Crank end float - again!

[Colonel Blink]

I know this has been discussed many times, but please bear with me....

I have done a fair amount of trawling through these fora, and it looks like G80/Mod18 crank end float is generally given as 0.020" min, with apparently a 'rough max' of 0.025" but with many saying not to get too hung up about it within reason. But it is this 'within reason' where my initial question lies!
My crank looks like it has about 1mm / 0.040" of float (though I've only measured it with a steel rule so far). Ken Bryant's excellent article says excess endfloat can cause oil pump wear, and indeed my oil pump does show this.
So what to do? The obvious answer is a simple 0.5mm shim on the timing side axle, yet the same article says not to use a steel shim but does not clarify why. I have no access to machining facilities so can't make up a spacer from phosphor bronze as recommended.
Why would using a steel shim loctited to the crank cheek be so bad? And if it is a no-no, then is it possible to tap the inner drive side bearing inward a little as a viable alternative in order to reduce the end float? It is a 1952 model so the drive side bearing is fixed axially.
Grateful for any help/advice/experienced views!

[Joker_Bones]

And if it is a no-no, then is it possible to tap the inner drive side bearing inward a little as a viable alternative in order to reduce the end float?

I assembled a 1955 G80 engine recently and that is how I set the end float.

This extract from Neill's book sort of covers it.

float1.JPG

float2.JPG

I heated the crankcase to fit the two drive side bearings with the spacer washer between. While the case was still hot the spacer moved freely between the two bearings but as the case cooled the spacer became tight between the bearings and the bearings stiff to rotate.
I wondered how tricky it was going to be to move the inner bearing back a little.
It wasn't too bad... I heated the case back with a hot air gun and you could just get a drift on the inner shoulder of the inner race and tap it back. The tricky bit was getting to finish up exactly where you wanted it to give the desired end float. I ended up tapping it too far and then squeezing it back with a puller.

[Joker_Bones]

IMG_20230723_134532~2.jpg

I ended up with 0.017 end float.

IMG_20230723_162818.jpg

[Joker_Bones]

It's a bit of a mystery to me that Neill says to avoid end loading of the bearing...
When the drive sprocket and shock aborber are fitted I imagine the spring pulls the crankshaft over to inner bearing, side loads it and eliminates any end float unless I'm misunderstanding what is happening?

[Duncan]

Hi Colin, If you review page 24 of this File on Christians Archive http://archives.jampot.dk/book/Workshop ... dition.pdf you will see the suggested method for moving the timing bush.

Page 7 of the Army technical book http://archives.jampot.dk/book/Workshop ... ndards.pdf fives a maximum end float of 0.050" so you do appear to be within tolerance, although you may need to improve your measurements to be sure.

You may struggle to reposition a bush that has not been touched for years.

My understanding of the minimum end float is to accommodate the differing expansion rates of the crankshaft and the crank cases, if it is too small there is a risk of the crank binding or in extreme cases even fracturing the cases.

[56G80S]

Although the later model as described in Neill's book, I had the same problem of the two drive side bearings tightening up.

As I had spent quite a lot of cash on the bottom half (axles, big end, drive side bearings and timing side bush) I was keen to ensure the timing side bush was line reamed and Ken de Groome did this for me as well as the adjustment to the drive side, which was to tap the inner bearing as described; he knew what he was doing though. He also re-assembled into the cases. 1200 miles (at least) into running in with the rebored barrel and new piston as well all is good.

His view was not to be overly concerned about the end float issue. As stated earlier in the thread, it all gets pulled to the drive side anyhow. One thing I did check was that once assembled, before replacing the barrel, the conrod/piston was exactly centred.

Others with more knowledge will chime in.

I do regret not converting all the oil pump blank end plate, nearest the gearbox, bolts to studs. I had to do one because of a weak thread.

Johnny B

[Colonel Blink]

Thanks for your inputs, everybody!

I do still have a modicum of bafflement however; my understanding of the oft-quoted Neill book is that the moving of the inner drive side bearing was called for purely to ensure that the inner races move independantly; and that moving the timing side bush was only recommended on the pre 1952(?) single diameter bush, presumably because moving the two diameter bush inwards would leave the flange unsupported.....???
However, given that on my engine although I can move the drive side inner races independently I do feel some frictional resistance, I think that I may try that route first... after all, 'move independently' can be code for 'just in contact' or 'have a gap between them'.... though I do wonder whether under the action of operational temperatures and the shock absorber spring pressure the bearing will just move back again.....

So no views as to why 'do not use a steel shim'.....?

Interesting to see that mine is near the Army 'condemnation limit'..... so nearly time to shoot it!

Thanks again!

[SPRIDDLER]

Page 7 of the Army technical book ...............gives a maximum end float of 0.050" so you do appear to be within tolerance, although you may need to improve your measurements to be sure.

Rather than the ruler that you're using if you don't have a vernier or dial gauge you'd get a more accurate check by using a combination of feeler gauges (we all have those !) to assess the end float.
Perhaps a steel shim isn't recommended as it would wear the timing side bush quicker than would a ph/br one (just a guess as I can't really think of any scientific engineering reason how it would wear the bush any quicker).

[Colonel Blink]

Hi Spriddler.... yes I will make a more accurate measurement before adjusting, it's just that my depth micrometer is at the bottom of an almost inaccessible cupboard in my garage....

I also wondered about the wear using a steel shim, but then thought that without the shim the bush flange would bear against the crank cheek, which I presume is steel...
As others have said, for most of the time the shock absorber would hold the crank away from the bush, but I did wonder whether during gear changes and shock loading the crank would momentarily shift to the timing side and back, hammering any shim and maybe cause it to break up? I doubt it, but I would use a steel rather than a stainless steel shim to reduce the brittleness...

[Colonel Blink]

I finally burrowed down through various boxes of 'stuff' to unearth my trusty Starrett depth mic with which to measure the crank end float. However, after all that effort it wasn't any help at all because of the lack of an accessible datum.... Luckily, Spriddler had come up with the viable alternative of feeler gauges.

Using said feeler gauges and a British Standard Mkl Thumbnail, I measured my endfloat at 0.95mm / 37 thou with the crankcases bolted together. The 22x32x0.5mm shim fitted perfectly snugly over the timing side axle, and bolting the crankcases back together gave the then expected 0.45mm / 18 thou. Although under the specified minimum, to me it still seems a lot - what as an engineering apprentice we would have termed "rattlin' around like a p..[appendage] in a top 'at". As such, I believe that my 18 thou is acceptable.

Looking at the inside of the casings and the crank, at some time they have been in contact; though how I'm not quite sure. Possibly someone in the past could have left the spacers out from between the two drive side ball bearings? They certainly stand proud now, and when fitted there is more than 0.5mm / 20 thou clearance between flywheel and casing.

Just need to clean things up with alkyfrol and loctite the shim to the flywheel (not that I think it needs to be) and I can get the crankcases together.