Nova let go today :(

[BB Mods's]

Running the roadrunner today, thought things were off to a good start.. hadn't burned a plug all day long, temps were good on the motor (183~197) then the boat got real fast, then real quiet. RX21 say good night.

Cant figure it out, the cir clip damage was after the piston shattered, evidence of this is lack of damage (by the clip) to the broken bits of piston. Cant figure it out... bearings were fine, glow plug survived to! guess its time to toss the 35 in the RR...

 

[Tim_Duggan]

I've can sympathise with ya, had 2 just like it in quick succession - tearing the piston bosses out. One on an RX21 and the other on a P5. Those engines had done a lot of work though! My RX21 was 8 years old and survived 3 boats!

Sleeve still OK? both of mine were unscathed. Suitable for new pistons. can't say the same for head buttons though!

 

[opio]

that sucks, i know ya got a few extra motors laying around lol

 

[aaron alberico]

BB MODS

pm sent

regards Aaron

 

[RaceMechaniX]

Tommy,

I'd think it was the circlip that cuased the failure. The two scratches on the side of the piston suggest something got wedged between the piston and sleeve. Once jammed that cuased the lower pin bosses to break when the crank tried to pull the piston down.

This happened to a Picco P5 I had. Sucks!

TG

 

[BB Mods's]

It was deffanatly the c clip that caused the scoring, but it did not cause the breakage, one of the c clips stayed in the piston (look at the pics hard) and the other i dug out of the piston's side, sleeve is ruined.

head button survived with out a scratch, the skirt was turned into a fine powder, with the exception of the 2 small frags that came from right under those 3 score marks.

 

[Geraghty]

Tommy,
I'd think it was the circlip that cuased the failure. The two scratches on the side of the piston suggest something got wedged between the piston and sleeve. Once jammed that cuased the lower pin bosses to break when the crank tried to pull the piston down.

This happened to a Picco P5 I had. Sucks!

TG

Take a closer look and consider this.......I'm a thinkin' that the failure starts with the wristpin breaking at one end.That cocks the piston in the bore breaking the boss and then letting the "C" clip loose from the groove.What got me thinkin' this way is I have repaired locked up motors that have had broken wristpins but did not tear out the pin boss in the piston.

I believe the wristpin is work hardening and failing from the constant shock hammering it takes at a 1000 times per second when the motor is at full song at 30K.

I have seen these failures quite a few times in older motors such as the RX21's,Picco EXR'S and older OPS's.I never see these failures in the newer motors leading me to believe that just maybe the "C" clips are not the source of the problem. :unsure:

Several years ago I started routinely replacing the wristpins on older motors coming through the shop.I figure that was cheap insurance to possibly save an almost impossible to find older piston & sleeve.

Those replaced wristpins go directly to the waste basket with the replaced bearings.

 

[Tom Foley]

Tommy,
I'd think it was the circlip that cuased the failure. The two scratches on the side of the piston suggest something got wedged between the piston and sleeve. Once jammed that cuased the lower pin bosses to break when the crank tried to pull the piston down.

This happened to a Picco P5 I had. Sucks!

TG

Take a closer look and consider this.......I'm a thinkin' that the failure starts with the wristpin breaking at one end.That cocks the piston in the bore breaking the boss and then letting the "C" clip loose from the groove.What got me thinkin' this way is I have repaired locked up motors that have had broken wristpins but did not tear out the pin boss in the piston.

I believe the wristpin is work hardening and failing from the constant shock hammering it takes at a 1000 times per second when the motor is at full song at 30K.

I have seen these failures quite a few times in older motors such as the RX21's,Picco EXR'S and older OPS's.I never see these failures in the newer motors leading me to believe that just maybe the "C" clips are not the source of the problem. :unsure:

Several years ago I started routinely replacing the wristpins on older motors coming through the shop.I figure that was cheap insurance to possibly save an almost impossible to find older piston & sleeve.

Those replaced wristpins go directly to the waist basket with the replaced bearings.

Good CSI work here ! Had a Mac 45 pin and a CMB 45 pin do the same thing ...

 

[BB Mods's]

Wrist pin and rod are not deformed, They survived the damage.

this motor is a NEW RX21 SS2, not the older motors.. that's why its so annoying...

 

[Mike Larson]

Tom! sad day..... not to in any way undermine Rod, for he is the expert hands down.... in the picture the crank looks fractured, and, i've had this twice from the epoxy crank ramping as shown in your pic..... if a small piece wedges between the case and the crank induction port, you have an instant seizure, and the resulting carnage..... yours just happened to be on the downstroke.......

i'd been advised by my builder of past, that, the ramping will not take the liberal slurry of afterrun oil i normally instill in my motors religiously, nor stand up to being stored for long periods of time and adhere to the crank with hope of regularity..... a switch to alchohol and air for maintenance was recommended..... while a dose of light air tool oil and constant inspection with a dental pick, my failures will be in time coming, especially with the shape of my stuff, but they all go, eventually, anyway, there's only so many turns in any given machine...... when nova's go it's sick....... sorry man.... i've found in my novice opinion at best that only by being seriously diligent on keeping tolerances at best will keep them running for long periods beyond the expected life of any motor subjected to violence we place on them.... rod and pin, new clips and bearings, are a given, expensive, and I've been known to "roll the dice" and lose more often than not.....

Possibly, Mr Geraghty could post minimal known tolerances or best case opinions on replacement on known worn parts, in terms we can relate to, and help us all gain in knowledge a little more......

I've had 'em last 5 years to date with 0 wear, and lost 2 in a month.... what to look for what to mic, and measure, deeming pre grenade replacement, would help anybody...... siding with winter, and most guys stuff idle, an inspection, and possibly saving a few explosions for guys, could be accomplished...... lets push an informative post, and gain in the experience.... motor guys?... mike

 

[BB Mods's]

The crank did not fail, This was a new motor, after the explosion Sunday, I tore the engine down, remove most of the red putty ramp (it was all there) and now ill be pressing a solid ramp into the crank, I to am not a fan of the red goop cranks.

 

[Tom Foley]

Wrist pin and rod are not deformed, They survived the damage.

this motor is a NEW RX21 SS2, not the older motors.. that's why its so annoying...

Wow , that really sucks , no apparent cause except defective piston ??

 

[Geraghty]

I am definitely no expert...I am only passing on what I have observed and have experienced..........

I have heard the same thing about after-run lubes attacking the red RTV crank filler ........I don't have any first hand experience with the red RTV crank filler,but that is about to change.I received my tube of RTV today from ReidRC and I am about to find out what does and does not attack it.......I am definitely going to be using it in the .12's we are playing with.

I like .001"to .0015" on the wristpin to rod clearance.Any wristpin/rod/piston assembly that doesn't feel good,comes out immediately and is visually checked for cracks.I take suspicious wristpins and roll them on a piece of glass.I have in the past found a few of them bent.I suspect the majority of them have been bent by a 24volt starter trying to roll the motor over when the motor was full of water.

Now to the question of longevity,I really don't have a steadfast opinion.I also have had 'em last 5 years and then lose one for no apparent reason,but by in large I have definitely seen more failures in the older motors........and then again,sometimes for whatever reason,sxxt just happens.........

Now I don't want anybody to think I find a bent or broken wristpin every other day of the week.I have maybe seen 20 bad wristpins over the past 15 years of doing this full time.

This is the only thing I know for sure........wristpins and "C" clips are cheap compared to rods and pistons & liners..........so if there is"any" doubt,I change em' out.........

 

[Preston_Hall]

Maybe the new motors are not as good. It is unlike the NR to do that.

Something none of you mentioned was how discolored the P&S are. I think you are running way too lean. That baked on brown gunk is even in the sleeve ports. If that is not caused by heat then I would use a different fuel or oil.

 

[Buckshot]

Maybe the new motors are not as good. It is unlike the NR to do that.
Something none of you mentioned was how discolored the P&S are. I think you are running way too lean. That baked on brown gunk is even in the sleeve ports. If that is not caused by heat then I would use a different fuel or oil.

Agreed.

A rich running motor will not show signs like this, but bad oil can. If it is a new motor with low run time the discoloration is a big flag about fuel conditions either too lean or bad oil. Not like a N/R to let go with out good reason but it has happened.

-Buck-

 

[SayMikey]

Maybe the new motors are not as good. It is unlike the NR to do that.
Something none of you mentioned was how discolored the P&S are. I think you are running way too lean. That baked on brown gunk is even in the sleeve ports. If that is not caused by heat then I would use a different fuel or oil.

Agreed.

A rich running motor will not show signs like this, but bad oil can. If it is a new motor with low run time the discoloration is a big flag about fuel conditions either too lean or bad oil. Not like a N/R to let go with out good reason but it has happened.

-Buck-

I dont know what kind of red rtv you are speaking of BUT id use gray diesel rtv as oils wont attack it after its setup. Found at your local ford dealer in a caulking tube. One should be a lifetime supply,or till the shelf life expires.

 

[Don Ferrette]

Something none of you mentioned was how discolored the P&S are. I think you are running way too lean. That baked on brown gunk is even in the sleeve ports. If that is not caused by heat then I would use a different fuel or oil.

I was wondering the same thing. One thing I learned a while ago (thanks to KP) was that all too often people run more oil in the small motors than needed. Also most tend to run far more water cooling than needed so the problem becomes two fold, the motor is colder than it should be and slogging through a "thick" fuel mix. That tends to get people to start really pinching down on the needle to "get it to go" and "clear out" and you wind up with a low oil situation from being too lean and the top of the liner being tight from being too cold that can lead to results alot like that pic. Now I'm not saying this is the case here but something to keep in mind. I do agree with the idea of taking a good hard look at the ramp "filler" causing a piston to stick & ripping out the wrist pin but too lean & too cold can and will do the exact same thing. I will say that once I started running 70% with 12% oil and really watching the head temps I found my 21 motors running faster, clearing out and really singing with longer bearing life and no failures, all the while running a richer mixture. Fuel makes power, the more fuel you burn the more power you make.

 

[BB Mods's]

The browning is normal for the oil mixture i use. It would have stayed that color until i leaned the motor down to normal running tune, this motor never made it that far, Thom Hammer says it has to be metallurgical in nature due to the large amount of powdered piston material present when the engines was pulled down.

 

[ALLAN YUEN]

Running the roadrunner today, thought things were off to a good start.. hadn't burned a plug all day long, temps were good on the motor (183~197) then the boat got real fast, then real quiet. RX21 say good night.

Cant figure it out, the cir clip damage was after the piston shattered, evidence of this is lack of damage (by the clip) to the broken bits of piston. Cant figure it out... bearings were fine, glow plug survived to! guess its time to toss the 35 in the RR...

h34r: Did you cut to file modified front end shaft on crankshaft ? because poor balance rotor and run viberate . the C chip fell off then bang to blow out P/S h34r: Look at your under piston color stain brown what kind of nitro company? or homemake brew ? <_< I believe bearing fail cause low oil or too much caster oil

 

[BB Mods's]

Home blend, that dark color is a ultra thin coating that's just dark in color, bearing's were fine, I don't give out my oil % but 3 years of running this mix, this has been the only failure in a novarossi I own.

The crank was static balanced, I don't have a vibration problem with this engine, the piston was not modified, nor was the sleeve in any way.