Onan 4000 Intake Manifold replacement

Here's a pic, you can see I've got the lower bolts loose, but there is a the metal piece keeping the intake manifold from sliding off the studs.

Looks to me that carb adapter was attached BEFORE the metal piece to the left (generator body?).

If that part to the left is the gen body, then I suspect the gen body WILL have to be separated from the engine before the carb adapter will ever come off the studs..

If the carb adapter is aluminum, you could have a new "ear" fabricated and welded on if you can find a welding/fab shop that specializes in in aluminum fab and repair..

If pot metal (zinc) you are out of luck, pot metal doesn't weld..

Doubt it is cast iron, pretty obsolete now days, welding cast iron is tricky, can be done but temps must be controlled to do it properly..

If nothing else, fabricate a bracket that you can bolt to the backside of the adapter (where the cast in PN info is)..

If it were me I would drop by a small engine repair shop and get their .02.

ksg5000 wrote:
If it were me I would drop by a small engine repair shop and get their .02.

Doubt you will find too many shops that will touch this with a 10 ft pole.

In rereading the OPs post, if the "ear" is in tact and all that is wrong is no threads, you can try a "helicoil" insert..

See HERE

Catalog and instructions HERE

In a nutshell, oversize tap and then the helicoil is inserted which brings the diameter back to the correct size for the bolt..

Should be able to buy in a kit with proper drill bit, tap and tools needed to do the job..

Looks like the cylinder head has to come off with the manifold.
Any automotive machine shop can remove the broken stud.

The broken piece of bolt is in the threads by the paper towel is stuffed in the intake manifold. I was able to remove some of the air cleaner housing and have better access to the busted bolt. I may be able to Dremel a hole in the bolt enough to get a bolt extractor on it and see if it’ll unscrew out.
Thanks for everyone’s input, it’s appreciated!

BeeeGeee wrote:
The broken piece of bolt is in the threads by the paper towel is stuffed in the intake manifold. I was able to remove some of the air cleaner housing and have better access to the busted bolt. I may be able to Dremel a hole in the bolt enough to get a bolt extractor on it and see if it’ll unscrew out.
Thanks for everyone’s input, it’s appreciated!

Careful of bolt extractors, they are hardened and tend to snap off making drilling out the hardened extractor a near impossible job.

I suspect the leftover bolt stuck inside may be cross threaded which most likely is why it twisted off in the first place.. If cross threaded, bolt extractor failure is most likely.

Don't envy you on this, looks like a really bad position to be working on but it is most likely the only way your gonna fix it without splitting gen from engine..

on edit..

Depending on your bolt size, I would suggest perhaps a internal pipe extractor.. They tend to be much stronger than most bolt extractors..

Looks like this..



Works like this..



Have resorted to using pipe extractors on stubborn bolts in the past after seeing someone else mention them.. Can work as long as you can find one that comes close enough to work in the hole you drilled in the stuck bolt..

Don't get me wrong, I suspect even the stout short pipe extractors can break off..

Gdetrailer- Thanks for your input, I didn't think to remove the cylinder head (and using the pipe extractor). I did a lot more digging and found the Cummings Service Manual with all the torque specs to retighten the cylinder head. If I can't easily get that small part of the bolt out or if it is cross threaded, I'll just remove the cylinder head and replace the intake manifold, probably be easier and quicker.

Thanks again for all the suggestions, this is a great source for info.

You bet!

Good luck and perhaps give folks an update on this thread on how things went..

Might be helpful for others facing similar situation in the future.

I have same gen and just replaced the carb.

Can you explain exactly which bolt is the issue? The one on top at paper towel, or the one on the bottom that has threads poking out of intake piece, but no bolt head?
If the lower one, then maybe you can work a nut onto the threads instead of trying to put new bolt through it. You will have to carefully clean the end of the bolt or just be really lucky that a nut will thread on. DO NOT cross-thread it though.

If I remember maybe that lower bolt was threaded in from the right side, and the one on the back side was from the left, as you can see the bolt head, but I am probably mistaken..

I assume though, that it is the top, as the lower part does not need to be messed with for a simple carb change. You should e able to just extract any broken pieces. You could literally make it work with a c-clam to hold the carb on, this just needs to be airtight so intake is not sucking air in after the carb.