NCBOB and all others,
I have a 6.5KW gas ONAN currently in my old 73 Winnebaago. It starts but does not "spring to life" and it runs smoothly . Problem is it stumbles badly when the AC kicks in and then claws its way back to speed after a couple of hunts. It ran that way from when I got her and the meter said 1200 hrs. History, unknown. I rebuilt the carb as in cleaned it. I did the adj where you turn in the mix till the throttle starts to react and then back off half a turn. The starter spins it up slowly and the cylinders seem even in compression. Nobody I ever talked to said the compression was even spececified. I would like to use this in my bus and I think 6.5 would be enough for pheonix and three AC units. Two shops said it should handle three without straining. Others have said that the old Onans run indefinately. These things are getting really cheap around Eugene,Or. and I wonder why they are a drug to the market.
Have some of these people lied to me? What is the real story? How can I test this unit? Is it big enough?
Thank you all
John
MANY THANKS MY FRIENDS
I now know what to do. I remember my compression was 70#s and I thought that was way low. I will install the new spring asap. I never thought to check the starter voltage and my bats are 25 feet from this puppy. I will get the new ignition system when I find a good source. I'll get a load manager if I need three ACs so that two can't try to start at the same time but that depends on the current outcome. I'll post my results in the spring. Special thanks to Tom for his heads up on the shelf life of gas.
Thank again
John
Hi John,
Your 6.5 is strong enough for 2 roof tops. Don't forget that compressors tripple their amp draw at startup. with 3 units,
while they are cycleing you can stall the gen or damange it!
Good Luck
Nick-
Hi John,
A cold dry compression test that show 70#'s would be reassuring. If it's lower than 70 but comes up when you add a bit of oil through the spark plug holes that would indicate that there might be a problem. By and large though, these Onan generator engines (providing they've been given decent oil change intervals, clean fuel and clean air) seem to run forever since they only run at 1800 RPM's.
Points and plugs are a normal maintenance item and shouldn't break the bank. They're readily available from your local dealer and are simple enough for the average owner to install. ;)
1200 Hours is not excessive. If your unit has the rectangular controller with the Start/Stop switch at the bottom alongside of the two 5 amp fuse holders..it's a Spec P, the latest and best of the bunch and should give you good service for quite some time. As Nick advised though..it will NOT carry 3 roof airs!
Some caveats. In setting engine RPM's. Use a freq. meter. Engine speed=Frequency and you don't want it higher than 61Hz..no load. There is NO voltage regulator on this unit. And do NOT crank the genset with a less than full charged lead acid battery of the proper size. The armature has a compound winding (both AC & DC) and are very expensive to replace or have re-wound. Cranking with a weak battery causes the captive smoke in the generator end to be released and you don't want to experience that! :(
If you don't have a manual for the set there is a fellow on the E place who specializes in both Onan and Gravely manuals and should have the proper book. Read it and trust it. There are only 16 errors in that manual but none that should affect your application.
(There are 28 in the comparable Marine Manual which we told them about long ago...but it still is printed with the same ones.)
Buy and trust Da Book (to borrow a term from Fast Fred) and enjoy a dependable source of auxiliary power.
NCbob
If you try everything that is mentioned on this board, and it still stumbles,--- Try removing the intake manafold, and check the intake valve openings. The 2 cylinder onan, is known to carbon up the intake valves, and the tops of the pistons, to the point it will not pull a load. I have seen them block the complete intake opening, next to the valve with a hard carbon. This is caused by the aditives added to modern day, no lead gasoline.
Might be worth a try.
Steve
ncbob,
My most sincere thanks for the tech info and encouragement. I will get the BOOK. I am a believer and was long before this board. Ex Radar Section NCOIC in USAF.
Best wishes to you in the new year.
John
N4RSN, :)
I will do that as soon as it warms up around here. I did the points and plugs a couple of times and the plugs were always much darker than I would have liked and I thought it was a rich condition under load. Air cooled eng like rich for heat reasons. Re adjusting the carb did not help but that really only affects idle mix. As ncbob pointed out it is a simple affair but those are the ones that stump me as I run out of ideas quickly. Have you heard that pouring some oil into the intake will saturate the carbon and cause it to dislodge when the engine heats up? There must be somthing you spray into the intake to decarbon an engine in this aerosol age.
Thanks again
John
Quote from: JohnEd on January 06, 2007, 07:03:36 PM
Ex Radar Section NCOIC in USAF.
John
Me too John. Then Philco TechRep for 20 years.
Richard
You will need to replace the governor spring. They get weak after awhile in use. And then readjust the setting Also I would replace the points with electronic ignitiion. For carbon i have always used a spray bottle of water and sprayed it into the carburetor while engine is running, just enough to keep the motor running, it will loosen up the carbon and blow it out the exhaust, It will not harm the engine.
Pete & Jean
Fantasy
Pete,
I remember that now. I heard that 35 years ago and did it to a couple of high mile cars I had back then. Don't know if it helped but it sure didn't hurt. A mech once told me that that procedure could warp a valve due to uneven cooling. Deep down I think it was sour grapes that he didn't think of it. I will take off the intake as per inst here and then try the water shock therapy. Thank you for your help.
John
I would also check the coil output, and only use N G K spark plugs, I diid on my apollo and ran great no hunting no carbon, also only used ONAN spark plug wires.
Pete & Jean
Fantasy
I had a 6.5 Onan commercial on my truck. I lasted a little more than 12,000 hrs and never had a head off. I think the oil pump drive broke and seized the engine. The first one had points and had to adjust the carburator when in altitude. The second one had electronic ignition-what a difference! Onan makes a electronic ignition kit to replace the points-highly recommend it. 6.5 will run 2 roof tops. If you want to run 3, go to a 10kw. I have a 10kw Powertech diesel gen and it runs three effortlessly. After my experience with the 6.5 Onan gasoline genset, they are resonably reliable, but you do have to fiddle with them, clean the spark plugs and periodically decarbon the heads (can be done without removing the heads-as demonstrated with my getting over 12,000hrs out of mine). Stick with Diesel, you'll be most pleased with the lack of fiddeling you have to do and also not having carry two fuels. Gasoline now only has a realistic tank life of about 6-8 weeks. Diesel- years. Good Luck, TomC
When I worked as a mechanic for a Cheverolet dealer in the early 70s, we had problems with "Carbon Knock" in the small block V8s. (they had a very close piston to cylinder head clearance). Frequently it was drivers who let their cars sit and idle to warm them up in the winter. GMs solution was to slowly pour a quart of Top Engine Cleaner into the carburator while the engine was running at a fast idle, then pour the last cup in fast enough to stall the engine. Let the car set for 15 minutes then re-start and rev up the engine. Chunks of carbon (along with a lot of smoke) would come out the exhaust. The Top Engine Cleaner appeared to be nothing more than automatic transmission fluild. Jack
PS: We also used the ATF to clean a greasy, dirty metal workbench.
Onan markets a product called 4C (Carburetor and Combustion Chamber Cleaner) which is in a spray can. In short..it's a carbon buster. It is best used when the engine is at operating temperature. For anything smaller than a 6.5 you can probably get by with a half can per application for for the 6.5 and larger Onan suggests that you use the entire can.
Do not have an applied load when using this product...it works best when the unit is unloaded. Run at normal speed and spray the product directly into the air intake..use about half the can. Engine will smoke slightly but it won't kill mosquitos in MN. In using the last half can you will want to use enough to actually smother the engine into a stop by the end of the spray...sometimes it requires pulling the throttle rod to a slower speed so that the engine will stop.
Allow unit to sit for 15-20 minutes and re-start. Allow to run normally to clear product out of system before re-applying load. I wouldn't wish to stand in line with the exhaust pipe...it gets your trousers dirty.
Another caveat. Do not ever grab the throttle rod and speed up the engine over normal operating speed. The generator end is designed to run at 1800 RPM and overspeeding could cause severe (read expensive) damage to the unit.
Good Luck all,
NCbob
Trak Auto/Auto Zone/Nappa/etc.. sell a product called Sea Foam. It has the same directions as the products already mentioned. Relatively cheap and easy to find. hth
Frank
Quote from: Slow Rider on January 07, 2007, 10:41:02 AM
Trak Auto/Auto Zone/Nappa/etc.. sell a product called Sea Foam. It has the same directions as the products already mentioned. Relatively cheap and easy to find. hth
Frank
Great stuff ! I use it a lot! BK ;D
Also PB Blaster sells a product called " Small Engine Tune-up" It works great, but, I have never gotten it to work on the carbon build up on the top side of the intake valve.
Most of our engines would run 3600 rpm, and run for 7 to 8 hours per day, 5 days a week, and they would still carbon up the intake valves.
The PB Blaster worked pretty good, but, still had to tear apart the intake after several hours.
This may not apply, with this problem, but, stick it in the back of your head, and you may be able to use it later.
Steve