Onan twin cyl information?

[B.M.800]

I have 2 twin cyl Onan engines. My google-foo is... pretty sucky I guess.

Engine #1, is on a 70s something or other sears suburban. The numbers on this engine are BG-MS/32729.

This engine has been giving me some troubles. Not running proper, would surge at low RPMs. Higher RPMs it would seem to be fine, then after a while it would start surging and die a embarrassing and tragic death...
Ive taken the carb apart and cleaned several times. I dont think this is the problem.

Further inspection, seemed a weak spark. It wouldnt fire. I dont remember if i was seeing much spark at the (kind of new)plugs, though these was at the points.
I found a page on testing the coil. Between the terminals there should be 3.8-4.7 OHMs. And 12,600-15,400 between the plug holes.
Im getting 4.3 on the terminals, and nothing on the plug holes. So this appears to be a problem...could this be what caused the surging?

Engine #2, I got as a spare for engine #1. Numbers are N52M-G7 0199/3580B.

I havnt done anything with this particular engine, but I would like to know what kind of HP it is supposed to be. Its about the same size as #1 so I figure it must be around 16-ish...

The coil on engine #2 reads something between the specifications above, so Im considering swapping coils.

Im also curious, what kind of plugs these should have, and what kind of oil they should use. Maybe any other useful tidbits of information.

 

[vpd66]

First off Onan engines aren't great go kart engines. Too heavy for the power they make and I've never seen anyone hot rod one. The parts for those engines are expensive so that drives up the price of good running used engines. The engine with the weak spark I would try a set of new point and properly gap them. I have a John Deere 318 garden tractor with an 18hp Onan twin and I've had to put points in it a couple times when it had running problems and it solved it. Spark plugs have them look them up at the parts store. Oil I like to use Shell Rotella 15w40. These are air cooled engines that run at a constant rpm under load for long periods of time. Thick oil is your friend. Compression test each engine.*They should be in the 100-130 range. If they have good compression then they should be healthy engines and be worth $200-$400.

 

[B.M.800]

These will be for the Suburban, no gokarts for these.

Did make a trip to the parts store. Engine #1 uses Champion RH18Y, #2 uses Champion RS17YX. However, they didnt have any... and neither did any of the other places I stopped at.

I forgot to ask about the oil.

 

[vpd66]

See if the parts store can cross reference the Champion plugs to a brand they stock. I personally wouldn't put a Champion spark plug in anything. Walmart has the best price on Shell Rotella oil.

 

[B.M.800]

I couldnt find the one type, but I found a cross reference on the internet. Hopefully soon Ill have mess of new plugs...

Any particular reason you dont like Champion plugs?

 

[vpd66]

Just bad luck in the past with them.

 

[B.M.800]

Ahh. I did end up ordering a few Champions... well see how they do. I dont remember the other kind..

Thanks for the replies anyways, Im kind of surprised theres not more people who know anything about anything about these engines.. Aside form the fact these aint your average gokart engines...

 

[Desertduler]

Ahh. I did end up ordering a few Champions... well see how they do. I dont remember the other kind..

Thanks for the replies anyways, Im kind of surprised theres not more people who know anything about anything about these engines.. Aside form the fact these aint your average gokart engines...

I am familiar with these Onan twin cylinder engines, these engines were used on a model of Crafco crack sealer machines that I used to work on when I was a heavy equipment mechanic. The ones that I worked on had a two piece intake manifold that required a special RTV sealant that sealed the two halves together which I still have some of the stuff, gasoline does not have any adverse effect on this sealant and it is very expensive (Dow Corning 730 RTV) besides being a flat head engine the intake valve timing on these engines close way late therefore reducing cylinder pressure just like a Briggs and Stratton flat head engine with what they call "Easy Spin Starting" which is not the best for performance. They are a decent industrial engine and I am sure that some improvements can be made to a degree but the late closing intake valves cannot be changed other than regrinding the camshaft. If you remove one of the cylinder heads watch the intake valve timing and you will see how late the intake valve closes all the way. See if this information helps you at all.
http://www.wfmfiles.com/download/manuals/CTM2_-_16_18_20_24_HP_Onan_Engines.pdf

 

[B.M.800]

Engine #1 has a 2 piece intake, Im not sure about #2.
Thats interesting, hopefully I wont have to open either of these up.

Thanks for the link!

 

[Mikegtrxu1]

As far as go kart-ish projects are concerned I have only really seen Onans used in modded lawnmowers used as workhorses or offroading/mudding. Would be kinda cool to see a modded one though.

You could check over the points and general ignition system for any faults. Make sure it is sparking properly, ect. Yeah and you should really get the right plugs. Be careful around electrics.

And also, just a word of advice on the mower itself. Is that thing an engine donor for something else or is that the basis for a project? If it is going to be parted out, id advise selling it as these seem to be getting valuable nowadays.

 

[B.M.800]

As far as go kart-ish projects are concerned I have only really seen Onans used in modded lawnmowers used as workhorses or offroading/mudding. Would be kinda cool to see a modded one though.

This is about what the plan is, though I wont do too much to the engine aside from a different exhaust.

You could check over the points and general ignition system for any faults. Make sure it is sparking properly, ect. Yeah and you should really get the right plugs. Be careful around electrics.

Thats the plan when I have the time.

And also, just a word of advice on the mower itself. Is that thing an engine donor for something else or is that the basis for a project? If it is going to be parted out, id advise selling it as these seem to be getting valuable nowadays.

Its what I have to work with. Wont do too much that cant be put back to original, aside from what the previous owners have done.
Came with a few attachments, and a deck the previous owner was starting to rebuild.