Flywheel ring gear question

XK
21

Looks like I’m headed down the same path Morris.
I’ll start with the 133 Flywheel and M45 starter, and bench test them before I install the engine.
The high-torque is the back-up plan.

Thanks to all for the info and advice.

22

I put a Fidanza in a few years ago and it’s really very good. My 4.2 revs like a Ferrari and no issues with stalling as these cars are light. On a 3.4 it would work even better. They are beautifully crafted.

23

I got my Fidanza flywheel a few days ago and I think there’s a problem. The bevel on the ring gear teeth is on the front (crank) side of the flywheel. Of course, my starter engages from the rear. I wonder if it is possible to just reverse the ring gear?

Tim

24

I have to comment You are fitting a Fidanza flyweel and worried about one correct nut on upper wishbone? regards terry

I am missing one of the C3320/5 1/2-20 ANF “Philadas” self-locking nuts for the upper wishbone shaft on my '51 XK120. Does anyone know of a source for these, or perhaps have a spare lying round that they are willing to part with?

25

Fair question. I am doing everything possible to keep as much originality as I can. My extreme preference would be to use my original 6-bolt flywheel. But I cannot find a ring gear that will fit it and replacement 6-bolt flywheels are simply not to be found. So far, the flywheel is the only concession to originality on the car. I would prefer to keep it that way if at all possible.

Tim

26

an 10 bolt flywheel will go onto a 6 bolt crank and you should be able to get one quite easily 132 teeth

1 Like
27

There are two XK120 flywheels on ebay right now…

28

Just to close the loop on this thread, I opted to send the Fidanza flywheel back and attempt to repair the ring gear that I had. I elected for this route after determining that the ring gear is not hardened - at least not hardened enough for a file to skate. The teeth were chewed up in two locations - the the two spots that the engine tends to naturally fall to when shut off. I restored the teeth by touching them up with the MIG and then some careful filing. I also clocked the ring gear 90 degrees from its original position so that the engine will tend to stop with fresh, unmolested teeth at the starter location.

It is also worth noting that the starting bushings are toast. There is probably 1/8" of radial play at the drive gear, and the starter was probably camming out of the ring gear as a result. So a starter rebuild is also on the agenda.

It will still be several months before the engine goes in so I won’t be able to judge the effectiveness of the repair, but my confidence is high.

Thanks for the help everyone.

Tim

29

Hi Tim,

Just read your posts and I want to make several comments.

You say that you clocked the ring gear 90 degrees from its original position. Did you somehow remove it from the flywheel and reposition it? If you moved the flywheel on the crank, that causes other issues.

If you look at the recent topics, we dragged up an old chestnut about gear reduction starters. Sounds like your original is clapped out and caused the tooth problem along with being a bad design to start with.

These new starters engage the front side of the ring gear where the teeth are pristine and you will never have another problem with it. No one will ever know as it is down in a dark recess of the engine bay. They sound like a Toyota, but spin faster leading to easier starts.

John Brady
678462

1 Like
30

Thanks John. When I say that I clocked the ring gear, I mean that I removed the gear from the flywheel and turned it 90 degrees. Obviously the flywheel is out of the car, as is everything else. The car is currently a bare chassis.

I want to see how well the factory starter works after a rebuild before I try an aftermarket starter but will do so if I have to.

Tim

31

Right. You can’t move a normal flywheel 90 degrees, only 180

But every original Jag XK flywheel I’ve ever seen is steel with integral teeth, no removable ring gear. The teeth don’t need a major chamfer if the pinion has a decent one.

32

True enough, but as I said in my original post, at some point in its past, this flywheel had the original teeth milled off and a replacement ring gear fitted.

Tim

33

By turning 180 degrees are you not messing up the balance of the crankshaft.

34

They are all balanced to zero I think.

Crank - balanced
Add flywheel - balance again and stamp ‘B’
Dampers are all zeroed before fitting so are interchangeable and not numbered

Clutches should also be balanced pre-fitment but my shop balances those too and marks flywheel and pressure plate for correct reassembly.

35

Hi
My name is Phil Wood , i am known as the Ring Gear guy in New Zealand.
Just to add my bit to this conversation if anyone is still interested .
I have rebuilt several XK Flywheels by machining the worn teeth off and shrinking on the correct replacement 132 Tooth Ring Gear (#270) which is an old Repco Australasian Part Number or C4809 which is the original British P/No.
If anyone is still interested you can contact me.

1 Like
36

Welcome to the loony bin!

Back in the day, when I ran a shop, for those cars that had machined-onto-the-flywheel ring gear teeth, I did the same.

1 Like
37

yes Repco an Australian Co dating back to the very early 1950’s made replacement ring gears long before anyone else in the world and I am suggesting maybe late 1950’s as it was a surprise that one of the LHD XK’s we brought over from the USA had a REPCO replacement ring gear!
Are you an XK owner?
terry