Large Model Association Forum

I have been running this engine for more than 6 years with no problems but after a bad arrival it developed a knock, which turns out to be crankshaft loose in the crank disc.
Anyone know if this can be repaired?

Pic attached

If the bore is in decent nick, the end of the shaft with the flat could be ground in the flat area, a bush made to put the fit back, cut away in the flat area, so the flat locates in the crank web, but i feel the shaft and its relative location may be worn out, nothing can be done with the crank web, without a lot of setting up and machining i dare say there is a woodfuff key on the taper on the front of the crank? Alternatively, tig weld it back in after weld prepping the crank web and the shaft wirh a decent chamfer, it would need a bush making to slide the shaft in, and sit the crank web against to hol it square, Its this, or its a boat anchor

Thanks Alan, would silver solder flooded in hold it?

No, too soft, braze will hold it, but the heat needed will soften the shaft, tig is direct, but i am not a welder, perhaps another could chip in here? Whats the crankweb made of? It looks cast, and i bet the crank location is cast as well, if theyvare both steel, your in with a chance, but as i said, a bush is needed to take tge crank, and sit against the crank web face, to hold tge assembly at 90 degrees to each other, i can do the bush, and the weld prep, but thats about it

No, too soft, braze will hold it, but the heat needed will soften the shaft, tig is direct, but i am not a welder, perhaps another could chip in here? Whats the crankweb made of? It looks cast, and i bet the crank location is cast as well, if theyvare both steel, your in with a chance, but as i said, a bush is needed to take tge crank, and sit against the crank web face, to hold tge assembly at 90 degrees to each other, i can do the bush, and the weld prep, but thats about it

Could both parts be turned til round then a bush fitted the axial pins fitted between each part say 4mm? Crank web looks cast will it turn ok?

If there is a woodruff key then the angle between it and the flat is critical for ignition timing.

The is a woodruff key but the ignition is electronic and fully variable, the pick up can rotate full 360

The critic is the flat, it will be there for a reason, do you mean drill through, and pin the parts together? I dont think thats doable, the shaft will/should be hardened and ground, the crank web is cast, no doubt, but cast out of what is the question, i doubt its cast iron, my moneys on steel, with the bores for the shaft and conrod being machined in,

What size boat then???

If the clearance is not too big, is it possible to hard chrome plate the end of the shaft to give a small interference fit, then use a freezer and oven to shrink fit the parts together.
On the other hand , with the rain we've had today maybe the boat option is the way to go

Gave up on the boat so started a repair! I have turned the end of the crankshaft down to 8mm then made a bush and pressed it on. Now got to figure out how to bore out the crank web? Maybe just set it up in a 4 jaw and go for it.

Would it be possible to use an adjustable reamer Barrie? Just a thought.

Tony

Hi Tony, there is a flat in crank web hole so I need to remove the flat first before getting the bore true.

If you were going to go in that direction, you should have put the shaft into the web and set the diam true right next to the web,
Not sure you have gone in the right direction with this, 8 mm is a tad small in the main area it were all the stress is generated, but best of luck wirh it Barrie

Thanks Alan, 8mm was the biggest diameter I could get and remove all the flat, that's why I went that small. With the web is it best to spin the web and bore it or mount the web fixed and then use a milling cutter?

Put it in the 4 jaw, clock the bore as best you can, then clock the face and then the bore again.

A note on shrink fits using hot and cold.

Liquid nitrogen will give 1 1/2 thou per inch shrinkage ( -200 degrees)
Dry ice will give half of that
Iron and steel can be heated to 200 degrees without effecting the hardness, again .0015 per inch
These are rough rule of thumb values.

On 8mm (1/3 of an inch) you can get 1 thou by having the parts at + and - 200

Theres not a lot of meat on the web, dont go mad with the boring, interesting notes on the shrinkage off Steve above, but you have to ask yourself, do you have nitrogen and a heat source? Or will it be the freezer for one, and the oven for the other? If i was boring it, i would leave the 4 jaw out of it, and bore some soft jaws, and maybe pack one jaw out, but do you have a set of soft jaws for your chuck? If you go the 4 jaw route,do as Steve suggests, its important to go back and forth with the clock, as it squares the face to the bore, Use the tailstock barrel front face against the crank webb to square it up, never fails! I personally would have gone with the alignment bush, and welded it, but hey ho, too late now, I wonder if todays so called engineers could come up with a way of repairing this sort of thing? I doubt it!