more than the surrounding air-cooled head, that an insufficient valve-lash, may cause a compression-leak and ultimately, even a burnt valve...

RE: Saito 125 poor performance problem
 

Flyer95 - Just out of interest, what is the all-up weight of your UCD? I'm planning on putting the 125 in a YT Adrenaline which will end up just over 4kg (about 9lb ish) and want it for freestlye flying. I'd guessed that a 15" diameter wouldn't cut it in the static thrust for hovvering, whilst a 16x4W would be too small a pitch for the more F3A style stuff. Probably your UCD is a good pound to pound-and-a-half lighter?

DarZeelon - thanks for the response and confirming my sanity! I'd checked the valve lash and tried the usual "virtually no gap" setting as well as a wider setting. I'm tending to agree with you about the heat soak which is backed up by togatoga's experience, but I'm past the limits of my knowledge. The UK service agent won't honour the warranty since I purchased the engine whilst living in California (fair enough), so I've just spoken to JD Haytree again and he is going to take a look at it. He's been a Saito service agent for 20+ years and is suitably intrigued by the symptoms I've described and has never seen anything like it before.

I'll post back when I get his verdict. Unless of course he discovers that I am a muppet and it's all my fault...

:-)

RE: Saito 125 poor performance problem
 

highside,
I am not sure about the all up weight for my UCD 60 and Saito125. I lost the plane in an mid-air-collision a few months ago so I can not weight it anymore[:o]:D Saito125 is however a very good matched powerplant for the UCD 60 and can easily hover and pullout at anytime. APC15x6 is a great allround prop for it. 16x4w is also equally good for funfly planes like the UCD but as you said a much slower prop.

RE: Saito 125 poor performance problem
 

Bummer. At least it was lost doing what it was designed for! I lost a 60 size pattern model a couple of years ago when my girlfriend fell over on it :-(

Whilst thinking about props I discovered this program:

http://www.geistware.com/rcmodeling/...r_selector.htm

It seems to be much more accurate than ThrustHP. I tried two case examples from models I currently fly (on APC props 14x6 and 17x12) and I reckon the static thrust it predicts is within about 5 to 10% of my experience.

It reckons a 16x6 at 9000rpm would yield about 5.3kg, or 1.25:1 for the adrenaline. If it'll swing a 16x7 at 8800, its 5.5kg (1.30:1). A 15x6 at 9800 is about 5.1kg.

Anyway, getting a bit off topic.

HS :D

RE: Saito 125 poor performance problem
 

highside...you said you measured the ring end gap @ .0075" (0.18mm or 7.5 thousanths )
The rule of thumb that I've always read about and gone by is .004" per 1 inch of cyl. bore.

Your .0075" would be enough for an almost 2" bore...so I doubt the ends are butting?

My WAG is that as things heat up, the cyl. might actually be expanding more than the ring material, and you are getting even more ring end gap, and thus blow-by?

What does the hot compression feel like immediately after shut down?

RE: Saito 125 poor performance problem
 

Quote:

---

ORIGINAL: highside

Whilst thinking about props I discovered this program:

http://www.geistware.com/rcmodeling/...r_selector.htm

It seems to be much more accurate than ThrustHP....

---

HighSide,


A better prop-calculation program is [link=http://mvvs.nl/prop-power-calculator.xls]the Reivers Prop-Power[/link].
It can either be used on the site, or (if you have MS Excel, or Google Office), be downloaded and used on your PC.

Quote:

---

Anyway, getting a bit off topic...

---

Well, what are you waiting for!? Fix your engine and go flying!