Onan 7000 Generator problems

Rich Biebel · 09-02-2014, 09:19 AM

Heads look clean..and loose on the lash is noisy but is better than tight.

I use a set of 4 chains with a loop I made up for those machines and have two overhead rolling cranes so lifting anything is easy.

I also have a 4' square all steel heavy work table for a bench....I do all my work on that or use a forklift for diesels......Makes it a lot easier to be able to raise or lower the machine to a good working height.....

Our shop was once a steel tank fabricating business. They made any size tank and the ceiling is 20' high.....and with the cranes they could build some very large tanks....

You'll be an expert on these when your done Sean.......

Sean Marconette · 09-02-2014, 09:54 AM

Rick,
Although spec states .004 for valve lash, as hot as these things run is that pushing it? Should I open up the lash more?

It make all the difference in the world to have the right tools to safely work on stuff. I was half tempted to make a spreader bar for the engine hoist instead of the lifting straps that I am using. But that means planning on having to work on this more in the future! Its sitting on jack stands until I work on it, otherwise it will be lifted 4' off the floor so I can access the bottom. I can't imagine working on this thing if it was last year before I built my shop.

The overhead cranes would be great, heck the fork lift would make this even easier to get this thing in and out of the trailer a lot faster. I am sure this is a tinker toy compared to the large generators that you typically work on!

Take care
Sean

Rich Biebel · 09-02-2014, 12:36 PM

Sean I set the valve lash with a .004" feeler gauge. The studs tend to loosen up from the heat. I always check the exhaust side studs to make sure their tight. The lash gets tighter as you lock the locknut.....Very tedious to get them right and tight....They seem to run much better with the lash set to .004" and I just advise my steady regular customers that we need to check the valve lash every other time I do a full service on them which is at 500hrs....assuming their machines are working well....

The heat transfer from the valves to the springs/retainers etc. is usually noticeable on the exhaust side just by the color of the metal of those parts.....

The exhaust stud can loosen up and a pushrod pops out and maybe damage a rocker......all this from the heat.....

Sean Marconette · 09-02-2014, 01:13 PM

I can set the 16 valves on my stocker quicker than I did on the 4 valves for the generator. It did take some trial and error on where I was and then locking the adjuster down how much more they would move. So that makes sense. Do the valves tend to loosen about .010" after 500 hrs? I could easily see where a pushrod could fall out of place if this maintenance was not performed.

Sean

Rich Biebel · 09-02-2014, 07:25 PM

Sean they do tend to get looser rather than tighter.
BUT if the exhaust does get tighter, the lash is so small it can lead to early head failure as I have described earlier.

This is a fairly common issue on small engines with solid lifters.

It was new to me when I first started working on this equipment.

They run fine cold and after a warm up and maybe some load gets applied they start to run badly.....shut it off....cools down.....cycle starts all over again....

Onan flathead engines did this pretty regularly......They had a very wide exhaust lash spec at .013"

Exhaust valve needs to touch the seat every cycle to shed some heat of combustion from the valve....No touch.....valve overheats and it magnify's the problem.....

Small engines were a whole new world to me going back 15-20 years ago...

Chasing some of these problems has always been a challenge to say the least....

Sean Marconette · 09-02-2014, 11:38 PM

Well all the parts arrived and it is back together and in the trailer. It seems to run smoother. The true test will be this weekend. I plan on testing if the weather holds up, otherwise it will be running in the driveway as a test.

I will keep you posted. Thanks for the help

Sean

Sean Marconette · 09-07-2014, 01:12 PM

Rich,
It looks like everything is fixed!! Although the weather was only 76 yesterday for a high, the generator did not have any issues. We even shut it down and let it sit for 10 min and it started right back up as we were packing up.

Again your help with this has been greatly appreciated. Having someone to help point you in the right direction is always a good thing. Thanks for everything!

Sean

09-02-2014, 09:19 AM	#1
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,315 Likes: 25 Liked 544 Times in 213 Posts	Re: Onan 7000 Generator problems Heads look clean..and loose on the lash is noisy but is better than tight. I use a set of 4 chains with a loop I made up for those machines and have two overhead rolling cranes so lifting anything is easy. I also have a 4' square all steel heavy work table for a bench....I do all my work on that or use a forklift for diesels......Makes it a lot easier to be able to raise or lower the machine to a good working height..... Our shop was once a steel tank fabricating business. They made any size tank and the ceiling is 20' high.....and with the cranes they could build some very large tanks.... You'll be an expert on these when your done Sean....... __________________ Rich Biebel S/C 1479 Stock 147R

09-02-2014, 09:54 AM	#2
Sean Marconette Senior Member Join Date: Mar 2006 Posts: 977 Likes: 796 Liked 275 Times in 76 Posts	Re: Onan 7000 Generator problems Rick, Although spec states .004 for valve lash, as hot as these things run is that pushing it? Should I open up the lash more? It make all the difference in the world to have the right tools to safely work on stuff. I was half tempted to make a spreader bar for the engine hoist instead of the lifting straps that I am using. But that means planning on having to work on this more in the future! Its sitting on jack stands until I work on it, otherwise it will be lifted 4' off the floor so I can access the bottom. I can't imagine working on this thing if it was last year before I built my shop. The overhead cranes would be great, heck the fork lift would make this even easier to get this thing in and out of the trailer a lot faster. I am sure this is a tinker toy compared to the large generators that you typically work on! Take care Sean __________________ Sean Marconette 84 Mustang 5060 SS/N

09-02-2014, 12:36 PM	#3
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,315 Likes: 25 Liked 544 Times in 213 Posts	Re: Onan 7000 Generator problems Sean I set the valve lash with a .004" feeler gauge. The studs tend to loosen up from the heat. I always check the exhaust side studs to make sure their tight. The lash gets tighter as you lock the locknut.....Very tedious to get them right and tight....They seem to run much better with the lash set to .004" and I just advise my steady regular customers that we need to check the valve lash every other time I do a full service on them which is at 500hrs....assuming their machines are working well.... The heat transfer from the valves to the springs/retainers etc. is usually noticeable on the exhaust side just by the color of the metal of those parts..... The exhaust stud can loosen up and a pushrod pops out and maybe damage a rocker......all this from the heat..... __________________ Rich Biebel S/C 1479 Stock 147R

09-02-2014, 01:13 PM	#4
Sean Marconette Senior Member Join Date: Mar 2006 Posts: 977 Likes: 796 Liked 275 Times in 76 Posts	Re: Onan 7000 Generator problems I can set the 16 valves on my stocker quicker than I did on the 4 valves for the generator. It did take some trial and error on where I was and then locking the adjuster down how much more they would move. So that makes sense. Do the valves tend to loosen about .010" after 500 hrs? I could easily see where a pushrod could fall out of place if this maintenance was not performed. Sean __________________ Sean Marconette 84 Mustang 5060 SS/N

09-02-2014, 07:25 PM	#5
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,315 Likes: 25 Liked 544 Times in 213 Posts	Re: Onan 7000 Generator problems Sean they do tend to get looser rather than tighter. BUT if the exhaust does get tighter, the lash is so small it can lead to early head failure as I have described earlier. This is a fairly common issue on small engines with solid lifters. It was new to me when I first started working on this equipment. They run fine cold and after a warm up and maybe some load gets applied they start to run badly.....shut it off....cools down.....cycle starts all over again.... Onan flathead engines did this pretty regularly......They had a very wide exhaust lash spec at .013" Exhaust valve needs to touch the seat every cycle to shed some heat of combustion from the valve....No touch.....valve overheats and it magnify's the problem..... Small engines were a whole new world to me going back 15-20 years ago... Chasing some of these problems has always been a challenge to say the least.... __________________ Rich Biebel S/C 1479 Stock 147R

09-02-2014, 11:38 PM	#6
Sean Marconette Senior Member Join Date: Mar 2006 Posts: 977 Likes: 796 Liked 275 Times in 76 Posts	Re: Onan 7000 Generator problems Well all the parts arrived and it is back together and in the trailer. It seems to run smoother. The true test will be this weekend. I plan on testing if the weather holds up, otherwise it will be running in the driveway as a test. I will keep you posted. Thanks for the help Sean __________________ Sean Marconette 84 Mustang 5060 SS/N

09-07-2014, 01:12 PM	#7
Sean Marconette Senior Member Join Date: Mar 2006 Posts: 977 Likes: 796 Liked 275 Times in 76 Posts	Re: Onan 7000 Generator problems Rich, It looks like everything is fixed!! Although the weather was only 76 yesterday for a high, the generator did not have any issues. We even shut it down and let it sit for 10 min and it started right back up as we were packing up. Again your help with this has been greatly appreciated. Having someone to help point you in the right direction is always a good thing. Thanks for everything! Sean __________________ Sean Marconette 84 Mustang 5060 SS/N