Rpms on onan

Does anybody know how to increase rpms on a B48m onan

Should have an adjustment on the throttle linkages somewhere. I wouldnt mess with the Onan too much, if something blows replacement parts are $$$$$$$$$$

3600 rpm max for an opposed onan... they are extremely strong and built to lug (torque rather than high rpm HP)  the 18 hp onan actally producrs about 26 hp at 3600 rpm

they were designed to be run continuously at 1800 rpm, and HP was rated at that rpm

I agree with what is said, also my Onan if rev'ed too high will vibrate pretty bad. If speed is what you want, I'd look into pulley sizes.

No it's for a pulling tractor the class it will pulling in is the 16-18 stock modified

So where will it produce the most horepower

I was only gonna rev it at about 4000 rpm is that to much

Are Onan engines pressure lubricated? If not I wouldn't wanna rev it too high without any oil mods.

It doesnt have a oil filter so I don't think it is pressure lubricated I might just run it at 3600

AllisKidD21 wrote:

Are Onan engines pressure lubricated? If not I wouldn't wanna rev it too high without any oil mods.

The 2 I happen to have are.



Who knows what the competitor engine was...

A Kohler magnum

Kleatus wrote:

It doesnt have a oil filter so I don't think it is pressure lubricated I might just run it at 3600

Yeah I wouldn't risk it with that ol' engine, if you are looking for high RPMS I'd go for a Briggs single. Unless it has to be horizontal shaft.

AllisKidD21 wrote:

Kleatus wrote:

It doesnt have a oil filter so I don't think it is pressure lubricated I might just run it at 3600

Yeah I wouldn't risk it with that ol' engine, if you are looking for high RPMS I'd go for a Briggs single. Unless it has to be horizontal shaft.

Briggs single for vertical, or a Honda GX series for horizontal. Both of which are way easier to find parts for if you mess something up, but will never produce the torque that the Onan does

Yeah Onans are work horses, pretty good for garden tractors and stuff. Also like CQ said, parts for Honda and Briggs engines are way easier to find and cheaper. As opposed to Onan parts, which can break you haha!

Kleatus wrote:

So where will it produce the most horepower

3600... hp drops off about that point... carb and exhaust limit high rpm, as does the valve spring pressures (valves start to float)

Kleatus wrote:

It doesnt have a oil filter so I don't think it is pressure lubricated I might just run it at 3600

My welder with a CCK doesn't have an oil filter but it is pressure lubed

it is pressure lubed... it has an oil pump... at least my 1969 version does

if it IS a B48m, it has an oil filter... it may be internal, on the pick up tube screen, but it should be there... the oil pump is like a vw pump... two gears that rotate and squeeze the oil between them creating the oil pressure.

http://www.searspartsdirect.com/model-number/b48gga0183475a/0776/1503500.html

Can't use Briggs cause it has to be horizontal and Hondas just wouldn't be a good torque motor but if I run the onan at 3600rpm it should be fine right and what kind of weight oil should I put in it I'm gonna put royal purple or Lucas in it

I think you want to run conventional dino oil. The synthetic eats away at the gaskets of older engines. That's what I've read anyway. For weight, I would just run normal SAE 30

Kleatus wrote:

Can't use Briggs cause it has to be horizontal and Hondas just wouldn't be a good torque motor but if I run the onan at 3600rpm it should be fine right and what kind of weight oil should I put in it I'm gonna put royal purple or Lucas in it

10w30 is what it was designed for... just like a car... as for additives, slick 50 (half a bottle) will help keep things cool


for pulling, the onan's torque is gonna help you more than the high rpm's horsepower... max torque is in the 25 to 2600 rpm range

It doesn't really matter because it's got a little oil leak coming from the oil pan or the front bearing cup which I just lapped the valve decarboned the piston and valve shaved the eyebrows a little set the valve lash and replaced the front seal in the bearing holder and replaced the gasket on the front bearing holder so 10w30 oil will be good for high temps

Do these old, (well atleast in my case... ) engines need a zinc additive? We have some old v8s that without the zinc the cam will eat itself... I dont believe oil is the same as it was 40 years ago.

Royal purple and Lucas have lots of zinc to prevent from engine wear and the metal from breaking down

Kleatus wrote:

Royal purple and Lucas have lots of zinc to prevent from engine wear and the metal from breaking down

slick 50 uses PTFE (Teflon).... it will run for quite a while WITHOUT oil.... don't use it on engines that are not broken in

Good info to know.