E: Engine Big End Replacement

[Cyborg]

you can take the small timing bearing out, it ll last for longer, if the crank is crooked

And leave extra slack in the primary chain.

 

[Cyborg]

i put it on the big mains and than both other bearing positions may not be more than 0,02mm (aim) but if 0,03mm (after two hards days of hitting it), make the clearance on the bearings a bit bigger.
one can not add them up.

Oh and i go from it that the cases are line drilled or does one say bored?

cheers

If I set my crankshaft and dial gauges up the same way as you show in your photograph, I get 0.0254mm on the drive side and slightly less than that on the timing side. The timing side should indicate even less, once I clean up the shaft and keyway a bit. I'll leave the small roller in place and wear earplugs.

The cases have not been lined bored. I have not yet found the courage to measure them.

As for using inches instead of mm. I live a 10 minute walk away from the US border, so normally speak their language.

 

[Bill Thomas]

Don't forget we are talking Comet, Which is much stronger / better than a Twin.
Can't wait to see the finished Bike. Cheers Bill.

 

[vibrac]

em.

As for using inches instead of mm. I live a 10 minute walk away from the US border, so normally speak their language.

AND its the language that the bikes were written in. don't forget that Mars shot when NASA tried to switch all those translated errors mount up
I wouldn't try to sort my BMW on inches so why worry the Stevenage Steeds with metric (unless given in the original specs)

 

[Cyborg]

AND its the language that the bikes were written in. don't forget that Mars shot when NASA tried to switch all those translated errors mount up
I wouldn't try to sort my BMW on inches so why worry the Stevenage Steeds with metric (unless given in the original specs)

or closer to home... actually a few miles away from me at the time was the Gimli Glider.

 

[Cyborg]

Don't forget we are talking Comet, Which is much stronger / better than a Twin.
Can't wait to see the finished Bike. Cheers Bill.

At the rate I'm moving, neither one of us will live long enough.

 

[rogerphilip]

So if the combined total runout (sum of both shafts) with the crankpin nuts torqued is within .002 either way I measure it (between centres or on rollers) can I call it a day?..... never mind, I can't bring myself to hit it again..... so I'm done until I start weighing whatever piston I'm going to use. Couldn't find a suitable stump, so made a crank holder on the bench and held a lead ingot between the flywheel the the large hammer. Holder also worked for torquing the crankpin nuts.

Sounds good to me, in fact, when you consider the sum total of components and the associated machining operations that go into the construction of a b/e/flywheel assy it is a tribute to the original craftsmen that said assy runs as true as it does. As a matter of interest have you checked for 'runout' on the faces and edges of the flywheels?

 

[mercurycrest]

When I was younger and did big ends, I always made certain the mainshafts were as true as possible in the flywheels and the ends drilled dead center before pressing it together. I never used a hammer, but used a block of oak to hit them on. I had a vice and a big bolt in a rod coupling to get it all straight and used this WW2 Flywheel jig to test it all. After reading all the input on rollers and knife edges, I think if I was building up another bottom end I'd still use this. And yes, I got those Dinky Toys in the 1950's..

flywheel jig.

 

[Cyborg]

Sounds good to me, in fact, when you consider the sum total of components and the associated machining operations that go into the construction of a b/e/flywheel assy it is a tribute to the original craftsmen that said assy runs as true as it does. As a matter of interest have you checked for 'runout' on the faces and edges of the flywheels?

No and I'm not sure if I want to know. I did check the flywheels to make sure they are parallel. I think my assembly method helped to get them that way. I didn't have to do any adjusting with that part of it. When checking the runout on the faces and edges, I would have to work around some of the "patina" from the last guy who did it.... again, not sure I want to know.

 

[Cyborg]

When I was younger and did big ends, I always made certain the mainshafts were as true as possible in the flywheels and the ends drilled dead center before pressing it together. I never used a hammer, but used a block of oak to hit them on. I had a vice and a big bolt in a rod coupling to get it all straight and used this WW2 Flywheel jig to test it all. After reading all the input on rollers and knife edges, I think if I was building up another bottom end I'd still use this. And yes, I got those Dinky Toys in the 1950's.. View attachment 17735 flywheel jig.

Before I started the assembly, I spun both wheels in the lathe to check the shafts and centres, and they were "ok". I thought about the oak stump or a big block of lead on a steel post, but if you saw an X-ray of my spine (#backspasm), you would probably understand why I used my Rube Goldberg crank holder with a piece of lead between the big hammer and the flywheel (instead of swinging a crank assembly). Using the creeper to get to the washroom isn't considered one my favourite things. BTW, nice jig you have there.