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SJN 05-24-2013 12:46 PM

OS 91 FS Surpass problems
 
1 Attachment(s)
Hi Guys.

I can not figure out whats up with my old 91 4 sroke.
I cant get it to idle without the glow atatched.
Even if it is runniong at about 1/3 throttle, and I remove the glow, it will imidiatly drop rpm, and finaly quit.
But at half throttle and up, then it will run.


I bought this engine used recently, and had to replace both bearings, and a cracked con-rod.
The engine was pretty gummed up with old castor, but I got it all cleaned up, and looking nice again.

Removed the valves, and cleaned them up completly, and also cleaned out the intake and exhaust ports.

The cylinder lining looks great, and the piston and ring also looks good and is free, and the compression is fine.

Cam timing dot is in line with the pushrods, and the valve overlap on both rockers are exactly equaly depressed on TDC.

I have tried to set the valve clearance tight and loose, and does not make a difference.

Tried 2 new F glow plugs.

No leaks around the glow plug, or the cylinder hed, nor the intake tube.

the breather is free, and oil is comming out of it.

I have adjusted the idle screw for a few hours, and easily found the sweet spot, and leaned it until it wont start, and richened it to the point where you realy had to open up the throttle alot to get it running at all.

I installed an ASP carb on it, and it does the same exact thing.

I took the tank apart, inspected it, leak checked it, and put it back together.

removed my fuel filter, just to see if that helped.

Fresh 5 % nitro caster/synth blend. Also tried allmost fresh 20% nitro full synth fuel.
It does run better on th 20%, but still dies slowly as before

Tried rinnung it without a muffler installed at all. Also without tank pressure, and it still does the same.

Last thing i did was disassembe the head completly again, and check the valve springs, and the valve stems again, and could not find anything wrong. No sticking valves, and no eccesive wear in the guides.


I have never had this problem with a 4 stroke before, and Im at a dead end.

What am i missing?




krayzc-RCU 05-24-2013 02:04 PM

RE: OS 91 FS Surpass problems
 
Quote:

I have adjusted the idle screw for a few hours, and easily found the sweet spot, and leaned it until it wont start, and richened it to the point where you realy had to open up the throttle alot to get it running at all.
in the past i adjusted my low by removing the glow and the engine did not drop in rpm, when ever my low was to rich it would die when i removed the glow..... but i am not glow expert just sharing my past :D

GarySS 05-24-2013 02:40 PM

RE: OS 91 FS Surpass problems
 
Did you also clean the carb (just a long shot).

BillS 05-24-2013 04:34 PM

RE: OS 91 FS Surpass problems
 

Quote:

ORIGINAL: SJN

Hi Guys.

I can not figure out whats up with my old 91 4 sroke.
I cant get it to idle without the glow atatched.
Even if it is runniong at about 1/3 throttle, and I remove the glow, it will imidiatly drop rpm, and finaly quit.
But at half throttle and up, then it will run.


I bought this engine used recently, and had to replace both bearings, and a cracked con-rod.
The engine was pretty gummed up with old castor, but I got it all cleaned up, and looking nice again.

Removed the valves, and cleaned them up completly, and also cleaned out the intake and exhaust ports.

The cylinder lining looks great, and the piston and ring also looks good and is free, and the compression is fine.

Cam timing dot is in line with the pushrods, and the valve overlap on both rockers are exactly equaly depressed on TDC.

I have tried to set the valve clearance tight and loose, and does not make a difference.

Tried 2 new F glow plugs.

No leaks around the glow plug, or the cylinder hed, nor the intake tube.

the breather is free, and oil is comming out of it.

I have adjusted the idle screw for a few hours, and easily found the sweet spot, and leaned it until it wont start, and richened it to the point where you realy had to open up the throttle alot to get it running at all.

I installed an ASP carb on it, and it does the same exact thing.

I took the tank apart, inspected it, leak checked it, and put it back together.

removed my fuel filter, just to see if that helped.

Fresh 5 % nitro caster/synth blend. Also tried allmost fresh 20% nitro full synth fuel.
It does run better on th 20%, but still dies slowly as before

Tried rinnung it without a muffler installed at all. Also without tank pressure, and it still does the same.

Last thing i did was disassembe the head completly again, and check the valve springs, and the valve stems again, and could not find anything wrong. No sticking valves, and no eccesive wear in the guides.


I have never had this problem with a 4 stroke before, and Im at a dead end.

What am i missing?




No one knows until the circumstances are fully understood.
Engine upside down?
Tank distance from engine?
Tank height from carb?
Bench testing or in airplane?

Appears you bought a junker and repaired it. Is the problem in the repair or in the engine/airplane set up?

Bill

Live Wire 05-24-2013 04:52 PM

RE: OS 91 FS Surpass problems
 
Check your cam timing:eek: could be one tooth off. Don't ask how I know[:@]

SJN 05-24-2013 11:00 PM

RE: OS 91 FS Surpass problems
 
Quote:

No one knows until the circumstances are fully understood.
Engine upside down?
Tank distance from engine?
Tank height from carb?
Bench testing or in airplane?

Appears you bought a junker and repaired it. Is the problem in the repair or in the engine/airplane set up?

Bill
Hi Bill

As you can see in the pictures, the engine is hanging down at a 7-8 o-clock position
The tank is up against the firewall with the rubber bung throught it actualy, so the fule line is very short.
I would say the middle of the tank is right at the carb level.
It has only been run in the plane.

The con-rod is brand new. so maybe it is because of this need to be run in first ?
Can it realy be draging down the rpm`s making it quit ? It seems very smoothe both before operation, and after.



Quote:

Did you also clean the carb (just a long shot).
Garry, The ASP carb is almst brand new, and the OS carb is from my 4 stroke helicopter which flew fine last time.
The engine acts exactly the sam with both carbs. The OS carb does meeter the idle mixture better though.



Quote:

in the past i adjusted my low by removing the glow and the engine did not drop in rpm, when ever my low was to rich it would die when i removed the glow..... but i am not glow expert just sharing my past
Karyz:

Yes, that is exactly what I expect also. So I keep on leaning the low end screw, but you come to a point where it is com,pletly closed, and then the engine will not start.


Cherokee Flyer 05-25-2013 04:40 AM

RE: OS 91 FS Surpass problems
 
I agree. be sure you set the cam timing right, with the mark toward the tube, not stright up.sounds like it is off one tooth.

L.

SJN 05-25-2013 07:17 AM

RE: OS 91 FS Surpass problems
 
Im pretty sure the cam is right.

With the rockers off, you can push the cam follower away, and make sure the dot is pointing directly up at the pushrods, so it is at the 11 and 5 o colck at TDC.
Besides, at TDC, in the exhaust/intake cycle, both the exhaust and intake valves are equaly open exactly at valve overlap period.

wcmorrison 05-25-2013 07:32 AM

RE: OS 91 FS Surpass problems
 
Sounds (1) too rich or (2) fuel blockage.  The engine is just not set up right yet.  It would not run fast if the valve time were off.  Clearances on the tappets is important but would not keep it from idling.  New con rod would not make much difference.  And air leak could be your problem, check the intake manifold gaskets/O-rings.  I had a Maggie with half the intake manifold gasket missing and it still ran fast but no idle.  Could be a tad piece of old Castor in the idle loop some where, in the spray bar.  Carbs are simple, take it apart and clean it up.  Sounds like a good engine, jest been sitting around for while.

Azzir325 05-25-2013 07:43 AM

RE: OS 91 FS Surpass problems
 
The thing that is consistent is

"I cant get it to idle without the glow atatched.
Even if it is runniong at about 1/3 throttle, and I remove the glow, it will imidiatly drop rpm, and finaly quit. "

There's a clue there. I know you changed the glow plug, but something is cooling it down as soon as you pull the driver. I am no expert in 4 strokers or valve clearances, but it could be the intake valve is letting in too much fuel. I don't know about how to adjust that, but a solution may be as simple as a plug with an idle bar. An idle bad shields the glow element from being splashed with raw fuel which cools it. Worth a try.
Rick

Campgems 05-25-2013 10:13 AM

RE: OS 91 FS Surpass problems
 
That orentation is hard to tune. Espically if the engine is running a bit rich. Oil puddles in the rocker cover and until the engine gets really warmed up, there is excessive oil being pulled in the valve guides. I have an O.S. 52 that was installed like yours that required the glow diver untilfor at least two minutes of running before Iattempted to fly it. This was on the first flight of the day. After that, it was just fine.

Tuning the carb though sounds like your major problem. Here is what Iwould try first.Ifyoudon't have a bench mount for you engine, throw together oneand get the engine running wellin a head up orentation. thenback in theplane and refine the adjustment as needed.

Tuningthe carb is a balancing act. Either needle too far from optimum will cause the engine to run OKat high butbadly or not at all belowhalf throttle, or run at idle but not well athigher RPM.

This is the sequence I use and has treatedme well.

Set both needleto the inital setting in the manual.The high speed is 2 to 2 1/2 turns out from closed at 1/4 throttle opening. Set the mix control per the instructions in the attached photo.

Now, with the engine running and warmed up a bit, and the glow driver off,open the throttle to full, and slowly lean the high speed for maximum RPMthen go to the rich side by 300 to 400 rpm.

Adjust the throttle to the lowest setting that will allow the engine to keep running and then without the changing the throttle, slowly lean the idle mix for maximum RPM.

Go back to full throttle and again adjust the high speed needle.

Back to idle, this time the idle speed should be considerably less that the first time, but again set the throttle to the slowest speed that will keep the engine running, and again very slowly, IE1 16 turn at a time, and remove the screw driver after each adjustment, adjust for maximum RPM.

Now work on the transistion. Run up the engine then go to full idle and let it run for 10 seconds or so the jam the throttle full open as fast as you can move the stick. If the engine dies, open the mixture screw 1/16 a turn and try again. If it bubbles and slowly gains RPM, then go lean on the idle by 1/16 turn and try again. The engine should jump from full idle to full throttle in less than two seconds. One second should be your goal.

Now, with the engine back in the plane, go through these adjustments one more time.

Last, on the valve adjustment, At TDC with both rockers loose, a 0.002" feeler should go freely between the rocker and valve stem, and a 0.004" feeler should be tight. This is on a cold engine.


The manual can be found at this linkhttp://www.rcuniverse.com/forum/m_10192403/anchors_10192403/mpage_1/key_/anchor/tm.htm#10192403

The pages are upside down,

For some reason I can't post the photo of the mix control inital setting, but it is on the third page of the manual on the above link.

Hope this helps

Don



tree2tree 05-25-2013 02:37 PM

RE: OS 91 FS Surpass problems
 
This a long shot, but you seem to have tried the usual things. It could be the airflow at the carb' intake. Perhaps the prop wash is disrupting the air going into the venturi. Try to protect the carb from prop air flow. Like I say - a long shot.

tree2tree 05-25-2013 02:40 PM

RE: OS 91 FS Surpass problems
 
Not related. but you are missing a top engine mount screw in the picture.

flycatch 05-25-2013 03:36 PM

RE: OS 91 FS Surpass problems
 
This is not a solution to your problem but I ran into the same thing with a Saito 2.2 FS. I got on the Saito forum and I was not alone with the idle problem. No one had a fix for the problem other than using an onboard glow driver. I installed one and never looked back. Investigating this problem further I learned that the carburetor that came with the engine was the same one used on the 1.8 FS. If I were you I would purchase an onboard igniter.

lopflyers 05-25-2013 04:09 PM

RE: OS 91 FS Surpass problems
 
Same here, I had that problem with a brand new Saito 100, the onboard glow ignitor solved it. $90

kochj 05-25-2013 04:17 PM

RE: OS 91 FS Surpass problems
 
Just a thought....
ARE the Bearings freedup on the crank shaft/ and the timming shaft???
If they are then >
Pull the engine, place in on a test stand. Mount the engine with head UP.....I had a magnum .91 that when inverted, had to have the low speed needle to the point of leaning out, or it would build up an foul N'quit....
I am assuming you know how to do the pinch test???? the engine should idle up, when pinched and then quit....
If at idle and you pinch it, and it runs and runs and 10 sec later, it increases rpm's then your LSN is too rich...
If when pinched and it quits almost immediately ... then too lean..
Reset the low idle needle to stock....
start with the Stock High speed needle as well...
And run it in...


If still not running at Low rpm's...... Perhaps it is your Ring/head that is WORN OUT.....

When running RC cars and the engine goes from working good, to NOT idling.... IT IS TIME FOR A REBUILD....


Hope all works out....

Campgems 05-25-2013 05:39 PM

RE: OS 91 FS Surpass problems
 
Good eye.


Quote:

ORIGINAL: tree2tree

Not related. but you are missing a top engine mount screw in the picture.

Campgems 05-25-2013 05:57 PM

RE: OS 91 FS Surpass problems
 
<div style="margin: 0in 0in 0pt"><span style="font-size: x-small">The pinch test is a good way to introduce pin holes in the fuel line. I quit using it after finding a spray that I though was a cob web floating out of the engine compartment when fueling the tank. Close examination showed the marks from pinching and the cut in the line. I don't use that method any longer, and have never missed it.</span></div>

Don


Quote:

ORIGINAL: kochj

I am assuming you know how to do the pinch test???? the engine should idle up, when pinched and then quit....
If at idle and you pinch it, and it runs and runs and 10 sec later, it increases rpm's then your LSN is too rich...
If when pinched and it quits almost immediately ... then too lean..


eddieC 05-25-2013 09:28 PM

RE: OS 91 FS Surpass problems
 
That engine will run fine inverted, sideways, or straight up - as long as the tank centerline and carb are the same. As that's a taildragger, prop up the tailwheel to keep the fuselage level. Four-strokes like nitro, I never run less than 10%. <div>Kochj's tuning is spot-on. </div><div>I'd suspect carb/tank height, or a leak in the fuel plumbing or intake. </div><div>What prop are you running, and what's the highest rpm it holds? </div><div>Last, test for overheating (lean run, water in fuel, too much prop). Run it for 2-3 minutes at high rpm, then shut down. Lick your (least favorite lol) finger, then touch the fins. If you can touch lightly for a couple seconds, it's good. If not, it's running too hot. </div>

SJN 05-25-2013 10:32 PM

RE: OS 91 FS Surpass problems
 
Thanks for all the sugestions guys, I apreciate the feedback. ;)

Im usinga 13x8 bolly prop....the only one my LHS had in stock.
I would have prefered a 15x6 for this sopwith camel.

I am the guy at the field who goes over and adjust`s the other guys engines when they give up on them, and I have never failed in tuning an engine until now.

The low speed needle is very responsive, and I can clearly see/hear, and feel the difference it makes when I lean and richen it on both carbs that I have ttried on this engine.
And it runs absolutly like a "normal" engine as long as the glow is on :)
I have not tried anything like this before.

But who knows, maybe the piston ring in this old engine needs to be replaced. I seems to have good compression, but maybe its different once running.


All 4 bolt are in the engnie mount.
The mount is from another plane, and I drilled new holes for it to fit the camel.
you can only just see the edge of the washer installed in the picture if you look close ;)

The 2 main bearings are brand new original os bearing i bought.
The 2 cam bearings also rotate fine, and are in good condition.

Im installing a microsense onborad glow driver for now, but I would not call it a permanent fix.
This engine should be able to run properly without glow no matter what.

I will check the intake o-ring again. I can blow into the carb, and it is airtight, but will try to suck negative pressure, and see if it makes a difference.

There is alot of oil in the rocker cover from the overhaul. Ill try remove the exess oil in there, ans see what happens.


757jonp 05-26-2013 02:45 AM

RE: OS 91 FS Surpass problems
 
I just experienced a similar problem with the same engine. Could not get satisfactory performance out of it until I determined that I had the idle screw out of whack. Once I got it reset to the proper position per the manual I was able to properly tune it.

One clue that led me to recheck the idle screw was that in order for it to run at high speed, the main jet was only opened about 3/4 of a turn. After resetting the idle screw, the main jet tuned for high speed is now about 2 turns out.

Hope this helps.

SJN 05-26-2013 03:07 AM

RE: OS 91 FS Surpass problems
 
Hi 757jonp.

Propblem is, if the idle screw is so much out of whack, then the transition from idle to full power would be pretty poor.
I can easily adjust it to be perfect.

Anyway...Im at work this weekend with 12 hour shifts....so not much going on at the modeling front for now ;)

1QwkSport2.5r 05-26-2013 05:27 AM

RE: OS 91 FS Surpass problems
 
An overly rich idle mixture will be masked somewhat if keeping the glow driver clipped on all the time.

Try this: I think it was Duke Fox that said the better way to set a carb is to leave the glow driver on, run to WOT and peak the main needle. Remove the glow driver. If the rpm drops, add more nitro. Once you get the top end nailed down 100%, then you can get the idle figured out. It's no surprise that guys running radial 4-strokes use copious amounts of nitro - it keeps the plug(s) lit better.

I also suggest using a different glow plug. I didn't care much for the OS F plug in my 4-stroke. I use Enya 3's or Fox idle bar plugs. Both work great and are half the cost of the OS F.

Azzir325 05-26-2013 05:45 AM

RE: OS 91 FS Surpass problems
 
Try that idle bar plug.

757jonp 05-26-2013 09:32 AM

RE: OS 91 FS Surpass problems
 
Hi back at you SJN!

Before I reset the low speed needle, I did get it to where it would transition pretty well. It just wouldn't run right at the top end if I had the idle adjusted. If I adjusted the top end, now the bottom wasn't right. I chased that around for a couple of tanks before I finally got a clue to what was happening.

BTW, most of the time I was doing this I did not have the glow starter attached. It would run, but not all that great, really rich w/ excessive smoke.

Puzzling part is the engine was previously mounted sideways and ran fine in a profile 3d type plane. Problems arose when I mounted it inverted in a new warbird I built. In between I never touched the idle screw... Not sure what happened there or why it ran so good before.



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