Last Dance at 1.2 Million Miles - 3216

[Rawze]

(08-08-2019 )Hammerhead Wrote:  

(08-08-2019 )Rawze Wrote:  Were the rod and main bearings done at 800k miles? -- If not -- THEN YOUR DRIVING A TICKING TIME BOMB!! and that thing is well due for an inframe at this point so that you don't loose the whole engine with a huge hole in the side of the block, no warning whatsoever, because of a wrist pin failure...

Please explain the wrist pin failure - rod & main bearing correlation.
I can't explain this properly, and I'm looking for someone to help me unscramble the thoughts into words.

when there is too much play (bearing wear) in the rod and main bearings, harmonics set in and cause the wrist pins to start to hammer on the rod bushings at the top of the rods. This wear is specifically at roughly the 5'o-clock position on the rod when looking at it TDC, perspective from the rear of the engine facing forward.

The rod bushings at the top of the rod are relatively-soft brass, and have no protection against this type of hammering or vibration. -- As they wear out, then it is steel on steel, and the top of the rod starts to eat into the wrist pin,.. overtime, the pin finally wears through, and the piston goes sideways in the block. <-- there is absolutely no way to detect this until it is too late.


There is a standing trend and clear pattern of this failure occurring for CM870 and CM871 engines that have not had their rod/main bearings changed at 800k like recommended here. The failures I have seen myself have all occured anywhere from 1.2 mil miles to 1.4 mil (one cm870 made it to 1.6 mil once though) miles on these engines. - There are not a whole lot of CM2250's and even less CM2350,s that make it anywhere near this mileage, but I can only assume they would have the same issue. Possibly though, the CM2350 may have this issue even sooner, and even sooner for the X15's, but only time will tell that one.

Some related info: -- I have seen a number of CM2350's with bad programs that were causing high detonation rates. This is mainly due to people using the factory injection timing, or worse yet, sometimes advancing it even further .. but have removed the EGR gas completely. <- The result is a high enough detonation rate to cause this same wrist pin hammering .. no one feels it or detects it. Engine seems to run smooth.

On those CM3250,s , so far, they all have failed with head gasket issues due to dropped liners (like I said, bad programming),.. and the brass is beat to snot at the top of the rods .. a failure was imminent,.. but in every case so far, it was a head gasket failure that happened first. <- I can only imagine that this will not always be the case, and there will be trucks that send a piston through the block with zero warning due to this, I just have not seen it yet.

Adding up 1+1 to get 17 ... LOL ... (just some thoughts here) ...

It seems clear that the CM2350's are a lot more prone to bad programming and this happening than the CM2250's or older lower comp[ression engines. <- makes me wonder if this is going to be a big engine killer for those X15's, especially tyhe high HP models with their 19:3 or 19:6 compression ratios.

I feel sorry for anyone who has an X15 if they have had a de-mandate done by someone not knowing exactly what the combustion cycle needs .. I see a lot of engine failures in their future.

Another related side-note: The wrist pins seem to be made of some seriously tough hardened steel,.. I mean seriously tough ... tool steel can't even hardly scratch one, it is that hardened, so one would think there is no way a wrist pin can fail and get sheered ... HOWEVER... They are only surface hardened, and are soft as butter in the center. I know this very well because I use old wrist pins for making things like collets, spacers, etc. (using my lathe). Once you get past that first 0.008" or so of that super-hardened coating, they are easy to machine.