947 Engine Balance Shaft

[mkov608]

I took my 99 GTX limited out about 1 month ago, at 6,600 rpm and 50+ MPH I heard a horrendous noise, and the engine shut off. With some good timing, a passer buy towed me back to shore. We loaded up the ski, and headed home. I had to wait several weeks (away on business) for time to take the engine out. Once we go it on the workbench, we split the case to find the balance shaft bearing at the front of the engine exploded. It was all over for the engine from that point. The bearing went through the case and the upper and lower portions look like I was using them for target practice. Both gears, the one on the crank and the one on the balance shaft, were severely damaged. Consequently, I’m in the market for a 947 engine. Now for the questions:

#1. Is it a common for the balance shaft bearing to fail? It looks like they have their own sealed bearings, but I’m thinking a better design would be to lubricate them the same way you lubricate the crank bearings.

#2. Can you run this engine without the balance shaft? Seems like it would just be easier to balance the crank and leave the balance shaft out of the equation.

#3. What is the difference between the 947 and 951 engines? I found a 951 engine on Ebay, but the individual said it’s not a suitable swap for a 947 engine. It looks just like my 947 engine.

Thanks in advance!

Mark

 

[Skatman]

Balance shaft questions.....

Well, I can answer all three of your questions with one answer. No. You can't eliminate the balance shaft. Because of the design of the engine, it has to be counter balanced. The idea of a harmonic balancer does seem like it would work. I wonder why they didnt' take that route.
The 717cc engines didn't use one.
Blowing the bearing on a balance shaft is like hitting the lottery. The odds are, you'll never win. Well, you just hit the lottery.
There is a plug on the back of the engine on the balance shaft side. When the engine is put together, their is 40 ml of SAE 30 weight oil put in for lubrication. The older models didn't have a plug for you to maintain or check, yours does. So, when you get a new engine, make sure you check that oil once a season. Your balance shaft failed probably from a seal failure.
Lastly, there is no difference between the 947cc or the 951. Like the 787cc is often referred to as a 800 and the 717cc as a 700, the 947cc engine is referred to as a 951.
You can go to www.sbtontheweb.com and find a replacement engine pretty cheap. Because your core exchange has been damaged, they will likely tack on a little extra for welding your casing. Give them a call, tell them what happened, they'll hook you up.
When the new engine comes, you'll have 10 days to take off all your parts and put on the new motor. Put your old one in the crate and ship it out. They couldn't make it any more simple.
Beware of ebay engines...........

 

[ScubaDoo]

:agree: Your right on the money Skatman.

 

[mkov608]

Thanks Skatman! After doing some more research, I have found that the 951 is commonly referred to at "type 947" (almost as bad as working on Pratt & Whitney jet engines). The boat mechanic at Apache Honda in Phoenix told my brother the same thing about the balance shaft failure. I'm going to buy my lottery ticket tomorrow!

Thanks for the Ebay advice too. We will probably go with a Sea-Doo engine from Apache since there is no core charge, and bro gets a huge discount there.

After looking at the destroyed engine case, it is evident the oil servicing port is in the center of the case very near where the water inlet hose connects to the engine and is accessed by removing a small hex bolt. I don't believe the caps you refer to is where the oil should go. Just inside the balance shaft bearing (on each end) there is an oil seal on to close off the cavity and retain the oil. If you put oil in there #1 it will run out just as fast as you put it in, and #2 the oil will never make it to the gears on the crank/balance shaft. However, I did notice on another post that on later engines (think is was the 787 engine) the drive gear for the balance shaft was moved from the center to the end of the shaft.