Are CRF450R's suffering from premature rod failures? Or something else?
Far be it from me to disparage red bikes.
I think Honda makes quality bikes.
Really...
However, I am noticing trend and I am not the only one.
It seems that Honda's CRF450R's suffer from what appears to be major rod failures far in excess from other manufactures.
There was some discussion here before on this subject.
I mentioned from my own experience that I buy CRF450R's more then any other of the manufactures with blown engines... Specifically broken rods.
Someone else quickly jumped to defend Honda's but I don't remember who.
I didn't say anything on this forum but in my own mind I concluded that Honda was using too light of a rod or had a quality control issue.
Well... I had a local engine builder come in my shop earlier this week and he complained that I never had any later model CRF450R engine cases or top ends.
I told him that was because every one I bought had suffered from a catastrophic engine failure and the parts he needs were always damaged.
So he then told me that the CRF450R's have weak rods which is what I always thought.
Today I picked up a 08 CRF450R.
Guess what?
Blown rod and destroyed top end.
So of course I'm thinking that this is another case of Honda's weak rod....
But not so fast.....
I stumbled across some info at a physics forum that may shed some light on the subject.
Q.Hi, I am an amtuer engine builder working on offroad race motorcycles. On the Honda Crf450 engines I have been working on, I have been having a large number off con rods failing in numerous ways.
I have had the the con rod snap right below the piston with no sign of bearing failure. I've had the con rod shatter into over 10 peices with no signs of bearing failure. I've also had the bottom of the con rod break as if the lower bearing has seized, but do bearing damage.
I have been told that with other engine mods I have performed that there is too much oil pressure causing a hydraulic lock of my lower bearing at sudden increases of rpm , thus destroying the con rod with no bearing damage. So I tried a ''relieved con rod'' so oil could escape more easily, but have had the same issues. There are no signs of detonation on the piston. I am running a piston with a lot of clearence to avoid thermal piston growth and seize. And the piston is not hitting the head or crank flywheels. Engines have blown at all different levels of rpm.
The engine is running peak 13,700 rpms, Bore and stroke is 96mm x 62.1, Comp ratio is 13.5:1, With my modifications I am getting about 20% more HP than stock. Could this just be too much power for these con rods? Any ideas for solutions to my problem would be greatly appreciated.
A.The rods have out lived there useful service life at these loads. The answer to this problem is to install an hour meter and replace the rod at a shorter service interval. I have built many of these motors. A CRF450 @ 60+ HP the dependable service life got very short. These motors are utilizing lots of handed down F1 technology.
Titanium valves are stock on these models.
Honda recommends inspection and/or replacement of pistons at ten hours.The pistons are slipper skirt and have to be run at .0015 piston to cylinder clearance.
The stock CRF450 piston skirt is only .828" tall by1.386" wide!
Real light weight. But a very short service life.
The days of a whole dependable race season on a motor are over.
Pete
So, the one I bought today had parts of the piston sticking out through the cylinder
Perhaps the problem has always been a piston design with a short service life...
Any thoughts?
