What would make a connecting rod break in a harley 1340 engine?

Answer 1

Low or no oil
got real hot
over rev'd
not shown any love
debri in case
dirty air filter
high miles
bad casting
out of balance crank
bearing went bad

Answer 2

Harley Connecting Rods

Answer 3

You don't give the mileage, or the conditions under which the motor went south. Ol' buttstink got a few causes right, but most of the stuff he mentions won't cause a con rod to go. The high miles may, under certain conditions (One of those being a casting with a flaw unless you have forged aftermarket rods.) make it go away, but a con rod does not use oil except at the bearing surfaces. (Piston end, and crankshaft end.)

Since you said the rod went, I'm assuming that you mean the rod actually broke, (Some question ambiguity here.) and did not seperate at either the piston or the crank. One cause here is giving the wick a healthy twist at low RPM. You can snap a rod if you are putting around at 1800-2000 RPM and then get on the throttle. Low RPM and "getting on it" are a bad combination. Most times the lower end will go if you do that on a regular basis. It just pounds the heck out of the crankshaft.

The fellow with the hydraulic lock info may be right, but it won't be fuel that caused it. You can't get enough fuel in a 1340 to cause it to lock, and still run. I have an S & S "E" model carb on my FXDWG. Hogs lean to the left when on the stand, and the carb and air cleaner is just sitting out in the wind and the rain. (I'm in Florida. After a heavy rain I have to remove my air cleaner cover and see how much water my carb has taken in. If I try to start it with a throat-full, I have no end of grief. Cover you say? I lost three covers in the last four hurricanes. And had enough water in my air cleaner cover, air filter, carb throat, to make a pot of coffee!)

But water will not leak into the cylinders. You have hydraulic lifters. When the motor stops, all valves return to their seats under spring tension. Here is the interesting part. If you keep sucking in water when you start. then you are washing off, diluting, the oil on the valve stem. When you first start up, that is when the valve stem is most vulnerable. If you do this enough, because oil needs to be pumped from the lower end to the top, then trickle down to the valves, and the tolerances are loose because the engine is not yet warmed up, you could eat a valve, (just the valve head if the stem goes) and that would jam in between the piston and cylinder dome. Bye, bye connecting rod!

I must admit I have never heard of a con rod going in a bike due to hydraulic lock. (Yes I lead a sheltered life, and treat my bike like the lady she is.) I have known it to happen to radial aircraft engines, and some cagers that are stupid enough to drive through large puddles at speeds that throw water up into the engine compartment in huge amounts.

Of all the parts of the motor, the actuall connecting rod has the easiest job. (Not at the journal ends, but the actual rod itself. If you managed to bust a rod, you must be a pretty special person. I'd like to get a bit more info on the actual location the rod broke, and the cause if you get a chance. Ride safe after the re-build. Ciao!

Answer 4

I don't know that the 1340evo is the best motor Harley ever built,I personally am partial to the older 74 c.i.d. shovelhead.I believe that what you do to the motor after you buy the motorcycle is very important. The stock Keohan carburator,right in the trash.S&S or my preference the Mikuni smooth bore along with after-market exhaust,can really bring out the power of any H.D. On the evo motors,you can't really run the 2 inch straight exhaust,as you could with HD motors years ago,because of a lack of back pressure.The evo motors perform much better with 1 3/4 inch straights.At least that is my belief.Harley-Davidson is the greatest motorcycle ever built,as any diehard motorcyclist will tell you.

Answer 5

That depends on where it broke. If it broke in the middle of the rod ,it could have been a flawed cast.
If it broke at the head or the base a bad bearing.
I've also seen heat seizures cause a rod to snap.

Answer 6

It's probably not broken - because, as any Harley guy on Yahoo answers will tell you, Harley's run forever and ever since the amf days, they never break down/

Answer 7

Being too cheap to spring for synthetic oil. Letting the oil get low. Putting too much oil in so it reaches the crank and foams up. The guy who assembled the engine or made the bearings having a hangover that day. Modifying the engine and exhaust when you don't know what you're doing. Sucking a quart of water into the intake. Pure orneriness.

Answer 8

Yep I agree high mileage attributes to of a lot of break downs, and Harley's thrive on their oil as we all know, So routine maintenance/services and checks is a must.... good luck on the rebuild friend

Answer 9

it could happen if the valves got jammed open that would be hit by the piston, normally damage would be restricted to the piston but there may have been a fault in the conrod, harley quality control has always been crap.

Answer 10

A faulty rod.