E: Engine Big End Replacement

oexing

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No need for a lathe for trueing a crank, in fact this "between centers" logic may look impressive and scientific - but isn´t . That way you can only guess what the crank ends may do once installed in the case but you do not know . Just get two alu plates or even two plates of plywood and cut a Vee in both to lay the crank in there. So this is like spinning on the inner bearings and you check with clock at the ends. The readings will be EXACTLY like in the engine, no guesswork from numbers you get from between questionable centers and runout on bearing seats.

Vic
 

Bill Thomas

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I agree Vic, I have a set of bearings like we had photos of a few months ago,
On legs, I also have V blocks I used years ago on my Goldstar,
But because I was just a mechanic, This is a bit tricky for me,
You can see my spare set of wheels and shafts, While they are apart it would be nice to have something to compare for after I have welded and bored the other wheels,
I bought another dial gauge,
But I have not found it easy, I must try what John said,
I don't think the centres are good on the shafts, It's all a bit of a pipe dream,
I am getting a bit old for this, I have been playing with Bikes for many years and have other Bikes that are running, So don't NEED another , But it would be nice,
You never know with me, I could suddenly get keen and get stuck in, I am hoping anyway.
Cheers Bill.
 

Pushrod Twin

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I work part-time in a bike shop and we rebuild quite a few roller bearing cranks, most are ok but we have the odd one that is out of round or too tight (funnily we don't seem to have any too loose)
When this occurs we have a Delapena bench honing machine like this we use to hone them out.View attachment 17578
Thank you for posting that Chris, I have an identical machine which I bought as a kitset. It had the appendage to the right of the adjustment handle, but I couldnt figure out what it should do or where it should go. I had never seen one on the American Sunnen equivalents I used. It appears to be a holder for tools. The holder is threaded and attached by a bolt from the inside of the housing so mine will remain unattached until such time as I have to dismantle the machine for some unforeseen maintenance.
 

oexing

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Ahmmm, what sort of runout can you check with half a crankshaft ?? Concentricity of outer dia. of webs relative to mainshafts ? That is no point at all, you want no runout at shaft ends, in case of Vincents at least the timing side -and that with complete assembly I´d say.
For lapping the i.d. of big ends to size and roundness I fabricate an alu taper round with max. 1 degree taper set on lathe. The lapping material/ring is cast iron, same internal taper and ring slotted and grooved so it can be expanded by lightly knocking it along the alu taper. For lapping apply diamond paste , 5 micron grit is allright for finish. With very slow speed on lathe you can get the big end perfect by feel for resistance when going along the cast iron ring. You cannot get any better perfection than by lapping, even block gages are lapped to size.

Vic

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Pleuel u. Läppring.JPG



fertiggeläppt.JPG
 

Pushrod Twin

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As I have said before, I once took my crank to one of our top blokes, And watched him "Hone", The big end eye by winding the rod round a large pin in the vise by hand, With grinding paste, Others on the Forum said this was OK, But it didn't impress me, Maybe I will have to do it at home, But my hole 560 crank will be a Bodge, Fingers and everything else crossed !!. Cheers Bill.
That "hone" process you refer to is more commonly known as "lapping" and is quite acceptable for removing small amounts of metal, tenths of thous, provided the lap is soft enough to hold the abrasive and kept parallel.
Like Oexing so graphically demonstrated above. :oops:
 
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Cyborg

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Ahmmm, what sort of runout can you check with half a crankshaft ?? Concentricity of outer dia. of webs relative to mainshafts ? That is no point at all, you want no runout at shaft ends, in case of Vincents at least the timing side -and that with complete assembly I´d say.
Vic



Well... I’d be checking to see if if the mainshafts were still straight. In a previous post I mentioned the crank had a broken crank pin. I checked the drive side shaft and flywheel and it was ok, I also checked the timing side and the shaft was bent. The point is.... I want to find out what if anything is bent before I assemble the crankshaft. There is no point in assembling the crankshaft, trying to align it and then discovering the shaft is bent.
 
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