Yanmar Crankshaft

[Castaway]

Hope to gain some knowledge about the counterweight assembly below the crankshaft on a Yanmar 4TN84-RJK.
We have a 1997 John Deere 1070 that has spun a rod bearing. After a failed seach for a replacement crank, we found a complete surplus engine with zero hours. Both new and old engines are 4TN84, but the new one has no counterweight assembly, or gear on the crank to drive it if we were to transfer from the old engine.
What differences should we expect?
Should this effect anything besides vibration?

[Wayne County Hose]

How about getting the rod journals cut and the rod journal honed back to circular? There are plenty of automotive engine shops that do this everyday.

[Castaway]

Thanks for the reply, That was our first plan, however #3 journal would take over .40 to clear and bearings are only available up to .25. We have even looked into having it built up then cut back down. But that is no longer recomended.
We have this new engine and plan to go thru with it. Just wanted some incouragement from someone familiar with this situation.

[RobJ]

Who didn't recommend building back up the journal. With a good shop there is nothing wrong with this...remember the bearing never touches the crank journal... I'd find a shop that does the larger diesels and talk the them. It's a cool process I've seen done once. They heat up the journal then spray on some powdered metal. then grind it down.

Those cranks and weights are factory balanced, you might have more trouble finding someone to do that that build up the journal.


Good Luck,
Rob

[sandman2234]

And if you want to try that build up process at home, i have the equipment. Looks like a smith torch with a weird box of powder sitting on it.
David from jax

[sandman2234]

Seems like a good automotive shop that specializes in balance of auto engines could give that missing balance a run for it's money. After all, it is just a weight hung in the right place. Not something that far beyond the ability of a good engine shop. Sounds like you have two options now...
David from jax

[Wayne County Hose]

Holy smokes, what we've done to crank journals on the race cars. You can move the journals by welding on metal and machining it off. I know you were looking for info on that motor swap, but adding material onto a crank journal is common on very high horsepower race engines. It's a piece of cake for your application.

[Castaway]

Somehow we have gotten away from the topic. Without being familiar with a counterweight assembly, it is hard to comprehend what it actually is. My question was not how to save the old crank. I have 5 years working in a parts house with machine shop, and 20 years in trucking while doing most all my own repairs, and hobbyist of Hot Rods building several race motors, and general motorhead.
The old crank is not to be saved. The new engine's crank does not have the gear built into the throw of the second journal that drives the counterweight assembly which is actually mounted inside the deep oil pan below the crankshaft.
I do appreciate everyone's input and I am familiar with the methods mentioned. The new engine is already purchased, zero hour, surplus engine, so my only concern is, if anyone else had incountered this, what should I be on the lookout for ? Thanks Again

[RobJ]

We'll I'll go again on topic. I reread everything and the new engine does NOT have a counterweight inside...correct?(this is like an opposing camshaft if I recall). So that might tell me it was designed for a much larger flywheel to correct this or it is not made to run at low rpms like a tractor is (say idling or throttle changes, FEL work, etc).

When I worked on engines 1 engine model could have several different specs. This could different pump specs, block drilled for external pump, etc.

But ours did not have an internal counterbalance shaft. About all you can do is give it a go.

Or, and I hate to say this, fix the old crank and install it in the new engine.

Let us know how this comes out please.

Good Luck,
Rob

[dfkrug]

Castaway:

I am a bit surprised that your 1070 has a balance shaft, which is designed
to counteract some of the rocking and/or rotational vibrations. At only
about 2-liters and with the heavy flywheels I see on these tractors, I
would not expect a balance shaft. The 3-cyl JD motors don't use them
and they are not as inherently balanced as a low-displacement 4-cyl is.

Anyway, I think RobJ has hit on the reason. The new engine you
bought may be designed for a different application. You did not say if
it came with a flywheel. Maybe the intended application is something like
a generator where some additional vibration is more tolerable?

If your new engine DID come with a flywheel, my inclination would be to
use it as-built. The old engine's flywheel may not work well on it.

(As and aside, I have not had a problem finding a machine shop to
balance a crank, one-cyl or 6-cyl.)