Pre-unit engines, crankshaft \ bush design

[Brandis]

From Roy Bacon:
" The pre-unit engines had a timing bush of 1.375 nominal bore and the very first type was only used in engines up to number XA7-600, after which the crankshaft design changed and the bush with it.  The new one had a larger flange."
When Roy says larger, does he mean the diameter of the bush or it'd thickness.  If they changed the crankshaft design, did the new bush fill a new gap?
Since I have engine 280 and the long stroke crankshaft coming from Portugal is probably a post #600 unit . .
Do I just do the assembly and see if the end play is OK?
Should I be considering buying a aftermarket bush and measuring it to compare? 
Should I drink stronger beer? How much should I panic ?

Adm edit: in the tech boards, Quote: "topic titles must be descriptive". Please always abide to this rule. Title edited.

[Swarfcut]

  How much should I panic? Not one itsy bitty bit for now.

 Another fairytale, then you can panic.

  That timing side bush indeed has a locating flange and the face of the flange  bears onto the web of the crank. The bush was originally a steel backed whitemetal lined affair, evolving into a steel carrier with a pegged insert, these days custom one piece bronze bushes are good choice. All in the Forum, debated at length as this bush, its condition, cleanliness and fit is the real deal breaker of the design. You'll also find reference to end fed cranks and the pro and cons of modifying or keeping things standard.

 The replacement crank may even fit your existing bush. Worst case you'll end up with a crankcase with a hole, a crank with a journal, you just need a custom bush to bridge the two. My guess is the crankcase will be the same as the rest and a bush will be no problem. Back then, pre-finished off the shelf replacement bushes were available. These days perfection demands the bush is line bored to match the drive side location.. Early engine uses a ball race on drive side, so no end float on crank, but a pre final assembly running clearance is recommended. All detailed in Service Sheet 208.

 YouTube is full of viddys about the cranks. Get a beer and see how it's done. Most examples apply to the later motor, but the basics are the same.


 I'm away for a couple of weeks...now panic.

 Swarfy.

 

[Brandis]

Thanks for the very detailed info.  As for the solution, let me quote Dylan Thomas.  "Easy for Leonardo."

I'll wait for the crank to appear.  Do a dry fit, and then get back to all y'all

When I saw the serial # on the engine in that old Connecticut warehouse, I thought, 'This will be a lot of fun.'   Little did I know.

[muskrat]

G'day Brandis.
To add to that. Even though the crank is captive with the drive side bearing an thus no end float, the gap between the crank and timing side bush should still be kept to 1.5-3 thou". Any larger oil will escape that way instead of going to the big ends.
An old d/s bearing with the id ground out a few thou (so it slides on the crank) can be used to measure the end float and corrected with shims.
Cheers

[Brandis]

Good point, Mate.  I had forgotten about the oil pressure issue.  My shims are standing by. 

[Colsbeeza]

Brandis,
To add the Muskrat's advice, measure the width of the old bearing and the new to calculate the shim stack needed. I found my new bearing and the old differed in thickness. Two other old bearings were different again.
Col

[RichardL]

Brandis,
To add the Muskrat's advice, measure the width of the old bearing and the new to calculate the shim stack needed. I found my new bearing and the old differed in thickness. Two other old bearings were different again.
Col

This may provide a starting point, but, IMHO, the final stack still needs to be determined by measuring end float. If using the dummy race, as suggested by Musky, then you need to measure the thickness of the dummy (don't you be pointing at me) and the thicknness of the final race  and compensate accordingly.

The very first time I tried to calculate shim stack I tried to measure between bearing faces with the case bolted together, then, measure to the outside of the crank webs. If one has the right big measuring tools, I still think this might work. I didn't, so it didn't.

Richard L.

[Brandis]

I don't mean to trivialize all your better skills and experience, but don't I just make sure the new roller bearing is firmly seated, assemble the crankcasecrankshaft (without rods) to the right torque and spin the shaft.  As I spin it by hand I try to move it side to side, reading the shaft end position with my lathe dial gauge.  And whatever it reads is the drift.
Am I a simpleton to think that's all I have to do?

[RDfella]

You got it, Brandis

[RichardL]

Brandis,

Yes, you have the point, sort'a. Maybe you already understood Musky's recommendation for using a dummy inner race when testing end float, but you haven't mentioned it. If you use your actual bearing for test fiiting the shims you will be pressing it on and "pullering" it off for every iteration of the test fits. Maybe you will get it the first time, but if it takes a few you will be kicking yourself.

Richard L.

[berger]

if i understand this correctly and maybe i don't! nothing unusual about that to use a spare bearing it has to measure up exactly the same width as well as the shoulder on the outer race where the inner race rollers sit. i tried an old bearing to do mine some years ago and then found a major problem because the new bearing wasn't exactly the same as the old one regarding the rollers and outer race lip/ shoulder. in simple terms the inner race didn't sit in the same position on the two bearings giving a different shim reading

[Brandis]

Hmm.    I wonder if I could fit a Honda 500 twin in that frame.

Just kidding.   

I think I'll count on good luck and an extra set of shims for when I screw up.  We haven't even talked about if the shaft is too long.  In any case, it's tied up in Portuguese Brexit paperwork before it hops to the UK and then the US.  So I'll get back to all y'all around Christmas.

[RDfella]

If you use your actual bearing for test fiiting the shims you will be pressing it on and "pullering" it off for every iteration of the test fits.

Not if you ease the mainshaft so the bearing is a light push fit. There's no valid reason for the bearing being a press fit as it becomes securely clamped in place by the cush drive.

[RichardL]

OK, but I'm not doing that. Brandis and others will decide for themselves.

Richard L.

[Greybeard]

There's no valid reason for the bearing being a press fit as it becomes securely clamped in place by the cush drive.

True 👍