onan 7.5 kw help!

[wmfels]

ok guys, my genny has been a hard cold start since the end of last season, but sunday while running it, it stopped and im suspecting an intake valve problem, either broken spring, retainer, or maybe stem,as im getting a kickback through the intake. does anyone have any knowledge of this model i believe its the mdje. has glow plugs and the heater element. i have no service manual, which would be nice. it wasnt a hard lockup or anything, so im hoping to be able to repair. any advise is greatly appreciated! thanks

[Avenger]

Why don't you pull the valve cover off and have a look before you get twenty pages of SWAGs?

[Boatsb]

I had a similar issue when the fuel preheater failed and disabled the intake air sensor causing the canuter valve to slam shut during startup. It ran backwards and the power reversed making the refrigerator hot and the water heater cold. Be careful it can also make you think someone can remotely diagnose your problem with little to no information.

[Glory]

I had a similar issue when the fuel preheater failed and disabled the intake air sensor causing the canuter valve to slam shut during startup. It ran backwards and the power reversed making the refrigerator hot and the water heater cold. Be careful it can also make you think someone can remotely diagnose your problem with little to no information.

Don't forget about the steam he ice maker will make!?

JM

[Canuck Dennis]

worst of all, the bikini's disappear for ever !!! and Obama gets re elected....omg...

[wmfels]

sorry, i re-read my post, guess i was a little out of it. called a medchanic he went out to look at it and agrees with me, but then says he doesnt want to work on it? we have no good marine diesel mechanics up here in minnesota. guess i will have to do it myself. found a service manual on line so i should be good. heading down to the boat fri

[Bob Bradley]

Nice talking to you yesterday. Sorry we got cut off so many times - radio free North Stonington is not the place to have a cell phone conversation. I solved my genny problems once and for all by installing a Norpro 9kW generator.

[gbharrington]

I have lots of MDJE parts. PM me if you need something.

[wmfels]

ok guys , my hunch was correct . broken valve spring and rocker! so tell me. what would you do? i know what my fix will be...boatsb, your problem with your canuter valve could have been solved with a rubberband around your sphincter port!

[Canuck Dennis]

cross fingers and pull the head

[Avenger]

I would get that cyliner's piston to TDC. Remove the rocker and spring and wiggle the valve around to see if you can tell if it's bent. Check the stem height against the other valves. If things look good it might be worth trying a new spring and rocker. You may have gotten lucky. OTOH, if the valve won't move or it's stuck in the down position.... well,.... you probably didn't.

Obviously it's not super simple, you'll want to look at everything or find someone who knows what they're looking at. But I like to be sure it's necessary before I start doing major surgery.

[Boatsb]

If scroddys suggestion wont work pull it and get it on a bench. Its so much easier to work on and pulling a genny is usually a sin h. If its a real mess replace it but those be gennys run forever if their taken care of.


FYI I know a guy with a rto 15 k onan if anyone is interested.

[wmfels]

thats what i was thinking, the valve slides freely, i rotated and seems to not be bent. had to heat a bolt on valve cover to get loose. sure would hate to snap a head bolt off . i'm going to just pick up parts needed and replace. and try that

[Avenger]

I'd still compare the valve stem heights and definitely bar the engine several revolutions by hand before you start it.

I'm not intimately familar with the innards of that particular engine, but usually the head is flat thus the valves are 90° to the piston, which on an IDI engine is fairly flat as well. So often, as long as the valve was able to move upward they'll survive something like that. OTOH, if they do get bent it's usually very little which can fool you into thinking it's okay.

I've got my fingers crossed for ya'. Good luck!

[wmfels]

Broken rocker arm, and part is obsolete from onan. I have some calls out to get a price
on a good used head, so well see what I come up with

[ncfathom]

Forget about onan. Their rep re giving help is lousy. I think the power plant is Cummins. Take the broken rocker to them and let them match. Good luck.

[wmfels]

yes it is cummins, we have an office here in minnesota.

[Avenger]

Cummins owns Onan. You can't hate one and love the other.

[Fanfare]

The total disinterest with which I was treated by Onan when inquiring for the part I needed cannot help but poison my view of Cummins. I could handle "Sorry, that engine is so old we can no longer supply that part." What I got, after at least a dozen phone calls to the factory and to dealers, was NOTHING. None of the promised call-backs, no nothing. Meanwhile I had a boatload of people with no power. OK, I took the hint. Out with the Onan, out of the boat, out of consideration for the replacement. It's been nearly a decade and I am still mad about it, and still mentioning it to people. This was the worst customer service I have ever encountered. I actually had to fly back to Florida and go to the old generator graveyard and get my own piece.

Now, if people want to respond to this with their over-and-beyond their Onan service expectation story, there is a lot of space below my post. Have at it. They sure lost my loyalty, and I had bought three of them over the years.

[wmfels]

Heres the follow up. I'm not sure exactly why the valve spring and rocker arm broke, but I'm pretty sure the valve lash was out of tolerance which can cause excessive wear on the components.T he rocker arm did appear to have excessive wear at valve stem contacting point. After removing the head,I found the push Rod had been bent,as well as the valve slightly, but still bent. Cold starts are fine now after replacing the head. The valve train is still intact on the old head, so I will check valve adjustment on the remaining valves and post later.

[q240z]

Yes, but how's the canuter valve?

[Avenger]

Still slammed shut I guess.

Thanks for the follow up info.

[sgharford]

An experience possibility related to this valve failure on your Onan MDJE 7.5kw generator. My MDJE was a little hard to start, but ran fine. However, the exhaust was louder than it should be, even with new muffler and rebuilt water pump. I decided to check valve clearances as I was sprucing the ole gal up. The clearances on the valves was something like 0.3", they are suppose to be 0.017" (1976 MDJE) – wayyyyyyy out of spec. There is no lock nut on the valve adjusting bolt, just one nut that has 'fingers' cut into top of it I assume are suppose to hold threads tight to bolt. Guess that doesn't work so well after 35 years/2200 hours running time. Anyway, it's about the easiest valve adjustment you are going to find on a engine and one I recommend to all who have this model. Perhaps your valves adjustments were way out like mine that eventually caused failure. Anyway, unit started and ran much better after adjustment and the excessive exhaust noise went away. Additionally, I think there is a possibility of exhaust valves sucking in raw water from mixing elbow if too out of whack. While you’re in there you may want to make adjustment to make sure you are getting 60Hz instead of 56Hz or 63 Hz, etc.