720 diesel knock

[johndeeregreg]

just bought the tractor with some transmission issues so got it in and tore transmission down, both sides apart flywheel, timing cover, clutch,
pulley, first reduction cover, ect. put it together and now it seems to have a knock that i don't remember it having before working on it. few
things to note

-endplay is at .009 (early style that uses shims to set endplay)
-clutch could use some work floating disks are rather loose on the driver splines and the 3 pins that the friction disks on plate go on are grooved
pretty good.
-knock seems to be worse with clutch disengaged
-tried it with all clutch parts out accept the driver and friction disk behind it
-checked injection pump timing but timing marks on pumps are off or something, if adjusted to line up on flywheel injection mark it pushes plunger
to far and cant roll engine over. as they are now the pump marks line up with flywheel mark on tdc, comparing location of mark with pump on my other
720 at same flywheel position the plunger marks seem to be in the same area in timing window. and it starts right up so i don't think it is timing
issue
-with flywheel bolts at 275 lbs i removed the tin nut and was able to rock flywheel back and forth a little on crank (forward and backward not side
to side), tightened flywheel bolts to 325 lbs and that seemed to eliminate being able to rock flywheel by hand.

what am i missing? or need to check?

 

[johndeeregreg]

should also add that the knock goes away as the engine is speed up, once its around 900 to 1000 rpm it isn't really noticeable.

 

[rlp in Co.]

The first time I heard my neighbors R model I thought it sounded like the rods were knocking!

 

[Dan in Ohio]

Sounds like a loose flywheel to me. If you could move that flywheel when tightened to 275 lbs. it is loose.

 

[coonie minnie]

I agree, if it was rocking a little at 275 lb, there is a flywheel problem. Check out the splines for wear. It may be time for a taper lock flywheel.

 

[buickanddeere]

Time for a taper-loc

 

[DONMYEIL]

You have several problems . Too much end play , should be .005 max . you had the left side apart and now have the timing gears out of time . You say the flywheel was loose at 275 ft. lbs. The flywheel is probably junk and maybe the crank as well. Sounds like the clutch drivers are junk as well and maybe the clutch end of the crank is worn out . Sorry to be the bearer of such bad news but you got took . This will be very expensive to repair even with used parts . Find an old JOHN DEERE mechanic and ask him .

 

[Blksmok]

All the symptoms of a worn crank and flywheel. A "good" flywheel and crankshaft will not have any rotational movement even before you torque it down. Only fix is a taper lock flywheel(~$900). Welcome to the expensive world of JD two cylinder diesels. Many of the 70/720/730 diesels were worked hard and poorly maintained during their lifetime and as a result many are just worn out. They can all be fixed, but at a prohibitive cost.

 

[johndeeregreg]

no i didn't have the timing gears off just had the cover off to work on the transmission. and i did check the timing marks on the gears while it was apart and they were all in register. book says end play should be .005 - .010 i thought i always heard they should be closer to .010 than to .005 because if they are to tight they will knock. i did have it at .004 or .005 the first time i tried it and then added a shim but it didn't change the knock any. the clutch driver seems tight on crank but it does need other clutch work.

 

[johndeeregreg]

if the splines on crank are worn will the taper lock take care of that to? i don't know which splines are worn, crank or flywheel. also why did knock become quieter with clutch engaged? is it because my clutch parts have wear and with it engaged it locks stuff together so it don't bang around as much?

 

[coonie minnie]

A guess it is better balanced with the clutch engaged... that is a definitie "the flywheel's loose" if the knock goes away with the clutch engaged, or under a bit of load.

Contact Allen Machine Works in Jonesboro TN. They were the manufacturer of the Taper Loc. They will likely be the cheapest source. Some of those flywheels used to be available through Worthington, Etc. but sometimes that means you pay the freight on them twice... once to them, and once to you.

 

[buickanddeere]

5 thou is too tight on the crank endplay and risks wiping out the composite material spacers . 10 thou is about ideal.
Flywheels work loose because some Bubba has previously removed the flywheel, re-used the old fasters and did not use a torque wrench . Over tightening the factory fasteners stretches them and the flywheel becomes loose.
Over torquing new grade 5 or 8 fasteners above 300lbft risks breaking a web on the flywheel.

 

[Blksmok]

In my experience, the crankshaft splines and the flywheel splines will both be worn. If you put a good original FW on that worn crankshaft you will eventually have the same problem. A taperlock will fix the problem on a worn crank if the wear is uniform and the splines are not "chunked out". If your FW is not cracked from over tightening, Allen Machine Works (Dave Darr) can rebuild it and you'll have about $500 -$600 (including freight there and back) into it by the time you're done. You should magnaflux it before you ship it to AMW to verify there are no hairline cracks as they will not touch it if it's cracked.

 

[buckeye al]

Over 30 years BC (before computers) I chased this same rabbit outta my 70D. The third time I tore it apart is when I determined it was the flywheel. Sure sounds like it's in the clutch but it isn't. Comes & goes with speed changes. Comes & goes with changes in load. Comes & goes with clutch engaged versus disengaged. Wear was barely detectable with naked eye. Bolts were so tight I twisted the drive lug off of a New Britain breaker bar trying to LOOSEN the flywheel without a cheater. It didn't budge. I didn't even own a torch back then. The Craftsman breaker bar solved that.

Once the flywheel was off there it was. A crack through one bolt bosses just like I think Buick & Deere said.

I'd bet money on it being yer flywheel.

Good luck.

 

[JLG]

My 720 had the same problem as you're having with your pump timing. Ended up figuring out that a previous owner had welded up and reground by hand the cam lobe that fires the injection pumps. Nuts! Hopefully we didn't have the same mechanic. I wasn't impressed with what he did to mine!

 

[johndeeregreg]

ok so i have a line on a used taper lock from a guy about 20 miles down the road that parts out 2 banger's and new gen's. he still has to take it off. anything i need to inspect closely before i hand over the cash for it?

thanks for all the responses by the way, i was afraid you guys would tell me what you did when i saw the flywheel move when torqued down. thats the down side of buying from an online auction from 500 miles away. i think i got it reasonable enough i could still come out on it if i wanted to.

 

[buickanddeere]

Better deal than finding that some Bubba had welded the flywheel to the crankshaft.

 

[David G]

How does the taper lock work?

Is any machine work required?

 

[buickanddeere]

The taper-loc is a clever adaptation of basic physics to jam a high pressure metal to metal tightening wedge between a set of tapered metal surfaces. Plus a mighty amount of sledge hammering and torquing the jam nut with a large wrench with a very long handle.

 

[David G]

Does the flywheel or crankshaft need to be modified for it?

 

[John Deere D]

Flywheel bore has been bored tapered:

Splined tapered wedge fits into flywheel bore:

As Flywheel is drawn up tapered wedge, assembled assembly becomes tight on Crankshaft:

 

[David G]

So it becomes a wedge.

Thanks for posting.