CMB 45 Rod Failure

[FloopyStat]

Guys,

the scenario is...

CAM45 running 50% nitro in Hydro... first outing....kaboom!

result... broken rod @ 1/4 inch from bigend. Took out case, piston, liner and enthusiasm!

Replaced all parts, first run again... 5minutes later...kaboom AGAIN!! exactly the same result.

I'm not a newbie... and beleive the motor was not abused..

Anyone else know of this occurring elsewhere???

Or alternatively..FIXING IDEAS?? (besides left shoulder throw)

 

[Bart Drieghe]

First of all , name ? floopystat sounds weird .

Second ,

when did it happen = full throttle ? , still running in P&L ?? , how much oil, compression ratio ? What load /prop ?

I've been running the evo versions for years now , never broken a rod .

Regards ,

Bart

 

[FloopyStat]

Hi Bart.

Thanks for reply. I have run CMB Evo for three years and no problem. Changed to Cam and then this.

Boat was at full throttle, running 2% caster & 16% syn. H22 prop. There were no burn marks on anything due to running lean. Plenty of exhaust smoke.

I am just at a loss that a new engine would perform like this. I also run the 67 and twin 90's. Love CMB. Just trying to work out if there is a problem that I can fix. Can't continue on this path or will have to sell my house to pay for new motor ever run.

 

[TOM MOORE]

Was the crank end of the rod black and or were the needles black? and was it gold or purplehead eng?

Tom.

 

[Tom v.d Brink]

wow that is really impressive breaking a steel rod like that.

did the pieces of the rod survive without rubbing to much other bits i.e can you

still see how it broke clearly?

maybe take some close pictures and post them i am sure there are some people that can tell you what happened more easy then.

 

[tracerbob]

Same thing happened to one of our boating buddies. Same engine (brand new), same situation. I've heard rumors it's a factory defect in the rods. I'd call tidewater. <_< Anybody else out there had this happen?

 

[Watercadet]

Full throtle at break in? Is that policy?

 

[PHIL THOMAS]

I had one that the rod could rub on the case and get hot, the clearance groove was machined in the wrong position allowing the rod to rub. If its not modified send it back to Tidewater maybe they will fix it.

P Thomas

 

[Bart Drieghe]

Full throtle at break in? Is that policy?

thats my question too .

Running in and at full throttle is asking for probs .

B : They use the sam rods as in the evo's so , it can't be that problem .

Oil is good , Nitro is detail .

Hows your compression ? very high ?

Hows the P&L ?? new , brandnew ? or already been ran in ?

If u're placing a new one , check first how it runs in the engine , rubbing somewhere ? hitting a spot ? it has to be something to break a rod

due to running lean

Running lean has nothing to do with this now , Breaking the rod hasn't got a link with the oil unless your needles are black , red because of lack of oil passing there .

Like i said , check first what could be stopping the engine but im sure that ,if u're p&L is new that u're asking for probs , the compression is high at that time , and the rod (and crankshaft ) have a lot of load at that time .

so : check first :

Does or can the piston be stopped somewhere in the sleeve ?

does the rod rub somewhere and can it be stopped somewhere in the engine ?

Compression ratio ?

Full throttle with new P &L ?????????

and , Pls , whats your name .

Bart

 

[tracerbob]

My buddies engines are always broken in carefully. As a matter of fact, he was breaking in this engine and was running on the rich sich side when grenaded. I have to agree with Phil's observation. That could very well be the problem.

 

[Scott Schneider]

Seen this a few times and in BOTH cases the PTO bearing on flywheel end had excessive axial play and allowed the crank to be pushed inward and in doing so used up the clearance gap on rod ~ Crank face to rotor face ~ causing the rod to grenade the big end.

I have had 1 of my MAC 45 do the same but caught it before it failed.

The 3 engines I describe were ALL using collet drives with the prop thrust transfered to the engine.

Check the end play on the PTO bearing, assemble crank into bearings with rear plate off, measure the distance from the thrust face of rod journal with crank pushed fully inward and measure to the cases gasket surface for back door. then measure width of rods big end, add those 2 numbers together and you have the distance rod is from the rotor. next measure distance rotor "in housing" is from the gasket surface. What you need is @ .015 to .025 clearance once assembled to make sure oil can get into needles on the ends as well and the cut slot and not have a clearance that is so tight that bearing starves for lube overheats the lower area of rod and go's BANG !!!

I hope this helps and if anyone can add to this please do. Scott

 

[[email protected]]

There's a slight chance that the end of the crank pin that seats the connecting rod is warped. When the press those out they can come out untrue, and not completly round. K&B used to have that problem and so you'd spin the motor to start it and it would break the rod.

 

[Wild Bill]

huh??

 

[craig]

Hey this is not funny i have had the same problem i am running 60% nitro and mine blew it's brains out too these things are not made for high loads look at these pictures and let me know what yours looks like no heat on bottom end or needles

View attachment 2046

 

[FloopyStat]

Wohoo!! Looks so similar to mine.. it's scary!! Methinks a trend is developing.

What to do??

View attachment 2047

 

[[email protected]]

YOA-ZA

what's going on w/your fingers?? You been coloring Easter eggs or something?? :blink:

 

[Tim Kish]

Has anyone thought about testing the hardness of the rod.

After reading the posts it seems to me that they may be to hard which would make them brittle.

I would contact CMB and ask them if they have had any problems with heat treating lately.

I have been in the tool and die industry for twenty years and it seems to me that they may be to hard.

I may be totally off on this but its something I would look into.

I can check the rockwell for you guy's if you want to send me a piece of the rod but you will need to find out what the hardness should be (rockwell).

A steel rod that beefy should be one of the last things to break in that engine unless there is a problem with the material.

Just a thought

Tim K

 

[[email protected]]

One other thing that I do to all my of my CMB's is to lap the piston. The box even has a sheet to tell you: "Lap the piston before using" and it comes with directions how to do it.

Did you try that?

 

[DaveMarles]

Thats a material failure and nothing to do with hardening. The steel conrod is only hardened inside the big end.

Send the thing back to the supplier. I saw one other CAM break like that and it must be a material issue. If it was a loose front bearing then the stressed part would be just below the little end.

Dave

 

[Tim Kish]

Unless they press a hardened insert into the crank end of the rod there is no possible way to harden such a small area without affecting the rest of the rod.

But you could be right about the material being bad.

Tim