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Looks like a .67. You shouldnt run it with the bearing in the pic. Im running 2 .67 motors with zero failures. And some time on a 91 with no failure.
 
Looks like a .67. You shouldnt run it with the bearing in the pic. Im running 2 .67 motors with zero failures. And some time on a 91 with no failure.
are you saying that the bearings that come with the motor are no good and should be replaced when bought new?
 
The break in process on these motors is very specific. Supposedly takes a gallon of fuel on the bench with very specific motor temperature profiles. You need a little water circulation pump. I got a little 12 volt job on ebay that should work nicely for about $20.

I did have one with bad the bad bearings and am glad that I didn't fire before it I got them changed out.
 
Hope that's not on the new .67 OB motor. I've put a gallon thru it, on the water, very rich with 1/2 throttle for at least the first 1/2 gallon. Seems to be ok. Will know more next year when the water is liquid again.
 
Looks like a .67. You shouldnt run it with the bearing in the pic. Im running 2 .67 motors with zero failures. And some time on a 91 with no failure.
are you saying that the bearings that come with the motor are no good and should be replaced when bought new?
Jamie,

Small bearings should be replaced if they have steel cage, new engines coming from Novarossi should now have the correct bearings.
 
Gas engines are tougher, but that happens when you push the limits. Nitro engines are a lot closer to the ragged edge. We holed the pistons on several nitro engines we dynoed. I don't have a picture of a gas engine that seized at over 15,000 rpm, but it looked a lot worse than the picture above. Attached is a picture of the relatively minor plug damage from running a Quickdraw on 40% nitro fuel. The piston and sleeve got nicked by the ground strap as it went out the exhaust. Also attached are pictures of one of the many CMB piston and sleeves we seized. It emphasized the importance of a really round bore. There was very little clearance due to an egg shaped bore just above the exhaust.

Lohring Miller

P1010001.JPG Liner failure.jpg
 
We never got the ABC CMB35 to develop full power without seizing. The ringed pistons all ran fine except for this particular one. It failed on the first dyno run. I measured the bore with my Sunnen bore gauge and found the issue.

Lohring Miller
 
I experienced a mystery rod failure on a NR 46 and after looking closely it appears to me that the wall thickness of the rod around the bottom bushing is extremely thin . Couple that with a press fit bushing and some heat and it may lead to this type of failure . I had about 8 heats on mine after break in . hoping for a new life this January at the Nitro race . JMHO .

20160127_181522.jpg
 
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They nova engine have a extremely tight fit between piston and sleeve. The take a good while to break in. If it sticks at high rpm the rod failure will look just like this.

I have a nova 91 with 8 tanks on it and still needs a wrench to get past the pinch if its mounted in the boat.

Exactly the same issue as with cmb 101 except the steel rod holds up and the piston pulls apart.

The upside to all of this is long lasting fit if properly broke in.

Also matters if the .46 has the less cooling or more cooling set up. And I dont use the lower cooling on a cmb 91/101 or nova 67/91. Cooling the lower part of the sleeve keeps the sleeve from expanding but the piston is still expanding.
 
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Good point Danny so I wonder why these manufacturers do things like this to begin with . A new boater would be **** out of luck with one of these new engines without proper guidance . Meanwhile car engines run and run . Closest thing to perfection for me has been the CMB VAC 91 , run a few tanks and hammer it . Of course it's no longer produced LOL .
 
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