My early XK120 has the fairly rare 6-bolt crank/flywheel. A previous owner had apparently fitted a new ring gear, but it has a few mangled teeth. I ordered a replacement ring gear, but it has an ID that is significantly larger than the OD of the milled land for the gear that was on the flywheel. I can’t seem to find the correct ring gear anywhere. It seems like they are all the same part that I already got. A couple of places that I called even seemed baffled that some flywheels are 6-bolt.
So, I am at a bit of a loss as to what to do next. I am open to replacing the flywheel, but I can’t find a 6-bolt type anywhere. One last resort option is to weld up and then file to shape the offending teeth. I can then also turn the gear when re-installing it so that the starter lands on a different spot on the gear. But my preference is to do it right and that doesn’t sound “right” to me.
Install a high torque starter. It comes at the ring gear from the opposite direction.
Moving the gear 1/3 way around is accurate. You can also have the teeth welded. No, they aren’t spanky-new but if you turn the gear or use the high torque starter those repaired teeth aren’t getting pounded as in the past.
A high torque starter is not a preferred option. I want as much of an original restoration as possible, warts and all. I’m not sure that coming at the ring gear from the opposite direction is a good solution. I gave some fleeting thought to just flipping the ring gear with that same thought. However, the rear side of the ring gear has beveled teeth. I can imagine that the flat faces of the unbeveled teeth would cause the starter gear to crash into them.
another possible solution might be o fit a ring gear from a 60s sedan (larger teeth ) and use a later starter and drive (looks very similar to original starter ). ??
Just double check the pcd of the bolt holes but I think the ten bolt flywheel fits straight onto the six bolt crank.
My six bolt crank is fitted with a ten bolt flywheel. I haven’t done the rebuild, only the stripdown so I am not sure if any other changes are required.
The six bolt has the bolts at 60 degrees, with two pins at 30 degrees from the bolts. The 10 bolt has the bolts at 30 degrees with the two pins also at 30 degrees. So far so good.
Now how about all the other dimensions, diameter of the recess, diameter of the teeth, depth of the recess, etc. If all are the same, then a 10 bolt flywheel ought to fit. 132 teeth Mark VII and Mark VIII are ok. I have one here to measure if you want to compare dimensions.
Beware of using one from a small saloon, as I recall this has been discussed on this forum, and people found they are smaller diameter on the teeth, identified by fewer teeth.
But if it was me, I would weld and hand file the old teeth. You’re not going to wear it out again. Tooth wear is caused by attempts to start with a low battery, or rust on the Bendix drive shaft.
Thanks Rob. I’ll take dimensions off of mine and post them for the benefit of others. If you have time to confirm that your dimensions are the same, so much the better.
