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Old 09-01-2010, 10:23 AM   #1
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Join Date: Apr 2009
Posts: 144
Onan 7kw Gold Marquis popping from carb

Like it's backfiring through the carb. Was working great before this last attempt (about 30 days ago). It's in storage so I can't work on it immediately.

Any gear heads that might have a "you dummy, it's ABCD" to check?

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Old 09-05-2010, 12:55 PM   #2
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Posts: 144
Just in case anyone else stumble onto this issue

Make: Onan Gold Marquis 7000
Model 7HGJAB-900A, Spec A
SN: G010266757
Installed in 2002 Damon Intruder

Rocker arm for exhaust valve on left cylinder was found broken:

By comparing the amount of travel in the valve to the inlet valve, and the valves on the right cylinder, the spring only compressed about 30% of the amount before ‘bottoming out’.

The cylinder head and springs were removed.

The inlet and exhaust valves on the right cylinder, and the inlet valve on the left cylinder all looked the same – all three had a rubber bushing with a spring on them.

The valve ‘sleeve’ on the left cylinder exhaust valve was raised quit a bit higher than the other valves – and the rubber bushing/spring were missing. The parts were all loose on the valve shaft.

The exhaust valve sleeve appears to have lid up higher inside the cylinder head, limiting the opening movement of the exhaust valve.

So, the questions are:

1) The exhaust valve sleeve be pressed out, and a new one installed so that it appears and operates as the other three do?
2) If so, what is the PN for the sleeve, and are there any special tools required to completely remove the existing defective sleeve – or install the new one?
3) If it cannot be rebuilt, what it the best source for a new cylinder head, PN and cost?
4) I will need a gasket kit for:
a. Cylinder to crank case
b. Valve cover gasket (for both left and right cylinders)
c. Intake manifold gaskets (for each cylinder connection point)
5) A service manual for this genset would also be a great find…
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Old 09-16-2010, 07:24 PM   #3
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Join Date: Apr 2009
Posts: 144
Turns out the engine, made by Robin America, Inc. (Subaru) for Onan/Cummins has a known design flaw. The attached technical service bulletin (TSB) describes the problem, and the solution - a redesigned cylinder head that has an integrated clip to hold the exhaust valve guide in place.

My engine falls squarely within the units built with this design issue - SN's and build dates all confirm. Even Cummins confirms this. Yet, because the unit is 8 years old (with 250 hours of total run time), it is my responsibility to have both heads replaced - at my cost.

I bought a new head ($320) for the failed cylinder (#1), new rocker arm, and new gaskets. After installing them, the thing purrs like a kitten. Still, I have to wonder how long before cylinder #2 gives up the ghost.

In my business, if I put out a product with a known defect, and customers start calling, we fix it - regardless of the age. It's the right thing to do, and it's what helps build a reputation for taking care of the customers. It's expensive, but sometimes there's no better way to demonstrate customer loyalty than having a problem and shining with stellar service.

Cummins argued that the cylinder head design was an 'improvement', and that they could not be held responsible for upgrading years-old units with the latest improvements. I can see that point of view, but IMO, redesigning a part that is known to slip, known to cause failure, known to cause damage is not simply improving a product. It's fixing a fatal flaw.

Oh well. Two beers for me... one for fixing it myself (I've never taken an engine apart before), and another for not coming unhinged over some lousy customer support.

For the record, if given a choice/alternative, I will not support Cummins/Onan products again.
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