Not a good day at the pond

[RonShaw]

Looks like it could be an unbalanced crank issue. I think I will hang the piston and rod on my stock NR rod and the OB reverse cank and check for balance matching after seeing these pics. I would make both balance the same before I would put the motor back together with the reverse crank. There could have also been a flaw in the casting of the case.

 

[RodneyPierce]

Ron, I think you will find that the rotating assembly's in these motors are no where near balanced... stock or otherwise.... its a counter balanced motor. The weight will always swing to the bottom.

To me it looks like a casting flaw or its just the picture. But the alloy looks darker around the break closest to the camera.

 

[Tim_Duggan]

Ron, I think you will find that the rotating assembly's in these motors are no where near balanced... stock or otherwise.... its a counter balanced motor. The weight will always swing to the bottom.

To me it looks like a casting flaw or its just the picture. But the allow looks darker around the break closest to the camera.

You can balance a crankshaft for a particular rpm range though, using a % of the piston/rod/wristpin/clips weight as a reference. http://www.prestwich.ndirect.co.uk/technical_balancing.htm

As Ron has said, you could use the original "normal direction" crankshaft as a good reference point to calculate the factory's chosen %, as I've not heard of any inboards doing this and I think they have Mallory slugs in them.

Another thing worth looking at is the flywheel.

 

[RonShaw]

Ron, I think you will find that the rotating assembly's in these motors are no where near balanced... stock or otherwise.... its a counter balanced motor. The weight will always swing to the bottom. To me it looks like a casting flaw or its just the picture. But the alloy looks darker around the break closest to the camera.

Rodney,

You are absolutely correct, it will never balance due to the design and running qualities of two stroke motors, but if the reverse crank's counter-balanced side is much heavier or lighter than the stock NR crank, that can cause huge problems. Design engineers spend a lot of time testing and on the dyno, finding just the right amount of weight to make these engines run properly in their useful RPM range. I have seen it happen way too many times in after market cranks, where this important step was overlooked. But, as I stated above, it could also just be a flaw in the casting of that case. If that is the "case", no pun intended..... , we need to keep an eye on all of our NR 46's to make sure it is an isolated event.

 

[RonShaw]

Ron, I think you will find that the rotating assembly's in these motors are no where near balanced... stock or otherwise.... its a counter balanced motor. The weight will always swing to the bottom.

To me it looks like a casting flaw or its just the picture. But the allow looks darker around the break closest to the camera.

You can balance a crankshaft for a particular rpm range though, using a % of the piston/rod/wristpin/clips weight as a reference. http://www.prestwich...l_balancing.htm

As Ron has said, you could use the original "normal direction" crankshaft as a good reference point to calculate the factory's chosen %, as I've not heard of any inboards doing this and I think they have Mallory slugs in them.

Another thing worth looking at is the flywheel.

Ding, ding, ding!!!!.........you are "spot on" Tim. Great information. I also didn't think about the flywheel but it should be checked as well.

 

[Dick Loeb]

Dosent look like it is bored on center or block has core shift ,case is thicker on RT side. :blink: :blink:

 

[RonShaw]

Dosent look like it is bored on center or block has core shift ,case is thicker on RT side. :blink: :blink:

Dick,

I see what you are talking about. It looks like the picture may have been taken at an angle making it look that way. Bob, can you take another picture of the broken end of the case to show straight-on wall thicknesses?

 

[RodneyPierce]

I didnt notice that either until Dick mentioned it.

 

[John Knight]

Dosent look like it is bored on center or block has core shift ,case is thicker on RT side. :blink: :blink:

Dick,

I see what you are talking about. It looks like the picture may have been taken at an angle making it look that way. Bob, can you take another picture of the broken end of the case to show straight-on wall thicknesses?

He is at the Internats now and may not be able to do it for a while. Thanks to Glenn the boat is back running and doing good now. He is fine tuning it for the race. He has a smile on his face now and that is good!

 

[RodneyPierce]

Dosent look like it is bored on center or block has core shift ,case is thicker on RT side. :blink: :blink:

Dick,

I see what you are talking about. It looks like the picture may have been taken at an angle making it look that way. Bob, can you take another picture of the broken end of the case to show straight-on wall thicknesses?

He is at the Internats now and may not be able to do it for a while. Thanks to Glenn the boat is back running and doing good now. He is fine tuning it for the race. He has a smile on his face now and that is good!

Great to hear that John!!!

 

[Bob Kensill]

Yes,the Novarossi .46 is fixed and running great. Thanks to all who helped,either with advise or parts. There is a new tunnel driver here at the Internats, Marty Davis! He is driving the Yellow vintage Leecraft. Lookout guys,he's got it on the ragged edge and turning pretty good too!

 

[RonShaw]

Yes,the Novarossi .46 is fixed and running great. Thanks to all who helped,either with advise or parts. There is a new tunnel driver here at the Internats, Marty Davis! He is driving the Yellow vintage Leecraft. Lookout guys,he's got it on the ragged edge and turning pretty good too!

Bob,

Glad to hear everything is going well. Good luck to you and Karen. Tell Marty good luck as well. If he could win with that DNE Leecraft that would be two wins in a row for team Leecraft at Charleston!!!!....

 

[Bob Kensill]

I did suffer one setback today. While breaking in my Novarossi 21,I broke the crankshaft. Got it back together again and ready for heat racing tomorrow.

 

[Blackout]

I did suffer one setback today. While breaking in my Novarossi 21,I broke the crankshaft. Got it back together again and ready for heat racing tomorrow.

Do you know what caused the crankshaft to break?

 

[Bob Kensill]

I don't know what caused that one to break or the one today! Only today when it broke,Otto creamed me. I think it was the fact that he let me have a part w/o paying. The only thing missing after the crash was that part. Maybe I will have better luck with the 40 boat. The weather here is great,if you want to go parasailing..

 

[Bob Kensill]

One last piece of good news at the Internats. Got to run the Novarossi .46 outboard through the timing traps one time before they put the equipment away. 3.5 seconds for the pass. That is only a half second off the record! Can't wait for a record trial to go for the record.

 

[Mark Leyde]

Good Luck tomorrow Bob.

Mark