Main bearing clearances on 819 engine

[LanciaFin]

Finally got to assemble my Flavia engine. The crankshaft was checked and polished by a machinist shop, and according to them, was good for standard bearings. However, after checking the clearances with Flexigauge, I got a clearance of about 0.075mm from all three main bearings. According to the technical data manual, the standard clearance for front and centre bearing is 0.020...0.047mm, and the wear limit 0.065mm. For rear main bearing the clearances are 0.020...0.035mm and 0.050mm.

Should the main journals be machined to undersize bearings, or are these clearances still ok? The oil pump has new gears and the big end bearings were all about 0.050mm or less, which is ok.

[LanciaFin]

Well, as I don't have a suitable micrometer, I measured the journals with a caliper. For front and center I got 59.98mm and for the rear 60.00mm. So as far as we can trust to the caliper, the journals should be well within factory specs. That would mean, that it's the bearings, that are not within specifications. They are Glyco-brand, new old stock.

The clearance of 0.076mm (0.003") seems to be a common recommendation for older American V8-engines with same main journal diameter, but is it ok for more refined Lancia-engine?

[lucasgeheniau]

A Caliper is for measuring +/- 0.05 mm, also when it has a digital reading. You should use a micrometer.

[racing]

In this case don t take a risk. Buy a micrometer. It is not as extensive as an destroyed engine.
With this claerence you are on the wrong side fore sure.
Regards Andreas

[LanciaFin]

You're right about the micrometer. Fortunately I found one from this city, and measured the journals. The front and rear were within tolerances (front at lower limit, the rear in between limits), but the middle one was under the tolerance for some 0.01-0.015mm. However, when the clearance measured with Flexigauge is added to these measurements, the result is, that the diameters of the new bearings are over tolerances for some 0.01-0.02mm.

Either the new half-bearings are thinner than they should, Flexigauge is not reliable, or the engine blocks don't meet well enough (the bearings stay oval.) I tried measuring the thickness of the new and old half-bearings (from the end corner where they are not worn), and it looked like the new bearings were 0.01-0.02mm thinner, but there may be some tar on the old bearings distorting the measurements.

So, to be sure, I'd need to measure the diameter and ovalization of the main bearings. Not possible without internal micrometer (which are harder to find from here.)

The mating surfaces of the engine blocks look clean and intact - I have cleaned them as much as possible without abrasive methods. Has this been an issue with other engines, or is there something I may have missed? Of course I did tighten the bolts to the specified torque.

[racing]

I have bought an inner diameter for an accepteble price in GB.
Have to look for the adress .will inform you soon i hope.
Maybe the innerdiameter of the housing is out of tolerance. Do not expect
that the bearings are oval. The middel bear will get the max load.
Regards

[racing]

http://www.machine-dro.co.uk/bore-gauging.html

look at this side.

Mayby you can go to a workshop and let them measure the crankcase bearings.

regards
Andreas

[LanciaFin]

Thanks for the link! I've already bought an internal micrometer from Ebay, just waiting for it to arrive.

[LanciaFin]

It is the bearings. All of them have a diameter of 60.05mm or a bit more, no matter how many times I measure them (even triple-checked the internal micrometer against an external one - matched every time!) Lancia & C. has given the tolerances of 59.987...60.014mm. If the bearings would meet these tolerances, the clearances would be perfectly within specifications. Well, apparently it's time to start shopping new bearings yet again.

[LanciaFin]

Oldtimer-motorenteile did not have bearings for me, but they kindly supplied me with data of main bearing housing diameter and thickness. The diameters were within tolerances, but my Glyco-bearings had 1.81mm thickness, when the specification is 1.828mm. With the specified thickness I'd get correct clearances for all journals.

I think there have been standard bearings with different thicknesses. With a journal on upper tolerance and bearing housing on lower tolerance, the clearance with my Glyco-bearings would be just about in the middle of the tolerance.