Hi all -

I'm replacing the crankcase on a used .46 LA due to worn mainbearing - is a break-in procedure necessary?

Thanks.

Terry

Hi all -

I'm replacing the crankcase on a used .46 LA due to worn mainbearing - is a break-in procedure necessary?

Thanks.

Terry

   Probably, to the extent break-in is "required" on any of these engines. Actually I would be quite interested in your results. I think almost all of the high fuel consumption at the beginning is due to the front bearing being too tight, and rapidly opening up when you first start running it.

    I would be particularly interested in any observations you might have on how warm the bearing area gets. When I started running my 25LA, the venturi and front of the case got very hot, and the fuel consumption was absurdly high. Over the next 20 runs or so, this went away, the venturi and bearing area stopped getting hot, and the fuel consumption  went down dramatically. The first 2-3 runs were particularly notable, but the engine was going richer and richer during flight over maybe 20-30 flights. It's steady as a rock now at about 50 flights.

   Of course you probably don't really need to break it in to avoid damage, it's safe enough to fly as long as you are aware of the issues.

     Brett

Maybe it was your crankshaft that was worn?  Or both crankcase and crank?  I usually break things before they wear out, but I'm pretty sure that if there was grit involved, both case and crank would have material removed.

The shaft front measures .4714", rear .470" with a few 10-thou of ovality.
The new case bearings measure .473".
Not much help without knowing factory specs though.

I'm thinking maybe it's just whatcha get from O.S.
My .20FP and .25 FP have discernible sideplay too.

Oh well - they run well enough right now.

Terry

I have had several LA series engines that were tight in the crank  / crankcase dept. Most of them wore (er I mean ran in) pretty fast. However one particular engine was still a bit tight when the P/L had worn out. It was fine after a little running on a new P/L. That is definitely a very rare case indeed.
Yes you would think that the sleeve bearing would wear out first. However this is not the case. Any nasty hard bits get embedded in the softer bearing material and this acts as a lap on the shaft. Thus it is usually the shaft that wears, especially if the engine has been lawn darted.
If I remember the storey correctly, the camshafts on the Merlin engine ran straight in the block material, i.e. there were no camshaft bearings as such. I think the engines could be rebuilt four or five times before the block was scrap due to too much clearance in the camshaft holes.
Yes it is counterintuitive, before you realise what is going on.

Andrew.