Crank Thrust Surface Trouble

[chimpvalet]

I've a nodular iron crank for an inline 4 cyl that's perfect in all bearing surfaces except the thrust flange. Damage to the flange arising out of oiling or assembly issues was discovered on disassembly and has been ground out leaving a thinner flange by perhaps 0.080". It looks just a little sketchy to my eye but might hold up to clutch loads. Other thoughts are welding up the flange ( thermal fractures to consider ), or adapting a different main bearing with integral thrust faces bearing up to a crank throw. Any advice?

Steve

[ProPower engines]

I've a nodular iron crank for an inline 4 cyl that's perfect in all bearing surfaces except the thrust flange. Damage to the flange arising out of oiling or assembly issues was discovered on disassembly and has been ground out leaving a thinner flange by perhaps 0.080". It looks just a little sketchy to my eye but might hold up to clutch loads. Other thoughts are welding up the flange ( thermal fractures to consider ), or adapting a different main bearing with integral thrust faces bearing up to a crank throw. Any advice?

Steve

What engine??

[BCjohnny]

Unless it's unobtainium, or had a lot of money invested in it, bin it and use another one.

[clshore]

Does this motor use the C shaped half moon thrust washers, or are they integral with one of the mains?

Triumph use half moon TW, and they are problematic, but you can get solid bronze replacements in desired thickness:

http://customthrustwashers.com/

It's not hard to make replacement half moons, but for the price, avoids the time and trouble of DIY.

[allencr267]

Does this motor use the C shaped half moon thrust washers, or are they integral with one of the mains?

Put a shim behind them if separate.

[Dan Timberlake]

How are you reducing crank end play, and restoring fairly accurate axial positioning?

As far as keeping the problem from repeating, is this a standard shift application ? Driving habits of Prolonged clutch release has killed more than one steel crank thrust bearing.

Nodular iron has the rep of requiring very specific finishing to achieve good results even in full hydrodynamic conditions, which the thrust bearing is not.
http://www.stealth316.com/misc/clevite- ... polish.pdf

[wyrmrider]

you can chamfer the mains parting line from the oil groove back to get some additional oil flow
and drill through the thrust (about .060 and make a pocket) then about .040 through the main web into the oil feed
for pressure oiling
IMHO the thrust pushes against the crank so the oil gap on the front is much bigger and easier for the oil to go that way than to oil the thrust

[clshore]

Does this motor use the C shaped half moon thrust washers, or are they integral with one of the mains?

Put a shim behind them if separate.

Most half moon TW are steel backing with a thin layer of bearing material.
That construction works well with the mains and rods, since they operate mostly in full hydrodynamic mode with an oil film between, and actual contact is rare.

But TW seldom operate in full HD mode, and contact predominates, leading to wear in actual service.
Once the thin layer of bearing material is gone, you have steel-steel contact, not a very good combo.
So a solid bronze TW is really a more durable solution.

A shim might work OK, but OP was talking about 0.080" additional clearance.
Takes about the same work to make a shim that thick as a solid TW.

Also, how is the TW retained?
Many just sit on the bearing cap ledge, if the shim is too thick, there's nothing left to hold the TW, unless you connect the shim and TW together.

[robert1]

here's a repair I did on a SBC a few years back.

[clshore]

Yup,
looks nice.
I prefer to use brass flat headed screws, JIC the washer gets worn down, avoids steel-steel contact.

You can get cored bearing bronze by the inch from usual metal suspects, use lathe to turn ID/OD to size, use a parting tool to slice off thickness you need.
Cut ring in half, voila, TW set!

[chimpvalet]

Glad to read so much response, thanks all! The motor is a Lotus 910, using the Vandervell half-moon shaped thrust bearings. The oiling mod chamfer remedy was distributed by Lotus in a TSB some years ago and I've so noted the need for that. The car is an Esprit, so standard trans only. The custom bronze bearings are something I'll look into for sure, stock retention is by way of a relief fly-cut into the #5 main bearing saddle in the block, the bearing then blocked in place once the lower half bearing support is brought into position.
Steve

[chimpvalet]

To ProPower and BCJohnny, the stroke increase provided by this crank is good for quite substantial gains in torque curve by all accounts. Rather costly to replace these, as well, hence the desire to see if worth salvaging. So beyond the return to dimensional spec in all aspects pertaining to the thrust bearing mount, and perhaps obtaining better bearings there's also the question of adequate meat remaining in the crank flange that takes the thrust load. Anyone care to suggest what would be a minimum acceptable thickness for the flange at it's base on the journal's edge? As said, there was metal taken out in cleaning up the face. Is it the consensus not to weld up that surface if judged too marginal for the job?
Steve

[ProPower engines]

To ProPower and BCJohnny, the stroke increase provided by this crank is good for quite substantial gains in torque curve by all accounts. Rather costly to replace these, as well, hence the desire to see if worth salvaging. So beyond the return to dimensional spec in all aspects pertaining to the thrust bearing mount, and perhaps obtaining better bearings there's also the question of adequate meat remaining in the crank flange that takes the thrust load. Anyone care to suggest what would be a minimum acceptable thickness for the flange at it's base on the journal's edge? As said, there was metal taken out in cleaning up the face. Is it the consensus not to weld up that surface if judged too marginal for the job?
Steve

If its a steel shaft and an under size bearing is available then just have it welded and re-grind to needed dimensions of the std thrust bearing.
Since this seems to be problematic the thrust material repair may be as suggested and use a more suitable material machined to fit the cap and add the extra lube hole to avoid doing this again.

[clshore]

The thrust load is almost entirely due to clutch plate pressure when pedal is depressed.
I can't see that as more than 400 lb, but you could measure it easily enough.

The point being that it's not a major load, and doesn't have a very high duty cycle.

If you fit solid TW, it's unlikely to see any significant wear in the future, I'd not weld it at this time.

[Dan Timberlake]

Hi ChimpValet,

Is this what you crank looks like, with the worn thrust face being the "front" face of the now 0.08" thinnner flywheel flange?
https://zhvmsq.bay.livefilestore.com/y1 ... CF9383.JPG

Do you know the operating history to understand why the thrust surface wore so badly? Prolonged time depressing the clutch is my guess. I imagine once the surfaces deteriorate at all the wear just takes off.

To make a thrust bearing hydrodynamic tricks must be played with the geometry. Industrial thrust bearings have tilting pads and carefully placed oil inlets to form a hydrodynamic oil wedge, which is necessary to support a thrust load for very long.
http://www.tpub.com/machines/1.htm159.gif

Adding insert edge chamfers for oil flow might help, but I think details like tapered pockets in the bearing thrust face likely help a lot, since stock bearings often are pretty featureless.
http://www.stealth316.com/misc/clevite- ... arings.pdf
And surface finish and direction of polishing really count when the going gets tough.