Jubilee Crank Gear - Replace or Reuse?

Mdparrott · Sep 4, 2015

Question for the Gurus....

So I get my replacement crank back from my other machine shop (replacement REPLACEMENT crank). MUCH better than the other crank my FORMER machine shop reworked.

The current crank has a much less worn gear on it that cleaned up nicely. I was going to reuse the original timing gears together as the weren't worn that bad. I figure at 61 years old they'd probably outlive me. I've always heard that you want to replace gears together.

Question... Would you reuse the gear that came with the crank I bought that has less wear? Would that hurt anything to put it with the reusable cam timing gear? Thoughts appreciated.

TIA.

Hobo,NC · Sep 4, 2015

That's a tuff question there is always the possibility of gear noise new are used... I would prefer to use a matched (if there is such a thang) set and not mix and match but nether would rule out possible gear noise... BTDT one time on a chevy 6 cly I had to install a new set even tho I could never see one thang wrong with the old set...... Its was a whiner

the bad it was my own chit I did not get paid either way I went...

You will have to make the call, new would be the best but I would use a used set if they look good...

Royse · Sep 4, 2015

Judgement call I guess.
If money permits I would go all new.
From my days of chain driven motorcycles, I don't put new
chain on old sprockets/gears or one mis-matched sprocket/gear.
So, my second choice after new would be to reuse all from
the original if they are in decent shape.
Your mileage may vary of course; dirt bikes in the sand may
live a harder life than your lubed timing chain will see.

Tall T · Sep 4, 2015

Now there's a new one on me,
a timing chain on a Jubilee.

Royse · Sep 4, 2015

(quoted from post at 22:30:01 09/04/15)
Now there's a new one on me,
a timing chain on a Jubilee.

ReallY?

Chain (noun) "a series of things linked, connected, or associated together"

Not a physical "chain" with links, although I can see how the
motorcycle reference could have confused the statement.

Tall T · Sep 5, 2015

Ah, you're British!

but still, never heard a timing gear array ever called a chain.

ASEguy · Sep 5, 2015

I would reuse the best old set. Gear to gear camshaft drives last a long time especially in an old tractor.

Ultradog MN · Sep 5, 2015

Interesting question.
I wouldn't buy new for sure.
Probably use the best of what was there.
They are very simple helical gears so I would have no problem mixing and matching.
Very different than a ring and pinion that you want to replace as a set.
Wear on ignition timing is adjusted by the distributor so no issues there.
Of course wear can cause some change in the cam timing. But since the valves are open like about 120 degrees,
a degree or two change in timing caused by wear won't make a lot of difference in performance on a low reving old tractor.
On a race engine it would/could be an issue though.
Consider also that many modern engines use OH cams and rubber belts. With a belt there is the potential for a Lot more stretching and
changing the cam timing than there is in your old gears. Same with worn timing chains. And those engines run a lot faster than yours does.
I would put it back together and not give it another thought.

NoNewParts · Sep 5, 2015

I would use the best of what I had after inspection.
With gears, checking the teeth for wear and burrs,
and more importantly the fit, and condition of any key slots.
after assembly, I'd get my nose down there and check for mesh/climbing while turning slowly.

probably just a personal superstition with me, I always consider
the crank gear part of the crank, and keep them together.

Mdparrott · Sep 5, 2015

Thanks for the input, fellas. Kind of what I was thinking given it's a low RPM engine but wanted to check.

The gear on my "new" crank was in surprisingly good shape but so was the crank. The salvage yard guy said when he removed it from the engine he saw "1972" on the bearings. Almost didn't even look like it needed to be turned, just polished. In surprisingly good conditions, a real good find.

I'll post pictures of the two side by side.

Royse · Sep 5, 2015

"but still, never heard a timing gear array ever called a chain."

Admittedly not the best choice of words in this discussion.
I could have called it a train with better understanding.

Tall T · Sep 5, 2015

Md

One thing I liked about a GM 235 that I have and rebuilt, was that the camshaft timing gear had a bakelite center and hard fiber teeth that made for easy mating with the same crankshaft gear and made for potentially quieter running.

Personally, if I were installing another crankshaft gear, I'd probably go with a new Jube camshaft gear and let it mate to the replacement crankshaft gear.

T

Edit
Not so much because of gear tooth wear but because of the new lay of the crankshaft and its plane of rotation

TheOldHokie · Sep 5, 2015

(quoted from post at 16:59:10 09/04/15) Question for the Gurus....

So I get my replacement crank back from my other machine shop (replacement REPLACEMENT crank). MUCH better than the other crank my FORMER machine shop reworked.

The current crank has a much less worn gear on it that cleaned up nicely. I was going to reuse the original timing gears together as the weren't worn that bad. I figure at 61 years old they'd probably outlive me. I've always heard that you want to replace gears together.

Question... Would you reuse the gear that came with the crank I bought that has less wear? Would that hurt anything to put it with the reusable cam timing gear? Thoughts appreciated.

TIA.

This is not rocket science and the gears can be replaced individually or as a pair. The main issue is excessive gear lash caused by wear on the sides of the gear teeth. All gears wear in service and that is something you should always measure when rebuilding the engine and correct if needed. In your case use the combination that has the least lash. If they are both worn to the point where they have excessive lash (more than about .010-.012) replace them with new ones - roughly $110 for the pair.

TOH

Mdparrott · Sep 6, 2015

How do I measure gear lash? Feeler gauge?

Tall T · Sep 6, 2015

You can use a feeler gauge. Clearance between the teeth of a new PAIR of gears should be between .002 and .006. the same desirable clearance goes if the cam gear is new and the crank gear used.

If tooth clearance is satisfactory you can use a dial gauge (like in OldHok's photo) to check for excessive runout. It is a slight wobble which makes for noisy gears. If the runout is more than .004, check the crank gear hub and camshaft end for burrs. The runout of the crankshaft gear shouldn't be more than .003.

More rocket science.

T

TheOldHokie · Sep 6, 2015

(quoted from post at 12:25:44 09/06/15) How do I measure gear lash? Feeler gauge?

Gear backlash is the pitch diameter clearance between the teeth of the gear. For used gears it will vary depending on the relative position of the gears (e.g wear is not even) so you should measure at multiple locations. You can use a feeler gauge to get a good approximation or a dial indicator as shown in the image to get a more accurate measure. It has nothing to do with run out.

TOH

Jubilee Crank Gear - Replace or Reuse?

Mdparrott

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