K&B 3.5 rod

[cjm102]

Hi all.

As far as I know there is two stock 3.5 rod's. There is square alloy and there is round. A friend snapped the square one the other day. I would like to know what is more reliable and stronger as a standered replacement.

Cheers

Chris

 

[Jerry Dunlap]

Personally, I think "It's six of one or a half dozen of the other." I've had both type fail. Stuff happens when you run nitro engines.

JD

 

[Geraghty]

Personally, I think "It's six of one or a half dozen of the other."  I've had both type fail.  Stuff happens when you run nitro engines.
JD

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They are all good if they are straight and clearanced properly.

I can count on one hand all the 3.5 K&B rods I have seen that have failed that I can't determine the cause as to why they failed.

 

[Watercadet]

Personally, I think "It's six of one or a half dozen of the other."   I've had both type fail.   Stuff happens when you run nitro engines.
JD

83924[/snapback]

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They are all good if they are straight and clearanced properly.

I can count on one hand all the 3.5 K&B rods I have seen that have failed that I can't determine the cause as to why they failed.

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Hey Rod- how would I measure clearence on the big end? Plasti gague won't work I have a rod and crank pin that I believe to have too much slop but don't have a way to measure it. Also have you seen a journal that has worn out of spec? I put a new rod/bushing and it still had too much wobble.

Is there a peformance advantage between the dogbone style and the flat style?

Adam

 

[andrew_v]

Personally, I think "It's six of one or a half dozen of the other."   I've had both type fail.   Stuff happens when you run nitro engines.
JD

83924[/snapback]

​

They are all good if they are straight and clearanced properly.

I can count on one hand all the 3.5 K&B rods I have seen that have failed that I can't determine the cause as to why they failed.

83944[/snapback]

​

Hey Rod- how would I measure clearence on the big end? Plasti gague won't work I have a rod and crank pin that I believe to have too much slop but don't have a way to measure it. Also have you seen a journal that has worn out of spec? I put a new rod/bushing and it still had too much wobble.

Is there a peformance advantage between the dogbone style and the flat style?

Adam

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Adam, What do you mean by dogbone and flat style? are you talking about the two different styles of square alloy conrods? (one looks plain and flat and the other has a groove milled out of the middle of it between the two bearings- see attatchment)

 

[Jerry Wyss]

Gawd, That engine has seen better days. I do believe thats what they call an "H"

Rod. The "dog bone" is all rounded and much more "narrow" in its "profile",,

I still run a dog bone in my Mod 7.5 and it has a fair amount of time on it.

The measured "Big End Play" is done in several ways, but I use the "Slight Slack"

Feeling" in the "Flywheel" metheod. Get the piston "stuck" in the "Pinch", "NEAR

TDC" and feel the "approx" 1/16th "slack", back and forth movement in the

Flywheel

remember I said NEAR TDC,,NOT TDC,,as there will be the "Over The TOP" "Bump" there.

 

[andrew_v]

Gawd, That engine has seen better days. I do believe thats what they call an "H"Rod. The "dog bone" is all rounded and much more "narrow" in its "profile",,

I still run a dog bone in my Mod 7.5 and it has a fair amount of time on it.

The measured "Big End Play" is done in several ways, but I use the "Slight Slack"

Feeling" in the "Flywheel" metheod. Get the piston "stuck" in the "Pinch", "NEAR

TDC" and feel the "approx" 1/16th "slack", back and forth movement in the

Flywheel

remember I said NEAR TDC,,NOT TDC,,as there will be the "Over The TOP" "Bump" there.

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So Jerry, If i were to order a rod direct from K&B mecoa, would they give me an "H" rod, or a plain flat alloy one? Has the "H" rod superceded the other two types of rods, because i know they only list one type as available on the order sheet.

See my old rod if your game. I did a good job on this one.

I strip my engine after every run, because i always fip it, and the water is i tiny bit salty. On tis paticular occasion, i mustnt have lubed it enough when i put it back together. I started it, reved it a little so it wouldnt stall while i tuned it and BANG!!!!!!

It ran for no more than 20 seconds. The engine wasnt even hot yet!

 

[Jerry Wyss]

I'm not really "Up" on what fits what concerning all the models of K&B engines. I've

spent most of my RC modeling life flying planes,,and I started out using O.S.

engines,,and when I started RC Boating the only OB you could get was a K&B

and I had lots of trouble with them,,I could Type for Two days of all the experiences. I've found them to be an "inferior" engine for the most part,,even

in airplane engines. Their best engine has been the 7.5,,and I can't explain it,,

I have one that I still run,,and the motor overall is 10 years old, but hasn't been

run from year to year consecutively. Gary Preusse would be your best source

for this stuff and his Ph# has been "Pecked" down on this site more than anybody

yet I can't seem to find it in my drawer.