Onan Mill Motor Maintenance

[Jim_Rogers]

I hope while you were doing all of that, you adjusted the valves?

Jim Rogers

[Andries]

Y'know, I didn't, but I should've.
The gasket kit I got from WM included gaskets for the valve cover plates, located just under the air intake manifold.
I'll do the valves and gaskets together was my thinking, IF the compression issue was fixed.
So giddy to have dodged the "engine replace" bullet, and milling with a fully powered machine made me put it aside for a while.
Thanks for the reminder, it'll be good to do both valves and gaskets in one shot.

[biggkidd]

  I've never seen an L head engine with adjustable valves and I work on small engines for a living. The newer overhead valve engines do mostly have adjustable valve clearances.

Larry

[Delawhere Jack]

The Onan has valve lash adjustment in the tappets (lifters). Fairly easy job, and fairly critical to keep adjusted.

Andries, thanks for the photos. I've got the same engine on my LT40 and it needs new valve guide seals. I was thinking that it may require removing the engine from the mill, but looking at your pics I think probably not.

Should be able to pull the heads, remove the valves and mic the valve stems with the engine installed. Got good compression on mine, but it smokes for a few seconds after starting due to oil leak down from the valves.

Looks like I've got the next item on my to do soon list.

[Delawhere Jack]

Getting gas in the oil can have an effect like using a "Super Detergent" oil, and loosen up all the gunk that has built up in the engine. Might not be a bad idea to do an oil and filter change ahead of schedule now that you've corrected the misfire.

[biggkidd]

Goes to show that working on small engines day in and day out doesn't teach you everything. In all the years I've done it I've only worked on two Onan's that I can remember and both of those were carb problems. There just aren't many Onan's around here. Thanks for setting me strait! 

  Larry

[Chuck White]

The Onan has valve lash adjustment in the tappets (lifters). Fairly easy job, and fairly critical to keep adjusted.

Andries, thanks for the photos. I've got the same engine on my LT40 and it needs new valve guide seals. I was thinking that it may require removing the engine from the mill, but looking at your pics I think probably not.

Should be able to pull the heads, remove the valves and mic the valve stems with the engine installed. Got good compression on mine, but it smokes for a few seconds after starting due to oil leak down from the valves.

Looks like I've got the next item on my to do soon list.

Nope, no need to pull the engine.

[bandmiller2]

Valve lash adjustment is critical especially on air cooled engines due to their wide temp. swings. Not enough clearance will tend to not let the valve seat properly and can/will lead to burning the valve. A dead give away is lack of compression when you pull over the engine or if the starter spins it faster than usual. A friend has a flywheel type splitter with an overhead valve Honda, wouldn't start, pulled it over very low comp. Valve lash was almost non existant adjusted and first pull. Likewise diesel injector timing is critical. Frank C.

[StimW]

Valve lash adjustment is critical especially on air cooled engines due to their wide temp. swings. Not enough clearance will tend to not let the valve seat properly and can/will lead to burning the valve. A dead give away is lack of compression when you pull over the engine or if the starter spins it faster than usual. A friend has a flywheel type splitter with an overhead valve Honda, wouldn't start, pulled it over very low comp. Valve lash was almost non existant adjusted and first pull. Likewise diesel injector timing is critical. Frank C.

You have to be careful, Honda uses compression release!

[Andries]

Thanks for the reminders re: the importance of valve adjustment. Jim Rogers and Delaware Jack both seem to have handle on this, but I don't have their experience, yet.  :D
My files on the Onan included the attached from Otto Farfan at WM in Indy, which was also probably a big fat hint to get'er done buddy!

[Jim_Rogers]

This is what happened to my valves from not adjusting them as they needed to be:



Jim Rogers

[Delawhere Jack]

Goes to show that working on small engines day in and day out doesn't teach you everything. In all the years I've done it I've only worked on two Onan's that I can remember and both of those were carb problems. There just aren't many Onan's around here. Thanks for setting me strait! 

  Larry

We all learn something new everyday.  ;)  As small engines go, the 24HP Onan is on the larger end of that scale. I learned about the valve adjustment issue with this engine right here on the FF. A lot of the mid 90's WM mills used that engine. Probably as much info here on the FF about it as on the rest of the Internet combined.

It's a pretty reliable design so long as you keep up with maintenance, very similar to the old VW Beetle engine.

[Delawhere Jack]

While we're on the subject, has anyone had to replace the valve guides?