Cracked exhaust manifold? - Onan generator (MDKAU)

[scubaman]

I'm having a problem with the generator and was hoping for pointers as to what might be wrong. On starting up the generator, a good puff of black smoke is belched out from the area circled in red in the pic.

Peering into the opening between the exhaust manifold and the resonator reveals no obvious exits for the smoke. Looking from top, the gasket between the block and the manifold looks ok. The amount of smoke suggests however, that there must be a substantial leak somewhere.

I'm a bit far away from cummins engineers at the moment, so any help would be greatly appreciated.

Just for reference, I had a cracked raw water pump earlier in the spring but I don't think this is related?

 

[volvopaul]

It's a Kubota engine . I'd say it's the gasket to head but recently I've had a few small Kubota and Perkins base engines that have had the exhaust elbow nearly complete blocked so I'd be taking it off for inspection, I doubt very much it's cracked.

 

[scubaman]

Thank you Paul!

I removed the exhaust manifold and found the culprit. Two of the three bolts holding the exhaust mixer in place had broken due to rust. Third broke when I tried to open it.

The question now is can the remains of the bolts be machined out.

I also need to get some new gaskets for the manifold and the mixer.

 

[ARE]

Thank you Paul!

I removed the exhaust manifold and found the culprit. Two of the three bolts holding the exhaust mixer in place had broken due to rust. Third broke when I tried to open it.

The question now is can the remains of the bolts be machined out.

I also need to get some new gaskets for the manifold and the mixer.

You found out exactly what I was about to tell you.

The first MDKAU's had a open mixer and relied on the gasket to seal the sea water between the mixer and the exhaust manifold, there was a recall by Onan to fit a new mixer which was sealed so sea water never touched the gasket.
This is the newer style with the end filled in.

So if you still have the old style mixer this will need replacing as well.

Regards Anthony

 

[BartW]

The question now is can the remains of the bolts be machined out.

It looks that you have to replace the part with the broken screws,

In case you want to re-use it and get the screws out,
you could try to:
drill a hole in the screw, if the screw is M6, drill 3mm hole,
and use a conical left hand threading tap,
they are available in sets, typical for this application,

 

[Portofino]

Its infuriating in a marine environment -two dissimilar metals one iron - cheapo steel (the studs ) are allowed to come in contact with sea water which acts as a great electrolyte - The alloy block just furs up .
You will end up taking the alloy block to an engineering shop to remove those # studs and re-tap ? Or replace the part(s) ?

Masse small gen sets are air cooled -sea water does not come in contact with the engine or windings

 

[scubaman]

You found out exactly what I was about to tell you.

The first MDKAU's had a open mixer and relied on the gasket to seal the sea water between the mixer and the exhaust manifold, there was a recall by Onan to fit a new mixer which was sealed so sea water never touched the gasket.View attachment 52359
This is the newer style with the end filled in.

So if you still have the old style mixer this will need replacing as well.

Regards Anthony

Thank you Anthony!

Would you by any change have the part numbers for the mixer and the manifold? I found a parts list for the MDKAU online, but that shows the old part with a separate gasket.

I've contacted a local car machining shop and am going to let them have a go at removing the bolts. I'm assuming that the old manifold is compatible with the upgraded mixer? Or does the panel think that the manifold has to be replaced as well?

Thank you again everyone!

Edit: Anthony, does the recall mean that a replacement would be available as a warranty part?

Greetings from lake Saimaa. Pic from our coffee break at anchor enroute to Lappeenranta.

 

[scubaman]

Reading this again with a bit more thought and studying the (alloy) manifold, it appears that it has corroded away and 'softened' somewhat, so I'm probably looking at getting a new manifold and mixer.

 

[ARE]

Thank you Anthony!

Would you by any change have the part numbers for the mixer and the manifold? I found a parts list for the MDKAU online, but that shows the old part with a separate gasket.

I've contacted a local car machining shop and am going to let them have a go at removing the bolts. I'm assuming that the old manifold is compatible with the upgraded mixer? Or does the panel think that the manifold has to be replaced as well?

Thank you again everyone!

Edit: Anthony, does the recall mean that a replacement would be available as a warranty part?

Greetings from lake Saimaa. Pic from our coffee break at anchor enroute to Lappeenranta.

I can not see because the gasket is still in place, but do you have the old style or new style mixer?

The new style mixer has part number of 0154-3163 and the gasket for this is 0155-3720, if you want a manifold this is 0154-3073-01 and the gaskets are 0185-6851 and 0130-5139. The manifold is the same as the current part you have.

Unfortunately the recall took place from 2002 until 2005, so you would not be able to claim any warranty now.

Regards Anthony

 

[scubaman]

Many thanks for the info, Anthony!

I'm not completely sure how to tell the difference between the old and the new one, but after having a brief look at it at the shop post cleaning, I'd say that the opening is wider on the part I have. How can I tell for sure?

Thank you for the part numbers. I've just gotten a message back from Seapower Marine and it seems that there isn't a manifold available anywhere in the moment right now. I'll see if I can get the gaskets locally.

Thanks again!

 

[volvopaul]

O

Many thanks for the info, Anthony!

I'm not completely sure how to tell the difference between the old and the new one, but after having a brief look at it at the shop post cleaning, I'd say that the opening is wider on the part I have. How can I tell for sure?

Thank you for the part numbers. I've just gotten a message back from Seapower Marine and it seems that there isn't a manifold available anywhere in the moment right now. I'll see if I can get the gaskets locally.

Thanks again!

The remaining studs will come out easily if you use some concentrated heat like an oxyacetylene no 2 welding nozzle , heat around the studs then grip with vice grips , alloy expands very quickly to heat so they should come out. If you can't find anyone look at sending it to me via a courier and I'll sort it. No need to drill broken studs out risking damage to the casting .

 

[ARE]

Many thanks for the info, Anthony!

I'm not completely sure how to tell the difference between the old and the new one, but after having a brief look at it at the shop post cleaning, I'd say that the opening is wider on the part I have. How can I tell for sure?

Thank you for the part numbers. I've just gotten a message back from Seapower Marine and it seems that there isn't a manifold available anywhere in the moment right now. I'll see if I can get the gaskets locally.

Thanks again!

Can you post a picture of the mixer with the gasket cleaned away? the new design is completely smooth except for the hole for the exhaust and the old design has an open ring where you can see the water injection spray ring.

I have a nearly new second hand manifold assembly in my garage if you get stuck.

Regards Anthony

 

[scubaman]

Paul, Anthony, thank you very much for your help!

I just got off the phone with the workshop. They've managed to remove one bolt, but the remaining two are giving them hard time... I suggested the method you mentioned, Paul . They have also machined the face of the mixer to make it level with the manifold. It had bent slightly around the last bolt holding it in place.

I've also found new gaskets which should arrive tomorrow. The manifold had corroded slightly but I'm hoping that with a new gasket and removed studs, they'll get it back into working order. I do realise however, that it's only a temporary fix as the underlying problem hasn't been addressed. Due to lead times for the replacement parts, I'm going ahead with this fix and hope it works and then change mixer in the winter if it proofs to be of the old design.

Unfortunately I don't have a pic of the cleaned up mixer at the moment. Will take one tomorrow when I go to the workshop. Anthony, thank you, it's very good to know there is a possible plan b, if they can't make it work.

 

[scubaman]

Got the new gaskets today and collected the manifold together with the mixer. First off, here is a pic of the mixer.

To me it looks very similar to the one on Anthonys pic.

I've re-assembled the generator and all that needs to be done prior to a test run is fill up with new coolant. As mentioned earlier, the manifold was slightly pitted but I'm hoping the seal will be good.

Managed to detach a connector from the exhaust temp switch, so I'll have to dig up the soldering iron in the morning.

Fingers crossed that everything works.

 

[Latestarter1]

Paul, Anthony, thank you very much for your help!

I just got off the phone with the workshop. They've managed to remove one bolt, but the remaining two are giving them hard time... I suggested the method you mentioned, Paul . They have also machined the face of the mixer to make it level with the manifold. It had bent slightly around the last bolt holding it in place.

I've also found new gaskets which should arrive tomorrow. The manifold had corroded slightly but I'm hoping that with a new gasket and removed studs, they'll get it back into working order. I do realise however, that it's only a temporary fix as the underlying problem hasn't been addressed. Due to lead times for the replacement parts, I'm going ahead with this fix and hope it works and then change mixer in the winter if it proofs to be of the old design.

Unfortunately I don't have a pic of the cleaned up mixer at the moment. Will take one tomorrow when I go to the workshop. Anthony, thank you, it's very good to know there is a possible plan b, if they can't make it work.

How old in genny? Onan put a campaign in place notifying ORIGINAL owners that modified replacement manifold was available F.O.C, however a good few slipped though the net and five years after expiry of original warranty Onan played hardball. The two failures I have come across were easily and inexpensively fixed by milling off exhaust face, TIG welding on plate and then flashing it over with the mill to true it up, job done.

Sadly new wave of Onan management nowhere near as flexible as they used to be.

 

[scubaman]

Good news is that I got the exhaust temp alarm fixed at a tv repair shop, so everything is now working normally.

Again, to me the mixer I have looks just as that on Anthonys picture. Also from LS's description of the remedy, I'm gathering that I have the new type mixer already in place? Pardon me if I'm being thick with this and have gotten it wrong.

If, I have the new design, I shouldn't have corroded parts on my hands I suppose.

 

[ARE]

Got the new gaskets today and collected the manifold together with the mixer. First off, here is a pic of the mixer.

To me it looks very similar to the one on Anthonys pic.

I've re-assembled the generator and all that needs to be done prior to a test run is fill up with new coolant. As mentioned earlier, the manifold was slightly pitted but I'm hoping the seal will be good.

Managed to detach a connector from the exhaust temp switch, so I'll have to dig up the soldering iron in the morning.

Fingers crossed that everything works.

So you already have the new style mixer fitted, I guess the corrosion around this area has just eaten the allen screw away.

Regards Anthony