Big End Bearing Replacement

[tevie54]

You're absolutely right, I'm wrong, the NC crank is pressure fed not splash fed, Ive just finished building my XR500 engine and for some reason thought the NC was was the same as the XR, My apologies.
However, I stand by the rest, do you really think that the 17 year old Japanese girls working on the Honda production line have got time to check every bearing, con rod and crank journal ? The crankshafts would have been machined on a CNC machine as would the con rods and Honda were pretty good at it even then. And you think I'm lucky? how about fitting a VF750SC crankshaft to a VF750F, one spins the opposite way to the other, I just turned all the bearings 180 degrees so the molecules all laid in the same direction and that particular VF clocked 145 on the speedo.
When I changed the crankshaft on my NC the new one (second hand) came with conrods so all I did was remove them and leave the bearings attached to the crank, as all the conrods are the same and the backs of the bearings are also I simply bolted the crankshaft onto the old rods.
NC30 engines are tough little things so I'm not surprised only one bearing picked up, it doesn't mean the rest of the engine is damaged, just use your eyes and common sense

[Variablevalves suck]

So the 17 year olds have time to machine (grind) all the conrods, cranks and cases, plus time to print a manual that shows how to plastigage the mains and rods but they don't have time left to actually plastigage the engines.
Why make different size shells then?
Manufacturers having a joke on are behalf maybe, I think not.

[VtypeV4]

how about fitting a VF750SC crankshaft to a VF750F, one spins the opposite way to the other, I just turned all the bearings 180 degrees so the molecules all laid in the same direction and that particular VF clocked 145 on the speedo.

As far as I was aware, both engines spun the same direction just that one was a 180 (F) crank and the other a 360(SC)? And one was a 5 speed and the other a six possibly?

As for shells and operating clearances, it's critical to get it right. Honda learned that the hard way not long after the CX came out with a succession of failures blighting what was an otherwise (largely) reliable machine. Personally I'd never order new (or old) shells for any engine without knowing the sizes..

[Neosophist]

I stand by the rest, do you really think that the 17 year old Japanese girls working on the Honda production line have got time to check every bearing, con rod and crank journal ?

Oh dear, I don't know if this is contempt for Honda or some attempt at adding weight to some hypothesis or lack of understanding how they engines were built up at the plant. Either way.

Have you ever checked the original valve shims on a VFR400/CBR400/CBR250?

These 17 year old girls who apparently don't give a shit about crank tolerances seem to go to the trouble of fitting valve shims to the nearest 0.01mm. Even though you can only buy them in increments of 0.05mm from the dealer as aftermarket parts, when the engines leave the factory they are were all fitted with the exact size shim to get their clearances spot on.

As for the bearing shells and cranks, I guess they don't have time to check them the way you would on a used engine with plasti-gauge.

However, these are new engines and due to the build / automation process when they are built at the factory, after the final finishing the parts are measured and labelled up, if it hasn't been worn off, old engines often still have their build numbers wrote on the cases.

Since the blocks have already been precision measured along with the crankshafts the assembler only has to look at the build documentation and put in the matching bearing shells and torque it up.

If you look behind the clutch you can see the bearing shells already installed as its stamped on there, such as ABBB ABAB etc.. how else do you think they get these codes if its just blind luck / don't give a shit? why not just stick all A's in there?

One of the main reasons these engines last so long is how well the quality of engineering was.

And yes, I've already acknowledged in my first post you can get away with some tolerance, but to advocate not checking something which if it is out of spec can easily fry the engine is just terrible advice.

Especially since it is so easy when you already have the block stripped to that extent.

[tevie54]

Surely all the crankshafts would have been ground on the same machine to the same size so therefore all the big end and main bearings will be the same, the only time you would need oversize bearings will be when you've had the crank reground therefore making the journals smaller.
The original poster is obviously trying to get his bike back on the road as quickly and cheaply as possible, all I am trying to do is show him an alternative to getting the crank reground and having to source new bearings of the correct size. Like I said, my crank came with conrods attached and as there was no play in any of the bearings it was perfectly safe to fit it to the existing conrods in the engine. You can split an NC engine horizontally without disturbing the heads or gearbox and after unbolting the big end caps you can just lift out the old crank. I've been building bike engines for the last 30 odd years, particularly V4s and big singles and I've never had a problem yet so don't call me lucky, I just use my eyes and my sense of touch.
Incidentally the VF750SC was a shaft drive six speeder and the VF750FD was a chain drive 5 speed, they were both 360 degree crankers but the SC rotated backwards, the VFR came out in 86 and that was a six speed as well but was a 180 degree crankshaft

[hunter]

So you think because you have been building engines for 30 odd years, you have nothing to learn,
Iv'e been building road and race engines for 40 odd years,And i'm still learning.
Iv'e build three of these engines in the last four months,And believe me i'm still learning.
These art mass produced items so machine tolerance is as good as it gets.
You cannot regind these crankshafts as you stated,So the avilability of three shell sizes allows you to select the correct size for each main bearing,The same applies to conrods.The cranks have identification marks for shell size on them and the crankcases are stamped for big end size,
It seems like you are suggesting we ignore the recomendations of one of the best,If not the best motorcycle manufacturer in the world,And throw it together.

[tevie54]

Who said anything about not learning anything, I'm just trying to help the guy, read the text! He has knocked out a big end bearing, are you telling me you would fit new bearings without regrinding the crank? Jeez what is it with people putting words in my mouth.
In the factory the crankshafts would be cast then machined roughly to shape, heat treated then ground to a very precise dimension, Honda being Honda would make sure that dimension was pretty consistent wouldn't they?
The bearings fitted would be standard size would they not? if different size bearings had to be fitted to each crankshaft then something would be very wrong with the machinery, it would not make financial sense to fit a different size bearing to every crankshaft.
Surely the only time oversize I.E. non standard bearings are used is when the crankshaft needs regrinding, now whether NC cranks can be reground or not I don't know but if they can then surely the cost of this must be getting on for the cost of a second hand crank, which is where my idea comes in, I'm just trying to save the guy some time and money.

[hunter]

You are completely missing the point,The shells in every(ALMOST) NC30 engine ever built have a combination of sizes.
I have probably five sets of casings under the bench,And only one of them is using the same size shells right through.
AAAA.I think that's one full set of brown shells.
As regards to his knocked out big end,I think common sence would tell him,You,And anyone else if the crank has damage then throw it away.They are not serviceable.

[tevie54]

What do you mean I'm missing the point, you have just confirmed MY point. the original poster has knocked out a big end bearing, if the crank is damaged and they can't be reground and suitable bearings found then buying a second hand crankshaft is the only other answer.

[Variablevalves suck]

No mate you are completely missing the point because you have NO understand of how engines are machined and then built.
If you machine metals/alloys etc you get wear on the cutting tool, you also get tiny differences between machines SO what happens is after parts are machined they are then sized, I know as I'm an qualified machine tool maker,
They are then graded with colour, number or letter codes, now if you put all the smallest or all the biggest sizes together you will have shit clearances in your motor or what ever you are building so you fit the correct part by gauging the clearances and then fitting the correct thickness bearing. Simple.
Honda ,Ferrari and nasa don't build perfect things without allowing for different machine tolerances.