engine re-power questions for the ss 16

Hello, this is my first post so I'm not sure what I'm doing yet but here goes. I bought an ss 16 suburban a couple of months ago that has a serious engine problem of acting like it's running out of gas after it warms up and I have to choke it to keep it running and mowing is next to impossible. After paying one of our local small engine repair shops more than 350.00 and having the same problem when I got it back I have bought another engine. I just purchased a briggs & Stratton 18 hp I/c opposed twin that looks a lot like the onan 16 hp that's in her already. My first question is " is the B&S opposed twin the same engine as the onan opposed twin and will everything just bolt up like it should or am I in for a complete fabrication to make it fit ???
Any tips for changing out the engine would be of great help as well.

thanks, bruce59

HI BRUCE
WELCOME TO THE SEARS TRACTOR SITE. FIRST THE B&S & ONAN IS FAR FROM THE SAME. I COLLECT SEARS SUBURBANS, HAVE 20 RESTORED SO FAR, SO I HAVE A BIT OF EXPERIENCE AFTER WORKING ON AUTOS FOR 60 YEARS MECHANICS COME NATURAL. OK THE ENGINE WILL SWAP, FIT THE MOUNTING HOLES IN FRAME, START UP FRONT, THE LEFT LOWER GRILL WILL BE TO GRIND A BIT OFF TO CLEAR BLOWER HOUSING, CHOKE & THROTTLE CABLES WILL BE TO MODIFY A BIT. ENGINE PULLY ON THE ONAN HAS A 1 1/8" BORE WHERE THE BRIGGS HAS A 1" BORE, READ A COUPLE OF POST BACK A GUY IS DOING THE SAME, SAID HE FOUND A BUSHING (SLEVE) TO FIT THE PULLY TO SHAFT, YOU WILL NEED TO LOOK AT THE ONAN ENGINE PULLY GUARD AND FABRICATE OR ADAPT IT TO THE BRIGGS, IF YOU DON'T THE CLUTCH BELT WON'T WORK RIGHT, ROPER USED BRIGGS ON THEIR TRACTORS, READ UP ON SEARS/ROPER TRACTOR HISTORY, SEARS WERE BUILT BY ROPER, SO ALL THE PARTS YOU NEED IS OUT THERE TO BE HAD, YOU WILL NEED TO CHANGE OUT THE IGNITION SWITCH, ONAN HAS A 12 VOLT COIL & THE BRIGGS HAS FLYWHEEL IGNITION SO THE BRIGGS HAS AN IGN. KILL WIRE FROM COIL, GET A NEW IGN. SWITCH FOR A TRACTOR WITH A BRIGGS OR TECUMSEH ENGINE, FROM NAPA OR WHO EVER, THE NEW SWITCH WILL BE MARKED ON BACK BY EACH TERMINAL WHERE EACH WIRE GOES, NOT TOO HARD TO FIGURE OUT. IF THE BRIGGS HAS A CHARGING CIRCUIT BEHIND FLYWHEEL YOU WILL FIND A WIRE ON ENGINE WITH A ROUND TERMINAL TO BE CONNECTED TO TH ACC. TERMINAL ON SWITCH, YOU WILL ALSO NEED TO GROUND THE IGN. SWITCH HOUSING FOR THE COIL KILL WIRE TO WORK. I FOUND A BIT OF BELT FIT DIFFERENCE BECAUSE OF CRANKSHAFT LOCATION IN BLOCK, TRY THE BELT YOU HAVE FIRST, BELTS CAN BE ANOTHER STORY. YOU MAY ENCOUNTER THE SAME PROBLEM WITH THE BRIGGS IF THE GAS TANK CAP IS NOT VENTING, BEEN THERE. MORE WHERE THIS CAME FROM. PLEASE CHANGE 30WT,TRANS. OIL, USE A 15/45 DIESEL OIL IN ENGINE, USE ONLY PREMIUM GAS WITH MARVEL MYSTERY OIL TO SAVE A LOT OF HEART ACHES, AND POCKET BOOK WORRIES. BUT JUST WONDERING IF YOU PAID $350 FOR NOTHING.
I THINK YOU WILL BE HAPPY WITH THE BRIGGS. PS WHAT EVER EXHAUST IS ON THE BRIGGS CLEAN OFF, TRIM BLOWER COVERS, GET SOME GALVANIZED PIPE FITTING, 2-1" LAWNMOWER SHOTGUN MUFFLERS AND TURN THE EXHAUST RIGHT OUT UNDER THE HOOD. THE AGAIN YOU CAN PROBABLY FIX THE ONAN FOR $15 OR LESS.
HAVE A GOOD ONE
GEORGIA SS
JIMMY

thanks Jimmy , I need the insight that you have. First I would like to say that as far as the 16 hp Onan goes that I loosened the gas cap while operating and it made no difference. The points, plugs and condenser as well as the fuel pump were replaced with new. It seems that engaging the mower deck seems to bring on the problem quickly but will do the same with in ten minutes of operation. I suspect that the problem is the head gasket. Maybe, maybe not but I had heard of others having the same problem and had been chasing it for months, I just don't want to go down that path. Funny though the engine does not really smoke that much or make knocking noises.
I am curious about the marvel mystery oil in the gas, what would be the reason for this ?? Should I do this in the new engine as well ??
I hope you guys stick with me through this engine swap as I'm sure I will need advise. With the modifications that you have already mentioned I can see an interesting job ahead.

gotta go ---thanks, bruce59

i have recently purchased a gt 18 that had the onan removed. i am replacing the engine with a briggs 18 opposed out of a late 80,s gt 18. the engine lines right up to existing holes on mine. the pulley is bigger on the onan,but if you search sleeves on ebay there is a person selling them for 24.99. like jimmy said,the ignition needs to be rewired as well as the charging system. search youtube for wiring help. as far as the exhaust,with some 1 inch pipe and fittings you should be able to get the onan muffler to work.Roger

thanks Mudpatrol1, I haven't started yet but am planning to as soon as I get a little welding finished on my old 71 triumph 650. I keep dragging my feet ever since Georgia ss said that I may be able to fix the mower with out changing out the engine. I had already tried the gas cap trick but still get the same problems after running awhile so I guess that I'll tear into it after I finish with another project or two.
I have already bought the sleeve for the 1" to 1 1/8 " shaft as well as a military surplus engine ( 18 hp B & S i/c opposed twin ) that is supposed to have no more that just bench test time on it . Hope that I can get enough info when needed to tackle the ignition and charging system. I can be a little thick between the ears sometimes but seem to manage to get things done if I get good info.
Have you finished your Gt ,did you paint yours as you did the work ?? Kinda thinking about painting mine since I'm going to all the trouble of the re-power . I will have to look and see if there is any color info here on the forum.
Well good luck and keep me posted how yours is coming along if not already finished . If you have any tips for me , they would be more than welcome.

have you checked the float on the onan? how is the ignition coil? those are the only 2 things i know of about the onan that can be a problem other then parts. the float disintergrates unless it has been replaced by a brass float. i have seen harley coils used in place of the onan as well. i havent gotten very far on mine other then getting the engine and sitting it into place,thats when i noticed its a bolt in.... old man winter is on its way,and i have alot of other things to do beforehand. most likely i wont get much further for at least a month.

If it starts to quit, and then comes back running when you use the choke, that in general is an indication of a lean carburetor mixture.  Am I correct in assuming that the $350. you originally paid a shop included a carburetor rebuild?  Here are a few suggestions off the top of my frazzled head:

1. Are you running a fuel filter? Even if the carb was clean at one point, you still need to have an in-line filter to keep it clean. If you get a filter you can look through, then you can see if fuel starvation from inadequate supply is causing a problem.

2. Are you comfortable disassembling the carburetor?  The float issue previously mentioned, along with the float level would be something I would look at closely. Don’t overlook the float valve and ensure it is not sticking closed. Also, I have seen more than one bad rebuild job on a carburetor….and may have done one or two in my lifetime. :-)  Double check that all is clean and air goes through all passages.

3. The engine swap would be a good idea for one major reason: Repair costs/parts on the Onan are higher. I get vibes you are putting it off because of the work involved, so my humble suggestion is to try some low cost repairs on the Onan until you can do the swap.

4. If you suspect a bad head gasket, then you may see evidence of where you are getting leakage. A quick and dirty compression check would give you a good idea if that is an issue. Also, those stethoscope things they sell at Harbor Freight would work tracking down the noise the bad head gasket would make.

5. If you still suspect an ignition problem, get an inline spark tester. I must say that I’ve only picked up one fault in many years of using this tool; a bad condenser on a 10 hp Tecumseh. Incidentally, the bad condenser was a new (off brand) condenser that was cutting out when warm.

Thanks for participating in discussion on the board! I hope you are able to track down the issue.

Great to get some more feedback from you guys. Mudpatrol1 sounds like we are in the same boat to a greater extent. About the carb. the " small engine mechanic " flatly refused to believe that the problem could be the carb. because it " looked real clean " and proceeded to run up the bill with imaginary electrical problems . He replaced the points( cleaned and set once and replaced at my expense the second time ) along with plugs and new condenser. Since the previous owner had put an electric fuel pump on the tractor that did not belong there I bought a carb. rebuild kit and insisted that the mechanic replace the fuel pump with the one that belonged on it.
It starts and runs great for about 10 to 20 minutes and begins to act like its running out of gas but if I can grab the choke in time I can usually keep it running. Reducing the throttle to about half way seems to help.
Some times I can get another ten minutes out of her before she just dies and sometimes i can start her again and sometimes i can't.
Today was one of those times that I got about 5 extra minutes and when she quit all I got was a frying noise when I hit the key, better check my cables while i'm at it.
Spence , you guys may have more experience with carburetors than I have. I have had the little Mikuni carbs off of my Triumph a few times and had no problems rebuilding them but I have heard a lot of people say the carb one these Onans is pretty complicated and I hesitate to tear into it. is there any rebuild diagrams available for this ?? Guess I don't have anything to loose by trying and somewhere around here I should have the rest of my rebuild kit for this although I do not believe that there are any floats in it.
there is an inline clear fuel filter installed in the line. The previous owner said that he had done some carb work done a year or two ago so maybe something was overlooked or left out.
Like most of us, there just does not seem to be enough time in a day to get all the things done that I have before me and my list gets longer every day since I just bought a house that needs , needs , needs long overdue maintenance. I have an acre lot to take care of so I can't ignore the little tractor much longer either . almost funny when I thought that since i finally live near a river full of salmon that i would just lay around and fish awhile and worry about that other stuff later, maybe next year.
Thanks for your interest and I'm always interested in any tips and info.--------Bruce

Just a quick note. I tried to mow with the original motor still in the tractor and this time I took a good look at the clear in-line fuel filter when I started it up, it appeared to be about 70% full of fuel. After mowing for about 10 minutes the usual cutting out began like she is running out of fuel , I kept her running and popped the hood open and got down to look at the filter and found that the fuel was just in the bottom of the filter, at about 10-15% of fuel in the filter. Is this normal or am I on the rite track to what is wrong with this thing ??? Could the floats cause this ??? I thought blocked fuel line but I have already taken air and blown through the fuel line to the tank and found it clear.
Any thoughts or knowledge on this ???
thanks bruce59

i,m going to assume you have a fuel pump? is the filter before or after the pump? what shape is the fuel line from the tank to the pump? this lovely new gas today eats up rubber,and although the line looks good it could be coming apart inside. the float could be causing the low level of fuel in the filter. you could rule this out by running the engine off a gravity fed tank from a old lawn mower etc... if it runs past your usual 10 minutes,then your issue is between the tank and filter. if not then its carb related.

Mudpatrol1, the filter is between the tank and the fuel pump. On the Onan engine the fuel pump is part of the base or attached to the side of the base of the carburetor. I will change out the fuel line and try her again , could not hurt anything. Never thought about the inside being rotted out and since I have no way of knowing how long the line has been on there it would be a good idea to change it anyway.
I should have something that I can make another fuel tank from around here and will give that a try if the line does not work. I have noticed that the tank on the tractor is a foot or two below the level of the carb so it may not take much to slow fuel delivery to the engine because of the lift.
If it's not still raining here tomorrow I'll try to get something done---
thanks, bruce59

Next things to check: something is restricting flow in the line, vacuum is preventing the fuel from getting to the pump, or the pump is weak.

One of your posts mentioned that the previous owner had mounted an aftermarket fuel pump. That is an important clue, pointing to the fact that the fuel problem may have been occurring for a while. If the same problem was happening with the aftermarket pump and now the original carb pump, then you are in the right track to look upward in the fuel delivery system.

Replacing the fuel line is a good start. Anything made of rubber that old (pulse hoses also) should be replaced as part of a maintence program. Are there hose clamps on the fuel line? You could also try another fuel filter, or take it out of the system.  Using a temporary tank will answer a lot of questions for a little work....if you have a tank you can use SAFELY!

You said that unscrewing the gas cap has no effect. It may not have an immediate effect considering the length the gas has to go, plus the fact that the pump has been sucking air. I don't remember if you said how long it will take before starting again following a shut off. Don't put the gas cap thought to rest just yet.

What is the condition of the inside of the gas tank? Is there scale that may be clogging the outlet to the hose?

I seem to remember something about the floats in these carbs giving owners a problem. The issue was solved by using a brass float I believe. Keep that in the back of your mind if all else fails.

Here's a youtube video of a guy working on a fuel pump. I don't think I'd be bending those reed flappers like he is unless I had another set, but the video gives you an idea what the inside of a pump looks like.

Thanks Spence, the weather seems to be braking for the better so maybe I'll get a chance to start work on this tomorrow along with hanging the doors that i just made for my newly built storage area. I have a few small gas cans here and can make a temp tank out of one of those.
Will get back in a day or two and thanks.

bruce59

Just wondering if you solved the problem with the Onan. If so, I'm sure those following the thread would like to know what you did to solve the problem.
I've had similar problems with my Onan 16 Twin in an SS-16 on three occasions. One was the float - the fiber floats swell and should be replaced with a brass float - readily available on eBay - I also replaced the high speed jet at the same time as the float. The carb on my SS-16 is a Marvel-Schebler (not DD). You can find the manual on line free. The second time it was a new set of points that were defective. The third time is was the fuel filter - a quick and cheap fix (about $4 at NAPA for a clear filter) - make sure it is installed correctly and use clamps to avoid leakage. You might also want to replace the vacuum line to the fuel pump - it might be leaking - again use clamps.  Good luck!

Can't understand where my posts keep going but I'll do this one last time. I got the Onan going and it is still running good. I found the problem while putting a basic rebuild kit into the carburetor. As it turns out the problem was that the fuel screw was nearly shut on the carb. fuel adjustment and that was starving the engine for fuel !!! All the BS that the small engine mechanic ( so called ) gave me about it has to be an electrical problem was just a red haring and just a plain waste of 350.00 that I sure could have used somewhere else.
Anyway that is all it turned out to be. Funny that something so simple could be such a complicated problem.
Bruce59

Georgia SS wrote:HI BRUCE
WELCOME TO THE SEARS TRACTOR SITE. FIRST THE B&S & ONAN IS FAR FROM THE SAME. I COLLECT SEARS SUBURBANS, HAVE 20 RESTORED SO FAR, SO I HAVE A BIT OF EXPERIENCE AFTER WORKING ON AUTOS FOR 60 YEARS MECHANICS COME NATURAL. OK THE ENGINE WILL SWAP, FIT THE MOUNTING HOLES IN FRAME, START UP FRONT, THE LEFT LOWER GRILL WILL BE TO GRIND A BIT OFF TO CLEAR BLOWER HOUSING, CHOKE & THROTTLE CABLES WILL BE TO MODIFY A BIT. ENGINE PULLY ON THE ONAN HAS A 1 1/8" BORE WHERE THE BRIGGS HAS A 1" BORE, READ A COUPLE OF POST BACK A GUY IS DOING THE SAME, SAID HE FOUND A BUSHING (SLEVE) TO FIT THE PULLY TO SHAFT, YOU WILL NEED TO LOOK AT THE ONAN ENGINE PULLY GUARD AND FABRICATE OR ADAPT IT TO THE BRIGGS, IF YOU DON'T THE CLUTCH BELT WON'T WORK RIGHT, ROPER USED BRIGGS ON THEIR TRACTORS, READ UP ON SEARS/ROPER TRACTOR HISTORY, SEARS WERE BUILT BY ROPER,  SO ALL THE PARTS YOU NEED IS OUT THERE TO BE HAD, YOU WILL NEED TO CHANGE OUT THE IGNITION SWITCH, ONAN HAS A 12 VOLT COIL & THE BRIGGS HAS FLYWHEEL IGNITION SO THE BRIGGS HAS AN IGN. KILL WIRE FROM COIL, GET A NEW IGN. SWITCH FOR A TRACTOR WITH A BRIGGS OR TECUMSEH ENGINE, FROM NAPA OR WHO EVER, THE NEW SWITCH WILL BE MARKED ON BACK BY EACH TERMINAL WHERE EACH WIRE GOES, NOT TOO HARD TO FIGURE OUT. IF THE BRIGGS HAS A CHARGING CIRCUIT BEHIND FLYWHEEL YOU WILL FIND A WIRE ON ENGINE WITH A ROUND TERMINAL TO BE CONNECTED TO TH ACC. TERMINAL ON SWITCH, YOU WILL ALSO NEED TO GROUND THE IGN. SWITCH HOUSING FOR THE COIL KILL WIRE TO WORK. I FOUND A BIT OF BELT FIT DIFFERENCE BECAUSE OF CRANKSHAFT LOCATION IN BLOCK, TRY THE BELT YOU HAVE FIRST, BELTS CAN BE ANOTHER STORY. YOU MAY ENCOUNTER THE SAME PROBLEM WITH THE BRIGGS IF THE GAS TANK CAP IS NOT VENTING, BEEN THERE. MORE WHERE THIS CAME FROM. PLEASE CHANGE 30WT,TRANS. OIL, USE A 15/45 DIESEL OIL IN ENGINE, USE ONLY PREMIUM GAS WITH MARVEL MYSTERY OIL TO SAVE A LOT OF HEART ACHES, AND POCKET BOOK WORRIES. BUT JUST WONDERING IF YOU PAID $350 FOR NOTHING.
I THINK YOU WILL BE HAPPY WITH THE BRIGGS. PS WHAT EVER EXHAUST IS ON THE BRIGGS CLEAN OFF, TRIM BLOWER COVERS, GET SOME GALVANIZED PIPE FITTING, 2-1" LAWNMOWER SHOTGUN MUFFLERS AND TURN THE EXHAUST RIGHT OUT UNDER THE HOOD. THE AGAIN YOU CAN PROBABLY FIX THE ONAN FOR $15 OR LESS.
HAVE A GOOD ONE
GEORGIA SS
JIMMY

@JIMMY: Since you have so many SS tractors, do you have any spare attachments? I am looking for a larger mower deck complete, a front plow assembly to get started. If you have anything else of interest, I would also be eager to hear about it. I live in zip code 48082 and have access to a loading dock. If you prefer, I can be reached directly at donparadowski@yahoo.com

I forgot to mention that I could use a snow blower also.