M35A2 Continental Multi Fuel - Harmonic Balancer cracked - why?

[oddshot]

Crank isn't a taper shaft. Its a .001 press fit on the hub.

After looking at the pictures on my computer and not my phone ... That crank is beat up a bit.

Absolutely correct on both counts.

Mayor Joe, From the pictures you posted ... you are holding at least part of your problem in the palm of your hand. That key is wasted ... I'm actually a bit surprised that you got it out of the crankshaft without pulling the front cover, oil slinger (aka, the "second seal") and the crank timing gear off. I just pulled the key out of Andy3's engine (the little engine that keeps on giving). The ONLY way I could remove it from the crankshaft was to remove the timing gear and drive it out with a BIG hammer and heavy drift.

After seeing your key, I would recommend STRONGLY that you do remove the front cover, oil slinger (aka, the "second seal") and the crank timing gear and carefully inspect your crank's timing gear for wear or cracks.

Make sure that a NEW key fits TIGHTLY in both the groves in your replacement harmonic balancer AND that timing gear.

Below are pictures of the key from Andy3's engine. this is what a new/usable one should look like.

 

[G-Force]

Before you go any further, see if you can slide the replacement damper on the crank without the key. From your pictures it looks like your damper has a loose fit on your crank (the rust spots on the crank surface are signs of what we call contact stress corrosion).
If the damper fits on by hand you should really replace the crank. Or drop it and have it spray welded back to standard.
And I tend to agree that your key is shot. And when you get a replacement you will probably find it fits tight in the damper hub but is loose in the crank keyway.

 

[welldigger]

That worn out key is allowing the balancer to shift from side to side ever so slightly when you step on the throttle and let off the throttle. As others have said inspect the key slot in the crank carefully. In fact when you get or make a new square key put it in the slot. If it doesn't fit tightly or if the key rocks side to side at all then you need to have a machine shop fill and recut that slot.

I go through this problem every so many years dealing with twin disk industrial clutches. They have an inner hub that is held in place with a key. When the key and key slots get worn it causes the inner hub to rock on the shaft. Usually this destroys the shaft and inner hub.

 

[Mayor Joe]

Wow - thanks to all of you for the feedback and input. Learned A LOT during this repair.

Soon after my last post, I managed to find the TM (thanks to SS) and found the correct removal AND re-install procedure for the damper. Reading that along with seeing the condition of the key (and keyway), I came to pretty much the same conclusion. I had already ordered a new key and when it arrived, I checked the fit and it was very tight. The new damper would not go onto the crank more than about 1/8", so I felt that was a good sign. However, at the front of the keyway, you could still see a widening to the counterclockwise side (opposite rotation), I realized that the damper must have been moving when torqued and wearing both the key and keyway (as was mentioned by welldigger). I removed the timing cover, oil slinger and inspected the gear and keyway. To address the damage to the keyway (since removing the crank was not a current option), I set the new key in place using Belzona 1100, and filled the area where the crank was worn. I consulted Belzona about the intended use and they agreed that it would serve that purpose. Before the Belzona set, I removed excess to ensure that the damper would not be restricted when installed. This holds the key in place and eliminates the "void".

We polished the exposed portion of the crank, new slinger, replaced the timing cover and seal and then installed the damper strictly following the TM -

1) "HEAT THE DAMPER" and install using welding gloves" - we used an induction heater to get the damper up to about 250 degrees
2) "Lubricate the crankshaft and damper hub" - we used engine rebuilding lube.
3) "Install damper using installer" - while still hot, we used a rod, the retaining washer and nut to slowly draw the damper onto the crank. It was very tight, but went on VERY smoothly.
4) I made a 'key plug / seal' out of EDPM rubber and installed it in front of the key (saw that on the TM blow up, but no one sold it).
5) We removed the rod, installed the retaining washer and bolt and torqued it to the 250 ft lb spec.

In my opinion, the damper installed before the one we installed four years ago was likely not installed correctly, leading to all of the conditions mentioned. When the one was installed 4 years ago, the key was not replaced, the damper wasn't lubricated or HEATED when installed, therefore the problem never got solved. I certainly can't / don't fault the friends who installed it 4 years ago, because in all of my conversations, no one seemed to disagree with how it was installed - even some serious diesel mechanics. None had heard of the need to lubricate AND heat the damper. Had I not taken the time to research the TM for both removal AND install, this would not have come to light - and we would have installed it wrong AGAIN.

Anyway, all in all, I'm VERY confident that we've minimized the condition and I'm certain that this should hold up a long time (last one held up for 4 years). I now have a replacement engine LDS465 - which would minimize my down time. Then I can rebuild the LDT, repair (or replace) the crank at my leisure (what's that?)

I truly hope that this information helps someone sometime.

Once again - THANK YOU ALL for your thoughts, comments, recommendations. I take these VERY seriously. I truly enjoy the honor of working on these Veterans and proud to be a part of the MV world and appreciate that there's a group of people out there willing to help in any way.

Be well - be safe!!

 

[Katahdin]

150 pound feet.



G.

I am replacing the harmonic balancer on my M109A3 and thought I should report there is an updated torque value. Per the May 1981 edition of TM 9-2320-209-34-2-1, page 2-114, the retaining bolt should be tightened to 225 to 250 pound-feet.

That is all, carry on!